INTRODUCTION

Imaging of spinal canal tumors and tumor-like masses has been revolutionized by the advent of magnetic resonance imaging (MRI), which is a sensitive modality for the identification and characterization of spinal lesions. Radiologic evaluation of these lesions focuses on localizing lesions into extradural, intradural extramedullary, and intramedullary compartments. Although this approach is somewhat artificial, because many lesions transgress compartments or can be found in different compartments, it is very useful for generating an appropriate differential diagnosis for a spinal mass (Table 10-1). Clinical information (in particular patient age) is helpful to further narrow and order the differential diagnosis of spinal lesions. This chapter begins with a brief discussion of imaging techniques used in evaluating spinal masses. This is followed by a discussion of imaging characteristics of the most common lesions that occur in each of the aforementioned categories, including a description of tumors, tumor-like cysts, and non-neoplastic tumor mimics. A discussion of spinal vascular malformations is beyond the scope of this chapter.

Table 10-1 Classification of Spinal Canal Tumors and Tumor-Like Masses

IMAGING MODALITIES

Radiographs, computed tomography (CT), CT myelography, MRI, and angiography are the modalities available for assessment of spinal canal lesions. Radiographs can be a useful screening test but are limited, demonstrating mainly the secondary effects of spinal lesions on the adjacent bony and paraspinal soft tissues. Expansion of the central canal, bony destruction and/or remodeling (including vertebral body scalloping and neural foraminal widening), thickening of the paraspinal soft tissues, and associated scoliosis are some of the findings that may be seen in the setting of an intraspinal lesion. A normal radiograph does not exclude the presence of an underlying spinal mass. CT demonstrates bony and soft tissue changes with a greater degree of conspicuity, but the intraspinal lesion itself may be subtle or impossible to detect. CT myelography, a technique whereby myelographic contrast is introduced directly into the thecal sac followed by CT imaging, increases sensitivity for detection of intraspinal disease over conventional CT. However, it is still less effective than MRI for assessing intramedullary and extradural disease, and, although equally sensitive to contrast-enhanced MRI for detection of intradural extramedullary spinal masses, it is more invasive.^1–3 CT myelography, therefore, typically is reserved for patients who have contraindications for MRI and sometimes for those with spinal hardware that causes excessive artifact on MRI. CT myelography demonstrates expansion of the cord or mass effect on the cord by spinal lesions but is limited in its ability to characterize the underlying lesion and may be insensitive for intramedullary lesions that have only minimal mass effect. Occasionally, CT myelography is a useful adjunct to MRI for cystic lesions within the spinal canal, where it is used to assess for communication with the cerebrospinal fluid (CSF) space.^4,5 In patients without contraindications, MRI is undoubtedly the modality of choice for evaluation of spinal canal lesions. It is the most sensitive and specific modality for both identifying and characterizing intraspinal lesions. Spinal angiography is reserved for vascular lesions, providing important information for preoperative planning and guiding endovascular treatment.

MRI of the spine involves greater technical challenges than imaging of the brain. The presence of bone housing the spinal canal creates large susceptibility gradients. The small size of the spinal canal and spinal cord limits spatial resolution. In addition, CSF pulsation introduces motion artifacts. MR techniques used in screening for spinal lesions include at least a T1- and T2-weighted sequence. Addition of a gradient echo (GRE) sequence is useful to evaluate for blood products. Intravenous gadolinium improves detection of intradural extramedullary disease and helps to characterize and delineate intramedullary lesions.^3,6 Evaluation in both the sagittal and transverse planes is important to confirm true findings and exclude artifacts. The role of these standard sequences in evaluating spinal masses is described in Table 10-2. Examples of the normal appearance of the spine when imaged with these standard sequences are shown in Figs. 10-1 to 10-3.

Table 10-2 Standard MRI Sequences for the Evaluation of Spinal Tumors

Fig. 10-1 Normal appearance of the cervical spine with MRI in a 25-year-old woman. A, Sagittal T1WI. The spinal cord is isointense to muscle. CSF is hypointense. B, Sagittal T2WI. The CSF is hyperintense. Apparent linear high signal within the anterior spinal cord is caused by truncation (Gibb’s) artifact. C, Axial GRE image. Susceptibility effects are accentuated with this sequence. However, CSF motion artifact is reduced.

