Spinal Disorders: Fundamentals of Diagnosis and Treatment Part 27 pps

This method is typically employed for CT guided nerve root blocks, facet joint blocks, CT discography, injections into the sacroiliac joints, sympathetic trunk blocks, vertebral body bio

are often unable to stay motionless for the 20 min required for a standard

exami-nation Hip flexion, which might relieve the patient’s pain, is only possible to a

limited degree in most magnet designs Proper analgesic medication prior to the

MR examination may be required in order to reduce patient discomfort and

pain-related motion artifacts

Computed Tomography

CT is the modality of choice for imaging of bone

CT has developed with amazing speed during the last few years Spiral CT with

continuous data acquisition appeared in routine work in the mid-1990s, and

multi-detector row CT at the end of the 1990s Initially, four detector rows were

employed which were quickly followed by 16, 40 and 64 detector rows At the time

of writing, this development has not yet come to an end Compared to MR

imag-ing, CT has several advantages CT shows bony details with a high spatial

resolu-tion

In plane spatial resolution of CT (pixel size) is approximately 0.25 – 0.5 mm

(depending on the system geometry and on the reconstruction kernel selected by

the user) and is therefore better than in typical MR protocols CT does not

inter-fere with the function of pacemakers and other electronic devices The

metal-related artifacts present in CT are metal-related to so-called beam-hardening, which

depends on the amount/size of implants and the atomic number of the implant

Such artifacts may be less pronounced or in a different place when compared to

CT is the imaging modality

of choice in an emergency situation

MR imaging Examinations in emergency room and intensive care patients are

preferably performed using CT because imaging times are shorter, patient access

is easier and no specialized (non-ferromagnetic, shielded) intensive care

equip-ment is necessary as for MR imaging

Contrast resolution

is inferior to MRI

On the other hand, the contrast resolution of CT is much inferior to MR

imag-ing in important structures such as the intervertebral discs, cerebrospinal fluid

and soft tissue The radiation dose is considerable in CT, e.g., 28 % of the medical

radiation dose in Switzerland is generated by CT examinations [46] CT

examina-tions of the lumbar spine (8.2 mSv) and of the sacroiliac joints (7.0 mSv) result in

a higher effective radiation dose compared to CT examinations of the cervical

(3.4 mSv) spine

CT fluoroscopy allows for interventional procedures

CT fluoroscopy allows real-time imaging of interventional procedures

Dur-ing these procedures, the radiologist activates intermittent or continuous image

acquisition with a foot pedal If necessary, the patient can be moved in the

crani-ocaudal axis using a joystick, placed within the reach of the radiologist’s elbow or

hand In order to protect the patient and the radiologist from high radiation

doses, low-dose imaging (lower mAs) is usually performed In addition, a

reduced number of pixels (reduced spatial resolution) and near-real-time image

reconstruction algorithms are commonly used in order to reduce acquisition

time [42] CT fluoroscopy allows imaging of a needle or other radiopaque devices

in real-time fashion during insertion This method is typically employed for CT

guided nerve root blocks, facet joint blocks, CT discography, injections into the

sacroiliac joints, sympathetic trunk blocks, vertebral body biopsy, and soft tissue

biopsy

DEXA is used for the determination of bone mineral density

CT is one of the many available tools for bone density measurement Bone

density within the vertebral body can be directly measured by simultaneously

scanning the vertebral body and phantoms with defined densities [15] This

method is not commonly employed, however, for a number of reasons The

most commonly employed method is dual energy X-ray absorptiometry

(DEXA), which reduces radiation dose and cost when compared to CT On the

other hand, this method is a projectional method and may overestimate bone

density in the presence of spondylophytes Dedicated small CT scanners have

pQCT allows fast losers

to be detected

been used for peripheral quantitative computed tomography (pQCT)

mea-surements [9] Such scanners are less expensive than standard CT scanners and provide highly reproducible results which may be used for early detection

of fast losers and for monitoring the effects of medication therapy Other methods mainly used for peripheral measurements (with variable predictive value for spinal fractures) are broadband ultrasonic attenuation (BUA) [44] and high-resolution MR imaging measurement of the trabecular bone volume fraction [47]

Imaging Protocol

When a single slice CT unit is used, the examination needs to be restricted to a few spinal segments Typically, the cervical spine is imaged with thinner slices

