Clinical brain mapping

The angular gyrus forms a similar horseshoe shape over the posterior end of the superior temporal gyrus.13,16Intraoperative mapping during awake craniotomy has demonstrated that lan-guag

Clinical Brain Mapping

Medicine is an ever-changing science As new research and clinical experiencebroaden our knowledge, changes in treatment and drug therapy are required.The authors and the publisher of this work have checked with sources believed

to be reliable in their efforts to provide information that is complete and ally in accord with the standards accepted at the time of publication However,

gener-in view of the possibility of human error or changes gener-in medical sciences, neitherthe authors nor the publisher nor any other party who has been involved in thepreparation or publication of this work warrants that the information containedherein is in every respect accurate or complete, and they disclaim all responsi-bility for any errors or omissions or for the results obtained from use of the infor-mation contained in this work Readers are encouraged to confirm the informa-tion contained herein with other sources For example and in particular, readersare advised to check the product information sheet included in the package ofeach drug they plan to administer to be certain that the information contained inthis work is accurate and that changes have not been made in the recommendeddose or in the contraindications for administration This recommendation is

of particular importance in connection with new or infrequently used drugs

Clinical Brain Mapping

Daniel Yoshor, MD

Associate Professor Department of Neurosurgery Baylor College of Medicine Chief of Neurosurgery

St Luke’s Episcopal Hospital Houston, Texas

Eli M Mizrahi, MD

Chair, Department of Neurology Professor of Neurology and Pediatrics Baylor College of Medicine Chief of Neurophysiology

St Luke’s Episcopal Hospital Houston, Texas

New York Chicago San Francisco Lisbon London Madrid Mexico City Milan New Delhi San Juan Seoul Singapore Sydney Toronto

publication may be reproduced or distributed in any form or by any means, or stored in a database or retrieval system, without the prior written permission of the publisher.

ISBN: 978-0-07-180596-4

MHID: 0-07-180596-6

The material in this eBook also appears in the print version of this title: ISBN: 978-0-07-148441-1,

MHID: 0-07-148441-8.

All trademarks are trademarks of their respective owners Rather than put a trademark symbol after every occurrence of a trademarked name, we use names in

an editorial fashion only, and to the benefi t of the trademark owner, with no intention of infringement of the trademark Where such designations appear in this book, they have been printed with initial caps.

McGraw-Hill eBooks are available at special quantity discounts to use as premiums and sales promotions, or for use in corporate training programs To contact

a representative please e-mail us at bulksales@mcgraw-hill.com.

TERMS OF USE

This is a copyrighted work and The McGraw-Hill Companies, Inc (“McGraw-Hill”) and its licensors reserve all rights in and to the work Use of this work is subject to these terms Except as permitted under the Copyright Act of 1976 and the right to store and retrieve one copy of the work, you may not decompile, disassemble, reverse engineer, reproduce, modify, create derivative works based upon, transmit, distribute, disseminate, sell, publish or sublicense the work or any part of it without McGraw-Hill’s prior consent You may use the work for your own noncommercial and personal use; any other use of the work is strictly prohibited Your right to use the work may be terminated if you fail to comply with these terms.

THE WORK IS PROVIDED “AS IS.” McGRAW-HILL AND ITS LICENSORS MAKE NO GUARANTEES OR WARRANTIES AS TO THE ACCURACY, ADEQUACY OR COMPLETENESS OF OR RESULTS TO BE OBTAINED FROM USING THE WORK, INCLUDING ANY INFORMATION THAT CAN BE ACCESSED THROUGH THE WORK VIA HYPERLINK OR OTHERWISE, AND EXPRESSLY DISCLAIM ANY WARRANTY, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE McGraw-Hill and its licensors do not warrant or guarantee that the functions contained in the work will meet your requirements or that its operation will be uninterrupted or error free Neither McGraw-Hill nor its licensors shall be liable to you or anyone else for any inaccuracy, error or omission, regardless of cause,

in the work or for any damages resulting therefrom McGraw-Hill has no responsibility for the content of any information accessed through the work Under no circumstances shall McGraw-Hill and/or its licensors be liable for any indirect, incidental, special, punitive, consequential or similar damages that result from the use of or inability to use the work, even if any of them has been advised of the possibility of such damages This limitation of liability shall apply to any claim

or cause whatsoever whether such claim or cause arises in contract, tort or otherwise.

To our parents, Shulamit and Joseph Yoshor, and Julia and Isaac D Mizrahi, who encouraged and

sustained us; and to our patients who inspire and teach us.

v

Contributors ix Preface xiii Acknowledgments xv

SECTION I: TECHNIQUES

Chapter 1. Surface Anatomy as a Guide to Cerebral Function 3

Gareth Adams, Jared Fridley, and Daniel Yoshor

Chapter 2. Structural Imaging for Identification of Functional Brain Regions 13

Jean C Tamraz and Youssef G Comair

Chapter 3. Functional MRI for Cerebral Localization: Principles and Methodology 31

Michael S Beauchamp

Chapter 4. Functional MRI: Application to Clinical Practice in Surgical Planning and

Intraoperative Guidance 45

Michael Schulder and Robin Wellington

Chapter 5. Neuropsychological Testing: Understanding Brain–behavior Relationships 55

Mario F Dulay, Corwin Boake, Daniel Yoshor, and Harvey S Levin

Chapter 6. The Wada Test: Intracarotid Injection of Sodium Amobarbital to Evaluate Language

and Memory 79

Brian D Bell, Bruce P Hermann, and Paul Rutecki

Chapter 7. Extraoperative Brain Mapping Using Chronically Implanted Subdural Electrodes 93

David E Friedman and James J Riviello, Jr.

Chapter 8. Brain Mapping in the Operating Room 103

Sepehr Sani, Edward F Chang, and Nicholas M Barbaro

Chapter 9. Anesthesia for Brain Mapping Surgery 109

Nicholas P Carling, Chris D Glover, Daryn H Moller, and Ira J Rampil

Chapter 10. Clinical Applications of Magnetoencephalography in Neurolog y and Neurosurgery 119

Panagiotis G Simos, Eduardo M Castillo, and Andrew C Papanicolaou

Chapter 11. Optical Spectroscopic Imaging of the Human Brain—Clinical Applications 131

Hongtao Ma, Minah Suh, Mingrui Zhao, Challon Perry, Andrew Geneslaw, and Theodore H Schwartz

vii

Chapter 12. Electrocorticographic Spectral Analysis 151

Mackenzie C Cervenka and Nathan E Crone

Chapter 13. Pediatric Brain Mapping: Special Considerations 167

Robert J Bollo, Chad Carlson, Orrin Devinsky, and Howard L Weiner

SECTION II: SYSTEMS

Chapter 14. Mapping of the Sensorimotor Cortex .189

Roukoz Chamoun, Krishna Satyan, and Youssef G Comair

Chapter 15. Mapping of Human Language 203

Nitin Tandon

Chapter 16. Mapping of the Human Visual System 219

Muhammad M Abd-El-Barr, Mario F Dulay, Paul Richard, William H Bosking, and Daniel Yoshor

Chapter 17. Mapping of Hearing .241

Albert J Fenoy and Matthew A Howard

Chapter 18. Mapping of Memory 269

Jeffrey G Ojemann and Richard G Ellenbogen

Index 277

Department of Neurological Surgery

Indiana University School of Medicine

Indianapolis, Indiana

Michael S Beauchamp, PhD

Department of Neurobiology & Anatomy

University of Texas Health Science Center

Department of Physical Medicine & Rehabilitation

University of Texas Medical School

Mackenzie C Cervenka, MD

Department of NeurologyThe Johns Hopkins University School of MedicineBaltimore, Maryland

Roukoz Chamoun, MD

Department of NeurosurgeryBaylor College of MedicineHouston, Texas

Nathan E Crone, MD

Department of NeurologyThe Johns Hopkins University School of MedicineBaltimore, Maryland

ix

Orrin Devinsky, MD

Comprehensive Epilepsy Center

Department of Neurology

New York University School of Medicine

New York, New York

Department of Neurological Surgery

University of Washington School of Medicine

Weill Medical College of Cornell University

New York, New York

Chris D Glover, MD

Department of Pediatrics (Anesthesiology)

Texas Children’s Hospital

Baylor College of Medicine

University of Iowa Hospitals and Clinics

Iowa City, Iowa

Harvey S Levin, PhD

Departments of Physical Medicine & Rehabilitation,

Pediatrics, Neurosurgery, and Neurology

Baylor College of Medicine

Houston, Texas

Hongtao Ma, PhD

Department of NeurosurgeryWeill Medical College of Cornell UniversityNew York, New York

Jeffrey G Ojemann, MD

Department of Neurological SurgeryUniversity of Washington School of MedicineSeattle, Washington

Challon Perry, MD

Department of NeurosurgeryWeill Medical College of Cornell UniversityNew York, New York

Ira J Rampil, MD

Department of AnesthesiologyUniversity at Stony BrookStony Brook, New York

Paul Richard, MD

Department of Neurological SurgeryUniversity of Pittsburgh Medical CenterPittsburgh, Pennsylvania

James J Riviello, Jr., MD

Division of Pediatric NeurologyDepartment of NeurologyNYU Comprehensive Epilepsy CenterNew York University

New York, New York

Paul Rutecki, MD

Department of NeurologyUniversity of Wisconsin School of Medicine andPublic Health

Department of NeurologyW.S Middleton Memorial Veterans HospitalMadison, Wisconsin

North Shore-LIJ Health System

Manhasset, New York

Theodore H Schwartz, MD

Department of Neurosurgery

Weill Medical College of Cornell University

New York, New York

Weill Medical College of Cornell University

New York, New York

Howard L Weiner, MD

Department of NeurosurgeryDivision of Pediatric NeurosurgeryComprehensive Epilepsy CenterDepartment of NeurologyNew York University School of MedicineNew York, New York

Robin Wellington, PhD

Department of Psychology

St John’s UniversityFlushing, New York

Daniel Yoshor, MD

Department of NeurosurgeryBaylor College of MedicineNeuroscience Center

St Luke’s Episcopal HospitalHouston, Texas

Mingrui Zhao, MD, PhD

Department of NeurosurgeryWeill Medical College of Cornell UniversityNew York, New York

