Advanced Neurospinal Imaging

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Identify parts of the spine labeled in Figure 42-1 .

For the answer, see the figure legend.

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What imaging modalities are most often used in the evaluation of spine pathology?

Radiography, computed tomography (CT), magnetic resonance imaging (MRI), myelography, discography, magnetic resonance angiography (MRA), computed tomographic angiography (CTA), and conventional angiography are utilized for spinal imaging.

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Describe the strengths, weaknesses, and most appropriate uses of CT in spinal imaging.

Radiography is often the initial imaging examination used to evaluate the spine. Pathologic conditions of the osseous spine, including fractures, degenerative changes, tumors, infections, and congenital anomalies (including transitional vertebrae), may be detected with radiographs. However, multidetector CT provides superior evaluation of the bony anatomy and of pathologic conditions. Images may be acquired rapidly and reconstructed at narrow intervals (0.6 to 1 mm) with edge-enhancing algorithms. Multiplanar and three-dimensional images can subsequently be created. In the setting of acute spinal trauma, CT has been shown to be more time efficient and significantly more sensitive than radiography for fracture detection. CT, in contrast to radiography, also allows excellent evaluation of retropulsed bone into the spinal canal. However, a higher radiation dose is associated with CT scanning compared with radiography. Dual-energy CT may also be employed in patients with spinal instrumentation to reduce artifacts related to metallic hardware. As a result, CT is often used to image traumatic and nontraumatic osseous spinal pathologic conditions. Although CT is inferior to MRI in its contrast resolution of the soft tissues within the spinal canal, including the spinal cord, nerve roots, epidural compartment, and subdural compartment, it does provide some information about these structures and is certainly superior to radiography.

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Describe the strengths and drawbacks of MRI.

MRI provides the best and most direct evaluation of the contents within the spinal canal, including the spinal cord, nerve roots, and epidural and subdural compartments. MRI also provides the most detailed evaluation of the soft tissues, including the intervertebral discs, ligaments, and musculature. Optimal resolution is obtained at high field strengths using phased-array surface coils. Numerous safety concerns arise, however, with the use of MRI. Patients undergoing this examination must be screened for implantable devices and/or retained objects, because many are not MR compatible. Ferromagnetic objects may become projectiles within the magnetic field and injure patients or health care providers. When MRI is performed in critically ill patients, MRI-compatible ventilators and monitoring devices must be used. When patients with spinal cord injuries are imaged, spinal precautions must be maintained, and fixation devices must be MRI-compatible. MRI of patients with prior spinal surgery is often of reduced diagnostic value because of artifacts arising from metallic hardware. Use of imaging sequences optimized for metal suppression, however, may mitigate these artifacts. MRI is also time-consuming and requires patient cooperation (i.e., remaining motionless) to obtain high-quality studies.

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In patients with contraindications to MRI, what imaging study can be used to assess the contents within the spinal canal?

In patients with suspected spinal cord or nerve root compression who cannot be evaluated with MRI, myelography is an alternative, although invasive, technique that may be used to evaluate the spinal canal contents. Myelography is performed most often in patients with contraindications to MRI or who have nondiagnostic MRI studies. Nonionic contrast material is instilled into the subarachnoid space of the spinal canal, typically via lumbar puncture. Risks of this procedure are low, but include headache, allergic reaction to the contrast material, infection, hematoma formation, neural damage, and seizure. The contrast material in the subarachnoid space outlines the spinal cord and nerve roots. Impressions on the contrast column and displacement of neural structures are findings indicative of a pathologic condition ( Figure 42-2 ). Myelography is often complementary with CT, which is performed after myelography for improved delineation of anatomy and spinal pathology.

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What is discography, and what are its indications?

Discography involves the injection of contrast material into the nucleus pulposus of the intervertebral disc, usually followed by CT scanning of the injected disc. This test is usually performed in patients with multilevel disc disease, axial back pain, or both, in an attempt to reproduce the patient's symptoms and identify the “culprit” disc. Patients with axial back pain, T2-weighted hypointense discs of reduced height, and concordant findings on discography have been reported to have improved outcomes following interbody and combined spinal fusion procedures. Patterns of contrast diffusion may suggest annular degeneration, fissures, or both, although imaging findings must be correlated with patient symptoms ( Figure 42-3 ).

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What is the primary role of catheter angiography of the spine?

Conventional spinal catheter angiography is primarily used for the detection, characterization, and possible endovascular treatment of spinal vascular malformations.

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What is spinal dysraphia?

Spinal anomalies with incomplete midline closure of mesenchymal, osseous, and neural structures are grouped under the term spinal dysraphia . Most defects occur in the lumbosacral region.

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Differentiate between open and occult forms of spinal dysraphia.

