Diskitis and Osteomyelitis

Pyogenic disk space infections are usually the result of a blood-borne agent, particularly from the lung or urinary tract. The pathogen lodges in the region of the endplate in the adult or the hypervascular disk edge in the child and destroys the disk space and the adjacent vertebral bodies. The disk space infection may be acute, in which case pain is invariably present, or it may be more chronic. The symptoms start with focal back pain and pro-gress to radicular, meningeal, and spinal cord involvement as the disease advances. Clinical settings include those cases in which there is a recent history of spine surgery or hematogenous dissemination from another infectious site. The lumbar spine is most frequently involved, possibly from the high rate of lumbar spinal surgeries (even with a low postoperative infection incidence) and genitourinary infections. The most common organism is Staphylococcus; other common causes include Streptococcus, Peptostreptococcus, Escherichia coli, and Proteus. The erythrocyte sedimentation rate is elevated and there is a leukocytosis in most cases of disk space infection.

Although gallium- and indium-labeled white blood cell radionuclide imaging is highly sensitive to inflammation, magnetic resonance (MR) imaging is the most specific method for cost-effective diagnosis. Conventional spin-echo images reveal the disk space to be of low signal intensity on T1-weighted images (T1WI) and high signal intensity on T2-weighted images (T2WI) as a result of the associated edema (Fig. 17-1). The disk space, adjacent vertebral bodies (particularly at the endplates), and, if present, the epidural or paravertebral soft tissues enhance. Unfortunately Modic type 1 marrow changes simulate those seen in diskitis/osteomyelitis and may enhance. High T2WI signal in the endplates of the vertebral bodies is the least reliable of the findings for diskitis/osteomyelitis. Erosions of the endplates and gadolinium enhancement of the disks become paramount. There is usually evidence of irregularity of the endplate or bony sclerosis (best seen on computed tomography [CT]). Look carefully for epidural or paravertebral abscesses.

Figure 17-1 Disk infection. A, Cervical disk infection after surgery. Sagittal T1-weighted image (T1W1) shows a prevertebral enhancing mass (arrows) and intraspinal enhancing epidural infection (open arrows) compressing the cord. Multiple disk spaces enhance. B, Sagittal T1WI shows a thoracic disk infection with compression of the spinal cord by associated epidural hematoma (arrows). C, The T2WI shows the cord draped over the diseased segment. D, A lumbar study shows a left paraspinal mass extending into the foramen. E, The sagittal T2WI to the left reveals high signal in the endplates on either side of the diseased disk. F, Note the marked enhancement of the disk at L3–L4 with a small epidural component.

Vertebral osteomyelitis usually occurs in the setting of disk space infection; however, osteomyelitis can occur without disk space infection from hematogenous dissemination directly to the vertebral body. The signal changes are similar to those in disk space infection. A three-phase technetium bone scan can differentiate cases of cellulitis from osteomyelitis based on the combination of increased blood flow and persistent osseous uptake on delayed images in osteomyelitis. This examination may not be specific, so that if there is a question of degenerative disease versus infection, a gallium scan or indium-111–labeled leukocyte scan may suggest an infectious process by demonstrating increased uptake and correlating it with the positive bone scan.

It is not uncommon to have spinal cord symptoms/signs without epidural compression in cases of pyogenic disk space infection or vertebral osteomyelitis. In this case, the cause may be a vasculitis of the medullary arteries or veins.

Renal Spondyloarthropathy

Patients undergoing dialysis can have changes in their spine (usually in the cervical region), which superficially may resemble infection (renal spondyloarthropathy). There is destruction of the disk space and adjacent vertebral bodies; however, the signal intensity on T2WI is usually low rather than high as in infection. Furthermore, there is no clinical evidence of infection. Amyloid deposition has been implicated as a possible cause.

Granulomatous Infections

The most common granulomatous infections of the spine are tuberculosis, brucellosis, and fungal infections (blastomycosis, cryptococcosis, and coccidioidomycosis).

