Ebook Neuroradiology - Key differential diagnoses and clinical questions: Part 1

(BQ) Part 1 book Neuroradiology - Key differential diagnoses and clinical questions presents the following contents: Computed tomography hyperdense lesions, T1 hyperintense lesions, multiple susceptibility artifact lesions, ring enhancing lesions, leptomeningeal enhancement, dural enhancement,...

Key Differential Diagnoses

and Clinical Questions

JUAN E SMALL, MD, M.Sc.

Section Chief, Neuroradiology Division Director, Neuroimaging Education Assistant Professor of Radiology Lahey Hospital and Medical Center Tufts University School of Medicine Burlington, Massachusetts

PAMELA W SCHAEFER, MD

Associate Director of NeuroradiologyClinical Director of MRIMassachusetts General HospitalAssociate Professor of RadiologyHarvard Medical SchoolBoston, Massachusetts

1600 John F Kennedy Blvd.

Ste 1800

Philadelphia, PA 19103-2899

NEURORADIOLOGY: KEY DIFFERENTIAL DIAGNOSES AND CLINICAL QUESTIONS ISBN: 978-1-4377-1721-1

Copyright © 2013 by Saunders, an imprint of Elsevier Inc.

Notices

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Library of Congress Cataloging-in-Publication Data

Small, Juan E.

Neuroradiology : key differential diagnoses and clinical questions / Juan E Small, Pamela W Schaefer.

p ; cm.

Includes bibliographical references and index.

ISBN 978-1-4377-1721-1 (hardcover : alk paper)

I Schaefer, Pamela W II Title.

[DNLM: 1 Diagnostic Techniques, Neurological–Case Reports 2 Nervous System Diseases–

radiography–Case Reports 3 Diagnosis, Differential–Case Reports 4 Neuroradiography–

methods–Case Reports WL 141]

Executive Content Strategist: Pamela Hetherington

Content Development Specialist: Margaret Nelson

Publishing Services Manager: Patricia Tannian

Project Manager: Carrie Stetz

Design Direction: Steven Stave

Printed in China

Last digit is the print number: 9 8 7 6 5 4 3 2

This book is dedicated to my beautiful wife and best friend Kirstin Thank you for helping me to understand the things that really matter in life, in ways I never could before we met Without you, my life would

be incomplete I love you and cherish our life together.

And to my parents, Aurora and Richard Without your support and unconditional love, none of my achievements would have been possible Thank you for encouraging

me to follow my heart.

Juan E Small

This book is dedicated to my wonderful husband, Douglas Raines, and my beautiful daughter, Sarah Raines, who always give me unconditional love, support, and wisdom.

Pamela W Schaefer

Massachusetts General Hospital

Harvard Medical School

Boston, Massachusetts

JUAN E SMALL, MD, M.Sc.

Section Chief, Neuroradiology DivisionDirector, Neuroimaging EducationAssistant Professor of RadiologyLahey Hospital and Medical CenterTufts University School of MedicineBurlington, Massachusetts

TINA YOUNG-POUSSAINT, MD

NeuroradiologistBoston Children’s HospitalProfessor of RadiologyHarvard Medical SchoolBoston, Massachusetts

SECTION EDITORS

Jewish General Hospital

Assistant Professor of Radiology

McGill University

Montreal, Quebec, Canada

DANIEL THOMAS GINAT, MD

Neuroradiology FellowHarvard Medical SchoolBoston, Massachusetts

MAI-LAN HO, MD

Resident, Scholar’s TrackDepartment of RadiologyBeth Israel Deaconess Medical CenterBoston, Massachusetts

LIANGGE HSU, MD

Assistant ProfessorHarvard Medical SchoolStaff NeuroradiologistBrigham and Women’s HospitalBoston, Massachusetts

SCOTT EDWARD HUNTER, MD

Neuroradiology FellowMassachusetts General HospitalBoston, Massachusetts

JASON MICHAEL JOHNSON, MD

Neuroradiology FellowMassachusetts General HospitalBoston, Massachusetts

HILLARY R KELLY, MD

NeuroradiologistMassachusetts General HospitalInstructor in Radiology

Harvard Medical SchoolBoston, Massachusetts

GIRISH KORI, MD

Neuroradiology FellowMassachusetts General HospitalBoston, Massachusetts

MYKOL LARVIE, MD, PhD

InstructorHarvard Medical SchoolRadiologist

Massachusetts General HospitalBoston, Massachusetts

GUL MOONIS, MD

Assistant ProfessorBeth Israel Deaconess Medical Center;Staff Radiologist

Massachusetts Eye and Ear InfirmaryBoston, Massachusetts

CONTRIBUTORS

Beth Israel Deaconess Medical Center

Harvard Medical School

Boston, Massachusetts

PAMELA W SCHAEFER, MD

Associate Director of Neuroradiology

Clinical Director of MRI

Massachusetts General Hospital

Associate Professor of Radiology

Harvard Medical School

Boston, Massachusetts

SANTOSH KUMAR SELVARAJAN, MD

Neuroradiology Fellow

Brigham and Women’s Hospital

Children’s Hospital Boston

Boston, Massachusetts

JUAN E SMALL, MD, M.Sc.

Section Chief, Neuroradiology Division

Director, Neuroimaging Education

Assistant Professor of Radiology

Lahey Hospital and Medical Center

Tufts University School of Medicine

Burlington, Massachusetts

HENRY S SU, MD, PhD

Neuroradiology FellowMassachusetts General HospitalClinical Fellow

Harvard Medical SchoolBoston, Massachusetts

KATHARINE TANSAVATDI, MD

Neuroradiology FellowMassachusetts General HospitalBoston, Massachusetts

NICHOLAS A TELISCHAK, MD

Radiology ResidentBeth Israel Deaconess Medical CenterDepartment of Radiology

Harvard Medical SchoolBoston, Massachusetts

BRIAN ZIPSER, MD

Neuroradiology FellowMassachusetts General HospitalBoston, Massachusetts

This book is based on the premise that one

of the most powerful learning techniques for

imaging interpretation is the presentation of

unknown cases Although primarily a case

book of unknowns, the style is intentionally

out of the ordinary, with several unknown

cases presented together The choice of this

format presented several challenges, but we

believe that the added value is well worth the

investment We are convinced that side-by-side

comparison and contrast of similar-appearing lesions is essential for building an invaluable visual database for imaging interpretation It

is with the hope of increasing our tic specificity that the format of the book was chosen

diagnos-Juan E Small, MD Pamela W Schaefer, MDPREFACE

We would like to gratefully acknowledge Lora

Sickora, Pamela Hetherington, Sabina Borza,

Rebecca Gaertner, Colleen McGonigal, Carrie

Stetz, and all the support staff and

illustra-tors at Elsevier for their help throughout this

endeavor We would also like to acknowledge

our mentors, fellows, and residents at sachusetts General Hospital, Brigham and Women’s Hospital, and Lahey Clinic Medi-cal Center for their persistent hard work and dedication to neuroradiology