The localization of cerebral function is a critical task

for both neurosurgeons and neurologists In Clinical

Brain Mapping we have addressed these localization

ef-forts from the perspectives of our different but, at times,

overlapping backgrounds and clinical interests One of

us is a neurosurgeon (Daniel Yoshor) and the other a

neurologist (Eli M Mizrahi) We began our discussions

about clinical brain mapping early in our careers as we

cared for adults and children with medically intractable

epilepsy who were being evaluated for epilepsy surgery

We have worked together for several years at the Baylor

Comprehensive Epilepsy Center considering the issues

of cerebral localization and weighing relative risks and

benefits of resective surgery for potential seizure

con-trol, as well as in resective surgery for brain tumors In

the course of our clinical practice, we realized the need

for a concise and practical, but comprehensive, guide to

clinical brain mapping In addition to our efforts with

patients, through our interactions with colleagues and

trainees, we realized that such a volume would be of

value to them both for reference and training This was

beginning of the current volume

Although initially considered within the context of

epilepsy surgery, Clinical Brain Mapping addresses a

wide range of clinical concerns It addresses the

tech-niques and functional bases for all clinical situations that

may require cerebral localization for diagnosis and

man-agement Most of the techniques described are now part

of clinical care, others are just now emerging technology

and not yet fully integrated into clinical practice, andsome techniques have their greatest utility in clinical re-search It is meant as a reference for neurosurgeons, neu-rologists, neuroradiologists, neuropsychologists, clinicalneuroscientists and others actively involved in the care

of those with or who are at risk for neurological ment through intervention

impair-We have organized the volume into two sections:

Techniques and Systems The Techniques section

con-sists of chapters considering specific methods of bral location: operative anatomy, structural neuroimag-ing, functional MRI, magnetoencephalography, opticalimaging, neuropsychological testing, Wada testing, spe-cial intraoperative mapping techniques, extraoperativebrain mapping with implanted electrodes, electrocortico-graphic spectral analysis, special brain mapping tech-niques for pediatric patients and anesthetic techniques

cere-for intraoperative brain mapping In the Systems section

there are discussions of somatomotor and sory function, language, vision, hearing, and memory.Each is written by experts in their respective fields.This book is intended to serve two purposes It hasbeen developed as a practical guide to brain mapping

somotosen-in the clsomotosen-inical settsomotosen-ing and it is also designed to presentthe scientific basis of the cortical systems that we wish

to localize and preserve in the care of our patients

Daniel Yoshor, MD Eli M Mizrahi, MD

xiii

Brain mapping is typically a collaborative effort in both

the clinical and research settings The development of

Clinical Brain Mapping has also been collaborative.

We are grateful to those who have been

instrumen-tal in its production, including the 47 contributors to

this volume who have given generously of their time

and expertise to write timely, insightful, and instructive

manuscripts

We have been fortunate to work in an enriched

environment that fosters expert patient care and

excel-lence in research The clinicians, scientists, trainees and

students at Baylor College of Medicine form an

invig-orating intellectual community, which has fostered our

interests and growth as researchers and clinicians

Simi-larly, St Luke’s Episcopal Hospital has encouraged and

supported our work and has proved to be a unique

in-stitution which promotes outstanding clinical care and

clinical research

We are also grateful to Robert G Grossman, MD,

and the late Peter Kellaway, PhD They initially taught

and mentored us, and then became professional

col-leagues and personal friends

Dr Yoshor acknowledges the influence of Nicholas

M Barbaro, MD, Mitchel S Berger, MD, and Raymond

L Sawaya, MD, in developing his interest in applying

brain mapping to clinical practice, and of John H.R

Maunsell, PhD, and Michael S Beauchamp, PhD, in veloping a research program that strives to use rigor-ous scientific methodology in studying human corticalfunction

de-Dr Mizrahi is grateful to his long-time colleaguesand collaborators in the Peter Kellaway Section of Neu-rophysiology, Department of Neurology, Baylor College

of Medicine, particularly James D Frost, Jr., MD, andRichard A Hrachovy, MD They continue to providevaluable insights into the neurophysiological aspects ofcortical mapping

As with any collaborative effort, there are manypeople who have contributed directly and indirectly to

Clinical Brain Mapping We are most grateful to our

co-workers, clinical and research colleagues, gists, trainees, and administrative staff for their diligenceand hard work on our behalf In particular, Lisa Rhodes,

technolo-R EEG/EP T., CLTM, has provided outstanding cal support for brain mapping studies in our patientsfor many years Kathleen Pierson and May-Lin Bassoprovided critical and expert administrative assistance Fi-nally, we express our sincere thanks to the editorial staff

techni-at McGraw-Hill Medical Publishing, Anne Sydor, PhD,Executive Editor, and Regina Y Brown, Senior ProjectDevelopment Editor and to Tilak Raj, Project Manager,Aptara Corporation, Inc

xv

SECTION I

TECHNIQUES

1

Chapter 1

Surface Anatomy as a Guide to

Cerebral Function

Gareth Adams1, Jared Fridley1, and Daniel Yoshor1,2

1Department of Neurosurgery, Baylor College of Medicine, Houston, Texas

2Neuroscience Center, St Luke’s Episcopal Hospital, Houston, Texas

HISTORICAL PERSPECTIVE

Our existing knowledge of a number of consistent

re-lationships between specific anatomic landmarks and

local cortical function allows the use of anatomy to

pre-dict function with considerable accuracy, even without

direct physiological confirmation in an individual

sub-ject Defining these landmarks with noninvasive

struc-tural magnetic resonance imaging (MRI) is routinely

used to infer regional function, as described in

Chap-ter 2, “Structural Imaging for Identification of Functional

Brain Regions.” Direct inspection of anatomic clues, in

particular examination of the exposed cortical anatomy

of the brain during craniotomy, can provide highly

useful clues to functional localization Because

intersub-ject variation in cortical anatomy and functional

local-ization is not insignificant, and because local pathology

such as a brain tumor maybe obscure anatomic clues,

accurate identification of functional regions often

re-quires physiological mapping through other techniques

presented in this book But anatomic landmarks

re-main invaluable, both as a primary method and as

an adjunct to the physiological techniques described

in this book, for plotting regional brain function This

chapter reviews anatomic methods for estimating

re-gional functional by simple visual inspection It is

bro-ken down into sections detailing anatomic techniques

for surface localization of underlying cortical anatomy,

and clues for localization of speech, motor and sensory

function, vision and hearing based on cortical surface

anatomy

Historically, the understanding of the presence of

localized brain function has been based on

experimen-tally created lesions in animals During a prominent

pub-lic lecture and scientific debate in 1881, Sir David Ferrier

convincingly showed that creating a lesion in a monkey’s

left posterior frontal cortex resulted in a right-sided

hemi-plegia, and that bilateral lesions in the superior

tempo-ral lobes resulted in deafness.1 This evidence buttressed

the localizationist theory, which held that brain tions are localized to specific areas of the brain Furtherunderstanding of the localization of human brain func-tion was based on correlating the neurological deficits

func-in patients with specific cortical lesions defined on mortem examinations.2For example, by performing au-topsies on patients with aphasia, Paul Broca was able

post-to localize the functional areas responsible for the duction of speech to the pars triangularis and pars oper-cularis of the dominant frontal lobe Carl Wernicke wasable to localize language comprehension to the poste-rior, superior temporal gyrus Correlation of lesions inthe occipital lobes from shrapnel and penetrating traumawith the visual field defects sustained by soldiers inWorld War II combat provided further localization ofvisual function in humans.3 Similarly, studies of sub-jects with cortical lesions and sensory and motor deficitsdemonstrated that motor and sensory functions are local-ized around the central sulcus.3 Collectively over a pe-riod of decades, a crude understanding of the anatomiclocation of functional regions emerged from thesestudies

pro-Two other methods have greatly further extendedour understanding of the functional organization ofhuman cerebral cortex Pioneering studies employingdirect cortical electrical stimulation in human neurosur-gical patients demonstrated consistent relationships be-tween cortical anatomy and cortical eloquence amongmany different subjects For example, Wilder Penfielddemonstrated through human cortical mapping duringplanning for cortical excisions that motor and sensoryfunction is localized around the central sulcus, and wasable to map a motor and sensory homunculus to thecentral area.2,4 More recently, the advent of structuraland functional MRI (fMRI) has had an explosive im-pact on our understanding of the consistent relation-ship between anatomy and regional function.5,6Studies

that combine both electrical stimulation and fMRI ping in individual subjects has further validated theserelationships.7−9

map-3

SYL VIAN

PO I NT

OCCIPIT

AL LOBE

Figure 1–1 Taylor–Haughton lines.Method for approximating the central sulcus and

sylvian fissure using the Taylor–Haughton lines (From Taylor and Haughton’s Some

Recent Researches on the Topography and Convolutions of the Brain.)

The location of important cortical anatomic features,

such as the sylvian fissure and central sulcus, can be

approximated from the external anatomy of the skull.10

Taylor–Haughton lines (Fig 1–1) can be simply

con-structed from external landmarks by drawing four lines

on the cranium The baseline, or Frankfurt plane, is

de-fined as a line passing the inferior margin of the

or-bit through the superior margin of the external

audi-tory meatus A second line is drawn from the nasion

to the inion across the top of the cranium and divided

into quarters Two more lines are drawn perpendicular

to the baseline The posterior ear line is perpendicular

to the baseline and passes through the mastoid process

The condylar line is perpendicular to the baseline and

passes through the mandibular condyle.11

The location of the sylvian fissure can be

approx-imated by drawing a line from the lateral canthus to

the three-quarter point along the Taylor–Haughton line

from the nasion to the inion The central sulcus can beapproximated by multiple methods One method to ap-proximate the central sulcus is to connect a point 2 cmposterior to the halfway point of the Taylor–Haughtonline across the top of the cranium with a point 5 cmabove the external auditory meatus A second method is

to connect the point on the Taylor–Haughton line acrossthe top of the cranium where it is intersected by theposterior ear line with the point on the approximatedsylvian fissure intersected by the condylar line.11 Othertechniques of localizing the sylvian fissure and centralsulcus based on external cranial landmarks have beendescribed, and like Taylor–Haughton lines, are alsoquite accurate.12

MOTOR AND SENSORY FUNCTION IN THE EXPOSED BRAIN

Motor and sensory functions are located in the Rolandiccortex surrounding the central, or Rolandic, fissure.Motor function is predominantly located in the anterior

wall of the central sulcus and in the precentral gyrus,

whereas sensory function is predominantly located in

the posterior wall of the central sulcus and in the

post-central gyrus The first step in identifying the Rolandic

cortex is to identify the central sulcus The position of

the central sulcus can be approximated on the surface of

the cranium using the techniques detailed in the

previ-ous section, and with the adjuvant use of image guidance

at surgery However, definitively identifying the central

sulcus at surgery can be difficult even in the absence of

anatomic abnormalities such as tumors or dysplasia,

par-ticularly since much of the sulcal and gyral anatomy may

be obscured by the draining veins and the pial vessels

The central sulcus separates the frontal and

pari-etal lobes Broca described the central sulcus containing

three curves and a superior and inferior genu Superiorly

the central sulcus extends from the interhemispheric

fissure and often extends onto the mesial aspect of

the hemisphere Inferiorly it is usually separated from

the sylvian fissure by the subcentral gyrus It is rarely

interrupted.13−15Localizing the central sulcus is possible

through its relationship to the sylvian fissure and to the

other surrounding sulci and gyri of the frontal, temporal,

and parietal lobes (Fig 1–2)