Multi-detector CT has

improved resolution and

shortened imaging time

compared to the thoracic and lumbar spine Multi-detector CT (MDCT) units

allow the acquisition of a large number of segments with thin slice thickness, within the same period of time Sagittal and coronal multiplanar reformations (MPRs) are more easily obtained and are of better quality based on such data sets Typical imaging protocols in the cervical, thoracic, and lumbar, spine, as well as for the sacroiliac joints, are shown inTable 2

Table 2 Imaging parameters for computed tomographya

Single-slice CT 16-row MDCT 64-row MDCT Cervical spine

Slice thickness C0 – C3 1 mm 16 × 16.75 mm 64 × 64.6 mm

C4 – C7 2 mm

C4 – C7 1.25

C4 – C7 2 mm

Thoracic and lumbar spine

Slice thickness 2 – 3 mm 16 × 16.75 mm 64 × 64.6 mm

Sacroiliac joints

a As used in our institution Kernel soft = image reconstruction algorithm for soft tissue; Kernel bone = image reconstruc-tion algorithm for bone; C = center, W = width The above algorithms are only for Siemens

CT units; differences with other manufacturers are likely

CT is superior to MR imaging in the evaluation

of bone abnormalities

Generally, MR imaging is the advanced modality of choice in imaging of the

spine As a screening, CT can be applied to diagnose or rule out disc herniation

particularly when an ossified herniation is suspected (Fig 11) However, there

are clinical situations where CT is superior to MRI CT should be preferred to

MRI when the bony structures have to be analyzed such as fracture of the spine

(Fig 12) or in cases of MRI contraindications

Figure 11 CT diagnosis of disc herniation

aCT scan at the L4/5 level (soft tissue window) demonstrating a right-sided mediolateral disc herniation.bCT scan at the

L5/S1 level (soft tissue window) is superior to MRI, showing a calcified, broad-based median disc herniation.

Figure 12 CT diagnosis of spinal fractures

a, b Standard radiographs demonstrate loss of height, widening of interpedicular distance and probable dorsally

extruded fragment.

c d

Figure 12 (Cont.)

c, dThis is confirmed by a

CT scan with image

refor-mation.

Such indications include:

) acute spinal trauma

) evaluation of spinal fusion

) planning of complex surgical procedures (e.g., osteotomies)

) spondylolysis

) complex vertebral deformities

) claustrophobia and contraindications to MRI

Contraindications, Artifacts, Side Effects

CT is relatively contraindicated during pregnancy Especially in pregnancy, but also in all other instances, the indications for CT should be considered carefully

Beam hardening artifacts are most commonly caused by metallic implants.

These artifacts depend on the volume, orientation and atomic number of the implant The artifacts are limited to the CT slices which include the metallic implants These artifacts are accentuated in the longitudinal direction of screws They appear as one or multiple thick lines which may be oriented in a

sunbeam-CT exhibits fewer artifacts

than MRI in the presence

of implants

like fashion and may cover large parts of the field of view Typical causes of beam

hardening artifacts are extensive dental implants, screws, cages, intervertebral disc prostheses, shoulder and hip prostheses, as well as pacemakers or drug pumps In the vicinity of implants, beam hardening artifacts tend to be less pro-nounced compared to susceptibility artifacts seen on MR imaging On the other hand, implants located far away from the spine (for example dental implants) may be more disturbing on CT images while MR images are not degraded in a clinically relevant fashion

Additional Imaging Methods Bone Scintigraphy

Bone scans are surpassed by

MR imaging and PET

99mTechnetium polyphosphonate scintigraphy, such as99mTc-methyl diphospho-nate (MDP) scintigraphy, has been used in an almost unchanged fashion for many years [41] For this examination, 500 – 800 MBq of99mTc is injected intrave-nously and images are obtained 2 – 3 h after injection The99mTc distribution at that time shows the activity of the osteoblasts and thus demonstrates bony turn-over activity Images acquired within a few minutes after the injection

demon-Bone scan remains a skeletal screening modality for tumors or infections

strate the vascularity of the tissue Bone scintigraphy is mainly used as a

screen-ing tool because it demonstrates the entire skeleton in a sscreen-ingle examination.