Mas-ACKNOWLEDGMENTS

Although this book does not have to be read

in sequence from cover to cover, it is essential

that the cases be approached as unknowns

Attempting to interpret several unknown

cases at once can be overwhelming To gain

the most from this text, the cases within a

series should be first interpreted

individu-ally The main challenge is to formulate a

specific differential diagnosis for each

indi-vidual unknown case We encourage readers

to then compare and contrast cases within

that series The goal is to find the often

sub-tle imaging characteristics that are specific

or highly suggestive of individual diagnostic considerations The text should be read only after this process has occurred Each series

of cases is supported by individual diagnoses,

a description of findings, and a brief sion of the various diagnostic considerations Additional cases illustrate other manifesta-tions and considerations important for the imaging interpretation of these entities We have tried to highlight major teaching points and hope that you benefit as much from read-ing this book as we have benefited from writ-ing and editing it

discus-HOW TO USE THIS BOOK

4 Brain and Coverings

E

CASE D: A 56-year-old man with generalized tonic-clonic seizures ADC, apparent diffusion coefficient; CT, computed tomography; gad, gadolinium.

hem-Case  B: Metastatic lung cancer

Case  C: Oligodendroglioma grade 2 (proven

by pathol ogy)

Case  D: LymphomaSUMMARY

The differential diagnosis of CT hyperdense lesions usually revolves around hemorrhagic products, calcifications, or hypercellular lesions CT attenuation value of hyperdense lesions in the brain can be helpful in determin-ing the etiology Attenuation of hyperdense hemorrhage in the brain ranges from 60 to 100

HU Calcifications typically have Hounsfield units in the hundreds Care must be taken when measuring small hyperdensities because volume averaging can underestimate the Hounsfield units MRI susceptibility-weighted images can also be helpful for differentiating these entities Intraparenchymal hemorrhage demonstrates susceptibility (low signal) with marked enlargement or “blooming” of the hemorrhage compared with its actual size Calcification typically shows low signal with little to no blooming Dense cellular packing does not show susceptibility

Determining the etiology of an chymal hemorrhage is important because it will affect prognosis, treatment, and manage-ment CT angiography is highly sensitive and specific for identifying an underlying vascular lesion Approximately 15% of intraparenchy-mal hemorrhages result from vascular lesions such as arteriovenous malformations and fis-tulae, aneurysms, dural venous sinus throm-bosis, moyamoya disease, and vasculitis If an underlying vascular lesion is not identified, common causes of intraparenchymal hemor-rhage in elderly patients should be considered Hemorrhages due to anticoagulation are usu-ally large, lobar hemorrhages, and hyperten-sive hemorrhages typically are located in the deep gray nuclei, brainstem, and cerebellum

intraparen-DESCRIPTION OF FINDINGS

• Case A: A small focus of hyperdensity

is present in the left middle cerebellar

peduncle The CT angiogram

demon-strates a tangle of vessels just lateral to

this focus of hemorrhage A conventional

catheter angiogram confirms the

pres-ence of an arteriovenous malformation

with arterial supply from the left

ante-rior infeante-rior cerebellar artery and

pon-tine perforators and early filling of the

straight, transverse, and sigmoid sinuses

The lesion was subsequently treated with

liquid embolic material (not shown)

• Case B: A left occipital lesion

demon-strates peripheral hyperdensity There is

surrounding edema with local mass effect

and effacement of the left occipital horn

After administration of contrast,

super-imposed enhancement is seen along the

peripheral portions of the mass On the

coronal reformats, an additional smaller

hyperdense right cerebellar lesion with

ring enhancement is noted Given the

patient’s history of lung cancer, these

find-ings are consistent with lung metastases

• Case C: Small, discrete hyperdensities

measuring 150 to 200 HU are consistent

with calcifications in the left occipital lobe

Surrounding parietal occipital

hypoden-sity and effacement of the left ventricular

atrium are noted CT angiogram

maxi-mum intensity projection image does not

demonstrate abnormal associated

ves-sels Gadolinium-enhanced, T1-weighted

MRI shows no associated enhancement

Marked T2/FLAIR hyperintense signal is

noted correlating with the CT

hypoden-sity Gradient echo imaging shows

cal-cific foci appearing as punctate foci of

susceptibility PET imaging demonstrates

a predominantly hypometabolic lesion

Pathologic evaluation after surgical

resec-tion revealed an oligodendroglioma

• Case D: A CT scan of the brain

demon-strates a mass lesion centered in the left

anterior basal ganglia There is an

irregu-lar hyperdense rim with a hypodense

center On MRI, the rim enhances and

has restricted diffusion characterized by

hypointensity on the ADC images The

findings are suggestive of a

hypercellu-lar lesion with internal necrotic or cystic

components The patient was given a nosis of lymphoma, and marked improve-ment of the enhancing lesion occurred after IV methotrexate was administered

diag-6 Brain and Coverings

If anticoagulation and hypertension are not

considerations, a gadolinium-enhanced MRI

with gradient echo sequences is obtained to

evaluate for other causes, such as amyloid

angiopathy, underlying neoplasms, and

cav-ernous malformations Amyloid angiopathy

is characterized by a lobar hemorrhage with

associated gray/white matter junction

micro-hemorrhages and/or leptomeningeal

hemosid-erosis on susceptibility-weighted sequences

Neoplasms that produce intraparenchymal

hemorrhage include high-grade gliomas and

metastatic tumors, such as melanoma and

renal cell carcinoma Frequently, an

underly-ing enhancunderly-ing mass is identified after

admin-istration of IV gadolinium However, an

underlying mass can be obscured by the

hem-orrhage, and follow-up MRI is recommended

if no clear cause for the parenchymal

hemor-rhage is identified and neoplasm remains in

the differential diagnosis Cavernous

malfor-mations may be the cause of acute

intrapa-renchymal hemorrhage in young children and

young adults They typically have a

hetero-genous “popcorn” appearance with a complete

hemosiderin rim on T2-weighted images and

no surrounding edema After acute

hemor-rhage, there is edema and the hemosiderin

rim may be obscured Clues to the etiology

are age and associated classic cavernous

mal-formations in other brain locations

(particu-larly in the familial form)

Calcifications can be either benign or

asso-ciated with pathology Intraparenchymal

cal-cifications are nonspecific and can be seen

in a variety of etiologies, including normal

deposition in the basal ganglia, prior cerebral

insult (e.g., infection, inflammation, or

isch-emia), vascular abnormalities (e.g., cavernous

malformations, arteriovenous malformations,

and fistulae), or neoplasms Primary intraaxial

central nervous system neoplasms that show

calcifications include astrocytomas,

oligoden-drogliomas, or, rarely, glioblastomas Case C is

a grade 2 oligodendroglioma Low-grade

oligo-dendrogliomas are slowly growing neoplasms

typically located in a cortical/subcortical

loca-tion, most commonly in the frontal lobe They

may cause scalloping of the adjacent

calvar-ium The majority demonstrate calcification

and about 50% show variable enhancement

Differentiation from other neoplasms is not

definitively possible with imaging alone

On CT, increased attenuation due to dense

cellular packing usually is seen with

lym-phoma and other small, round, blue-cell

tumors, such as peripheral neuroectodermal

tumors and medulloblastomas, but increased density also can be seen in glioblastomas Lym-phoma is characteristically located in the deep white matter and deep gray nuclei On MRI, the high cellularity is reflected by isointensity

to brain parenchyma on T2-weighted images, restricted diffusion with hyperintensity on diffusion-weighted images, and hypointensity

on ADC maps Lymphoma typically strates avid homogenous enhancement in immunocompetent patients In immunocom-promised patients, lymphomas may demon-strate rim enhancement with nonenhancing regions of central necrosis In contrast with acute hemorrhage, lymphomas do not have susceptibility Lymphomas usually rapidly respond to treatment with IV methotrexate, radiation therapy, or steroids

demon-DIFFERENTIAL DIAGNOSISAcute hemorrhage

CalcificationHighly cellular neoplasmsPrevious contrast

PEARLS

• Underlying etiologies for acute renchymal hemorrhage should be further assessed by CT angiogram

intrapa-• When patients with intraparenchymal hemorrhage have negative CT angiogram findings and no history of hypertension or anticoagulation, a gadolinium-enhanced MRI with gradient echo sequences should

be performed to assess for underlying malignancy and amyloid angiopathy, respectively