Tuberculosis (TB) most often affects the lower thoracic spine (Pott disease, tuberculous spondylitis), is indolent, and is frequently associated with epidural disease, particularly paravertebral, subligamentous, or psoas muscle abscesses. Vertebral body destruction with relative sparing of the disk space occurs late in the disease (Fig. 17-2). Because of the infection, a gibbus deformity may develop. The posterior elements may be involved, and the infection can spread along the anterior longitudinal ligament and involve multiple levels, spreading anteriorly. The disk can be of normal intensity on noncontrast MR but usually enhances. Spinal deformity is common. Approximately 50% of patients have obvious pulmonary disease. The diagnosis of TB requires isolation of the bacillus, characteristic histopathologic changes, or response to antibiotic therapy. Table 17-1 contrasts the features of bacterial infection, TB, and neoplasm. The usual differential diagnosis includes sarcoidosis, fungus, and brucellosis, but a calcified inflammatory mass, particularly one that affects the psoas muscle in the lumbar area, is classic for TB.

Figure 17-2 Tuberculous osteomyelitis. A, Sagittal T1-weighted image (T1WI) shows spread along the anterior longitudinal ligament (arrow). Observe the intraspinal epidural abscess (open arrows). B, Another case with diskitis and osteomyelitis. Sagittal T1WI reveals anterior prespinal mass and thecal sac compression by an anterior epidural mass. C, Off-midline sagittal T2WI nicely illustrates the bright disk and dark anterior ligament (arrows) confining the infection. D, Note the bone necrosis on postcontrast scans. E, Psoas abscesses (asterisks) are present bilaterally.

Table 17-1 Salient Features of Nontuberculous Bacterial Infection, Tuberculosis, and Neoplasm

Brucellosis is diagnosed by positive blood culture or serologic studies. Culture from biopsy is not definitive and usually contains nonspecific inflammatory changes. Brucellosis has a predilection for the lower lumbar spine generally, with less destruction of the vertebral body and disk space. Paravertebral mass and spinal deformity are rare.

Epidural Abscess

Epidural abscesses are the result of either direct extension of vertebral osteomyelitis or hematogenous dissemination from an infectious source. Staphylococcus aureus is the most common pathogen (45%), with the remainder being gram-negative rods, anaerobes, mycobacteria, and fungi. Patients are septic, with frequent histories of intravenous drug abuse, immunosuppression, urinary tract infections, recent surgery, and cardiac infections; these patients present with tenderness over the spine, back pain, and progressive neurologic impairment. There is an association with blunt spine trauma with hematoma formation and secondary infection. The abscess is usually located in the dorsal epidural space, probably because of the close approximation of the ventral dura and the posterior longitudinal ligament limiting anterior spread of the abscess. Incidentally, this is also why epidural hematomas predilect posteriorly.

MR is the modality of choice for imaging epidural abscesses (Fig. 17-3). The epidural mass has low signal intensity on T1WI and has high signal on T2WI. Uncomplicated, the cord has normal signal. There are three patterns of enhancement: (1) homogeneous enhancement, representing diffuse inflamed tissue with microabscesses (phlegmonous granulation tissue); (2) peripheral enhancement consistent with frank abscess, including a necrotic center; and (3) a combination of tissue enhancement and frank abscess. The first pattern may be difficult to discern in the lumbar spine without the use of fat-saturation techniques to distinguish between enhancement and epidural fat, which can be diffusely infiltrated by the inflammatory process. Epidural abscess produces symptoms by sheer mass effect or septic thrombophlebitis with cord edema and infarction. Think about spinal cord infarction secondary to thrombophlebitis in the setting of epidural abscess and high signal on T2WI in the cord. Meningitis (with increased intensity of the cerebrospinal fluid [CSF] on T1WI and enhancement of the CSF and nerve roots) can occasionally be identified along with the epidural abscess.

Figure 17-3 Epidural abscess. A, Postcontrast T1-weighted image shows an epidural rim-enhancing collection (arrow) at the L5–S1 level that grew Staphylococcus aureus. B, The axial scan shows that the collection (arrow) is centered along the right facet joint but also extends into the posterior paraspinal soft tissues (A).

Subdural empyema has a similar presentation to epidural abscess, although it is much rarer in occurrence. Additionally there are iatrogenic causes, including lumbar puncture, anesthesia, and diskography. Discrimination between the subdural and epidural compartments is usually difficult on MR. Hopefully you can see the dark dural borders around the collection in a subdural empyema as opposed to the epidural collection, which is usually bordered by epidural fat/bone/ligaments.