Bone scintigraphy may also be useful in assessment of disease activity For local

diagnosis, however, bone scintigraphy has mainly been replaced by MR imaging,

which provides similar information regarding disease activity but adds

anatomi-cal details The role of specialized scintigraphic methods such as111In,67Ga, or

anti-granulocyte antibody scintigraphy has declined due to the increasing use of

MR imaging, the advent of positron emission tomography (PET) and also

because some of the methods do not perform in the spine as well as in peripheral

bones due to the relatively large proportion of cell-rich hematopoietic bone

mar-row This interferes with the detection of abnormalities such as infection and

neoplasm which are also characterized by a large number of cells Independently

of this discussion, bone scintigraphy has a limited role in detecting Langerhans’

cell histiocytosis and multiple myeloma [21], which both tend to be

inconspicu-ous on99mTc bone scintigraphy

Positron Emission Tomography

PET is increasingly used for staging of tumors and for the assessment of infection

Imaging with PET requires expensive equipment, especially if combined with a

CT scanner (PET-CT) The tracers required for PET have short half-life periods

of between a few minutes (15O: t1/2 = 2.1 min) and approximately 2 h (18F: t1/2

= 110 min) Therefore, the cyclotron generating the tracers has to be within an

adequate distance of the PET scanner A large number of different tracers are

available However, PET is typically performed with18FDG (18

fluorodeoxyglu-cose) Doses of between 200 and 600 MBq of18FDG are intravenously injected

Scanning starts after a delay of 30 – 40 min [40] This method demonstrates areas

of increased glucose metabolism which typically are present in tumors and

infec-tion PET can provide images of large parts of the body within a single

examina-tion and is increasingly used for staging of tumors but also for the assessment of

infection Its role is not limited to bone but may be even more important for

imaging of soft tissue, lymph nodes and abdominal organs

Myelography

Myelography can be associated with serious side effects

For lumbar myelography the injection of contrast is typically performed at the

L2/3 level with a thin (22G) needle Rounded needles have been advocated in

order to reduce traumatizing of the dura and nerve roots but are not universally

used Application of 2.5 – 4.5 g iodine (8 – 15 ml of a contrast agent containing

300 mg/ml iodine) results in a sufficient intrathecal contrast [18] Water-soluble,

non-ionic, iso-osmolar types of contrast agent produce the fewest side effects.

Side effects mainly include pain, which may be similar or different from the pain

usually experienced Pain is most commonly found in patients with severe

steno-sis of the spinal canal Severe side effects of myelography such as seizures are

infrequent [38] However, the injection of ionic contrast media is strictly

contra-indicated because a severe form of seizure called “ascending tonic-clonic seizure”

has been reported after inadvertent intrathecal injection of such ionic contrast

agents [5, 38] Prolonged side effects are most often related to the puncture itself

Liquor leakage through the dural puncture site can cause severe headache, which

can last for several days or even weeks Blood patches with approximately 8 ml of

the patient’s own blood have been suggested for treatment of prolonged

symp-toms

Immediately after intrathecal contrast administration, radiographs are

obtained with the patient in the prone and lateral decubitus position as well as

prone oblique radiographs (approximately 15°/30°, commonly positioned under

b

c

Figure 13 Myelography and CT

myelography

Positional radiographs inaflexion andbextension,

demonstrating segmental stenosis of the spinal

canal, most pronounced at the L3/4 level.cCT at

the L3/4 level, confirming stenosis of the spinal

canal Gas within degenerated disc.

Functional examination

rarely has a diagnostic

or therapeutic impact

fluoroscopic control, in order to better demonstrate the entire course of nerve

roots) Functional examination in flexion and extension does not appear to have

an impact on the diagnostic and therapeutic decision-making in the presence of

an MRI examination and is not routinely done in our center [36, 48, 50] Myelo-graphy is commonly combined with CT of the spine (CT myeloMyelo-graphy) (Fig 13) The acquisition parameters are similar to those for standard CT (see CT chapter) Compared to standard CT, intrathecal contrast medium outlines the intradural space and any filling defects within this space or abnormalities impinging on the dural sac Stenosis of the spinal canal or the lateral recesses as well as the influ-ence of disc herniation on intradural structures may even be more clearly dem-onstrated than by MR imaging

Direct cervical myelography with craniocervical injections has largely been replaced by MR imaging or CT myelography obtained after lumbar injection Indications for myelography or CT myelography in the era of MRI are very rare and are restricted to the following conditions:

) postoperative spine with marked susceptibility artifacts in MRI

) unclear conditions with suspected functional stenosis

In all other cases MRI should provide enough information about foraminal or spinal canal stenosis Only in a few cases is additional CT without intrathecal contrast administration necessary to distinguish between osteophyte formation and disc protrusion within the intervertebral foramen, mainly in the cervical spine

MR myelography (MR imaging performed after intrathecal injection of MR

contrast media) has rarely been employed but appears to be feasible No adverse

The diagnostic value

of MR myelography

is questionable

reactions other than those known from conventional myelography were found in these patients However, the technique of intrathecal administration of gadopen-tetate and related contrast media has so far not been approved by the responsible state agencies and the additional diagnostic effect is questionable