• Increased attenuation on CT tion due to dense cellular packing usually

examina-is seen with lymphoma and other small, round, blue-cell tumors These lesions usu-ally show dense, homogeneous enhance-ment and restricted diffusion and do not have susceptibility

• Attenuation of hyperdense hemorrhage in the brain typically ranges from 60 to 100

HU, whereas calcifications typically have Hounsfield units in the hundreds Calcifica-tions have little to no blooming on suscep-tibility-weighted images, in contrast with hemorrhage, which has marked blooming

Computed Tomography Hyperdense Lesions

SUGGESTED READINGS

Dainer HM, Smirniotopoulos JG: Neuroimaging of

hem-orrhage and vascular malformations, Semin Neurol

28(4):533–547, 2008.

Delgado Almondoz JE, Schaefer PW, Forero NP, et al:

Diagnostic accuracy and yield of multidetector CT

angiography in the evaluation of spontaneous

intrapa-renchymal cerebral hemorrhage, AJNR Am J

Neurora-diol 30(6):1213–1221, 2009.

Koeller KK, Rushing EJ: From the archives of the AFIP:

oli-godendroglioma and its variants: radiologic-pathologic

correlation, Radiographics 25(6):1669–1688, 2005.

Koeller KK, Smirniotopoulos JG, Jones RV: Primary

cen-tral nervous system lymphoma: radiologic-pathologic

correlation, Radiographics 17(6):1497–1526, 1997.

Lee YY, Van Tassel P: Intracranial oligodendrogliomas:

imaging findings in 35 untreated cases, AJR Am J

Roent-genol 152(2):361–369, 1989.

Morris PG, Abrey LE: Therapeutic challenges in primary

CNS lymphoma, Lancet Neurol 8(6):581–592, 2009 Osborn AG: Diagnostic neuroradiology, St Louis, 1994,

Mosby.

Stadnik TW, Chaskis C, Michotte A, et al: weighted MR imaging of intracerebral masses: com- parison with conventional MR imaging and histologic

Diffusion-findings, AJNR Am J Neuroradiol 22(5):969–976, 2001.

10 Brain and Coverings

T1 Hyperintense Lesions

DIAGNOSIS

Case A: Late subacute hematoma in a patient

with amyloid angiopathy

Case B: Hemorrhagic metastasis (renal cell

carcinoma)

Case C: Ruptured dermoid cyst

Case D: Colloid cyst (with proteinaceous con­tents)

Case E: Neurocutaneous melanosisSUMMARY

Intrinsic T1 hyperintensity (T1 shortening)

on MRI can be due to the presence of blood products, fat, melanin, proteinaceous mate­rial, or calcification

Hemoglobin has different signal charac­teristics on MRI depending on its oxidative state Subacute phase methemoglobin (both intracellular and extracellular) has intrinsic T1 hyperintense signal Intracellular meth­emoglobin also demonstrates blooming on susceptibility­weighted sequences A history

of recent trauma or anticoagulation makes the diagnosis of T1 hyperintense intracranial hemorrhage straightforward Patients with a history of hypertension may have deep gray nuclei and brainstem or cerebellar T1 hyper­intense subacute hemorrhages Lobar T1 hyperintense lesions with associated gray/white matter junction foci of susceptibility suggest amyloid angiopathy in older patients Furthermore, in the appropriate clinical set­ting, intraparenchymal T1 hyperintense lesions should raise the concern for meta­static disease Intrinsic T1 signal can be seen

in hemorrhagic metastases (e.g., renal cell, lung, thyroid) Intrinsic T1 hyperintensity associated with metastatic melanoma may

be due to either hemorrhagic components

or intrinsic T1 shortening from melanin

In many cases, an underlying mass can be identified on contrast­enhanced sequences

If an underlying mass is not identified, it is important to obtain follow­up imaging to rule out an underlying enhancing lesion initially obscured by the hemorrhage In younger patients, T1 hyperintense hemorrhages may result from underlying vascular lesions such

as caver nous malformations (a “popcorn” appearance with complete hemosiderin rim

on gradient echo and T2­weighted sequences)

or arteriovenous malformations

Melanin­containing lesions, such as neuro­cutaneous melanosis, also should be con­sidered in the differential diagnosis of T1 shortening when the clinical setting is appro­priate Neurocutaneous melanosis is a rare congenital phakomatosis associated with multiple cutaneous melanocytic nevi and benign or malignant central nervous system