Meningeal Sequelae

Infections of the meninges are discussed in Chapter 6. The sequela of bacterial meningitis may be arachnoiditis, which at times is associated with syringomyelia or acquired arachnoid cysts (see section on Cystic Lesions in this chapter). In addition, cysticercosis can cause arachnoiditis (and rarely subarachnoid and spinal cord cysts). Pachymeningitis (thickened dura mater) has many causes (Box 17-1).

Clinically, meningeal infection may lead to symptoms of myelopathy or radiculopathy, which can progress to paralysis. These symptoms are related to compression of nerve roots and spinal cord by thickened dura. Infarction and cord cavitation are potential late sequelae of leptomeningitis or pachymeningitis. MR reveals poor definition of the cord or subarachnoid space on T1WI and diffuse thick enhancement of the leptomeninges.

Sarcoidosis

Only 6% to 8% of patients with neurosarcoidosis have spinal cord lesions, with the most common location being the cervical region. Sarcoidosis can manifest as nodules on the surface of the cord, which can appear similar to tumor nodules from subarachnoid seeding and can be associated with cord enlargement. Rarely, sarcoid nodules may be on individual nerve roots. As in the brain, intramedullary lesions result from infiltration of the Virchow-Robin spaces (Fig. 17-4). Intramedullary sarcoidosis can present as a diffuse inflammatory lesion or as a discrete mass. Unfortunately, patients with sarcoidosis on or off steroids have an increased rate of spinal TB or fungal infection, which obscures matters further.

Figure 17-4 Sarcoidosis of cord. A, The T2-weighted image shows abnormal intramedullary signal throughout the cervical spinal cord. B, On postcontrast scanning, the surface enhancement superiorly is combined with gross parenchymal intramedullary enhancement lower down. Cystic change is present.

The lesions demonstrate intermediate to high intensity on T2WI with diffuse leptomeningeal or nodular enhancement.

Intramedullary Lesions in Acquired Immunodeficiency Syndrome

A variety of conditions affect the cord in patients with acquired immune deficiency syndrome (AIDS); these are listed in Box 17-2. Vacuolar myelopathy, identified in patients with AIDS (AIDS-associated myelopathy), is defined as vacuolation in the spinal white matter associated with lipid-laden macrophages, typically involving the dorsal columns and lateral corticospinal tracts, although it may occur anywhere (Fig. 17-5). Degeneration of the corticospinal tract has also been reported, especially in children. Its incidence has been reported to be between 3% and 55%. The etiology is unknown but may be related to either primary or indirect effects of human immunodeficiency virus (HIV), secondary infectious agents, nutritional deficiencies (especially of vitamin B₁₂), or toxic effects of drugs. The vertebral marrow can also be affected by these conditions. High intensity on T2WI is seen in a spinal cord that may be large, normal, or small. Nothing is specific about the MR appearance to separate AIDS-associated from other non-AIDS intramedullary lesions.

Figure 17-5 Vacuolar myelopathy. A, Thoracic spine involvment in vacuolar myelopathy is not uncommon. As seen on this T2-weighted image, long-segment disease is the norm. B, Postcontrast images show necrosis (arrow) of the conus region. Posterior predilection is typical (C).

Transverse Myelitis and Multiple Sclerosis

Transverse myelitis is an inflammatory condition of the spinal cord associated with rapidly progressive neurologic dysfunction, usually with numbness, paresthesias, and paraparesis. The term indicates either bilateral dysfunction of the spinal cord or partial unilateral abnormality. Diseases causing this condition include acute disseminated encephalomyelitis (see Chapter 7), multiple sclerosis, connective tissue diseases (lupus, rheumatoid arthritis, and Sjögren disease), sarcoidosis, vascular malformations, and vasculitides. Idiopathic cases also exist. The spinal cord is focally enlarged with high signal on T2WI and may enhance (Fig. 17-6).

Figure 17-6 Transverse myelitis. T1-weighted image shows an enlarged enhancing cord at T11 (arrowheads). Multiple sclerosis had been previously diagnosed in this patient.