Naidich et al published a systematic method of

identifying the anatomic relationships of the low-middle

convexity in 1995.16 The first step is to identify the

syl-vian fissure, which separates the frontal and

tempo-ral lobes It is composed of five rami, with the long

obliquely oriented section visible on the cortical surface

designated as the posterior horizontal ramus The

ante-rior horizontal ramus and anteante-rior ascending ramus

ex-tend superiorly from the anterior section of the posterior

horizontal ramus forming a characteristic V or Y pattern

These rami divide the inferior frontal gyrus from anterior

to posterior, into the pars orbitalis, pars triangularis, and

pars opercularis The frontal convexity is divided into

superior, middle, and inferior gyri by the superior and

inferior frontal sulci These sulci extend posteriorly and

fuse with the precentral sulcus Anterior and parallel to

the precentral sulcus is the precentral gyrus The middle

frontal gyrus often run into and fuses with the precentral

gyrus, forming a characteristic sideways capital T shape

The postcentral gyrus lies posterior to the central

sulcus It is typically narrower than the precentral

sul-cus At its inferior border, it is bounded posteriorly by

the posterior subcentral sulcus, giving the inferior end of

the postcentral gyrus a characteristic widened

appear-ance The postcentral sulcus is located parallel to the

central sulcus immediately posterior to the postcentral

gyrus It can be a single long sulcus or may be divided

into multiple segments The parietal convexity is

sepa-rated into the superior and inferior parietal lobules by

the intraparietal sulcus The posterior ascending ramus

of the sylvian fissure hooks superiorly into the inferior

parietal lobule The horseshoe-shaped gyrus in the

ante-rior infeante-rior parietal lobule supeante-rior to and surrounding

the termination of the posterior ascending ramus of thesylvian fissure is the supramarginal gyrus The superiortemporal gyrus runs parallel to the sylvian fissure, firstposteriorly then superiorly It is capped by the angulargyrus, another horseshoe-shaped gyrus making up theposterior portion of the inferior parietal lobule The char-acteristic roles of these areas in language-related func-tion are described in a separate section later

Primary motor and sensory function (Fig 1–3), asdemonstrated by Penfield,4are organized along the pre-central and postcentral gyri in a somatotopic map, which

he represented with a homunculus superimposed ontothe cortex This homunculus is positioned with its feetwithin the interhemispheric fissure and its head ex-tending toward the sylvian fissure, and represents asomewhat crude, albeit useful, oversimplification of theorganization of motor cortex

The cortical representation of motor hand function

is typically located in the superior portion of the tral sulcus along the middle genu of the central sulcus.The curve of the middle genu of the central sulcus be-comes more pronounced in the depths of the centralsulcus, forming a knob or omega shape This knob was

precen-identified by Broca as the pli de passage moyen

Stud-ies using fMRI have demonstrated that this area is thecortical functional location of hand motor function, inthe precentral gyrus and on the anterior surface of thecentral sulcus, and hand sensory function, in the pos-terior surface of the central sulcus and the postcentralgyrus.14,17−19 This precentral knob is usually not visible

initially during surgery as it is obscured by the arachnoidand bridging veins and is deep within the central sulcus.The same area can be located intraoperatively by rely-ing on other landmarks of the frontal lobe, as it is on thecentral sulcus opposite the intersection of the superiorfrontal sulcus with the precentral sulcus

Tongue sensory function is located within the ferior widening of the postcentral gyrus immediatelyabove the sylvian fissure Face sensory function is lo-cated in the narrow portion of the postcentral gyrus su-perior to the tongue functional region.20

in-While these anatomic landmarks do provide somelocalization of motor and sensory cortical function, it can

be very difficult intraoperatively to identify the ated gyri and sulci, especially with a limited exposure.These landmarks can provide initial localization allow-ing the targeting of further studies to verify the location

associ-of the motor and sensory cortex, by phase reversal associ-of matosensory evoked potentials waveforms or by directcortical electrical stimulation.21

LANGUAGE-RELATED FUNCTION

Language function is classically separated into two maincortical areas Wernicke’s area is involved in language

temporal gyrus (STG), and middle temporal gyrus (MTG) are identified (continued)

Figure 1–2 (Continued) In panel G, the intraparietal

sulcus (8), the supramarginal gyrus (SMG), and the

angular gyrus (AG) are identified.

comprehension, including both spoken and read

lan-guage and is located in the posterior, superior

tempo-ral gyrus Broca’s area is involved in the production

of speech and is located in the inferior frontal gyrus,

classically localized to the pars triangularis and pars

op-ercularis These two areas are connected by the

arcu-ate fasciculus In reality, there is significant variation in

the location of speech function between subjects.22−24

Surgical resections involving potential speech areas are

usually performed with the patient awake, which allows

cortical mapping of speech function through

intraopera-tive stimulation Recent studies have shown that speech

function has a much wider distribution across the frontal

lobe outside of the classical Broca’s area and is more

Figure 1–3 Identification of motor and sensory cortex A In the left panel, primary

motor cortex is located in the precentral gyrus, with hand function (H) localized

perpendicular to the end of the superior frontal gyrus B In the right panel, primary

sensory cortex is located in the postcentral gyrus Tongue sensory (T) is located in

the widened area of the postcentral gyrus close to the sylvian fissure Face sensory

(F) is located in the narrow strip superior to tongue sensory, and hand sensory (H)

superior to face sensory.

fused across the temporal lobe outside of the classicalWernicke’s area.24,25However, it is still useful to be able

to identify the classical locations of these areas to serve

as a starting point for cortical mapping (Fig 1–4).Broca’s area is classically described as being located

in the pars triangularis and pars opercularis of the rior frontal gyrus The inferior frontal gyrus is bounded

infe-by the sylvian fissure inferiorly and the inferior frontalsulcus superiorly The anterior horizontal ramus and an-terior ascending sylvian ramus extend superiorly fromthe sylvian fissure into the inferior frontal gyrus in a Y or

V shape.16These two rami divide the inferior frontal cus into three parts, the pars orbitalis, pars triangularis,and pars opercularis, from anterior to posterior The in-ferior frontal gyrus is bounded posteriorly by the centralsulcus Quinones-Hinojosa and colleagues used intraop-erative mapping correlated with MRI to locate Broca’sarea in relation to the sulci defining the inferior frontalgyrus.7 They proposed a method for localizing Broca’sarea based on the intersection of lines drawn from de-fined points in the inferior frontal gyrus The first line isdrawn from the opercular tip posteriorly at a 45◦ anglebetween the sylvian fissure and the anterior ascendingsylvian ramus The second line is drawn superiorly, per-pendicular from the sylvian fissure at the level of the pre-central sulcus The third line is drawn anteriorly, parallel

sul-to the sylvian fissure at the level of the inferior tip of thecentral sulcus The intersection of these three lines pro-vides an estimate of the location of Broca’s area Whilethis technique does provide an estimated location forBroca’s area, it is only an estimate and accurate localiza-tion of speech function is best determined with intraop-erative or extraoperative cortical stimulation mapping

Figure 1–4 Localization of speech Broca’s area (B) is classically located in the pars

triangularis and pars opercularis of the inferior frontal gyrus Wernicke’s area (W) is

located in the posterior portion of the superior temporal gyrus and the supramarginal

gyrus However, direct stimulation during awake craniotomy has demonstrated

speech function over a much wider area than the classical speech areas, as indicated

by the red outlines compared to the blue outlines of the classical speech areas.

Wernicke’s area is classically located in the

poste-rior, superior temporal gyrus and in the supramarginal

gyrus of the inferior parietal lobule adjacent to the

syl-vian fissure These areas can be identified by locating

the sylvian fissure The superior temporal gyrus runs

between the sylvian fissure and the superior temporal

sulcus, which runs parallel to the sylvian fissure The

posterior portions of both the sylvian fissure and the

superior temporal sulcus hook superiorly and terminate

in the inferior lobule of the parietal lobe The

supra-marginal gyrus is the anterior portion of the parietal

lobe, which forms a horseshoe shape over the

poste-rior end of the sylvian fissure The angular gyrus forms

a similar horseshoe shape over the posterior end of

the superior temporal gyrus.13,16Intraoperative mapping

during awake craniotomy has demonstrated that

lan-guage function is highly variable between subjects and

can be widely dispersed over the temporal lobe and

pari-etal lobe outside the classical Wernicke’s area.24

FUNCTION

Primary visual cortex (V1) is located in the occipital lobe

on the mesial surface both within the calcarine sulcus

and on the surrounding cortex The visual cortex is

or-ganized in a retinotopic map with the fovea located

pos-teriorly near the occipital pole The vertical meridian is

located at the calcarine fissure and the horizontal

merid-ian is deep within the calcarine fissure Functional MRI

mapping of the visual cortex has demonstrated that the

V1 is located mostly within the folds of the calcarine

fissure The fovea is located posteriorly near the tal pole Peripheral vision is located anteriorly There issignificant magnification of the retinotopic map near thefovea, with a much larger cortical area corresponding

occipi-to the area around the fovea Other visual areas extendsuperiorly and inferiorly from the calcarine fissure, cor-responding to areas V2, V3, and V4.26−29An area homol-ogous to the middle temporal (MT) region is located atthe junction of the temporal, parietal, and occipital lobes

in humans (Fig 1–5) This area is involved in processing

of movement.30 −32

The calcarine sulcus is located on the mesial face of the occipital lobe It extends posteriorly from thesplenium of the corpus callosum to the occipital pole

sur-It is divided into an anterior and posterior portion bythe parietal-occipital sulcus The posterior portion of thecalcarine sulcus splits into a Y shape as it approachesthe occipital pole, with the superior portion of the Ysometimes extending onto the lateral surface of the oc-cipital lobe The calcarine sulcus ranges from 2.5 to 3 cmdeep.14,15 The MT region is located near the junction of

the temporal, parietal, and occipital lobes.30−32

FUNCTION

Penfield and Rasmussen localized hearing function tothe superior temporal gyrus by direct electrical stim-ulation of the human cortex Further studies usingpositron emission tomography, fMRI, and direct corticalrecordings have demonstrated that the auditory cortex is

Figure 1–5 Localization of vision The primary visual cortex (V1) is located within the

calcarine sulcus, extending slightly out onto the medial surface of the occipital lobe

(left panel) The fovea (F) is represented at the occipital pole Additional retinotopic

visual areas spread out from the calcarine sulcus and extend onto the lateral surface

of the occipital lobe Middle temporal (MT), which is involved in motion tracking, is

located near the parieto-occipital-temporal junction.

located bilaterally on the superior temporal gyrus both

on the exposed cortical surface and in the depths of

the sylvian fissure on the transverse temporal gyrus of

Heschl (Fig 1–6) The primal auditory field is thought

to be primarily located in the posteromedial portion

of Heschl’s gyrus Brugge et al have demonstrated the

presence of three auditory cortical fields, with two on

Heschl’s gyrus and one on the posterolateral surface of

the superior temporal gyrus.33 −35

Figure 1–6 Localization of hearing Primary auditory

cortex is located in Heschl’s gyrus (H) buried on the

temporal lobe surface buried within the sylvian

fissure Auditory cortex also extends onto the lateral

temporal lobe on the posterior superior temporal

gyrus, as indicated by the blue outline.