DESCRIPTION OF FINDINGS

• CASE A: An oval, nonenhancing, T1

hyperintense right parietal abnormality is

evident Associated T2 hyperintensity and

peripheral susceptibility are seen There

also is surrounding edema The findings

are consistent with a late subacute hem­

orrhage in a patient with a known history

of amyloid angiopathy

• CASE B: A mass centered within the

right cerebral peduncle demonstrates T1

hyperintense foci and heterogeneous T2

hyperintense signal with surrounding

edema The postcontrast T1­weighted

image demonstrates an avidly enhanc­

ing mass consistent with a pathologically

proven hemorrhagic renal cell carcinoma

metastasis

• CASE C: A large heterogeneous mass

with regions of T1 hyperintensity and an

associated sinus tract is centered within

the midline inferior posterior fossa No

enhancement is identified There are fat­

fluid levels in the frontal horns of the

lateral ventricles with chemical shift arti­

fact on the T2­weighted images as well

as multiple small T1 hyperintense foci

consistent with fat within the bilateral

sylvian fissures These findings are con­

sistent with a ruptured dermoid cyst

• CASE D: A large, oval, well­

circumscribed, T1 hyperintense, T2

hypointense, nonenhancing intraventricu­

lar mass is noted in the region of the fora­

men of Monro The location and imaging

characteristics of this lesion are consistent

with a proteinaceous colloid cyst

• CASE E: There are bilateral medial tem­

poral and right thalamic intraparenchy­

mal as well as scattered leptomeningeal

T1 hyperntense lesions No associated

enhancement is identified These findings

are consistent with melanocytic deposits in

a patient with neurocutaneous melanosis

12 Brain and Coverings

melanotic lesions Its intracranial imaging

characteristics are due to the proliferation of

melanocytes in the leptomeninges or paren­

chyma As such, multiple T1 hyperintense

lesions generally are evident Because symp­

toms usually manifest by 2 to 3 years of age,

a pediatric patient with cutaneous lesions

and these imaging characteristics should sug­

gest this diagnosis despite its rarity Hydro­

cephalus is seen in two thirds of symptomatic

patients due to obstruction of CSF flow

Fat­containing lesions, such as lipomas or

dermoid cysts, also should be considered in

the differential diagnosis of T1 shortening

Dermoid cysts often are midline in sellar/

parasellar, frontal, and posterior fossa loca­

tions and are believed to be due to inclusion

of surface ectoderm early during embryo­

genesis Twenty percent are associated with

sinus tracts When uncomplicated, these

lesions are not associated with enhancement

Confirming the presence of fat is helpful with

CT or fat­saturated sequences on MRI T2

signal is variable Dermoid cyst rupture can

present with disseminated foci of intracra­

nial T1 hyperintensity due to spillage of lipid

contents into the subarachnoid space or intra­

ventricular compartment Because of density

differences, lipid droplets or fat fluid levels

are antidependent Dermoid rupture can

cause chemical meningitis due to meningeal

irritation from the internal contents, which

can result in leptomeningeal enhancement

Hydrocephalus may develop from blockage

of arachnoid granulations

Protein­containing lesions also should be

considered in the differential diagnosis of

T1 hyperintense lesions The location of a protein­containing lesion is the most impor­tant clue to diagnosis For instance, colloid cysts, which arise from the inferior aspect of the septum pellucidum, typically are pres­ent in the region of the foramen of Monro These lesions are well­circumscribed, nonen­hancing cystic lesions that are hyperintense

on T1­weighted images when the protein/mucin content is relatively high When a well­ circumscribed, homogeneous, T1 hyper­intense lesion is centered in the region of the pituitary gland, a craniopharyngioma or Rathke’s cleft cyst should be considered.SPECTRUM OF DISEASE

See Figure 2­1

DIFFERENTIAL DIAGNOSISHemorrhagic lesions: Hematomas, hemor­rhagic infarcts, hemorrhagic infections (e.g., herpes simplex encephalitis), hemor­rhagic neoplasms, vascular malformations, and thrombosed aneurysms

Fatty lesions: Lipomas, dermoids, and terato­mas

Melanin­containing lesions: Melanoma metasta­ses and intraparenchmal and leptomeningeal melanosis

Protein­containing lesions: Colloid cysts, Rathke cleft cysts, craniopharyngioma, and atypical epidermoid

Figure 2-1 A 56-year-old man with history of metastatic melanotic melanoma Axial T1 precontrast image

(A) demonstrates a T1 hyperintense lesion centered in the left caudate nucleus Postcontrast T1 image (B)

also demonstrates a smaller enhancing lesion along the medial aspect of the left parietal lobe, with

surround-ing edema evident on FLAIR (C) It is difficult to determIne whether the caudate lesion enhances Susceptibility

blooming is not associated with the intrinsically T1 hyperintense lesion; the signal characteristics could be secondary to extracellular methemoglobin or melanin The imaging characteristics of metastatic melanoma may vary from patient to patient depending on whether the lesions represent melanotic melanoma metasta- sis, amelanotic melanoma metastasis, or hemorrhagic metastasis.

T1 Hyperintense Lesions

Calcified/ossified lesions or lesions with min­

eral accumulation: Endocrine/metabolic

disorders, calcified neoplasms, and calcify­

ing infections

PEARLS

• An imaging interpretation error is to

mistake intrinsic T1 hyperintensity for

enhancement The imaging interpreter

should closely compare T1 precontrast and

T1 postcontrast sequences to avoid this pit­

fall

• Side­by­side scrutiny of precontrast and

postcontrast sequences is invaluable for the

identification of areas of subtle enhance­

ment, a finding that markedly tailors the

differential diagnosis

• Follow­up imaging in the setting of a paren­

chymal hemorrhage is required to rule

out an underlying enhancing vascular or

neoplastic abnormality obscured by mass

effect exerted by the hematoma

SIGNS AND COMPLICATIONS

• Dermoid cyst rupture with spilling of lipid

components results in a chemical meningi­

tis when the contents of the ruptured cyst

involve the subarachnoid spaces If spilled

lipid obstructs arachnoid granulations, hydrocephalus may develop

• Hydrocephalus is seen in two thirds of symptomatic patients with neurocutane­ous melanosis due to obstruction of CSF flow

SUGGESTED READINGS

Atlas SW, et al: MR imaging of intracranial metastatic

melanoma, J Comput Assist Tomogr 11(4):577–582,

Huisman TA: Intracranial hemorrhage: ultrasound, CT

and MRI findings, Eur Radiol 15(3):434–440, 2005.

Osborn AG, Preece MT: Intracranial cysts: radiologic­

pathologic correlation and imaging approach,

Radiol-ogy 239(3):650–664, 2006.

Stendel R, et al: Ruptured intracranial dermoid cysts,

Surg Neurol 57(6):391–398, 2002.

Zaheer A, Ozsunar Y, Schaefer PW: Magnetic resonance

imaging of cerebral hemorrhagic stroke, Top Magn

Reson Imaging 11(5):288–299, 2000.

CASE A: A 48-year-old asymptomatic man with a strong family history of cerebral microhemorrhage GRE,

gradient refocused echo.

16 Brain and Coverings

CASE B: An 87-year-old woman with a history of hyperlipidemia, hypertension, and heart disease GRE,

gradient refocused echo.

CASE D: A 65-year-old woman with a history of breast cancer presenting with difficulty walking GRE,

gradient refocused echo.

18 Brain and Coverings

DIAGNOSIS

Case A: Familial cavernous malformations

Case B: Hypertension

Case C: Diffuse axonal injury

Case D: Hemorrhagic metastases (breast

cancer)

Case E: Amyloid angiopathy

SUMMARYCerebral microhemorrhages appear as scat-tered punctate foci of susceptibility on GRE/susceptibility images Typically, chronic microbleeds are associated with hyperten-sion, amyloid angiopathy, and other causes of small vessel vasculopathy

Microhemorrhages resulting from chronic hypertension typically are located in the deep gray nuclei, deep white matter, brainstem, and cerebellum Approximately 56% of patients with an acute hypertensive hemorrhage have associated microbleeds Patients with chronic hypertension usually have periventricular white matter FLAIR/T2 hyperintensity.Microhemorrhages resulting from amyloid angiopathy typically occur in patients older than 60 years, in a cortical/subcortical distri-bution with sparing of the deep white mat-ter, basal ganglia, brainstem, and cerebellum Approximately 75% of patients with a lobar hemorrhage resulting from amyloid angi-opathy have associated microbleeds at gray/white matter junctions Patients with amyloid angiopathy usually have periventricular white matter FLAIR/T2 hyperintensity and can also have leptomeningeal hemosiderosis Patients with the rarer inflammatory form of amyloid angiopathy have associated vasogenic edema and leptomeningeal enhancement