With idiopathic acute transverse myelitis, the clinical course occurs over days to weeks. Pathology reveals demyelination, perivascular lymphocytic infiltrates, and necrosis. The lesion extends over multiple spinal cord segments and involves the entire cross-section of the spinal cord. There is high intensity on T2WI with variable enhancement patterns (nodular, meningeal). In some cases, the cauda equina enhances, suggesting a possible relationship with Guillain-Barré syndrome. It has been hypothesized that this is a result of a small-vessel vasculopathy (perhaps immunologically mediated), either arterial or venous, affecting gray matter as well as white matter (Fig. 17-7).

Figure 17-7 Guillain-Barré. A, Guillain-Barré radiculitis is one potential source of a diffusely enhancing cauda equina, with or without enlarged nerve roots. B, In this case, the meningeal irritation was also evident intracranially with enhancing cranial nerves III and IV.

Multiple sclerosis (MS) affecting the spinal cord is visible on MR in 70% to 80% of patients and produces myelopathic signs and symptoms. It can be confined solely to the spinal cord (5% to 24% of cases), which may account for the “negative” brain MR findings in patients with definite disease. MS lesions are isointense or of low intensity on T1WI and high signal on T2WI. Sixty percent of the spinal cord lesions occur in the cervical region. The typical MS spinal cord lesion does not involve the entire cross-sectional area, is peripherally and posteriorly located, does not respect gray-white boundaries, and is less than two vertebral body segments in length (90% of the time). The cord is usually normal in size, with enlargement seen in 6% to 14% of cases (Fig. 17-8). The majority of lesions are patchy in location and demonstrate enhancement if the patient is referred for problems related to new spinal cord signs/symptoms. Spinal cord parenchymal loss, especially in the cervical region, can be detected over the course of the disease. Lesions in the spinal cord account for less than 20% of total disease burden. Nevertheless, a strategically placed lesion can cause profound disability. One other point: MS is a common disease, so beware of unusual presentations, particularly in young patients.

Figure 17-8 Multiple sclerosis on parade. A, Multiple high signal intensity foci are depicted on this sagittal T2-weighted image (T2WI) through the cervical cord. B, An axial T2WI through the cervical cord shows focal involvement of the right side of the cord. C, The plaque enhances. D, The next study should be the brain FLAIR sequence; voilà, on this, one can see Dawson’s fingers at play—multiple periventricular plaques.

It is useful to image the brain if questions are raised concerning the cause of the transverse myelitis, because asymptomatic high signal abnormalities in young adult brains help favor MS as the cause of the transverse myelitis. Try the sagittal fluid-attenuated inversion recovery (FLAIR) scan and look at the callosal-septal interface (Fig. 17-8D).

If you see transverse myelitis and optic neuritis, consider Devic syndrome. There may not be intracranial demyelination and the disease shows long-segment (more than five vertebral body segments) cord disease rather than limited-segment (one or two segments) disease, as in MS (which would more likely show intracranial white matter disease). Devic syndrome is usually monophasic, has a more rapid debilitating course and worse prognosis than MS, and is seen in older patients. Early diagnosis has been aided by the discovery of a target serum autoantibody, NMO-IgG.

Lupus Myelitis

This is a recognized complication of systemic lupus erythematosus presenting as transverse myelitis with back pain, paraparesis or quadriparesis, and sensory loss. The spinal cord may be enlarged with high intensity on T2WI involving four to five vertebral body segments (more than in MS) of the cord (Fig. 17-9). Contrast enhancement can be detected in approximately 50% of cases. Etiology of the lesion is vacuolar degeneration from an autoimmune process or ischemia.

Figure 17-9 Lupus myelitis. A, As opposed to multiple sclerosis, this case of lupus myelitis involves multiple disk levels (arrowheads) and the entity favors the central aspect of the cord (B).

Subacute Combined Degeneration

Subacute combined degeneration, a complication of cobalamin (vitamin B₁₂) deficiency, causes a myelopathy affecting the cervical and upper thoracic spinal cord, but it can also produce lesions in the optic tracts, brain, and peripheral nerves. Clinical findings include paresthesias of the hands and feet, loss of position and vibratory sensation, sensory ataxia, spasticity, and lower extremity weakness. Pernicious anemia, the inability to absorb vitamin B₁₂ due to inactivation of intrinsic factor (secreted by gastric parietal cells), is the most frequent cause of vitamin B₁₂ deficiency in the United States (along with bariatric surgery). Diseases that affect the terminal ileum, where the vitamin B₁₂-intrinsic factor complex is absorbed (i.e., regional enteritis, Crohn disease, or tropical sprue) can produce vitamin B₁₂ deficiency. Pathologically, demyelination and axonal loss in the posterior and lateral spinal cord columns is seen.