Fig. 10-2 Normal appearance of the thoracic spinal canal in a 24-year-old woman. A, Sagittal T1WI. The spinal cord is intermediate signal intensity (isointense to muscle). CSF is dark on this sequence. Mild endplate irregularity is seen within a lower thoracic vertebral body, consistent with Schmorl’s type changes. B, Sagittal T2-weighted fast spin echo (FSE) image. CSF is bright on this sequence. Areas of reduced signal are seen within the CSF space posterior to the spinal cord in the upper thoracic region as a result of CSF flow artifact. C, Sagittal short tau inversion recovery (STIR) image. This is a fat suppressed T2-weighted sequence. CSF flow artifact is seen on this image, similar to that in B. D, Axial T2-weighted FSE image. The distinction between the intramedullary, intradural extramedullary, and extradural spaces is often best appreciated in the axial plane.

Fig. 10-3 Normal appearance of the thoracic spine in a 42-year-old woman. A, Sagittal T1WI. The bright epidural fat is more prominent than in the previous example. B, Sagittal T2-weighted FSE image. CSF flow artifact is prominent in this case, causing reduced signal within the intradural space. C, Sagittal post-gadolinium T1-weighted fat saturated image. A small amount of normal linear vascular enhancement is present. D, Axial T2-weighted FSE image. CSF flow artifact is much worse in this case than in the prior example. The CSF space appears almost isointense to the cord on this image, making intradural lesions difficult to detect. E, Axial post-gadolinium T1-weighted fat saturated image.

Some newer pulse sequences have been investigated for use in spinal imaging with variable results. These include fluid-attenuation inversion recovery (FLAIR), short tau inversion recovery (STIR), diffusion weighted imaging (DWI), diffusion tensor imaging (DTI), and MR spectroscopy (MRS) (Table 10-3). FLAIR is a heavily T2-weighted sequence that nulls signal from CSF and thus may increase conspicuity of hyperintense lesions in close proximity to CSF. Despite its utility in brain imaging, FLAIR has been less successful in the spine and has shown to be less sensitive than standard T2-weighted sequences in assessment of cord lesions.^7–10 STIR (a fat suppressed T2-weighted sequence) is commonly used to assess for vertebral body involvement in the setting of trauma or infection but also may have useful application in detecting intramedullary disease. Several studies have demonstrated increased sensitivity of STIR for cord disease in multiple sclerosis (MS) relative to other T2-weighted sequences.^10,11 However, STIR is limited by reduced signal to noise ratio and greater sensitivity to motion than standard T2-weighted sequences.⁸ DWI is an MR technique that is sensitive to the random motion of water molecules in tissues over microscopic distances (5–20 microns) and can generate a map of the average apparent diffusion coefficient (ADC). Reduced ADC is seen in acute cerebral stroke and aids early detection of infarcts, improving accuracy over conventional MRI.¹² DWI also has become an invaluable technique for assessing other intracranial diseases, including applications in infection, tumors, and cysts. DWI in the spinal cord and spinal canal has been more difficult to implement than in the brain because of technical factors, in particular susceptibility from the vertebrae and limited spatial resolution. Although DWI is not currently routinely used for spinal cord imaging at most institutions, DWI techniques have been developed that are practical for use in the clinical setting.^13,14 DTI, an application of DWI that measures diffusion anisotropy and thus can be used to trace white matter tracts within the brain and spinal cord using statistical methods, is of great interest in spinal cord tumor imaging. DTI demonstrates a high degree of anisotropy in the normal spinal cord, which is disrupted by spinal cord tumors, a feature that may be helpful to depict the full extent of spinal cord lesions more accurately than conventional imaging and perhaps eventually map out involvement of key spinal cord white matter tracts.^15,16 MRS is a technique that can obtain biochemical information about tissues being studied by creating a spectrum of metabolites within a region of interest. Currently, a number of technical factors preclude use of MRS in the spine, but future advances may make this technique both possible and useful in spinal cord imaging.⁸