The diagnosis of hemorrhagic ses should be considered when additional enhancing lesions with susceptibility and sur-rounding edema are seen A study in the liter-ature noted that 7% of melanoma metastases were identified best on GRE images The most common hemorrhagic cerebral metastases are melanoma and renal cell carcinoma Breast carcinoma and lung carcinoma hemorrhage less frequently but are the most common cerebral metastases and should be considered Thyroid carcinoma and choriocarcinoma also produce hemorrhagic lesions, but they rarely metastasize to the brain

metasta-Lobar or deep acute hemorrhage in young patients with additional foci of susceptibil-ity can suggest the diagnosis of multiple cav-ernous malformations, especially if there is

a classic heterogeneous lesion with a plete hemosiderin ring and no surrounding edema In patients with a family history of this condition, an autosomal dominant inher-itance pattern is seen It is noteworthy that these familial lesions are not associated with developmental venous malformations

com-DESCRIPTION OF FINDINGS

• Case A: Familial cavernous

malforma-tions: A patient with a familial history

presents with multiple foci of

susceptibil-ity, the largest of which (pons, left corona

radiata) demonstrate a typical “popcorn”

appearance with central heterogeneity and

circumferential complete rings of

hypoin-tense signal on T2-weighted images,

with-out mass effect or edema

• Case B: Hypertension: Multiple

cere-bral microhemorrhages involving the deep

gray nuclei, brainstem, and cerebellum in

a patient with a history of hypertension

There also are periventricular T2

hyper-intensity and bilateral deep gray nuclei

lacunes

• Case C: Diffuse axonal injury: A patient

with a history of trauma with

microhe-morrhages involving the cerebral gray/

white matter junctions, corpus callosum,

and the left middle cerebellar peduncle

There is restricted diffusion in the genu

and splenium of the corpus callosum as

well as the right corona radiata

• Case D: Hemorrhagic metastases

(breast cancer): A patient with a history

of malignancy with prominent foci of

sus-ceptibility, T1 hyperintensity, associated

enhancement, and surrounding

vaso-genic edema

• Case E: Amyloid angiopathy: A patient

older than 60 years with multiple cerebral

microhemorrhages in a peripheral pattern

(cortical/subcortical distribution)

spar-ing the deep white matter, basal ganglia,

brainstem, and cerebellum There is also

moderate periventricular white matter T2

hyperintensity

Multiple Susceptibility Artifact Lesions

In the setting of trauma, diffuse axonal

injury should be considered

Microhemor-rhage associated with diffuse axonal injury

is most often seen at gray/white matter

junc-tions and in the corpus callosum,

subcorti-cal and deep white matter, and dorsolateral

brainstem In addition to punctate foci of

sus-ceptibility, diffusion restriction may be seen

at sites of diffuse axonal injury

Lastly, any cause of vasculitis, whether

infec-tious or inflammatory, should be considered In

particular, septic emboli, fungal infections, and

radiation and chemotherapy changes should be

considered in the appropriate clinical setting

In addition, causes of small vessel

vasculopa-thy, such as sickle cell disease or cerebral

auto-somal dominant arteriopathy with subcortical

infarcts and leukoencephalopathy, should be

Findings suggestive of hypertension include:

• “Central” predominant microhemorrhages

involving the deep gray nuclei, deep white

matter, brainstem, and cerebellum

Findings suggestive of amyloid angiopathy

include:

• Patients generally are older than 60 years

• A “peripheral” pattern with a cortical distribution

cortical/sub-• The deep white matter, basal ganglia, brainstem, and cerebellum generally are spared

Findings suggestive of hemorrhagic ses include:

metasta-• History of malignancy

• Enhancement associated with scattered foci of susceptibility with surrounding edema

Findings suggestive of multiple cavernous malformations include:

• History: young age and family history

• Lesions with typical popcorn appearanceSIGNS AND COMPLICATIONS

Signs and complications generally are related

to acute hemorrhage and local mass effect Patients with amyloid angiopathy and numer-ous microhemorrhages may present with dementia

SUGGESTED READINGS

Blitstein MK, Tung GA: MRI of cerebral

microhemor-rhages, AJR Am J Roentgenol 189(3):720–725, 2007.

Chao CP, Kotsenas AL, Broderick DF: Cerebral amyloid

angiopathy: CT and MR imaging findings,

microbleeds, AJNR Am J Neuroradiol 20:637–642, 1999.

Gaviani P, Mullins ME, Braga TA, et al: Improved tion of metastatic melanoma by T2*-weighted imaging,

TABLE 3-1    Young vs Older Patient

Younger Patient Older Patient

CASE A: A 39-year-old man who had a dental procedure several weeks earlier now presenting with right

leg numbness and weakness Ax, axial; Cor, coronal; DWI, diffusion-weighted imaging.

22 Brain and Coverings

CASE C: A 70-year-old male smoker presenting with shortness of breath and headache of 3 weeks’

duration Ax, axial; Cor, coronal; DWI, diffusion-weighted imaging.

CASE B: A 37-year-old woman with a 1-month history of right-sided numbness presenting with a 3-day

his-tory of right-sided weakness Ax, axial; Cor, coronal; DWI, diffusion-weighted imaging.

CASE D: A 41-year-old man with a 3-week history of recurrent sinus infections now presenting with rapid

onset of headache and confusion Ax, axial; Cor, coronal; DWI, diffusion-weighted imaging.

CASE E: A 36-year-old man with a history of chronic renal disease who had two kidney transplants now

presenting after a generalized seizure Ax, axial; Cor, coronal; DWI, diffusion-weighted imaging.

24 Brain and Coverings

DIAGNOSIS

Case A: Abscess

Case B: Multiple sclerosis

Case C: Metastasis

Case D: Glioblastoma multiforme

Case E: Lymphoma (large B-cell lymphoma consistent with posttransplant lymphoprolif-erative disorder)

SUMMARYSeveral important imaging characteristics of ring-enhancing lesions often can lead to a more specific diagnosis:

1 Multiplicity

2 Thin versus a thick/irregular rim of enhancement

3 A thicker outer margin of rim enhancement

4 An incomplete rim of enhancement

5 The presence of adjacent perivascular enhancement

6 A T2 hypointense rim

7 Central restricted diffusion

8 The degree of perilesional edema

A solitary ring-enhancing lesion is usually due

to a neoplastic process, infection, or elination In decreasing order of frequency, solitary ring-enhancing lesions represent glio-mas, metastases, abscesses, or demyelinating lesions

demy-Multiplicity, on the other hand, in ing order of frequency, suggests metastases, pyogenic abscesses, demyelinating lesions, or opportunistic infections

decreas-In an adult patient, a heterogeneous lesion with a thick, irregular, and nodular rim of enhancement suggests a necrotic neoplastic lesion, such as glioblastoma multiforme or metastasis

An abscess often presents with specific clues to the diagnosis, including homoge-neous central restricted diffusion, an often T2 hypointense peripherally enhancing rim, con-siderable surrounding edema, and a thicker wall toward the cortex/periphery Because abscesses tend to grow away from the well-vascularized gray matter, thinning of the medial wall is seen Hematogenous abscesses (in the setting of endocarditis, cardiac shunts, and pulmonary arteriovenous malformations)