Box 17-3 provides the differential diagnosis of degenerative lesions involving the posterior columns. This includes nitrous oxide toxicity, copper deficiency, and vacuolar myelopathy. On T2WI, high intensity is observed longitudinally in the posterior columns (Fig. 17-10). After treatment, this can regress and disappear if caught early enough; however, if undetected, permanent axonal loss and gliosis results. The bone marrow can also be low intensity on T1WI and T2WI associated with enhancement, indicating benign hyperplasia of the hematopoietic marrow (secondary to the pernicious anemia).

Figure 17-10 Subacute combined degeneration. A, Sagittal scan shows abnormal signal predominantly in the posterior spinal cord. B, On axial scans one can see the configuration of the posterior column disease. Although vitamin B₁₂ and folate deficiency are the classic etiologies for this appearance, copper deficiency should also be on the differential diagnosis.

Arachnoid Cyst

Arachnoid cysts occur on a congenital basis or result from trauma, postoperative scarring, or inflammation. On CT myelography, you can see an extramedullary mass, which may compress the cord. The cyst may or may not fill with contrast on delayed imaging. On MR focal impression on the cord can be seen with intensity similar to that of CSF without enhancement (Fig. 17-12). Carefully scrutinize the smoothness of the cord; any indentation suggests the presence of arachnoid cyst. These cysts can be under pressure and produce a myelopathy.

Figure 17-12 Arachnoid cyst. A, Sagittal T1-weighted image (left) and T2-weighted image (right) demonstrate a cerebrospinal fluid (CSF) collection (+) behind the thoracic spinal cord remodeling bone. The spinal cord is pushed anteriorly by this posterior CSF-containing mass. This arachnoid cyst has produced spinal cord atrophy and compression. B, Axial images through the region of the arachnoid cyst (+) demonstrate posterior compression and mild atrophic change in the spinal cord.

Tarlov Cyst

Cystic dilation of the sacral root pouches (Tarlov cysts) can be large and may be associated with bone erosion (Fig 17-13). They occur in about 5% of individuals and vary in size from a few millimeters to several centimeters. These are caused by a ball-valve phenomenon at the ostium of the nerve root sheath with CSF flowing into the cyst with arterial pulsation. After instillation of subarachnoid contrast, these cysts may or may not fill. These may or may not be symptomatic (rare cause of sciatica). Those that are symptomatic and do not readily communicate with the subarachnoid space may be treated with fibrin glue ablation. The differential diagnosis includes meningocele, arachnoid cyst, neurofibroma, and dural ectasia. The Nabors classification of spinal meningeal cysts includes extradural cysts without spinal nerve roots (type I), with spinal nerve roots (type II [Tarlov cysts]), and intradural cysts (type III, intradural arachnoid cysts). Anterior sacral meningoceles herniate into the presacral space and are usually unassociated with nerve roots and as such are type I cysts. When there is an associated anorectal malformation (imperforate anus), bony sacral defect (scimitar sacrum), and presacral mass (cyst/teratoma/meningocele), the term Currarino’s triad is used.

Figure 17-13 Humongous sacral root cysts. There is very little spinal canal left on this T2-weighted image because of the confluent sacral root cysts in this patient. (see also Fig. 16-33).

Epidermoid Cyst

Epidermoid cysts represent less than 1% of intraspinal tumors, with a higher incidence in children. They are usually extramedullary but rarely can be intramedullary, and can be congenital or acquired. Congenital epidermoids result from displaced ectoderm inclusions occurring early in fetal life, perhaps from faulty closure of the neural tube, usually in the lumbosacral region. The acquired cysts result from lumbar puncture with inclusion of skin tissue in the spine. On MR, a discrete mass, which has variable signal intensity depending on the cyst contents, is present (Fig. 17-14). The lesion can calcify and can be associated with peripheral enhancement in rare instances. Inclusion of endoderm results in an enterogenous cyst that is lined by mucin-secreting cells, which can produce contents with similar intensity (high signal on T1WI and T2WI) to mucoceles. These can be associated with developmental defects in the skin and vertebral bodies, and with fistulous communications to cysts in the mediastinum, thorax, or abdomen. Other cysts include dermoid cysts (which contain fatty elements) and ependymal cysts (which follow CSF intensity). A dermal sinus tract may coexist in up to one fourth of cases, in which case the epidermoid or dermoid may be both intramedullary and extramedullary.