Table 10-3 Potential Sequences for Evaluation of Spinal Tumors

EXTRADURAL LESIONS

Extradural lesions, which by definition are outside of the dura, usually arise from the osseous spinal structures, intervertebral discs, and surrounding soft tissues (including vessels, nerves, fat, and paraspinal muscles). These lesions cause focal displacement of the thecal sac and its contents away from the mass. Radiographs may demonstrate secondary effects of the lesion on the bony structures, including bone destruction or scalloping, expansion of the central spinal canal, and paraspinal extension. CT myelography shows extrinsic compression of the thecal sac and decrease in the ipsilateral CSF space. MRI shows the dura draped over the mass and may show an epidural fat cap (Box 10-1).¹⁷ The most common epidural masses are degenerative, including disc protrusions, osteophytes, and synovial cysts. Infection and hematomas may present as epidural masses. Of neoplastic lesions, metastases to bone with extradural extension are the most common.^17,18 Imaging of lesions of the vertebrae (with and without epidural extension) was discussed in the previous chapter. Here we discuss epidural lesions that were not previously mentioned.

EPIDURAL LIPOMATOSIS

This is a rare condition manifested by excessive deposition of unencapsulated fat in the epidural space, resulting in cord and cauda equina compression with neurologic symptoms. Most cases are seen in association with long-term exogenous steroid use or conditions in which there is elevated endogenous production of steroid (such as in Cushing’s disease). Cases may occur as a result of morbid obesity or with no cause evident.¹⁹ In approximately 60% of cases, involvement of the mid to lower thoracic spine is seen with fat predominantly posterior to the cord. The remaining 40% of cases involve mainly the lower lumbar region with fat surrounding the circumference of the thecal sac (Box 10-2). A combination of thoracic and lumbar involvement is sometimes seen.²⁰ CT and MR demonstrate increased epidural fat and diminished subarachnoid space, with tapering of the thecal sac and a Y-shaped configuration seen in the transverse plane (Fig. 10-4).^21,22 Epidural lipomatosis does not enhance nor does it cause bony erosion.^17,20 Fat suppression is helpful on MRI to confirm the presence of adipose tissue (Box 10-2).

Box 10-2 Epidural Lipomatosis

• Rare condition of excessive deposition of unencapsulated fat in epidural space

• Associated with exogenous or endogenous hypercortisolemia

• Typically a result of chronic steroid use

• May occur in morbid obesity or with no etiology evident

• 60% thoracic, 40% lumbar

• CT and MR demonstrate increased epidural fat and diminished subarachnoid space

• Y configuration of thecal sac, tapering of thecal sac, crowding of nerve roots

Fig. 10-4 Epidural lipomatosis within the lumbar spine. A, Sagittal T1WI. Prominent epidural fat is seen anterior and posterior to the thecal sac, extending from the L3–4 level to the sacrum. Note the accentuated tapering of the thecal sac. B, Axial T1WI at the L4–5 level. Note the Y configuration of the thecal sac.

EPIDURAL HEMATOMA

Extravasation of blood into the epidural compartment of the spine may be caused by trauma or instrumentation but also can occur spontaneously, especially in the setting of anticoagulation or coagulopathy (Box 10-4). An epidural hematoma is rarely the sequelae of hemorrhage from a spinal vascular malformation.^27,28 MR and CT myelography demonstrate an elongated, often multisegment, extra-axial mass encasing or displacing the thecal sac.²⁰ MRI signal characteristics depend on the age of blood products and are usually heterogeneous. Hyperintensity on T1WI, heterogeneity with foci of low signal on T2WI, and susceptibility demonstrated with GRE are helpful features in making the diagnosis (Fig. 10-5).^29,30 Enhancement may be seen, especially along the margins of an epidural hematoma (Box 10-4).^20,30

Box 10-4 Epidural Hematoma

• May be spontaneous as a result of anticoagulation/coagulopathy or instrumentation

• Rarely caused by a vascular malformation

• Long-segment extra-axial mass encasing or displacing cord or cauda equina

• MRI characteristics depend on age of blood products: isointense, hypointense, or hyperintense on T1WI; heterogeneous on T2WI; susceptibility on GRE

• Enhancement along margins of collections

Fig. 10-5 A 58-year-old man who presented with a spontaneous epidural hematoma. A, Sagittal T1WI of the cervical spine. A mildly hyperintense epidural mass is seen extending from C4 to C6 posterior to the spinal cord and compressing it anteriorly. B, Sagittal STIR image. The mass is hyperintense (similar to CSF). The dark, thin dura is displaced anteriorly by the hematoma. C, Sagittal GRE image. Susceptibility from the blood products gives rise to low signal within and around the hematoma that makes it more conspicuous. D, Axial T1WI at the C5 level. The hematoma is seen within the right posterior epidural space. E, Axial GRE image at the C5 level. The margins of the lesion are defined by a thin dark line (as a result of susceptibility from blood products).