DESCRIPTION OF FINDINGS

• Case A: There is a 3-cm left

pari-etal lesion with a thin, T2 hypointense

peripheral rim, smooth enhancement,

prominent surrounding edema, and

cen-tral restricted diffusion Of note, the ring

of peripheral enhancement is slightly

thicker toward its cortical margin

• Case B: There are multiple

supra-tentorial white matter T2 hyperintense

lesions The largest lesion in the left

parietal lobe measures 2.7 cm and

dem-onstrates a thin, smooth, incomplete

rim of enhancement Despite the size

of this lesion, a paucity of surrounding

edema and mass effect is noted There is

restricted diffusion in the periphery of

the lesion but not in the center Lesions

in the right frontal and right occipital

lobe also enhance

• Case C: A 2.2-cm right cerebellar

ring-enhancing lesion without associated

restricted diffusion is identified Of note,

there is an enhancing internal septation

as well as irregularity, nodularity, and

varying thickness of the enhancing wall

• Case D: A 5-cm, heterogeneous right

occipital mass demonstrates a thick and

nodular rim of enhancement No internal

restricted diffusion is noted However,

DWI hyperintensity associated with the

enhancing rim suggests hypercellularity

Subtle ependymal enhancement is noted

along the walls of the temporal horn of

the right lateral ventricle Marked

sur-rounding edema and mass effect are

noted

• Case E: This patient was receiving

long-term immunosuppression There

is a 1.1-cm ring-enhancing lesion

cen-tered in the posterior left middle frontal

gyrus with surrounding edema There is

mildly restricted diffusion in the rim of

the lesion but not in the center There

is minimal surrounding linear

enhance-ment along perivascular spaces as well as

overlying dural enhancement

Ring-Enhancing Lesions

are usually multiple and present at gray/

white matter junctions Perilesional edema is

usually quite prominent

Ring enhancement associated with

demy-elination is often incomplete or open Open

ring enhancement (i.e., crescentlike

enhance-ment) greatly increases the likelihood that

the lesion represents demyelination (the

like-lihood ratio is five times greater than that of

a neoplasm and 17 times greater than that

of infection) Nevertheless, because of the

higher incidence of neoplasms and infection,

these entities still remain considerations with

this pattern of enhancement Further

sup-port for this diagnosis comes in the form of

multiple white matter lesions seen in a

typi-cal distribution, such as at the typi-callosal-septal

interface, and oriented perpendicularly to the

ventricular surface

Primary CNS lymphoma is a rare form

of extranodal non-Hodgkin lymphoma

Pri-mary CNS lymphoma has a distinct imaging

appearance because of its hypercellularity

and high nuclear/cytoplasmic ratio, as well

as the disruption of the blood-brain

bar-rier Masses are commonly hyperdense to

isodense on computed tomography and

dem-onstrate dense homogeneous enhancement

On magnetic resonance imaging, lesions are

commonly hypointense to gray matter on

T1-weighted images and isointense to

hyper-intense on T2-weighted images, with the

hypercellular nature of these lesions resulting

in DWI hyperintensity and ADC

hypointen-sity Although avid homogenous

enhance-ment is usually seen in immunocompetent

patients, imaging tends to be more variable in

immunocompromised patients, and lesions

may be heterogeneously enhancing or ring

enhancing Importantly, linear

enhance-ment at the margins of the lesion tracking

along Virchow-Robin perivascular spaces is highly specific Hemorrhage, calcification, and necrosis are rare prior to treatment In immunocompetent patients, intracranial lesions are solitary 70% of the time, whereas

in immunocompromised patients, lesions are equally likely to be multiple versus solitary Approximately 85% of lesions are supraten-torial, with more than 60% of intracranial lesions occuring in a periventricular loca-tion and 12% of lesions involving the corpus callosum The identification of a “transspa-tial” lesion (i.e., a lesion involving both the intraaxial and extraaxial space) often can be

an important clue for the diagnosis of cranial lymphoma Trans-spatial lesions typi-cally have intraparenchymal enhancement with adjacent dural enhancement

intra-SPECTRUM OF DISEASEThe spectrum of disease is detailed in the preceding section

DIFFERENTIAL DIAGNOSISThe differential diagnosis is provided in Table 4-1

cen-TABLE 4-1 Solitary vs Multiple Ring-Enhancing Lesions

Solitary Ring-Enhancing Lesion Multiple Ring-Enhancing Lesions Common Metastases, glioblastoma multiforme, abscess,

subacute intracerebral hematoma, subacute cerebral infarction, radiation necrosis

Metastases, multiple sclerosis, neurocysticercosis, abscesses Less common Tumefactive demyelinating lesion, neurocysticercosis,

lymphoma, toxoplasmosis, tuberculoma Acute disseminated encephalomyelitis, opportunistic infections, tuberculosis,

lymphoma, neurosarcoidosis, glioblastoma multiforme Rare Subacute lacunar infarction, fungal infection,

parasitic infection Vasculitis, Lyme disease, intravascular lymphoma, parasitic infections

26 Brain and Coverings

• An incomplete rim of enhancement

sug-gests a demyelinative lesion

• The presence of hypointense ADC

asso-ciated with the areas of enhancement, as

well as adjacent perivascular

enhance-ment, suggests lymphoma in an

immuno-compromised patient Trans-spatial lesions

also suggest lymphoma

SIGNS AND COMPLICATIONS

Signs and complications are predominantly

related to mass effect and the specific location

of the lesion

SUGGESTED READINGS

Eichler AF, Batchelor TT: Primary central nervous tem lymphoma: presentation, diagnosis and staging,

sys-Neurosurg Focus 21(5):E16, 2006.

Masdeu JC, Quinto C, Olivera C, et al: Open-ring ing sign: highly specific for atypical brain demyelin-

5

Leptomeningeal Enhancement

JUAN E SMALL, MD

Ax T1 Post Sag T1 Post Cor T1 Post

CASE A: A 44-year-old man who had upper respiratory infection symptoms 4 weeks earlier now presenting

with severe headache, purulent otorrhea, irritability, and progressive decline of mental status Ax, axial; Cor, coronal; Sag, sagittal.

Ax T1 Post Sag T1 Post FS Cor T1 Post FS

CASE B: A 38-year-old woman with a history of diabetes insipidus and hyperprolactinemia presenting with

a complex partial seizure Ax, axial; Cor, coronal; Sag, sagittal.

Ax T1 Post Sag T1 Post Cor T1 Post

CASE C: A 58-year-old woman with 5-week history of fever and headache now presenting with increasing

confusion, vomiting, and lethargy Ax, axial; Cor, coronal; Sag, sagittal.

28 Brain and Coverings

Ax T1 Post Sag T1 Post Cor T1 Post

CASE D: A 2-year-old girl with a history of seizures presenting with a decline in language function

Ax, axial; Cor, coronal; Sag, sagittal.

Ax T1 Post Sag T1 Post Cor T1 Post

CASE E: A 22-year-old man recently diagnosed with communicating hydrocephalus of unknown cause now

presenting with intractable headaches, lightheadedness, and episodes of near syncope Ax, axial; Cor, coronal; Sag, sagittal.