Myeloceles and myelomeningoceles are two types of open spinal dysraphia. Neural tissue (the neural placode, with or without associated meninges) protrudes through the spinal canal and soft tissue defects. Associated abnormalities include Chiari II malformation, hydrocephalus, syringohydromyelia, spinal lipomas, dermoid and epidermoid inclusion cysts, agenesis of the corpus callosum, diastematomyelia, and abnormal spinal curvature. In the occult form of spinal dysraphia, the defects are covered by skin, and no neural tissue is exposed. Occult dysraphias include meningoceles, dorsal dermal sinuses (epithelial-lined tubes connecting the spinal cord and skin), and fat-containing lesions (lipomyelomeningoceles, filum terminale lipomas, and intradural lipomas). Midline cutaneous stigmata (dimples, nevi, and hairy patches) are often present.

10

What are the clinical findings and imaging features of a tethered spinal cord?

The conus medullaris in adults normally terminates at approximately the L1-L2 level. With a tethered spinal cord/thick filum terminale syndrome ( Figure 42-4 ), the conus medullaris is identified at L2 or below, and the filum terminale is greater than 2 mm in thickness. Associated anomalies (lipomas, diastematomyelia, and myelomeningoceles) are common. Patients typically present in childhood or young adulthood with pain, dysesthesias, bowel or bladder dysfunction, spasticity, and/or kyphoscoliosis.

11

List and describe caudal spinal anomalies.

Caudal spinal anomalies are malformations of the distal spine, spinal cord, and meninges associated with disorders of the hindgut, kidneys, urinary bladder, and genitalia. Caudal spinal anomalies include the following:

• Caudal regression syndrome : Varying degrees of lumbosacral agenesis with renal and anogenital anomalies and possible fusion of the lower extremities ( Figure 42-5 ).

  

• Terminal myelocystocele : Cystic dilation of the distal spinal cord, which is tethered, associated with partial sacral agenesis or spina bifida.

• Anterior sacral meningocele : A cerebrospinal fluid (CSF) filled sac that protrudes into the pelvis anterior to the sacrum.

• Occult intrasacral meningocele : A mild dural developmental anomaly, a meningeal-lined cyst communicating with the remainder of the thecal sac via a narrow channel, with associated remodeling of the sacrum.

• Sacrococcygeal teratoma : The most common presacral mass in children, containing tissue from all three germ layers (endoderm, mesoderm, and ectoderm) and often cystic and solid.

12

What are the split notochord syndromes?

Persistent midline adhesions between endoderm and ectoderm can result in splitting of the notochord. With this split, paired hemicords (diastematomyelia) may result. Persistent endodermal-ectodermal adhesions or communications may produce dorsal enteric fistulas and neuroenteric cysts.

• Diastematomyelia predominantly occurs in female patients. In 85% of cases, the split occurs between T9 and S1. The cord is split by a fibrous, osseous, or osteocartilaginous septum, and the hemicords may or may not share a dural sac. Associated neurologic and orthopedic anomalies are common ( Figure 42-6 ).

  

• Dorsal enteric fistulas are very rare and extend from the mesenteric surface of the gut through the prevertebral tissues, vertebrae, and spinal cord to the dorsal skin surface.

• Neuroenteric cysts are most often intradural, extramedullary cystic masses in the thoracic region. Vertebral anomalies are seen in less than half of the cases.

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What are Tarlov cysts?

Tarlov cysts are CSF-filled dilations of sacral nerve root sleeves ( Figure 42-7 ). They are common generally incidental findings detected on spinal CT and MRI scans. They may reach large proportions and may be associated with osseous remodeling/expansion of neural foramina. They originate at the level of the dorsal root ganglion and may result from trapping of CSF. They are rarely symptomatic, but on occasion may compress the adjacent nerve root. Dural ectasia, Tarlov cysts, other perineural cysts, and spinal meningoceles may be seen in association with systemic diseases including connective tissue disorders (such as Marfan's syndrome and Ehlers-Danlos syndrome) as well as phakomatoses such as neurofibromatosis type I (NF-1).

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What is arachnoiditis?

Arachnoiditis refers to inflammation of the nerve roots of the cauda equina with adhesion of the nerve roots to each other, to the thecal sac, or both. Causes of arachnoiditis include prior surgery, prior intraspinal hemorrhage, inflammatory conditions such as sarcoidosis, prior intrathecal therapy (e.g., chemotherapeutic agents), and prior myelography, particularly with pantopaque. Patients may present with nonspecific back pain, paresthesias, or both. The key imaging features of this diagnosis are abnormal morphologic features and distribution of nerve roots, which may or may not enhance. Three imaging patterns have been described. The nerve roots may be centrally clumped, appearing as a “pseudocord” within the thecal sac. Alternatively, the nerve roots may be adherent to the periphery of the thecal sac (i.e., the “empty sac” appearance) ( Figure 42-8 ). Uncommonly, the nerve roots may clump together to form a large, mildly enhancing mass, which fills the thecal sac.

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