Image Guided Injections

Image guided injections such as nerve root blocks or facet joint injections are

discussed in Chapter 10 Fluoroscopy and CT (possibly CT fluoroscopy) are

most commonly employed as guiding methods for such procedures although MR

imaging has also been suggested for this purpose

Ultrasonography

Sonography has a limited role in imaging of the spine

Ultrasonography does not play an important role in imaging of the spine

Retro-peritoneal abnormalities are commonly examined from ventrally with a

trans-ducer suitable for abdominal imaging (commonly a curved array transtrans-ducer

with a frequency of 3.5 – 5 MHz) The evaluation of the contents of the spinal

canal cannot easily be performed sonographically The bony surfaces

surround-ing the relevant structures prevent a consistent evaluation

Sonography has been used to guide periradicular injections in the lumbar

spine [13] and it has also been used as guidance for lumbar sympathetic trunk

blocks [20] There may be a role for intraoperative sonography in spinal cord

tumors or malformations but probably not typically for the evaluation of

degen-erative disc disorders and other common spine abnormalities [12]

Sonography is routinely used for the assessment

of cervical arteries

Duplex sonography and color Doppler sonography are excellent tools for

eval-uation of the vertebral and carotid arteries [3] The vertebral arteries can be

injured in different types of spinal trauma (such as vertebral artery dissection in

cervical fractures extending into the transverse foramen) Alternatively, MR

imaging (loss of the flow void within the artery), MR angiography with

intrave-nous injection of MR contrast media or CT angiography after injection of iodine

containing contrast media can be obtained to demonstrate abnormalities of the

vertebral arteries [45]

Indications for Spinal Imaging

There are no universally accepted and standardized indications for the

applica-tion of imaging modalities in spinal disorders However, the following imaging

algorithms are enhanced by evidence from the literature and resemble a “best

practice” approach as used in our spine center

Acute Low Back Pain Without Radicular Symptoms, Without Trauma

In acute non-specific low back pain, imaging

is usually not necessary

In acute low back pain, imaging is not recommended during the first 6 weeks of

a pain episode if:

) spinal infection or

) tumor

can be excluded

Upright anteroposterior and lateral radiographs of the lumbar spine are the

basis of imaging Radiographs give an overview and demonstrate bony details and

indirect signs of disc degeneration including reduced disc height, sclerosis of the

vertebral endplates, spondylophytes as well as osteoarthritis of the facet joints In

Standard radiographs demonstrate transitional anomalies which may be overlooked on MRI

cases of anomalies of the transition between the lumbar spine and the sacrum,

conventional radiographs are important for definition of the lumbar segments

Calcifications are easily recognizable on standard radiographs Standard

radio-graphs are obtained with the patient in the upright position, which is only

possi-ble with very few MR scanners In addition, degenerative or inflammatory

find-ings of the sacroiliac joints are often recognized on these standard examinations

Specific MR imaging questions are related to the presence of:

) disc degeneration

) disc herniation

) nerve root compromise

) facet joint osteoarthritis

) spinal canal stenosis

) spondylodiscitis

) rare findings (e.g., intra- and extradural tumors)

Sacroiliac disorders may be

overlooked using standard

MRI protocols

Suspected abnormalities of the sacroiliac joint should be specifically mentioned

in the request for the MR examination because the imaging protocol has to be adapted (Angled) coronal or axial images covering the entire sacroiliac joint as well as sequences able to recognize inflammatory disease such as STIR (short TI inversion recovery) or contrast-enhanced T1 W fat-suppressed sequences are added in this situation

The use of MR imaging without standard radiographs may be considered when abnormalities are suspected which are not typically associated with bone abnormalities

CT and myelography are not relevant in acute low back pain Imaging guided nerve root blocks or facet joint blocks may be useful for obtaining more precise topographical diagnostic information, for determination of the relevance of MR abnormalities and for therapeutic purposes (see Chapter 10)

Acute Low Back Pain With Radicular Symptoms

MR imaging is superior

to CT for the assessment

of radiculopathy

Imaging considerations are similar to those described above The difference is in timing Imaging is performed at the beginning of the diagnostic work-up In the presence of motor weakness (M3 and worse) imaging is performed as an emergency examination MR imaging usually represents the method of choice because it dem-onstrates the location and extent of nerve root compromise Standard radiographs are not necessary for the initial analysis but should be obtained prior to surgery