Case C: Tuberculous meningitis

Case D: Sturge-Weber syndrome

Case E: Leptomeningeal gliomatosis

SUMMARY

The most common causes of

leptomenin-geal (pia/arachnoid) enhancement are

bacte-rial and fungal meningitis, leptomeningeal

carcinomatosis, and neurosarcoidosis Less

common etiologies include vasculitis,

glio-matosis, Sturge-Weber syndrome, and

moy-amoya disease Rare causes include Wegener

granulomatosis, Lyme disease, dural

arterio-venous fistula, meningioangiomatosis, and

neurocutaneous melanosis Leptomeningeal

gliomatosis is very rare

Unfortunately, most causes of

leptomenin-geal enhancement have similar appearances

However, two key factors often can help narrow the differential diagnosis The easi-est is determined first by attempting to dif-ferentiate infectious from noninfectious entities, a prospect often aided by a sug-gestive clinical history or imaging findings suggesting the source of infection Second, the pattern of enhancement can help tailor the differential diagnosis Uncomplicated bacterial meningitis typically demonstrates thin, smooth leptomeningeal enhancement Entities classically presenting with thick, nodular, basal predominant enhancement include tuberculous meningitis, fungal men-ingitis, neurosarcoidosis, pyogenic menin-gitis, and neurosyphilis Entities with more diffuse nodular leptomeningeal enhance-ment include meningeal carcinomatosis, lymphomatous meningitis, and leukemia Very thick, smooth, basilar leptomeningeal enhancement can suggest the unlikely diag-nosis of leptomeningeal gliomatosis in the setting of a chronic aseptic meningitis pat-tern of presentation

SPECTRUM OF DISEASE

As previously indicated, most causes of tomeningeal enhancement can have a simi-lar appearance, and it is important to realize that entities that typically present with thin/smooth, nodular, or basilar enhancement can have an atypical appearance (for exam-ple, meningeal carcinomatosis that presents with a thin rather than a nodular pattern of enhancement)

lep-DIFFERENTIAL DIAGNOSISThe differential diagnosis of leptomen-ingeal (pia-arachnoid) enhancement can be summarized broadly into infectious, inflam-matory, vascular, neoplastic, and traumatic etiologies (Box 5-1)

Infectious meningitis results in geal enhancement because of the breakdown

leptomenin-of the blood-brain barrier Uncomplicated bacterial meningitis usually results in thin, smooth enhancement

Tuberculous and fungal forms of meningitis are often basilar predominant and confluent

In addition, fungal and tuberculous tis may produce thicker nodular enhancement

meningi-in contrast to the typical bacterial menmeningi-ingitis enhancement pattern

DESCRIPTION OF FINDINGS

• Case A: There is a thin, smooth pattern

of leptomeningeal enhancement with

left mastoiditis evident as the source of

infection

• Case B: There is a markedly nodular

pattern of leptomeningeal enhancement

slightly more prominent in the basal

cisterns and the hypothalamic region

There is also bilateral trigeminal nerve

involvement Thoracic imaging (not

shown) demonstrated mediastinal and

pulmonary sarcoidosis

• Case C: There is a thick and nodular

pattern of leptomeningeal enhancement

predominantly involving the basilar

ci sterns

• Case D: A thin, smooth pattern of right

temporal parietal leptomeningeal

enhance-ment is noted There is associated cortical

atrophy, ipsilateral choroid plexus

hyper-trophy, and a prominent medullary vein A

port-wine stain was seen on physical exam

• Case E: There is very thick, smooth

leptomeningeal enhancement

predomi-nantly involving the basilar cisterns

30 Brain and Coverings

Leptomeningeal carcinomatosis is typically

nodular or masslike and more diffuse

How-ever, it is important to note that carcinomatous

meningitis can appear as thin and smooth

Neurosarcoidosis often demonstrates a

nod-ular pattern with basilar predominance, and

cranial nerve involvement often is present

Sturge-Weber syndrome typically

demon-strates thin, smooth leptomeningeal

enhance-ment associated with cortical atrophy with

gyriform calcification, as well as ipsilateral

choroid plexus hypertrophy In addition,

prominent medullary and ependymal veins

can be visible

Moyamoya disease demonstrates

enhance-ment of multiple engorged pial and

parenchy-mal collateral vessels due to slow flow The

internal carotid, proximal middle cerebral,

and anterior cerebral artery flow voids are

absent or small There frequently are

associ-ated acute and chronic hemorrhages and/or

infarctions

Meningioangiomatosis is a rare

hamar-tomatous cortical and leptomeningeal

mal-formation usually appearing as a calcified

cortical mass with a linear, granular, and/

or gyriform cortical and leptomeningeal

enhancement pattern

Neurocutaneous melanosis may

demon-strate diffuse leptomeningeal enhancement

Primary diffuse leptomeningeal gliomatosis

is an exceedingly rare neoplastic condition of meningeal glial cell infiltration without evi-dence of a primary parenchymal tumor This condition should be considered in the differ-ential diagnosis of chronic aseptic meningitis Although very rare, imaging features include a very thick, smooth, basilar predominant lepto-meningeal pattern of enhancement

PEARLSThe following entities typically present with thin, smooth leptomeningeal enhancement:

• Bacterial meningitisThe following entities can present with basal-predominant, nodular enhancement:

• Meningeal carcinomatosis

• Lymphomatous meningitis

• LeukemiaSIGNS AND COMPLICATIONSWhen considering infectious etiologies, look carefully for a possible source of infection, areas of parenchymal infarction or hem-morrhage due to arterial or venous sinus thrombosis, intracranial collections of pus, or abscesses

SUGGESTED READINGS

Jicha GA, Glantz J, Clarke MJ, et al: Primary diffuse

lep-tomeningeal gliomatosis, Eur Neurol 62(1):16–22, 2009.

Smirniotopoulos JG, Murphy FM, Rushing EJ, et al: Patterns of contrast enhancement in the brain and

meninges, Radiographics 27(2):525–551, 2007.

BOX 5-1 Types of Differential Diagnoses

Infectious: Bacterial meningitis, viral meningitis,

tuberculous meningitis, fungal meningitis,

neuro-syphilis

Inflammatory: Langerhans cell histiocytosis,

sarcoid-osis, Wegener granulomatsarcoid-osis, chemical meningitis

(ruptured dermoid)

Neoplastic: Leptomeningeal gliomatosis, melanoma,

sarcoma, lymphoma; cerebrospinal fluid spread

of tumor such as medulloblastoma, germinoma,

and pineoblastoma; and metastatic carcinomatosis

(breast, leukemia/lymphoma, lung, melanoma,

gastrointestinal carcinoma, genitourinary

carcinoma)

Traumatic: Old subarachnoid hemorrhage, surgical

scarring from a prior craniotomy, the sequela of a

lumbar puncture, or contrast leakage

32 Brain and Coverings

Dural Enhancement

DIAGNOSIS

Case A: Spontaneous (primary)

intracra-nial hypotension (IH) (imaging and clinical

criteria); improved after treatment with an epidural blood patch

Case B: Chronic shunting for aqueductal nosis with pachymeningeal thickening that has been stable over many years

ste-Case C: Disseminated breast cancer with biopsy-proven osseous metastases

Case D: Posttransplant B-cell erative disorder (proven by a biopsy of a mass centered in the basal ganglia)

lymphoprolif-Case E: Neurosarcoidosis, based on negative neoplastic and infectious workup, biopsy of mediastinal nodes consistent with sarcoid-osis, and central nervous system findings sta-ble for many years on imaging