Figure 17-14 Lumbar epidermoid. A, Lumbar myelogram mass in the L3 region. The mass is delineated by contrast. B, Computed tomography scan following the myelogram reveals what appears to be a cystic lesion surrounded by contrast. C, Sagittal T2-weighted scan with the epidermoid (high intensity) easily seen. D, Axial T1-enhanced image reveals a rim of enhancement surrounding the lesion.

Syringomyelia (Syringohydromyelia)

In the fetus and in newborns the central canal (in the central spinal cord gray matter) contains a small amount of CSF and is lined by ependymal cells. You should also know that the central canal extends from the obex of the fourth ventricle to the filum terminale. In the region of the conus medullaris the canal expands as a fusiform terminal ventricle, the ventriculus terminalis (fifth ventricle), which completely obliterates by about age 40 years. There are probably variations in the patency of the central canal with maturation. States that alter the flow of CSF (Chiari malformations, arachnoid cysts, and adhesions) or that produce abnormal CSF pressure ultimately result in transmission of the fluid pressure into what is left of the central canal. How precisely this occurs is open to much speculation, but you can imagine higher CSF pressure transmitted along the perivascular spaces and into the interstitial spaces toward the central canal. This dilates the central canal remnant and, depending on where it is patent, is associated with the development of varieties of syringohydromyelia.

There are three types of syringohydromyelia. The first is a central canal syrinx that communicates with the fourth ventricle and is associated with hydrocephalus. These are produced by obstruction of CSF circulation distal to the outlets of the fourth ventricle. The second occurs in a region of the central canal that is dilated but does not communicate with the fourth ventricle. Here we are referring to those associated with Chiari I malformations, intradural extramedullary tumors, arachnoid cysts/arachnoiditis, cervical spinal stenosis, basilar invagination, and so on (Fig. 17-15; Box 17-5). The first and second cases have also been termed hydromyelia. There may also be cases of asymptomatic localized dilation of the central canal without any predisposing factors such as Chiari malformation (there are exceptions to any theory).

Figure 17-15 A, Chiari I malformation with hydromyelia. Sagittal T1-weighted image (T1WI) has tonsils (arrow) below the foramen magnum (asterisk) and has a hydromyelic cyst (c). B, Glial adhesions in a syrinx. Glial adhesions (arrows) are identified on this sagittal T1WI of a large syrinx. This linked-sausage appearance is classic in syringohydromyelia.

The third differs from the first two in that it is centered in the spinal cord parenchyma and is not centered in the central canal (Box 17-6). These are found in watershed regions of the spinal cord and associated with direct spinal cord injury such as trauma or infarction. This is usually termed a syrinx.

A situation has recently been described in which alterations of CSF flow are recognized before syringomyelia occurs. The spinal cord becomes edematous and appears enlarged with high intensity on T2WI. This has been termed a presyrinx. This condition appears reversible if the condition producing the altered CSF pressure is treated.

To add further confusion to the story the general terms syrinx and syringohydromyelia have been advocated to be used to lump all the conditions together.

Rarely an eccentric intra- and extramedullary syrinx can be identified. This can be confused with arachnoid cyst. One wonders if at least a few of the arachnoid cysts noted with syringomyelia may actually be eccentric syrinxes. An evaginated syrinx has been termed an exosyrinx (Fig. 17-16).

Figure 17-16 Exosyrinx. A, Sagittal T2-weighted image (T2WI) with syrinx protruding from posterior cord (arrows). B, Axial T2WI show the posterior extent of the syrinx beyond the confines of the spinal cord (arrows).

Post-traumatic myelomalacia is a lesion with cord cavitation, associated with significant spinal cord trauma, including hemorrhage or infarction. Altered CSF dynamics from adhesions may predispose to development of syrinx formation in this myelomalacic cavity. The question for radiologists in this setting is to determine if there is cystic or noncystic myelomalacia. The former is a treatable cause of myelopathy. Although not perfect, cystic myelomalacia should follow CSF intensity on all pulse sequences, whereas noncystic or microcystic myelomalacia is high signal on proton density-weighted images (PDWI) and T2WI. You can also try intraoperative ultrasound, but that has low relative value units/minute. Our recommendation: Use the T1WI to distinguish cystic and noncystic myelomalacia.