There are several disc herniation classification systems (see Chapter 18) cur-rently in use [6, 7, 22] Today, the most frequently used system is the one suggested

by Modic and coworkers [22]:

) normal: no disc extension beyond interspace (DEBIT)

) bulging: circumferential, symmetric DEBIT around the endplate

) protrusion: focal or asymmetric DEBIT into the canal, the base against the

parent disc is broader than any other diameter of the protrusion

) extrusion: focal, obvious DEBIT, the base against the parent disc is narrower

than the diameter of the extruding material itself

) sequestration: the extruded material has lost its connection to the parent disc

Often more important than the description of the shape of the intervertebral disc

is its influence and relation to the adjacent nerve roots, which is crucially depen-dent on the width of the spinal canal [10] Pfirrmann et al [29] showed good

inter-observer reliability in following the nerve root compromise classification system

(see Chapter 18):

) no compromise: normal epidural fat layer visible between nerve root and disc

) contact to nerve root: no epidural fat layer visible between nerve root and

disc; nerve root is in normal position and is not dorsally deviated

) deviation of nerve root: nerve root is displaced dorsally by disc

) compression of nerve root: nerve root is compressed between disc and the

wall of the spinal canal; it may appear flattened or be indistinguishable from disc material

CT is inferior to MRI in this situation and is only indicated in the case of

contra-indications for MRI Imaging guided treatment such as nerve root blocks or facet

joint blocks may be employed for therapeutic rather than diagnostic purposes

Spinal Cord and Cauda Compression Syndromes

Spinal cord and cauda equina compression represent an emergency indication for MR imaging

A suspected spinal cord and cauda equina compression syndrome is an emergency

situation requiring immediate MR imaging If no clear diagnosis such as a large

disc herniation or intraspinal hemorrhage can be made, a tumor within the spinal

cord has to be excluded In such cases, contrast enhanced MRI should be obtained

and imaging should be extended to include the thoracic and cervical spine

Acute Trauma

Trauma is typically imaged with standard radiographs and CT

Imaging starts with standard radiographs in two planes If conventional

radio-graphs lead one to suspect vertebral fracture or if they are equivocal, CT with

multiplanar reformations is employed Increasingly, CT is even used as a primary

examination, especially in polytraumatized patients If a multidetector CT

(MDCT) is available, the acquired data sets can be used for reconstruction of the

spine with adequate image quality [32] MR imaging can be necessary for

identi-fication of radiologically occult fractures (Figs 14 – 16) and bone contusions

MRI reveals additional information regarding:

) herniated disc material

) epidural or intramedullary hematoma (Fig 15)

) post-traumatic myelopathy

) spinal cord transsection (Fig 15)

) injury to the posterior support structures

c

Figure 14 Acute trauma

aSagittal T1 W andbsagittal STIR sequences as well ascaxial T2 W sequence of a patient with an acute trauma of the

thoracic spine Anterior collapse of the vertebral body is visible in all sagittal sequences and posterior dislocation of a

broad-based fragment into the spinal canal (arrowheads) Caused by edema and hemorrhage, there is low signal within

the bone marrow in the T1 W (curved arrow) image In the fluid-sensitive STIR sequence, edema is much more

conspi-cuous (black arrow).

a b

c

Figure 15 Spinal cord lesion

aSagittal T1 W andbT2 W sequences as well ascaxial T2 W sequence of the thoracic spine after a car accident Anterior

collapse of the vertebral body and bone marrow edema is visible in both sagittal sequences (asterisk) There is disruption

of the spinal cord and dislocation (curved white arrows) There is hemorrhage and myelopathy within the spinal cord (straight black arrow) Hemorrhage can be seen in the anterior epidural space (arrowheads) and also in the posterior epi-dural space (straight white arrow) The epi-dural sac is compressed (curved black arrows).

Figure 16 MRI in acute and old osteoporotic vertebral fractures

aSagittal T1 W andbT2 W sequences as well ascsagittal STIR sequence of the thoracic spine in an osteoporotic patient.

There is collapse of three different vertebral bodies The acute fracture (asterisk) of one vertebral body can be identified

by the low signal in the T1 W (asterisk) sequence and high signal within the bone marrow in T2 W (black arrow) and STIR (white arrow) sequences Only a slight signal increase near the endplate of the adjacent vertebral body is visible in the STIR sequence (curved arrow), which can be caused by degeneration or some minor infraction There is also an old verte-bral body fracture (arrowhead) visible without bone marrow signal alterations.