Heschl’s gyrus is located completely within the vian fissure It is bounded posteriorly by the posteriortransverse supratemporal sulcus, which originates at thesylvian fissure and extends from the lateral surface ofthe temporal lobe with an anterior oblique orientation.Anteriorly, Heschl’s gyrus is bounded by the anteriortransverse temporal sulcus The gyrus extends eitherobliquely or perpendicularly to the sylvian fissure.13

While there is significant variation in the cortical surfaceanatomy of the human brain there are some constantsthat can be used to roughly identify functional locations

of motor function, sensory function, speech, and vision

on the cortex Anatomic and functional imaging prior

to surgery can provide initial localization of function.Combining these imaging techniques with knowledge

of the relationship between cranial anatomy and the derlying cortex allows the planning of a targeted cran-iotomy Once the craniotomy has been performed thecombination of image guidance and the anatomical land-marks described in the preceding sections can be usedfor initial targeting of further localization of function us-ing techniques such as awake craniotomy with directstimulation for speech mapping or phase inversion forlocating the motor and sensory cortex Because there

un-is significant variation in the location of cortical tion between subjects, anatomical clues should only beused as a starting point for other mapping techniques todefinitively identify the cortical functional locations

func-䉴 PEARLS AND PITFALLS

tThere is significant variation between subjects

both in the sulcal and gyral anatomy and in the

location of function on the cortex

tDuring a craniotomy, even locating the central

sulcus and the surrounding Rolandic cortex can

be difficult due to limited exposure, overlying

arachnoid membrane, and surface vessels

tThe central sulcus is best identified by following a

stepwise pattern of identification of surrounding

sulci that have relatively little variance between

subjects The sylvian fissure is the most reliable

starting landmark

tBroca’s area is classically located in the pars

trian-gularis and pars opercularis, which can be

iden-tified by finding the classic V or Y shape of

the anterior ascending and anterior horizontal

ra-mus of the sylvian fissure However,

intraopera-tive mapping has shown that speech function is

distributed over a much larger region of the

frontal lobe outside the classic Broca’s area

tWernicke’s area is classically located in the

su-perior temporal gyrus at the posterior end of

the sylvian fissure, sometimes extending into the

supramarginal gyrus of the parietal lobe

Lan-guage mapping has shown that lanLan-guage function

is distributed over a larger region of the

tempo-ral lobe, particularly posterior and inferior to the

classic Wernicke’s area

tPrimary visual cortex is reliably located on the

mesial aspect of the occipital lobe mostly within

the folds of the calcarine sulcus with the fovea

represented at the occipital pole Other areas of

the visual cortex extend out onto the surface of

the occipital lobe Area MT, involved with tracking

of motion, is located on the lateral cortical surface

near the junction of the occipital, parietal, and

temporal lobes

tAuditory cortex is located bilaterally in Heschl’s

gyrus buried within the sylvian fissure and in the

posterior portion of the superior temporal gyrus

tAnatomical landmarks should only be considered

as a starting point for further localization using

other techniques, particularly when working close

to eloquent areas involved in motor, sensory, and

speech function

REFERENCES

1 Tyler KL, Malessa R The Goltz-Ferrier debates and the

triumph of cerebral localizationalist theory Neurology

2000;55(7):1015-1024

2 Boling W, Olivier A, Fabinyi G Historical contributions

to the modern understanding of function in the central

area Neurosurgery 2002;50(6):1296-1309, discussion 1310

1309-3 Fishman RS Gordon Holmes, the cortical retina, and thewounds of war The seventh Charles B Snyder Lecture.Doc Ophthalmol 1997;93(1-2):9-28

4 Penfield W Epilepsy and the Functional Anatomy of theHuman Brain, 1st edition Boston: Little Brown, 1954,

pp xv-896

5 Van Essen DC, Dierker DL Surface-based and probabilisticatlases of primate cerebral cortex Neuron 2007;56(2):209-225

6 Gaillard WD Functional MR imaging of language, ory, and sensorimotor cortex Neuroimaging Clin N Am2004;14(3):471-485

mem-7 Quinones-Hinojosa A, Ojemann SG, Sanai N, et al erative correlation of intraoperative cortical mapping withmagnetic resonance imaging landmarks to predict localiza-tion of the Broca area J Neurosurg 2003;99(2):311-318

Preop-8 Krings T, Schreckenberger M, Rohde V, et al tional MRI and 18F FDG-positron emission tomographyfor presurgical planning: comparison with electrical cor-tical stimulation Acta Neurochir (Wien) 2002;144(9):889-899; discussion 899

Func-9 Bartos R, Jech R, Vymazal J, et al Validity of primarymotor area localization with fMRI versus electric corticalstimulation: a comparative study Acta Neurochir (Wien)2009;151(9):1071-1080

10 Ribas GC, Yasuda A, Ribas EC, et al Surgical anatomy of croneurosurgical sulcal key points Neurosurgery 2006;59(4 Suppl 2):ONS177-ONS210; discussion ONS210-ONS211

mi-11 Greenberg MS, Arredondo N Handbook of Neurosurgery,6th edition New York: Thieme Medical Publishers, 2006,

pp xii-1013

12 Reis CV, Sankar T, Crusius M, et al Comparative study

of cranial topographic procedures: Broca’s legacy towardpractical brain surgery Neurosurgery 2008;62(2):294-310;discussion 310

13 Tamraz JC, Comair YG Atlas of regional anatomy of thebrain using MRI Berlin: Springer, 2000

14 Yousry TA, Schmid UD, Alkadhi H, et al Localization ofthe motor hand area to a knob on the precentral gyrus Anew landmark Brain 1997;120(Pt 1):141-157

15 Rhoton AL Jr The cerebrum Neurosurgery 2002;51(4Suppl):S1-S51

16 Naidich TP, Valavanis AG, Kubik S Anatomic ships along the low-middle convexity: Part I–Normal spec-imens and magnetic resonance imaging Neurosurgery1995;36(3):517-532

relation-17 Boling W, Olivier A, Bittar RG, Reutens D Localization ofhand motor activation in Broca’s pli de passage moyen JNeurosurg 1999;91(6):903-910

18 Boling W, Parsons M, Kraszpulski M, Cantrell C, Puce A.Whole-hand sensorimotor area: cortical stimulation local-ization and correlation with functional magnetic resonanceimaging J Neurosurg 2008;108(3):491-500

19 Boling WW, Olivier A Localization of hand sensory tion to the pli de passage moyen of Broca J Neurosurg2004;101(2):278-283

func-20 Boling W, Reutens DC, Olivier A Functional topography

of the low postcentral area J Neurosurg 395

2002;97(2):388-21 Kombos T, Suess O, Funk T, Kern BC, Brock M

Intra-operative mapping of the motor cortex during surgery

in and around the motor cortex Acta Neurochir (Wien)

2000;142(3):263-268

22 Lubrano V, Roux FE, Demonet JF Writing-specific sites

in frontal areas: a cortical stimulation study J Neurosurg

2004;101(5):787-798

23 Simos PG, Papanicolaou AC, Breier JI, et al

Localiza-tion of language-specific cortex by using magnetic source

imaging and electrical stimulation mapping J Neurosurg

1999;91(5):787-796

24 Sanai N, Mirzadeh Z, Berger MS Functional outcome

af-ter language mapping for glioma resection N Engl J Med

2008;358(1):18-27

25 Ojemann SG, Berger MS, Lettich E, Ojemann GA

Localiza-tion of language funcLocaliza-tion in children: results of electrical

stimulation mapping J Neurosurg 2003;98(3):465-470

26 Sereno MI, Dale AM, Reppas JB, et al Borders of

multiple visual areas in humans revealed by functional

magnetic resonance imaging Science

1995;268(5212):889-893

27 Tootell RB, Hadjikhani NK, Vanduffel W, et al Functional

analysis of primary visual cortex (V1) in humans Proc Natl

Acad Sci U S A 1998;95(3):811-817

28 Yoshor D, Bosking WH, Ghose GM, Maunsell JH

Recep-tive fields in human visual cortex mapped with surfaceelectrodes Cereb Cortex 2007;17(10):2293-2302

29 DeYoe EA, Carman GJ, Bandettini P, et al Mapping striateand extrastriate visual areas in human cerebral cortex ProcNatl Acad Sci U S A 1996;93(6):2382-2386

30 Tootell RB, Taylor JB Anatomical evidence for MT andadditional cortical visual areas in humans Cereb Cortex1995;5(1):39-55

31 Tootell RB, Reppas JB, Kwong KK, et al Functional ysis of human MT and related visual cortical areas usingmagnetic resonance imaging J Neurosci 1995;15(4):3215-3230

anal-32 Watson JD, Myers R, Frackowiak RS, et al Area V5 ofthe human brain: evidence from a combined study us-ing positron emission tomography and magnetic resonanceimaging Cereb Cortex 1993;3(2):79-94

33 Brugge JF, Volkov IO, Oya H, et al Functional localization

of auditory cortical fields of human: click-train stimulation.Hear Res 2008;238(1-2):12-24

34 Fenoy AJ, Severson MA, Volkov IO, Brugge JF, Howard MA3rd Hearing suppression induced by electrical stimulation

of human auditory cortex Brain Res 2006;1118(1):75-83

35 Howard MA, Volkov IO, Mirsky R, et al Auditory cortex

on the human posterior superior temporal gyrus J CompNeurol 2000;416(1):79-92

Chapter 2

Structural Imaging for Identification of

Functional Brain Regions

1Department of Neuroscience and Neuroradiology, Saint-Joseph University, Beirut, Lebanon

2Department of Neurosurgery, American University of Beirut, Beirut, Lebanon

Leuret and his pupil Gratiolet1 first attempted to classify

brain fissures before Meynert2 expanded on this

find-ing and gave a detailed account of the regional

varia-tions existing in the cortical mantle and their structural

and functional relationships A large body of literature

from the second part of the 19th and the early 20th

cen-turies reported on sulcal patterns in the human brain

Encephalometry, pioneered by Ariens Kappers in 1847,3

was one of the most extensively used methods to study

the brain Major contributions to our understanding of

cortical architecture and surface morphology were made

by von Economo and Koskinas,4who in 1925 developed

a highly detailed nomenclature for cortical surface

pat-terns, accompanied by a description of the

cytoarchitec-tural peculiarities of each region

The evolution of brain imaging followed a

sim-ilar path High-field, 3.0-T MR now provides a

high-resolution sectional atlas of each imaged brain region

and allows us to obtain a comprehensive rendering of

an entire brain in three dimensions (3D) Knowledge of

the gyral and sulcal anatomy and its variations remains

essential in understanding the relationship between

mor-phology and function

FISSURAL PATTERNS

The classification of cerebral sulci as primary, secondary,

or tertiary is widely used by neuroanatomists Primary

fissures can be described using comparative and

ontoge-netic approaches On the basis of comparative anatomy,

sulci found in all gyrencephalic primates may be defined

as primary Embryologically, these fissures appear early

in telencephalic development On reviewing previous

works and the work of Larroche and Feess-Higgins,5we

classified primary sulci as those appearing before the

30th week of gestation (Table 2–1) Secondary (Table2–2) and tertiary sulci (Table 2–3) occur later in devel-opment and are responsible for giving the adult brainits characteristic highly involuted and gyriform appear-ance For a better understanding of the sulcal and gyralanatomy, we will focus primarily on the primary andsecondary sulci Tertiary sulci are subject to marked in-dividual variations and are, therefore, difficult to iden-tify on MRI; only those that are relatively constant acrosssubjects will be annotated