EPIDURAL ABSCESS

Epidural spinal infection with abscess formation usually results from hematogenous spread of disease primarily to the intervertebral disc, typically from infection of the skin, urinary tract, or respiratory system. Direct spread from paraspinal infection also may occur but is less common. Predisposing factors include diabetes mellitus, trauma, alcoholism, and intravenous drug abuse (Box 10-5). Epidural anesthesia and analgesia also are associated with increased risk. Pyogenic organisms (most often Staphylococcus aureus) are the most common pathogens.^31,32 MRI is the imaging tool of choice and should include the entire spinal axis to exclude multiple sites of involvement.³² The posterior epidural space may be more commonly involved than the anterior, and the abscess can extend over multiple segments.³³ Abscesses are classically isointense to hypointense to the cord on T1WI, hyperintense on T2WI and STIR images, and demonstrate rim enhancement (Fig. 10-6). Homogeneously or heterogeneously enhancing phlegmon may often be seen in some infections without frank abscess formation (Figs. 10-7 and 10-8).³⁴ Associated findings of spondylodiscitis, including vertebral body endplate erosion and disc space narrowing, are helpful in some cases in making the diagnosis. High signal on DWI with reduced ADC has been demonstrated in spinal epidural abscesses and also may be helpful to confirm the diagnosis.³⁵

Box 10-5 Epidural Abscess

• Predisposing factors: Diabetes mellitus, trauma, alcoholism, intravenous drug use, chronic illness, epidural anesthesia or steroid injections, discitis

• Posterior epidural space more common than anterior epidural space

• Multisegmental

• Look for associated findings of spondylodiscitis with adjacent enhancing epidural phlegmon and peripherally enhancing fluid collection

• Abscess is isointense to hypointense to cord on T1WI, hyperintense on T2WI and STIR, hyperintense on DWI, dark on ADC, and peripherally enhances

Fig. 10-6 A 57-year-old man with a cervical epidural abscess. A, Sagittal T1WI of the cervical spine. An isointense epidural mass/collection is seen posterior to the cord, extending from C4 to T2. B, Sagittal T2WI. The lesion is hyperintense on this sequence. C, Sagittal post-gadolinium T1-weighted fat saturated image. The majority of the lesion enhances with a small, focal, non-enhancing collection at the C6 level. There is no evidence of osseous involvement with osteomyelitis/discitis. D, Axial post-gadolinium T1-weighted fat saturated image at the C6 level. Rim enhancement with central non-enhancing material is consistent with a frank abscess.

Fig. 10-7 A 1-year-old boy who presented with hypotonia and was diagnosed with osteomyelitis/discitis at T12–L1 with a small associated epidural phlegmon. A, Lateral radiograph of the lower spine demonstrates disc space narrowing and endplate irregularity at T12-L1, consistent with osteomyelitis/discitis. B, Anteroposterior radiograph. The findings are more subtle in this projection. C, Sagittal T2-weighted MR image of the lower thoracic and lumbar spine. In addition to disc space narrowing and endplate irregularity, there is high signal within the T12 and L1 vertebral bodies as well as within the intervertebral disc. A small, high signal epidural collection is seen posterior to the T12 and L1 vertebral bodies. D, Sagittal post-gadolinium T1WI. The T12 and L1 vertebral bodies, intervertebral disc, and small epidural phlegmon enhance. A frank rim-enhancing abscess is not seen.