Cysts Associated with Neoplasia

Neoplasms of the spinal cord commonly have cysts associated with them. These cysts have been termed tumoral (or intratumoral) and nontumoral (reactive) (Fig. 17-17). Cysts rostral or caudal to the solid portion of the tumor (nontumoral) are secondary to dilation of the central canal. They do not enhance, are not echogenic on intraoperative ultrasound, do not have septations, and usually disappear after resection of the solid lesion. Allegedly, fluid produced by the tumors dilates the central canal, producing the cyst. Tumoral cysts (more common in astrocytoma) occur within the tumor and may show peripheral enhancement.

Figure 17-17 Neoplastic cysts gallery. A, The tumoral cyst is not as evident on the sagittal T1-weighted image (T1WI) as it is on the T2WI (B) where a fluid-fluid level (arrowheads) in the cervical spine is seen. C, In this case the cyst above the tumor is reactive and nonneoplastic. It is bright on axial T2WI imaging (D), but it does not enhance (arrowheads) on the postcontrast study (E). As one would expect, the tumor does enhance (arrow).

Intramedullary Lesions

Magnetic resonance imaging has had a huge impact on the diagnosis of neoplastic diseases of the cord. Spinal cord tumors represent approximately 5% of central nervous system (CNS) neoplasms. Neoplasms have three general characteristics: (1) They tend to enlarge the cord either focally or diffusely, (2) on T2WI they produce high signal intensity, and (3) they nearly always enhance (Fig. 17-18). Tumors involving the cord may be primary, such as astrocytoma or ependymoma, or metastatic. It is virtually impossible to separate ependymoma from astrocytoma, but we will provide tricks of the trade to improve the coin flip. Symptoms include pain, weakness, and muscle atrophy. Box 17-7 provides the differential diagnosis of the enlarged spinal cord. This is an essential diagnosis to know—memorize it! You must appreciate, however, that not all enlarged cords are neoplasms. As can be appreciated from Box 17-7, inflammatory and demyelinating diseases may enlarge the spinal cord. Especially in young patients with acute or subacute myelopathic symptoms, you should not glibly suggest that an enlarged spinal cord with high T2 signal represents a tumor. Rather, think about the case, assess presence of enhancement (absence unusual in tumors), get an MR of the brain, and assess whether there are additional lesions. In this patient population, corroborative findings might favor a demyelinating process, such as MS, over a spinal cord tumor.

Figure 17-18 Intramedullary breast metastasis. A, Sagittal T1-weighted image (T1WI) demonstrates an enhancing intramedullary breast metastasis. Metastases generally evoke considerable edema and mass effect. B, T2WI also shows the extent of the edema, which involves the entire cervical cord. The metastatic nodule is identified (arrow).

Astrocytoma

These neoplasms make up approximately 40% of spinal tumors and usually occur in children (representing 82% of pediatric intramedullary tumors) and adults in their third to fifth decade of life (mean age, 29 years). Males are affected more than females. The thoracic cord is most commonly involved followed by the cervical region. The tumors are hypercellular, generally large without obvious margins, and involve the full diameter of the cord but are more eccentric than ependymomas. The presentation is of pain and paresthesias followed by motor signs. In children, 90% of lesions behave as grade 1 pilocytic astrocytomas with a good prognosis, and 10% are fibrillary, usually seen in older children. Astrocytomas are graded I to IV, with I being the pilocytic astrocytoma, II the low-grade or fibrillary astrocytoma, III the anaplastic astrocytoma, and IV the glioblastoma multiforme. Most of the spinal cord astrocytomas are low grade, with less than 2% being glioblastomas. Adults have a worse outcome related to the infiltrative nature of the lesion.