CEREBRAL HEMISPHERE

Brain sulcation is most efficiently investigated using MRI surface renderings However, anatomic correlationsmay also be achieved indirectly using cross-sectionalanatomic atlases based on definite referentials6,7,8,9,10,11

3D-or by using two-dimensional (2D) MR slices12 typicallyencountered in clinical practice, particularly those ex-tending from the lateral aspect of the hemisphere toreach the insular level, or those showing a parasagittalview

SYLVIAN OPERCULA

The lateral or sylvian fissure is the major landmark onthe lateral surface of the brain It develops in the 14thweek of gestation and is the most important and con-stant of the cerebral sulci It may be divided into threesegments The first, or hidden stem segment, extendsfrom the lateral border of the anterior perforated sub-stance and courses over the limen insula in a posteriorlyconcave path before ending at the falciform sulcus, sep-arating the lateral orbital gyrus from the temporal pole.The second, or the horizontal segment, is the longest and

13

䉴 TABLE 2–1 CLASSIFICATION OF BRAIN

Weeks of Gestation Sulcal Maturation

13–15 Early sylvian fissure

16–17 Cingulate sulcus

Callosal sulcusParieto-occipital sulcus19–20 Calcarine

22–23 Circular sulcus

25–26 Central sulcus

Superior temporal sulcus (left)Superior part of precentral sulcusOlfactory sulcus

28–30 Intraparietal sulcus

Inferior frontal sulcusBranching of lateral sulcusParacentral sulcusCollateral sulcusSuperior frontal sulcus

the deepest, coursing on the lateral surface of the

hemi-sphere The third segment is limited anteriorly by the

transverse supratemporal sulcus, separating Heschl’s gyri

from the planum temporale and cutting into the superior

temporal gyrus This last segment is complex and

asym-metrical, and correlates with hemispheric dominance In

right-handed individuals, it ascends at an acute angle on

the nondominant right side, whereas on the left side it

assumes a superiorly directed oblique course (Fig 2–1)

Several branches are distinguished on the second

segment; two sulci of similar length (2–3 cm) are noted

cutting into the inferior frontal gyrus: the horizontal

ra-mus and the vertical rara-mus run divergent courses and

define a triangular space whose apex faces the sylvian

fissure These rami begin as branches from the sylvian

fissure, either separately in about two-thirds of subjects

or from a common trunk in the other one-third The

Frontal lobe Precentral

FrontomarginalOrbitofrontalRostral sulciParietal lobe Subparietal

Occipital lobe Paracalcarine sulci

Lateral occipitalTransverse occipitalLunate

Temporal lobe Rhinal

Transverse temporalInferior temporalInsular lobe Sulcus centralis insulae

Frontal lobe Intermediate frontal

DiagonalRadiateAnterior subcentralParietal lobe Transverse parietal

Intermediate sulciPrimary intermediateTemporal lobe Sulcus acousticusOccipital lobe Various individual variations

terminal segment usually bifurcates at its terminus, ing long terminal ascending and short terminal descend-ing branches The latter is the shallower posterior trans-verse supratemporal sulcus found on the right in abouttwo-thirds of cases The cortical regions adjacent to thelateral sulcus are the frontal, parietal, and temporal op-ercula covering the insular lobe

form-Figure 2–1 Three-dimensional MR sagittal cut through the perisylvian region 1, lateral fissure; 1a, ascending ramus of lateral fissure; 1b, horizontal ramus of lateral fissure; 1c, common trunk of ascending and horizontal rami; 1d, terminal ascending ramus; 1e, terminal descending ramus; 1f, temporal planum; 1g, anterior transverse supratemporal sulcus; 1h, posterior transverse temporal sulcus; 1i;

intermediate transverse temporal sulcus; 2, central sulcus; 3, inferior precentral sulcus; 4, inferior postcentral sulcus; 5, inferior frontal gyrus; 6, precentral gyrus; 7, postcentral gyrus; 8, frontal operculum; 9, parietal operculum; 10, superior temporal gyrus; 11, supramarginal gyrus; 12, inferior frontal gyrus, pars triangularis; 13, inferior frontal gyrus, pars orbitalis; 14, inferior frontal gyrus, pars opercularis; 15, transverse temporal gyri; 16, superior temporal sulcus; 17, middle temporal gyrus.

The horizontal ramus is a deep sulcus originating

from the lateral sulcus and cutting through the inferior

frontal gyrus to reach the circular sulcus of the insula

at its anterior border Superiorly, it does not reach the

inferior frontal sulcus It is absent on the right in 8% and

on the left in 16% of cases, according to Ono et al.13

This ramus forms the anterior border of the pars

trian-gularis (part of the classic Broca’s area), which is limited

posteriorly by the vertical ramus In the absence of the

horizontal ramus, a diagonal sulcus may mimic the usual

triangular shape of the pars triangularis, but will not

ex-tend to the insular level

The vertical ramus is defined by its extension to the

circular sulcus of the insula.14 It arises from the lateral

fissure as a separate sulcus or from a common trunk

with the horizontal ramus in one-third of the cases It is

almost constant, absent in 3% of cases,14 and does not

reach superiorly the inferior frontal sulcus

SULCUS

The inferior precentral sulcus is an important landmark,

representing an extension of the inferior frontal sulcus

in about 30% of subjects

The central sulcus is a deep sulcus that extends

verti-cally across the convexity and separates the frontal lobe

from the parietal lobe The central sulcus runs

anteri-orly oblique from superior to inferior It is typically

com-posed of three curves defined by a superior genu (knee)

and an inferior genu These genua are convex anteriorly

with an intervening concave bend The cortex located

between these genua represents the portion of the

pre-central gyrus that innervates the arm Smaller spurs cut

into the adjacent gyri as well as two submerged and

an-nectant gyri are often noted, one at the superior and

one at the inferior end of the central sulcus The straight

length of the adult central sulcus is 9 cm± 0.6 cm, and

when the central sulcus is measured with its curves, it

measures 10 cm± 0.7 cm.15

The central sulcus is deepest at the level of the

hand–arm representation, which lies roughly at the

mid-portion of the sulcus At the level of the face

represen-tation, corresponding to its first 3 cm, it is slightly less

deep, averaging 15 mm At the level of the trunk

repre-sentation, the recurrence of the annectant gyrus reduces

its depth to 12 mm In the interhemispheric portion,

which is the site of the leg representation, the sulcal

depth approaches 13 mm The central sulcus is rarely

interrupted along most of its course along the lateral

Figure 2–2 Three-dimensional MR view of the lateral aspect of the brain 1, central sulcus; 2, superior frontal sulcus; 3, superior precentral sulcus; 4, inferior frontal sulcus; 5, inferior precentral sulcus; 6,

intermediate frontal sulcus; 7, lateral sulcus; 8, postcentral sulcus or ascending segment of intraparietal sulcus; 9, superior postcentral sulcus; 10, intraparietal sulcus, horizontal segment; 11, lateral occipital or descending ramus of intraparietal sulcus;

12, Central gyrus; 13, annectent gyrus or “pli de passage” between middle frontal gyrus and precentral gyrus; 14, postcentral gyrus; 15, superior frontal gyrus; 16, middle frontal gyrus; 17, inferior frontal gyrus; 18, superior parietal gyrus; 19, inferior parietal lobule; 20, common stem of vertical and horizontal rami; 21, diagonal sulcus; 22, posterior subcentral sulcus; 23, transverse temporal sulcus;

24, superior temporal sulcus; 25, inferior temporal sulcus; 26, superior temporal gyrus; 27, middle temporal gyrus.

hemisphere, until it terminates inferiorly just short of thelateral fissure, with a hook-like end at its inferior marginthat contributes to the frontoparietal operculum Anas-tomoses with the subcentral, precentral, and postcentralsulci occur in about 50% of cases Extension into thelateral fissure is found in less than 20% of cases, with

an anastomosis with the anterior or posterior subcentralsulci Superiorly, the rolandic sulcus reaches the supe-rior border of the hemisphere and may extend over themesial aspect of the hemisphere as a small sulcus givingthe appearance of a comma,16 found in about 70% ofcases (Fig 2–2)

The inferior frontal sulcus arises anteriorly at the level

of the lateral orbital gyrus, and courses roughly parallel

to the lateral sulcus It is a deep sulcus almost reaching

Figure 2–3 Three-dimensional MR view of the

superior aspect of the brain showing the sulcation

and gyration of the upper central region 1, central

sulcus; 2, superior precentral sulcus; 3, superior

postcentral sulcus; 4, medial precentral sulcus; 5,

superior frontal sulcus; 6, marginal ramus of callosal

sulcus; 7, Precentral gyrus; 8, superior extent of

precentral gyrus; 9, postcentral gyrus; 10, superior

extent of postcentral gyrus; 11, superior frontal gyrus;

12, superior parietal gyrus; 13, interhemispheric

fissure.

the insular plane and ending at the inferior precentral

sulcus More developed and constant than the superior

frontal sulcus, it is interrupted in about 30% of cases

SULCUS

The superior frontal sulcus arises from the orbital

margin of the hemisphere and courses parallel to the

interhemispheric fissure, extends along about two-thirds

of the frontal lobe and gradually separates from the

interhemispheric fissure It is frequently doubled or

interrupted along its course,13 and ends posteriorly at

the precentral sulcus in a T-shaped branching in half of

cases (Fig 2–3) Anteriorly, it may anastomose with the

frontomarginal sulcus

In two-thirds of cases, the precentral sulcus is divided

into superior and inferior precentral sulci, which are

sep-arated by a connection between the precentral and the

middle frontal gyri, with the latter extending into the

central motor cortex It is composed of three segments

in about 15% of cases The precentral sulcus courses

an-terior and parallel to the central sulcus and is formed by

the posterior bifurcations of the inferior and the superior

frontal sulci The superior end of the inferior precentralsulcus is located anterior to the inferior end of the supe-rior precentral sulcus (Fig 2–1) The inferior end of theinferior precentral sulcus may connect with the lateralsulcus either directly or through the anterior subcentral

or the diagonal sulcus The superior precentral sulcus isusually smaller than the inferior precentral sulcus, andhas a complex relationship with the rolandic motor cor-tex It rarely reaches the superior hemispheric border,and instead is replaced by one or two sulci: a horizontalsulcus running parallel to the interhemispheric fissure,that is, the shallow marginal precentral sulcus; and themedial precentral sulcus, a vertical sulcus situated an-terior to the precentral sulcus and perpendicular to theinterhemispheric border Therefore, there is no clear sul-cal demarcation between the supplementary motor area(SMA) and the primary motor cortex (Fig 2–3)