Fig. 10-8 A 20-year-old man with chronic granulomatous disease and atypical infection with Aspergillus, affecting the thoracic and lumbar spine. A, Sagittal T1WI of the thoracic spine. Heterogeneous low signal is seen within the T8 through T10 vertebral bodies without evidence of bony destruction. Sparing of the disc space, as noted here, is seen with atypical infections or neoplasms. Epidural and anterior paraspinal soft tissue is seen at the affected levels with encroachment on the neural foramina. B, Sagittal T1WI lateral to A. The paraspinal component of the mass is demonstrated in this image. C, Sagittal T2WI of the thoracic spine. The affected vertebral bodies are mildly heterogeneous and hyperintense. D, Sagittal post-gadolinium T1-weighted fat saturated image of the thoracic spine. The affected vertebral bodies and the associated paraspinal and epidural phlegmon enhance avidly. E, Sagittal post-gadolinium T1-weighted fat saturated image lateral to D. F, Axial T2WI at the T10 level. The high signal vertebral body and epidural and paraspinal soft tissue are shown. Rib and pleural involvement is also present and is appreciated better in the axial than the sagittal plane. G, Sagittal T1WI of the lumbar spine. Pathological fracture of the L4 vertebral body is present with retropulsion into the spinal canal. A small amount of epidural and paraspinal soft tissue is seen extending above and below the L4 vertebral body. H, Sagittal T2WI of the lumbar spine. High signal is seen extending through the fractured L4 vertebral body. A small amount of high signal also is seen in the L3 vertebral body. I, Sagittal post-gadolinium T1-weighted fat saturated image of the lumbar spine. The affected vertebrae, as well as the epidural and paraspinal involvement, enhance.

SYNOVIAL CYST

Synovial cysts are almost always associated with degenerated facet joints and usually do not present a diagnostic dilemma. The appearance of a round, sharply marginated, posterolateral, extradural cystic mass communicating with the facet joint is characteristic (Fig. 10-9). MRI signal intensity of these lesions varies depending on the protein content and the presence of calcification or hemorrhage (Fig. 10-10). Mild rim enhancement may be seen (Fig. 10-11). These lesions may be difficult to detect on CT unless calcification, intracystic gas, or hemorrhage is present (Box 10-6).^36,37

Fig. 10-9 Synovial cyst at the L4–5 level. A, Sagittal T2WI of the lumbar spine demonstrates a round, well-circumscribed, hyperintense, cystic lesion within the posterior epidural space at the L4–5 level. B, Sagittal T1WI of the lumbar spine. The lesion is slightly higher in signal intensity than the CSF but is subtle and difficult to appreciate on this sequence. C, Sagittal post-gadolinium T1-weighted fat saturated image of the lumbar spine. A thin rim of enhancement is seen surrounding the cyst. D, Axial T2WI at the L4–5 level. The relationship to the adjacent right facet joint is confirmed in the axial plane. There is fluid in both facet joints, and facet hypertrophy is noted, typical of facet degeneration.

Fig. 10-10 A 60-year-old man with prior CT-guided aspiration of a synovial cyst at L4–5 presented for evaluation after his symptoms recurred. A, Sagittal T2WI of the lumbar spine. A uniformly low signal mass is seen within the posterior epidural space at L4–5. B, Axial T2WI confirms that the lesion is adjacent to the right facet joint, consistent with a synovial cyst. The presence of uniform low signal throughout the lesion indicates likely calcification or hemorrhage. C, Axial T1WI. The lesion is isointense to hypointense throughout. D, A CT was performed to assess for the potential of CT-guided aspiration of the synovial cyst. Sagittal CT reconstruction shows that the lesion is heavily calcified and not amenable to aspiration. E, Coronal CT reconstruction. F, Axial CT image at the L4–5 level.

Fig. 10-11 L4–5 synovial cyst that extended outside of spinal canal rather than the more typical epidural location. A, Sagittal T1WI of the lumbar spine. An isointense to hypointense mass is seen in the posterior paraspinal soft tissues posterior to the L4–5 facet joint. Degenerative changes, including disc space narrowing, are present at this level. B, Sagittal T2WI. The lesion is well-circumscribed, hyperintense, and has a thin hypo-intense rim. C, Sagittal STIR. Nulling of signal from fat makes the cyst more conspicuous. D, Sagittal post-gadolinium T1-weighted fat saturated image. A thin rim of enhancement is seen. E, Axial post-gadolinium T1-weighted fat saturated image. Enhancement also is present within the adjacent degenerated facet joint.

Box 10-6 Synovial Cyst

• Posterolateral extradural cystic mass communicating with facet joint

• 90% in lumbar spine, most commonly at L4–5

• Round, sharply marginated

• Difficult to detect with CT unless calcification, hemorrhage, or intracystic gas present

• Mild rim enhancement

• Variable signal characteristics on MR depending on protein content, calcification, hemorrhage

• Almost always associated with facet degeneration

SEQUESTERED DISC FRAGMENT

Protruded disc material may detach and become displaced from the parent disc. The extruded, sequestered disc fragment usually is found in the anterior epidural space but may occasionally migrate posteriorly or through the neural foramen.³⁸ Although peripheral enhancement may be seen, the disc material itself usually does not enhance.^17,38,39 Additional findings of degenerative disc disease are helpful in making the diagnosis (Fig. 10-12).