SUMMARY

Intracranial Hypotension/Hypovolemia— Primary and Secondary

The syndrome of intracranial hypotension (IH) or hypovolemia encompasses a broad spectrum of clinical and imaging findings related to CSF leaks The leak may be pri-mary (also known as spontaneous IH) or secondary Primary IH is believed to occur from a combination of weakness in the dural sac and minor trauma, with the leak usually occurring in the spine, whereas secondary IH results from breaching of the dura from iatro-genic manipulation, such as a lumbar punc-ture or cranial or spinal surgery The classic clinical syndrome is that of a postural head-ache that is aggravated in the standing posi-tion and relieved in the recumbent position However, IH has many clinical presentations that may range from atypical headaches or focal neurologic deficits to coma, highlighting the importance of imaging in making an accu-rate diagnosis

The most important imaging modality for the diagnosis of IH is MRI The classic finding

on MRI of the brain is diffuse smooth meningeal thickening and enhancement without nodularity or evidence of leptomen-ingeal disease In one report, pachymeningeal thickening was detectable on FLAIR in 74%

pachy-of cases Engorgement pachy-of the venous sinuses and cerebral veins in patients with IH may be seen on conventional and magnetic resonance angiography and is reflected in the convex contour of the undersurface of the domi-nant transverse sinus on sagittal T1-weighted images, known as the VDS The combination

of diffuse pachymeningeal enhancement and

DESCRIPTION OF FINDINGS

• MRI scans from five patients

demon-strate diffuse pachymeningeal

enhance-ment

• Case A involves diffuse smooth

pachy-meningeal enhancement, small subdural

effusions, caudal displacement of

supraten-torial structures, low-lying cerebellar

ton-sils, prominence of the pituitary gland with

the pituitary protruding beyond the

mar-gins of the sella, and a prominent transverse

sinus with a convex inferior border (known

as venous distention sign [VDS]) Note the

absence of leptomeningeal enhancement

or pachymeningeal nodularity

• Case B involves marked diffuse

thick-ening and enhancement of the

pachy-meninges, a positive VDS sign, small

subdural effusions, and mild prominence

of the pituitary gland, along with a

ven-tricular shunt with its tip in the frontal

horn of the right lateral ventricle and

slit-like ventricles (also note the artifact from

the shunt apparatus outside the

calvar-ium) The brain does not have a sunken

appearance despite the marked

pachyme-ningeal thickening

• Case C involves pachymeningeal

enhancement with areas of nodularity,

unlike the other cases shown in which the

pachymeningeal enhancement is smooth

Closer inspection of the images reveals

mul-tiple skull lesions Also, note the concave

inferior border of the transverse sinus (a

negative VDS sign), unlike in cases A and B

• Case D involves diffuse smooth

pachy-meningeal enhancement in addition to

a heterogeneously enhancing mass

cen-tered in the right basal ganglia A

nega-tive VDS sign is noted

• Case E involves mild diffuse

pachy-meningeal enhancement in addition

to extensive nodular leptomeningeal

enhancement Nonspecific areas of FLAIR

hyperintensity also are noted, along with

a negative VDS sign

34 Brain and Coverings

a positive VDS sign have a high accuracy for

the diagnosis of IH Many other ancillary

signs of IH exist that are not always present,

but when combined with the aforementioned

signs, they further support the diagnosis of

IH These ancillary signs include subdural

collections that are usually small and are

fre-quently hygromas but may be hemorrhagic

Caudal displacement of the supratentorial

structures resulting in draping of the optic

chiasm over the sella and tonsillar herniation

mimicking a Chiari I malformation may be

present In addition, the pituitary gland may

be enlarged The latter finding is often

dif-ficult to determine with certainty given the

relatively small size of the gland and

varia-tions in gland size based on the patient’s age

and sex However, pituitary enlargement may

be suggested if extension of the gland above

the margins of the sella is observed

Chronic shunting may present with

fea-tures of IH, likely as part of the continuum of

the same pathophysiologic process However,

the implications are different because some

imaging findings of IH, such as

pachymenin-geal enhancement, can represent an expected

finding in a patient with a shunt and, in

iso-lation, does not warrant any intervention

Case B is an example of chronic shunting

Different hypotheses have been proposed

to explain why some patients with chronic

shunting and pachymeningeal enhancement

are asymptomatic and do not have a sunken

appearance of the supratentorial structures;

these hypotheses are beyond the scope of this

text The discovery of a positive VDS sign is

not a surprising finding in Case B, although

thus far the sign has not been specifically

studied in this patient population It also

is noteworthy that the case presented is an

extreme example of pachymeningeal

thicken-ing and enhancement and a wide spectrum

of findings may be seen with shunting,

rang-ing from minimal enhancement to prominent

enhancement with marked thickening

Although diffuse pachymeningeal

enhance-ment is a sensitive sign of IH, it is not a specific

sign in isolation, and it is imperative that the

images be evaluated carefully for additional

signs suggesting alternate diagnoses The

presence of nodularity or any leptomeningeal

enhancement argues against IH and

man-dates consideration of a neoplastic process

Even without any leptomeningeal

enhance-ment, pachymeningeal enhancement can be

seen with metastatic disease, especially in the

presence of skull metastases, as in Case C

Such pachymeningeal thickening and ment does not necessarily represent neoplas-tic invasion of the dura and can represent

enhance-an inflammatory reaction Presumably, such enhancement may be seen with metastases from any primary malignancy, but common extracranial sources include breast and pros-tate metastases Pachymeningeal enhancement also can be seen with hematologic malignan-cies, as in Case D

A variety of inflammatory and infectious conditions also can present with pachy-meningeal thickening and enhancement, although many are readily distinguishable from IH based on their pattern and distribu-tion Neurosarcoidosis and Wegener granu-lomatosis are included in these conditions, among others Patients with neurosarcoid-osis usually have leptomeningeal disease,

as shown in Case E, along with mal lesions, which allow this condition to

parenchy-be distinguished from IH In addition, VDS and other ancillary findings seen in patients with IH are absent Rare conditions such

as idiopathic hypertrophic pachymeningitis also can manifest as diffuse pachymeningeal enhancement and can be distinguished from

IH using the additional signs of IH previously described

SPECTRUM OF DISEASEThe most sensitive and widely reported sign

of IH is diffuse smooth pachymeningeal enhancement Two recent studies also suggest that the VDS sign is a highly accurate sign of

IH, and when combined, these two signs are highly suggestive of IH Additional but less specific signs described earlier can be seen in

a subset of cases, and when combined, they further support the diagnosis of IH

DIFFERENTIAL DIAGNOSISChronic shunting and cranial or spinal sur-gery (likely representing a similar patho-physiologic process)

Neoplasm (most commonly metastases from breast, prostate, or hematologic malignancies)Inflammatory and infectious processes, such

as sarcoidosis, Wegener granulomatosis, and tuberculosis

Idiopathic hypertrophic cranial gitis