The intraparietal sulcus is divided into three parts, theascending postcentral, horizontal, and descending or oc-cipital segments The ascending segment is a vertical seg-ment that corresponds to the inferior portion of the post-central sulcus and may extend, especially on the righthemisphere, to the lateral sulcus The horizontal or trueintraparietal segment has variable relationships with theinferior and superior postcentral sulci, but is continuouswith both the inferior and superior postcentral sulci inalmost 40% of cases The inferior postcentral segment iscontinuous with the superior postcentral sulcus in about60% of the cases The postcentral sulcus shows widevariations and is frequently deeper than the central sul-cus Its horizontal segment is one of the deeper sulci

in the human brain (2 cm in depth) The descendingsegment almost always terminates in the occipital lobeand may even reach its pole This segment shows aT-shaped ending in about two-thirds of cases,13 de-scribed as the transverse occipital sulcus The superiorend of the postcentral sulcus terminates most frequently

on the lateral aspect of the hemisphere without sion to the medial aspect, in a Y-shaped configuration

exten-At this Y-shaped end, it is joined by the marginal mus of the cingulate sulcus as it extends to the lateralaspect of the hemisphere indenting its superior border

the rolandic cortex on the interhemispheric surface

SULCUS

The superior temporal sulcus, one of the oldest of theprimate brain, is also called the parallel sulcus because

it follows closely the course of the lateral fissure (sylvian

fissure) It is a deep sulcus (2.5–3 cm) almost reaching

the level of the inferior border of the insula Infrequently,

it divides into anterior and posterior segments, usually

below the inferior end of the central sulcus At the level

of the central sulcus, an inconstant sulcus acousticus may

be present, which originates from the parallel sulcus and

courses toward the lateral fissure, limiting the anterior

extent of the gyrus of Heschl The posterior part of the

parallel sulcus is the angular sulcus, which penetrates

into the inferior parietal lobule

The frontomarginal sulcus is fairly constant and deep,

found at the frontal pole parallel to the orbital margin

It is connected posteriorly with the middle frontal

sul-cus more frequently than with the superior frontal It

separates the transverse frontopolar gyri from the

fron-tomarginal gyrus inferiorly

OF THE CEREBRAL HEMISPHERE

The convolutions on the lateral aspect of the cerebral

hemisphere determined by these primary fissures are the

inferior, middle, and superior frontal gyri, the pre- and

postcentral gyri, and the inferior and superior parietal

convolutions, in the suprasylvian region, and the

supe-rior, middle and inferior temporal gyri, in the infrasylvian

region The gyri of the parietal and the temporal lobes

merge posteriorly with the variable occipital gyri, which

in turn are generally delimited by a superior, lateral, and

inferior occipital sulci (Fig 2–2)

The frontal lobe, the largest of the hemisphere, is

com-prised of four gyri The gyri on the lateral aspect of

the frontal lobe are the inferior, the middle, and the

su-perior frontal gyri, which follow a course that roughly

parallels the superior border of the hemisphere

Me-dially, the frontal lobe consists of a hook-like gyrus

bounded inferiorly by the cingulate sulcus Posteriorly,

the precentral gyrus parallels the central sulcus, which

forms the boundary between the frontal and parietal

lobes

The inferior frontal gyrus is situated between the

inferior frontal sulcus and the lateral sulcus and includes

both horizontal and vertical rami These rami divide the

gyrus into three parts: the pars orbitalis, the pars

trian-gularis, and the pars opercularis The orbital component

Figure 2–4 Three-dimensional MR view of the brain showing the sulcal and gyral pattern of the inferior frontal region and the anterior speech cortical area.

1, lateral sulcus; 2, horizontal ramus of lateral sulcus;

3, ascending ramus of lateral sulcus; 4, radiate sulcus; 5, inferior precentral sulcus; 6, diagonal sulcus; 7, central sulcus; 8, anterior subcentral sulcus;

9, posterior subcentral sulcus; 10, precentral gyrus;

11, annectent gyrus; 12, postcentral gyrus; 13, pars opercularis of inferior frontal gyrus; 14, pars triangularis of inferior frontal gyrus; 15, pars orbitalis

of inferior frontal gyrus; 16, superior temporal gyrus;

17, middle frontal gyrus; 18, superior frontal gyrus;

19, frontomarginal gyrus; 20, inferior parietal lobule.

runs into the basal orbital aspect of the hemisphere Theopercular component merges with the lower extension

of the precentral gyrus, together constituting the frontaloperculum The inferior frontal gyrus is more devel-oped in the dominant hemisphere, particularly the parstriangularis and pars opercularis, which together formBroca’s area, the cortical region that is most essentialfor expressive speech The pars triangularis is traversed

in more than one-third of cases by the radiate sulcus(Fig 2–4)

The middle frontal gyrus is located between the ferior and the superior frontal sulci and is separated fromthe precentral gyrus posteriorly by the precentral sulci

in-It is connected to the precentral gyrus by a deep nectent gyrus It is traversed by an inconstant interme-diate frontal sulcus, which usually ends as a part of thefrontomarginal sulcus

an-The superior frontal gyrus is situated between thesuperior frontal sulcus and the dorsal margin of thehemisphere It continues on the medial aspect ofthe hemisphere as the medial frontal gyrus and is con-nected posteriorly to the central gyrus The precentralgyrus is located between the central sulcus and the in-ferior and superior frontal sulci It is limited inferiorly

by the lateral sulcus and extends superiorly to reach the

superior border of the hemisphere, where it is

continu-ous with the paracentral lobule on the medial aspect of

the hemisphere (Fig 2–2)

The parietal lobe is located superior to the lateral

fis-sure and behind the central sulcus, extending

posteri-orly to an arbitrary line connecting the lateral extent of

the parieto-occipital sulcus to the preoccipital notch It

extends to the medial aspect of the hemisphere as the

medial postcentral gyrus anteriorly and as the precuneus

gyrus posteriorly Its largest portion on the lateral surface

of the hemisphere is divided into three gyri by the

intra-parietal sulcus: the inferior intra-parietal, the superior intra-parietal,

and the postcentral gyri

The postcentral gyrus is found posterior to the

cen-tral sulcus, with its lower end connected to the inferior

precentral gyrus The inferior parietal lobule is situated

between the lateral fissure inferiorly, the horizontal

seg-ment of the intraparietal sulcus superiorly, and the

as-cending postcentral segment of the intraparietal sulcus

anteriorly It is composed from front to back as the

supramarginal gyrus arching over the terminal

ascend-ing ramus of the lateral fissure, the angular gyrus archascend-ing

over the extremity of the upturned branch of the

paral-lel sulcus, and the posterior parietal gyrus, which may

cap the posterior end of the inferior temporal sulcus

The supramarginal and the angular arched convolutions

are separated by a short sulcus, the primary intermediate

sulcus.17 The angular gyrus may be separated from the

posterior parietal by the secondary intermediate sulcus18

(Fig 2–5)

The superior parietal lobule is located dorsal to the

inferior parietal lobule, limited inferiorly by the

intra-parietal sulcus, anteriorly by the superior postcentral

sulcus, and extends posteriorly to the lateral extremity

of the parieto-occipital sulcus, beyond which it passes

into the occipital lobe as the arcus parieto-occipitalis

or the superior parieto-occipital “pli de passage” of

Gratiolet.19

Somewhat pyramidal in shape, the temporal lobe has

lateral, basal, and dorsal aspects and an anterior apex

or pole The lateral aspect is bounded superiorly by the

lateral fissure, which separates it from the frontoparietal

lobes Caudally, it is continuous with the inferior parietal

lobule superiorly, and with the occipital lobe, inferiorly

Ventrally, the temporal lobe extends to the collateral

sul-cus at the basal aspect of the hemisphere, which

sepa-rates it from the limbic lobe The lateral convolutions of

the temporal lobe, oriented anteroposteriorly, are three

Figure 2–5 Three-dimensional MR view of the lateral aspect of the brain showing the sulcal and gyral anatomy of the inferior temporo-parieto-occipital region and the posterior speech cortical area 1, interhemispheric fissure; 2, lateral sulcus; 3, terminal ascending ramus of lateral sulcus; 4, parallel sulcus;

5, terminal ascending branch of parallel sulcus or angular sulcus; 6, intraparietal sulcus, horizontal segment; 7, sulcus intermedius primus; 8, sulcus intermedius secundus; 9, superior occipital sulcus; 10, transverse occipital sulcus; 11, lateral occipital sulcus;

12, inferior temporal sulcus; 13, Postcentral gyrus; 14, inferior parietal lobule; 15, superior parietal gyrus; 16, supramarginal gyrus; 17, angular gyrus; 18, posterior parietal gyrus; 19, superior temporal gyrus; 20, middle temporal gyrus; 21, inferior temporal gyrus; 22, inferior occipital gyrus; 23, superior occipital gyrus;

24, middle occipital gyrus, 25 occipital pole.

in number: the superior, middle, and inferior temporalgyri (Fig 2–2)

The superior temporal gyrus is located between thelateral fissure above and the parallel superior temporalsulcus below Its anterior extent contributes to the for-mation of the temporal pole, and its posterior extremitymerges with the supramarginal gyrus The dorsal surface

of this gyrus called the operculoinsular surface is dividedinto an opercular and an insular segment The former islocated in relation to the frontal and parietal operculaand the latter is related to the insula One or two trans-verse temporal gyri of Heschl,20 cross the dorsal aspect

of the superior temporal gyrus, obliquely forward, at thedepth of the lateral fissure More frequently doubled onthe right side, these gyri are separated at least partly by

an intermediate transverse temporal sulcus These gyriare posteriorly separated from the planum temporale,

by the transverse supratemporal sulcus of Holl21 nating from the lateral fissure The frontal boundary ofthe Heschl gyri is marked by the anterior limiting sulcus

origi-of Holl

The middle temporal gyrus is separated from the

superior temporal gyrus by the superior temporal sulcus

and bounded inferiorly by the inferior temporal sulcus,

which is regularly interrupted This gyrus is continuous

posteriorly with the angular gyrus superiorly, and with

the occipital lobe inferiorly

The inferior temporal gyrus is bounded superiorly

by the inferior temporal sulcus and extends inferiorly

over the basolateral border of the cerebral hemisphere,

to the inferior surface limited by the occipitotemporal

sulcus It is largely discontinuous extending like the

oc-cipitotemporal gyrus close to the preoccipital notch At

this level, it is continuous posteriorly and inferiorly with

the inferior occipital gyrus

The occipital lobe occupies the posterior aspect of the

hemisphere and is the smallest of all hemispheric lobes

It is formed by the presence of two longitudinal

parieto-occipital “plis de passage” of Gratiolet: the first occupies

the superior aspect of the hemisphere and joins the

su-perior parietal gyrus to the susu-perior occipital gyrus,

lim-ited laterally by the occipital segment of the intraparietal

sulcus; the second joins the angular gyrus to the

mid-dle occipital gyrus This gyrus is the largest of the lateral

aspect of the occipital lobe and may be subdivided into

superior and inferior portions by the occipital lateral

sul-cus, which may anastomose anteriorly with the parallel

sulcus Two other temporal occipital “plis de passage,”

which are separated by an inconstant inferior occipital

sulcus that may correspond to a side branch of the

in-ferior temporal sulcus, occupy the inin-ferior lateral aspect

of the occipital lobe The anterior extent of the inferior

occipital gyrus is ill-defined and continuous anteriorly

with the inferior temporal gyrus (Fig 2–5)