Fig. 10-12 Disc protrusion with extrusion. A, Sagittal T1WI of the lumbar spine. A posterior disc protrusion is seen at L5–S1 with isointense material extending inferior to the disc space, representing extruded disc material. B, Sagittal T2WI. The dark disc material is more conspicuous against a background of bright CSF. C, Axial/oblique T1WI at the L5–S1 level. The disc material extends down into the left lateral recess. D, Axial T2WI at L5–S1.

EXTRADURAL ARACHNOID CYST

An extradural arachnoid cyst (EAC) is a congenital or acquired CSF-filled outpouching of arachnoid that protrudes through a dural defect (Box 10-7). Most EACs are found in the lower thoracic spine, posterior or posterolateral to the cord.⁵ MRI demonstrates a long-segment extradural mass that follows CSF signal characteristics on all sequences. CT myelography may show communication with the CSF space.^17,40

Box 10-7 Extradural Arachnoid Cyst

• CSF-filled outpouching of arachnoid that protrudes through dural defect

• Congenital or acquired

• Two-thirds are in mid to lower thoracic spine, posterior or posterolateral to thoracic cord; cervical uncommon

• Long-segment CSF–equivalent extradural mass that causes cord compression or myelographic block

• Bony changes caused by mass effect—widened pedicles, scalloping, pedicle erosion

• Differential diagnosis: Traumatic meningocele (usually large extra-spinal component), lateral thoracic meningocele (usually neurofibromatosis type 1), sacral meningocele (Figs. 10-13 to 10-16)

Fig. 10-13 A 9-year-old man who presented with L5 radiculopathy. MRI shows cystic epidural mass that either represents an extradural arachnoid cyst or sacral meningocele. A, Midline sagittal T1WI of the lumbar spine. A well-circumscribed posterior epidural mass is seen within the sacral spinal canal, causing expansion of the bony canal. The mass is isointense to CSF on all imaging sequences. B, Sagittal T1WI to the left of A. C, Midline sagittal T2WI. D, Sagittal T2WI to the left of C. E, Axial T2WI at the S1 level. The cyst is outside the dura and compresses the thecal sac anteriorly and to the right. The bony spinal canal is expanded, indicating a long-standing process. F, Axial T2WI below E. G, Sagittal post-gadolinium T1-weighted fat saturated image. The cyst does not enhance. H, Axial post-gadolinium T1-weighted fat saturated image.

Fig. 10-14 A 62-year-old man who has post-traumatic epidural cyst and tethering of the cord at T5 with focal cord atrophy. The patient had a remote history of trauma. A, Sagittal T1WI of the thoracic spine. A well-circumscribed low signal lesion is seen in the posterior epidural space at T5. The adjacent spinal cord has focal decreased caliber and is tethered posteriorly. B, Sagittal T2WI of the thoracic spine. The lesion is high signal, consistent with a cyst. C, Sagittal post-gadolinium T1-weighted fat saturated image. The cyst does not enhance. D, Axial T2WI at the T5 level shows the cyst and the markedly decreased size of the cord. E, Axial CT myelogram image at the T5 level. The attenuated spinal cord is angulated in configuration and sits right up against the posterior dura. The cyst is present posterior to the dural sac at this level and is higher density than the surrounding epidural fat. F, Sagittal reconstruction of CT myelogram. The cyst is shown to communicate with the CSF space with mild hyperdensity caused by partial filling with myelographic contrast. At the time of trauma a small tear of the dura likely occurred at this level causing this acquired epidural arachnoid cyst and cord tethering with possible cord herniation.

Fig. 10-15 Lateral thoracic meningocele. This single image from a contrast enhanced CT of the chest demonstrates a fluid density lesion extending out from the thoracic spinal canal, causing bony expansion and remodeling consistent with a long-standing lesion. A smooth, thin rim of enhancement is seen.