The insula of Reil is the smallest of the cerebral lobes

found in the depth of the lateral fissure It is triangular

in shape with an apex directed anteriorly and inferiorly,

called the monticulus, and overhangs the falciform

sul-cus and the preinsular region The latter is connected

to the anterior perforated substance through the limen

insulae The insula is separated from the frontoparietal

and the temporal opercula by the circular sulcus

The insula proper is constituted of convergent gyri

presenting a fan-like arrangement, usually separated into

three short and one or two long convolutions by the

cen-tral sulcus insulae, the deepest and longest of all insular

furrows reaching the circular sulcus It originates from

the superior limiting sulcus and is directed obliquely

to-ward the falciform sulcus The insular lobe covers the

lentiform nucleus, separated from it laterally to mesially

by the extreme capsule, the claustrum, and the externalcapsule The sulci of the insula bear a relatively constantrelationship with the overlying cortical sulci The centralsulcus appears to be continuous with the central sulcus

of the insula, interrupted at the level of the hidden tral operculum

THE PRECENTRAL GYRUS

Anatomically, the precentral gyrus can be divided intofour segments, defined by its three bends and the para-central lobule

The inferior segment is convex anteriorly, and it

is close to the lateral fissure, which marks the inferiorboundary of the precentral gyrus It commonly commu-nicates with the postcentral gyrus, forming the centraloperculum Medially, it reaches the insula and frequentlycommunicates with the pars opercularis of the frontallobe

The middle segment is convex posteriorly Thejunction between the inferior and middle segments ischaracterized by a tapering of the gyrus, which corre-sponds to the transition area between face and thumbrepresentation This segment has no clearly defined lim-its anteriorly, as it extends into the premotor area, due

to the interruption of the precentral sulcus in this region.Posteriorly, it is sharply bound by the central sulcus andmedially by the corona radiata

The superior segment is convex anteriorly In itsinitial segment, it is sharply distinct from the premo-tor cortex Toward the interhemispheric fissure, theseboundaries become difficult to define as this gyrusmerges with the SMA It is sharply bound posteriorly

by the central sulcus, superiorly by the interhemisphericfissure, and medially by the corona radiata The direction

of the superior segment assumes a less oblique coursethan that of the middle segment

The paracentral segment occupies the posterior tent of the paracentral lobule with no sharp anterior

ex-boundaries Posteriorly, it appears to be demarcated for

a short distance by the central sulcus Most stimulation

studies do not, however, corroborate a functional

cor-relate to this anatomy, as primary motor and sensory

responses are not elicited in the inferior portion of the

paracentral lobule

THE POSTCENTRAL GYRUS

The postcentral gyrus can also be divided into four

seg-ments Its configuration closely resembles the precentral

gyrus Inferiorly, in the opercular region, it is wider and

thicker than its motor counterpart The middle and

su-perior segments are thinner and more sharply defined

by the postcentral sulcus Superiorly, since the

postcen-tral sulcus terminates caudal to the marginal ramus of

the cingulate sulcus, the primary sensory area of the leg

extends beyond the paracentral lobule

The premotor cortex is a transitional area located

be-tween the frontal pole and the primary motor cortex Its

boundaries in humans are not well defined and gyral

patterns in this region appear to vary considerably

be-tween subjects The anterior boundary is arbitrarily

de-fined as a line joining the anterior extent of the SMA with

the frontal eye field Posteriorly, the premotor cortex is

delimited by the precentral sulcus

REPRESENTATION IN THE

CENTRAL CORTEX

Although there is clear evidence for a functional overlap

in the representation of specific body areas,24 the

pri-mary motor and sensory cortices that straddle the central

sulcus follow a generally orderly pattern of somatotopic

organization that is well represented in the classic

ho-munculus of Penfield and Rasmussen.22 These authors

hypothesized that the motor and sensory units were

ar-ranged in horizontal strips extending from precentral to

postcentral sulci and across the central sulcus Thus, the

sensorimotor cortex can be divided from inferior to

su-perior into four functional units:1the face unit, extending

from the lateral sulcus (sylvian fissure) superiorly to

ap-proximately 3 cm;2 the hand–arm unit, starting with the

thumb representation corresponding to the inferior genu

and ending at the shoulder area;3the trunk unit,

border-ing on the interhemispheric fissure;4 the leg–foot unit,

located at the mesial aspect of the hemisphere within

the paracentral lobule (Fig 2–2)

THE LOCALIZATION OF THE CENTRAL SULCUS

Different approaches have been used for the localization

of the central sulcus Historically, indirect approacheshave relied on skull landmarks and, more recently, onbrain reference coordinates Two widely used indirectmethods are the Talairach method based on the AC–PC(anterior commissure–posterior commissure) referenceplane8,25,26,27,28and the Olivier method based on the cal-

losal reference plane.29,30,31Direct anatomic approaches

rely on identification of the central sulcus with ern imaging modalities Various authors have describedlandmarks for localization of the central sulcus, whichare visible on axial and sagittal MR scans,12,32) Iden-

mod-tification of the superior frontal sulcus and the distinct

“hand know” on axial MR image usually permits forward identification of the central sulcus On sagittalimages, the marginal ramus of the cingulated sulcus canusually be followed superiorly to identify the postcentralsulcus, which lies one sulcus posterior the central sulcus.Using oblique 2D cuts obtained parallel to the “fornicealreference plane,” the pericentral anatomy can be eas-ily and precisely displayed.62 All these 2D methods lackthe ability to visualize the full extent of the central sul-cus For this reason, 3D MR has been used as a superioralternative Another approach relies on direct identifica-tion of the sensorimotor cortex using functional imagingtechniques such as positron emission tomography, mag-netoencephalography, or functional MRI While thesemethods add additional complexity to image acquisition,they allow identification of sensorimotor cortex in sub-jects with aberrant anatomy, such as patients with corti-cal dysplasia or with tumors that efface nearby gyri andsulci

IMAGING OF THE ANTERIOR SPEECH AREA

The anterior speech region was defined byBroca33,34,35,36 as including the posterior third of theleft inferior frontal gyrus Rasmussen defines the speecharea as including the pars triangularis and pars opercu-laris of the dominant frontal lobe However, extensivecortical stimulation studies by Penfield and Roberts,37

Penfield and Rasmussen,22 Ojemann et al.38 and Sanai

et al.90 have shown marked individual variations in theanterior speech area In fact, many cortical stimulationand functional imaging studies have shown anteriorspeech representation outside of the anatomicallydefined Broca’s area (Fig 2–4)

Broca’s anterior speech area includes the

cytoar-chitecturally defined Brodmann’s area 45 This speech

area is anatomically limited anteriorly by the horizontal

ramus of the lateral sulcus and posteriorly by the

in-ferior segment of the precentral sulcus Inin-feriorly it is

limited by the posterior ramus of the lateral sulcus and

superiorly by the inferior frontal sulcus Two gyri thus

constitute this area, the pars triangularis and the pars

opercularis of the inferior frontal lobe The pars

trian-gularis is limited anteriorly by the horizontal ramus and

posteriorly by the vertical ramus of the lateral sulcus

It is characteristically U-shaped in the dominant

hemi-sphere and Y-shaped in the nondominant hemihemi-sphere

It is traversed superiorly by the incisura capitis branch

of the radiate sulcus The pars triangularis extends deep

into the third frontal convolution, reaching the level of

the insula The pars opercularis is located in between the

vertical ramus and the inferior precentral sulcus It is

lim-ited inferiorly by the sylvian fissure, reaching the inferior

frontal sulcus superiorly It communicates with the pars

triangularis superiorly and anteriorly Posteriorly and

in-feriorly it can communicate with the precentral gyrus It

may be divided into two parts by the shallow diagonal

sulcus.14 More frequently found on the left (72%) than

over the right (64%) side, the diagonal sulcus appears

to almost always be connected to the sylvian fissure on

the right and only infrequently on the left, according to

Ono et al.13

IMAGING OF THE POSTERIOR

SPEECH AREA

Because of its marked variability,37 the anatomic

local-ization and extent of the posterior speech area is

diffi-cult and can only be determined by cortical stimulation

Functional MRI has contributed some insight into the

organization and localization of speech

Numerous stimulation studies and cortical excisions

most frequently infrasylvian and includes the posterior

extent of the first temporal convolution and the mid and

posterior second temporal gyrus Speech appears not

to extend to the third temporal convolution (the

infe-rior temporal gyrus) and is, in some cases, exclusively

suprasylvian Thus, it is localized to the supramarginal

and angular gyri The inferior parietal lobule is divided

into three contiguous convolutions: the supramarginal,

the angular, and the posterior parietal gyri, which are

separated by two intermediate sulci The primary

inter-mediate sulcus is present in 24% of cases on the right

side and in 80% on the left The secondary intermediate

sulcus is present in 64% of cases on the right and 72% on

the left.13 Variations of the gyral pattern of the inferior

parietal lobule were pointed out by Naidich et al.12whoreported the presence of accessory supernumerary gyri

in the inferior parietal lobule: a presupramarginal gyrus,found in 16% of cases on the left and 4% on the rightside, and a preangular gyrus found in 28% on the leftand 16% on the right side

The posterior speech area includes: Heschl’sgyrus,20 the temporal planum, the parietal operculum,the parietal and temporal speech related gyri

Heschl’s gyrus is a hidden arch-like gyrus locatedentirely within the lateral sulcus and assuming a poste-rior oblique orientation within the supratemporal plane.This relationship is seen on axial MR cuts performed inthe sylvian plane orientation, as obtained using the “CH–