Fig. 10-16 Patient with neurofibromatosis type 1 (NF-1) and associated dural ectasia and meningoceles. A, Off-midline sagittal T2WI. The T3 to T5 neural foramina are markedly expanded with cystic lesions noted, consistent with meningoceles. B, Posterior vertebral scalloping is noted with a patulous central spinal canal within the upper thoracic spine, consistent with NF-1 and dural ectasia. C, Axial T2WI demonstrates contiguity between the intradural space and the meningocele.

INTRADURAL EXTRAMEDULLARY LESIONS

Intradural extramedullary lesions arise inside the dura but outside of the spinal cord or cauda equina. These lesions tend to displace the spinal cord and enlarge the ipsilateral subarachnoid space with a sharp interface between the undersurface of the mass and the CSF space (Box 10-8). Nerve sheath tumors (schwannomas and neurofibromas) and meningiomas account for the vast majority of intradural lesions. Paragangliomas and CSF-disseminated metastases are relatively rare neoplasms of the intradural space. Tumor-like cysts, including arachnoid cysts, epidermoids, and neurenteric cysts, are non-neoplastic lesions that may be seen in the intradural space and may cause symptoms such as spinal cord or nerve root compression. Lipomas are considered congenital developmental lesions and are associated with a tethered cord but may be an incidental finding and may not present until adulthood.

Box 10-8 Characteristics of Intradural Extramedullary Lesions

• Inside the dura, outside of the spinal cord

• Displace spinal cord

• Enlarge ipsilateral subarachnoid space

• Sharp interface with CSF space—“CSF cap”

SCHWANNOMA

Schwannomas are grossly encapsulated neoplasms of the nerve sheath in the peripheral nervous system that typically arise from the dorsal sensory root. They account for approximately 30% of all spinal tumors and 70% of intraspinal tumors and occur with fairly uniform distribution throughout the spine.¹⁸ Most lesions are sporadic with peak incidence between 30–60 years of age (Box 10-9). Lesions are usually solitary unless associated with an underlying genetic condition such as neurofibromatosis type 2 (NF-2), schwannomatosis, or Carney syndrome.²⁰ Lesions are generally benign, although malignant degeneration may occur.⁴¹ Classically, schwannomas are well-circumscribed, lobulated or dumbbell shaped, enhancing spinal masses that often show cystic degeneration and/or hemorrhage. Approximately 70–75% of lesions are intradural, 15% are completely extradural, and 15% are a combination of intradural and extradural.¹⁷ Intradmedullary schwannomas have been reported but are rare (<1%).^42,43 On CT, lesions are usually isodense to the spinal cord with lower density cystic changes, adjacent bony remodeling (enlarged neural foramen and expanded canal), and either peripheral or solid enhancement.^20,44 Calcification is rare. On MRI, lesions are typically isointense to the cord on T1WI, with the exception of rare melanotic schwannomas, which are hyperintense.^45,46 Most lesions are bright on T2WI, with some lesions demonstrating a “target” appearance with a bright rim and dark center. Enhancement is usually intense and may be homogeneous, heterogeneous, or peripheral (Figs. 10-17 to 10-19).^41,44,45,47 Melanotic schwannomas are a rare variant of schwannomas composed of melanin-producing cells with features of Schwann cells. These lesions have an increased incidence of local recurrence after resection as well as an increased likelihood of metastasis compared with typical schwannomas and require careful long-term follow-up. Melanotic schwannomas also may be challenging to differentiate from malignant melanoma, which has a much worse prognosis.⁴⁸

Box 10-9 Schwannoma

• Slow-growing neoplasm of the nerve sheath in the peripheral nervous system; rarely may undergo malignant degeneration

• Accounts for 70% of intraspinal tumors, 30% of all spinal tumors

• Peak age 30–60 years, male to female ratio even

• 70–75% intradural extramedullary, 15% completely extradural, 15% dumbbell—both intradural and extradural, rarely intramedullary (<1%)

• CT: Sharply marginated lesion, isodense to cord, adjacent bony remodeling

• MRI: Isointense to cord on T1WI (except for melanotic schwannoma), 75% hyperintense on T2WI, 40% cystic change, 10% hemorrhage; occasional target sign—high intensity rim, low intensity center

• Intense enhancement: Uniform, heterogeneous, or peripheral

• Variable vascularity demonstrated with angiography

• All spinal nerve root tumors are neurofibromas in NF-1, schwannomas or mixed tumors in NF-2

• Differential diagnosis: Neurofibroma, meningioma, myxopapillary ependymoma

Fig. 10-17 A 44-year-old with C1 schwannoma. A, Sagittal T2WI of the cervical spine. Expansion of the C1–2 neural foramen is caused by a well-circumscribed, round, hyperintense mass. B, Sagittal post-gadolinium T1-weighted fat saturated image. The mass enhances avidly and uniformly. C, Axial post-gadolinium T1-weighted fat saturated image at the C1–2 level. The upper cervical cord is displaced to the right by the enhancing mass, which causes bony remodeling and extends out of the neural foramen.