PC (chiasmatico-commissural) reference plane.”40,41 Its

anatomical landmarks are: the chiasmal point (CH) teriorly and the PC posteriorly, readily shown on a mid-sagittal MR scout view

an-Heschl’s gyrus is limited anteriorly and posteriorly

by transverse supratemporal sulci According to Baileyand von Bonin, the posterior transverse supratemporalsulcus is the most constant sulcus and is easily visualized

on the lateral surface of the temporal lobe originatingfrom the sylvian fissure with a distinct anterior obliqueorientation, located in close proximity to the postcen-tral sulcus It separates Heschl’s gyrus from the planumtemporale The anterior transverse supratemporal sulcusconstitutes the anterior border of Heschl’s gyrus, reach-ing the lateral aspect of the temporal lobe at the level ofthe central sulcus The intermediate sulcus is inconstantand does exist when two Heschl’s gyri, mainly on theright side, are noted.42 As Duvernoy notes, the sulcusacusticus is the furrow that originates from the parallelsulcus and heads toward Heschl area Heschl’s gyri aretypically larger and more obliquely oriented on the leftside and shorter on the right side (Fig 2–1) Although

it is assumed that the entire Heschl’s gyrus corresponds

to the primary auditory cortex, stimulation studies haveelicited responses from its posteromedial extent close

to the level of the insula.43 Strainer et al.,44 using puretone activation, showed different tonotopic organizationwithin Heschl’s gyri, depending on the frequency of theauditory stimulus: responses elicited for tones in thelower frequencies (1000 Hz) predominated in the lat-eral transverse temporal gyrus, whereas those of higherfrequencies (4000 Hz) appear localized in the medialtransverse temporal gyrus

The temporal planum is a triangular cortical face, apparent as early as the 29th week of gestation,51

sur-studied initially by von Economo and Horn45and quently by others.27,42,46,47,48,49,50It is limited laterally by

subse-the lateral sulcus and anteriorly by subse-the posterior verse supratemporal sulcus Its posterior limit is not welldefined Habib et al.52,53,54 and Steinmetz et al.,55,56,57considered the terminal descending branch of the lat-eral sulcus as the posterior limit In the absence of

trans-this branch, the temporal planum includes the entire

supratemporal extent of the third division of the sylvian

fissure (Fig 2–1) Cytoarchitecturally, it corresponds to

the posterior portion of area 22 of Brodmann In most

in-dividuals, the left temporal planum is wider than its

right-sided counterpart and is formed by several small gyri

that assume a superior oblique orientation The

right-side planum has a smaller cortical surface and a flat

surface.54,58 Dominance of the left cerebral hemisphere

for speech was noted early in the 19th century by Marc

Dax in 1836,63 promoter of the concept of speech

local-ization in the left hemisphere followed by Paul Broca36

and Wernicke,64 according to Alajouanine.65

Imaging identification of the posterior speech area

has been carried out extensively by Salamon and

collaborators54,59,60,61 using the bicommissural AC–PC

coordinates These authors demonstrated that the

peri-sylvian cortical speech area and the inferior parietal

lob-ule may be reliably explored using a limited number

of cuts (four slices, 5 mm thick), oriented parallel to

the bicommissural plane, and performed at 45 mm and

50 mm above the reference line, to display the posterior

part of the first and second temporal gyri, and at 60 mm

and 70 mm, to explore the supramarginal and angular

gyri.60 Using MRI, the temporal planum is best explored

in the axial plane using CH–PC coordinates and in

coro-nal plane perpendicular to the sylvian CH–PC reference

as obtained using the PC–OB (posterior commissure–

obex) reference plane This coronal approach permits

identification of the sylvian fissure followed on more

posterior sections on the left and located higher on the

right It allows a direct evaluation of the depth of the

planum and an easy depiction of Heschl’s gyri on both

sides The axial cuts performed parallel to the CH–PC

ref-erence plane, which corresponds to the sylvian fissure

orientation plane,39,40,62best evaluate the supratemporal

region displaying, from anterior to posterior, the gyral

anatomy of the planum polare, the transverse temporal

gyri, and posteriorly the temporal planum

CEREBRAL HEMISPHERE

The specific gyral patterns characteristic of the

inter-hemispheric area are influenced by the development of

the callosal connections Sulci and gyri of the mesial

as-pect of the hemisphere are evident on a sagittal and

2D-parasagittal cuts of the brain (Fig 2–6)

THE ROSTRAL SULCI

Also called the callosomarginal sulcus, the cingulate

sul-cus begins below the rostrum of the corpus callosum,

Figure 2–6 Two-dimensional MR parasagittal cut of the brain, showing the main sulci and gyri of the mesial aspect of the hemisphere 1,callosal sulcus; 2,

cingulate sulcus; 3, marginal ramus of cingulate sulcus; 4, central sulcus; 5, paracentral sulcus; 6, parieto-occipital sulcus; 7, subparietal sulcus; 8, superior rostral sulcus; 9, inferior rostral sulcus; 10, calcarine sulcus, posterior segment; 11, calcarine sulcus, anterior segment; 12, transverse parietal sulcus; 13, cingulate gyrus; 14, medial frontal gyrus;

15, paracentral lobule; 16, postcentral gyrus; 17, precentral gyrus; 18, subcallosal gyrus; 19, fronto-orbital gyri; 20, isthmus cinguli; 21, cuneus; 22, precuneus; 23, lingual gyrus; 24, parahippocampal gyrus; 25, parietolimbic “pli de passage”; 26, cuneolingual gyrus; 27, retrocalcarine sulcus; 28, frontopolar gyri; 29, gyrus descendens; 30, temporal pole.

in the subcallosal region, before it sweeps around thegenu paralleling the corpus callosum, separating the me-dial frontal gyrus from the cingulate gyrus, ending as amarginal ramus in the parietal lobe and separating theprecuneus from the paracentral lobule The marginal ra-mus has a fairly constant relationship to the central sul-cus, ending about 10 mm posterior to it Up to threeinterruptions are frequently noted along its course lead-ing to invaginations of the mesial frontal gyrus into thecingulate gyrus, as the “plis de passage frontolimbiques”

of Broca (Fig 2–6)

The superior rostral sulcus courses orly around the rostrum of the corpus callosum and endsclosely behind the frontal pole It is roughly parallel tothe anterior cingulate sulcus and is very frequently dou-bled by an inferior, shallower accessory rostral sulcus(Fig 2–6)

SULCUS

The parieto-occipital sulcus is a deep, constant sulcus

of the primate brain, situated on the posterior mesial

aspect of the hemisphere, extending downward from

the dorsal margin forward to the caudal aspect of the

splenium where it joins the stem of the calcarine sulcus

It continues as the external incisure on the lateral aspect

of the hemisphere for a short distance (about 10–12 mm)

cutting deeply into its edge A line connecting the

parieto-occipital incisure to the preoccipital notch draws

the arbitrary boundary on the lateral surface separating

the occipital lobe from the temporal and parietal lobes

THE STRIATE VISUAL CORTEX

The calcarine sulcus arises behind and just below the

splenium of the corpus callosum and proceeds

posteri-orly toward the occipital pole This deep sulcus is

di-vided into two segments at the point of its junction with

the parieto-occipital sulcus The first, cephalad to this

junction, is the anterior calcarine sulcus The second is

the posterior calcarine sulcus, a caudal division that

typ-ically ends posteriorly in a bifurcation on the medial

as-pect of the hemisphere One or two submerged gyri, the

anterior and the posterior cuneolingual folds of D´ejerine,

may be found within the posterior calcarine segment,

and may be seen on parasagittal MR images The

up-per and the lower lips of the posterior calcarine sulcus

and the lower lip only of the anterior calcarine sulcus,

correspond to the striate visual cortex (area 17)

The striate or primary visual cortex is limited

pos-teriorly by the lunate sulcus, when present, and may

extend beyond the occipital pole of the hemisphere for

a distance of 1–1.5 cm This extension onto the medial

posterior aspect of the occipital pole shows important

individual variations The cortex of the visual sensory

area identified histologically by a white line (or

stria-tion), the line of Gennari, which is a layer of myelinated

terminals of optic radiations fibers The parieto-occipital

sulcus limits the striate cortex anteriorly An average of

67% of the visual cortex is buried in the depth of the

calcarine fissure and its branches The area of the striate

cortex is greater below than above the calcarine fissure,

extending about 2 cm more anteriorly The striate

cor-tex is situated between the cuneus, a wedge-shaped area

located above the calcarine sulcus whose surface is

gen-erally indented by one or two small sulci, and the lingual

gyrus lying below, between the calcarine sulcus

superi-orly and the collateral sulcus inferisuperi-orly (Fig 2–6) The

cuneus and lingual gyri are both part of the extrastriate

visual cortex

Considering the functional and anatomic aspects of

the visual cortex,66 there is general agreement regarding

the following conception of cortical representation: the

upper half of each retina is retinotopically represented

in the dorsal part of the occipital striate cortex and the

lower half in the ventral part Regarding the disposition

of the macular fibers, Holmes considered it to be located

on the tip of the posterior pole of the cerebral sphere, whereas according to Polyak, a wide distribution

hemi-of these fibers along the calcarine sulcus is observed.The striate cortex (area 17) is intimately related tothe parastriate cortex (area 18), which lies in a portion ofthe occipital lobe contiguous to the latter The Gennariband is not found in this area The peristriate area (area19) is much larger than area 18, lying on the lateral as-pect of the cerebral hemisphere and extending beyondthe medial aspect of the hemisphere to surround theparastriate area from above and below Most of the peri-striate area lies in the posterior part of the parietal lobe

It extends inferomedially to the posterior portion of thetemporal lobe (Fig 2–5)

Considering imaging, many authors have proposedreference planes and have tried to describe the ideal an-gulations to use with respect to the orbitomeatal line or

to an anthropologically based line.39,40,62,67,68,69,70,71,72,73,

The best compromise would be a reference plane able for exploration of both the optic pathways and thebrain For this reason, the neuro–ocular plane, as theanatomophysiological and anthropological cephalic ref-erence plane, appears to be the most suitable for study-ing the visual pathway.68,69,71,72 It is, in our opinion,also efficient enough for evaluation of the retrochias-matic pathways in routine practice In order to facilitatethe neuroanatomical approach and optimize topometricstudies of the brain and the retrochiasmal visual path-ways, the CH–PC line, defining a CH–PC reference plane

suit-is used.39,40,74,75

The calcarine fissures and striate cortex are shown

on the midsagittal cut of the brain, and may also be picted on coronal and axial cuts Their close relationship

de-to the occipital horns of the lateral ventricle may aid intheir recognition However, there is no ideal cephalicorientation for studying the calcarine fissures, as theyare variable in shape among individuals Note that theCH–PC reference line intersects posteriorly the commonstem of the parieto-occipital and calcarine sulci

OF THE CEREBRAL HEMISPHERE

Seven gyri constitute the mesial hemisphere.76 Theseare described as follows, from anterior to posterior(Fig 2–6)

THE GYRUS RECTUS

The gyrus rectus is limited inferiorly by the floor of theanterior cranial fossa, laterally by the olfactory sulcus,and superiorly by the superior rostral sulcus (Fig 2–7)