Fig. 10-18 A 32-year-old woman with L5 schwannoma. A, Sagittal T1WI of the lumbar spine. A large, lobulated, well-circumscribed soft tissue intensity mass is seen at the L5–S1 level. The mass causes bony remodeling with scalloping of the posterior aspect of the L5 vertebral body and expansion of the L5–S1 neural foramen. B, Sagittal T2WI of the lumbar spine. The mass is heterogeneously hyperintense with several small cysts within it. C, Sagittal post-gadolinium T1-weighted fat saturated image. The lesion enhances avidly, but heterogeneously. The cystic areas do not enhance. D, Axial post-gadolinium T1-weighted fat saturated image at the L5 level. The relationship to the spinal canal and bony structures is demonstrated well in the axial plane.

Fig. 10-19 A 54-year-old man who presented with left thigh pain. MRI was performed to assess for degenerative disc disease, and an L2–3 schwannoma was discovered. A, Axial T1WI at the L2–3 level. Asymmetry of the nerve roots is seen as they exit the neural foramina. A small round isointense mass is seen arising from the left L2 nerve root. B, Axial T2WI. The mass is isointense to mildly hyperintense to the nerve root. C, Axial post-gadolinium T1-weighted fat saturated image. The mass demonstrates rim-enhancement. D, Sagittal post-gadolinium T1-weighted fat saturated image.

NEUROFIBROMA

Neurofibromas are unencapsulated neoplasms of the nerve sheath. They are less common than schwannomas and have a peak incidence between 20–30 years of age. Most lesions are sporadic, solitary tumors (Box 10-10). However, multiple neurofibromas (especially those of the plexiform type) are typically seen in NF-1. Lesions may be localized, diffuse, or plexiform in morphology.²⁰ Imaging characteristics may be indistinguishable from schwannomas, especially for the localized types. However, hemorrhage and cystic degeneration are less common. A target appearance of peripheral hyperintensity on T2WI with central low to intermediate signal intensity has been described as more common in neurofibromas than in schwannomas.^49,50

Box 10-10 Neurofibroma

• Unencapsulated neoplasm of nerve sheath

• Peak age 20–30 years, less common than schwannomas

• Cervical region most common

• Three patterns: Localized, diffuse, or plexiform

• Similar appearance to schwannomas, but hemorrhage uncommon; target sign more common than schwannomas

• 90% are sporadic solitary tumors

• 13–65% of NF-1 have spinal neurofibromas (Figs. 10-20 and 10-21)

Fig. 10-20 A 3-year-old child with NF-1 and plexiform neurofibroma within the cervical spine and neck. A, Sagittal T1WI of the cervical spine. A soft tissue mass is seen at the C5 to T1 levels within the lateral portion of the spinal canal and causing bony remodeling of the adjacent vertebrae. B, Sagittal T2WI. The mass has heterogeneous signal on this sequence. The spinal cord is displaced and compressed anteriorly and to the right. C, Sagittal T2WI lateral to B. The mass expands and extends through the neural foramina of the cervical spine. The large anterior paraspinal component is appreciated on this image. D, Sagittal post-gadolinium T1-weighted fat saturated image. The mass enhances heterogeneously. E, Sagittal post-gadolinium T1-weighted fat saturated image lateral to D. F, Coronal post-gadolinium T1-weighted fat saturated image of the chest. The full extent of the paraspinal component of the mass is appreciated in this plane. Bilateral paraspinal involvement is present, left much greater than right. The mass extends to involve the left axilla. G, Axial post-gadolinium T1-weighted fat saturated image at the C5–6 level. The mass does not invade the dura at this level but does compress the thecal sac and cord anteriorly and to the right. The neural foramen is expanded, and the paraspinal component of the mass has an infiltrative, irregular contour.

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