These tumors may produce mild scoliosis, widen the interpediculate distance, and cause vertebral scalloping but less than ependymomas. They are isointense to low intensity on T1WI and high intensity on T2WI. The average length of involvement is seven body segments. They have an associated cystic component in 60% of cases (usually tumoral with small irregular or eccentric morphology), which may be appreciated on T1WI as hypointensity (Fig. 17-19). Hemorrhage is uncommon. Syrinx is common in the pilocytic variety. Enhancement is the general rule, although it may be uneven compared with the intense enhancement of ependymoma. Malignant potential is generally less than that of brain astrocytomas. Exophytic components are sometimes present. The size of the tumor does not necessarily reflect its malignant potential (repeatedly we see that size is overrated). These tumors are associated with neurofibromatosis type 1 (NF-1), infiltrating and not generally resectable.

Figure 17-19 Astrocytoma of thoracic spinal cord. A, Sagittal T1-weighted image (T1WI). B, Postcontrast axial T1WI reveals homogeneous enhancement in the tumor. C, Sagittal postcontrast T1WI. D, Observe the extensive nonenhancing reactive cysts in the cervical region above the tumor.

Ependymoma

Ependymomas are generally more focal (involving an average of 3.6 vertebral body segments), although they can be extensive (reported to involve 15 vertebral body segments), and as they arise from ependymal cells from the central canal, they tend to occupy the central portion of the cord. They account for 50% to 60% of spinal cord tumors in the third to fifth decade of life (most common intramedullary neoplasm in adults) and may be associated with neurofibromatosis type 2 (NF-2). In children they are uncommon except when NF-2 is coexistent. Although unencapsulated, these glial neoplasms are well circumscribed, noninfiltrating, histologically benign with slow growth and, in certain circumstances, totally resectable. They most commonly involve the sacral or cervical spinal cord (44%), with extension into the upper thoracic spinal cord in an additional 23%. Twenty-six percent are located in the thoracic cord alone. Symptoms are generally mild, delaying diagnosis, with back or neck pain the most common complaint, followed by sensory deficits and motor weakness, and bowel and bladder dysfunction. The 5-year survival is more than 80%. Metastatic spread to extraspinal sites includes the retroperitoneum and lymph nodes. Ependymomas outside the CNS (broad ligament and sacrococcygeal region) have a strong association with spina bifida occulta.

They appear isointense to hypointense with respect to the cord on T1WI and may have a multinodular high signal picture on T2WI that occupies the whole width of the cord. Commonly there is edema surrounding the tumor. Ependymomas have a propensity to hemorrhage, with hypointense rims (“cap sign”) on T2WI, that histopathologically represent residual hemosiderin from hemorrhage. Ependymomas may cause subarachnoid hemorrhage. Hemosiderosis has also been reported to result from ependymoma. Enhancement is common, and the tumor may have sharply defined, intensely enhancing margins. They may be associated with extensive cyst formation (in up to 84% of ependymomas; mostly nontumoral cysts but tumoral cysts may also occur), which does not usually enhance. Other associated radiographic findings include scoliosis, canal widening with vertebral body scalloping, pedicle erosion, and laminar thinning (Fig. 17-20). Diffusion tensor imaging has been utilized to distinguish ependymoma, which displaces outwardly but does not infiltrate white matter tracts, from astrocytomas that disrupt the descending fibers.

Figure 17-20 Ependymoma. Axial CT (A) sagittal T1-weighted (T1WI) (B), T2WI (C), and postcontrast fat-suppressed (D) scans show the intradural extramedullary myxopapillary ependymoma, which is well defined and very bright on T2WI. E, Different more classic ependymoma in the cervical spine, with “cap sign” inferiorly and good margins superiorly. F, This ependymoma (between the arrows) is also well-defined. G, T2- weighted sagittal scan in another ependymoma shows low intensity inferiorly, which is more clearly demonstrated to be hemorrhage or calcification on the gradient echo scan (H).

Ependymoma is the most common primary spinal cord tumor of the lower spinal cord, conus medullaris, and filum terminale (6.5% of spinal ependymomas) and often produces a lobulated mass. Thus, these neoplasms can be both intramedullary and intradural extramedullary (affecting the filum).

Myxopapillary ependymoma (13% of all spinal ependymomas) may affect the filum terminale with extension into the conus and the subcutaneous sacrococcygeal region. The mean age at diagnosis is 35 years and the lesion is more common in males. The presentation is of low back pain, leg pain, lower extremity weakness, and bladder dysfunction. These lesions are multilobulated, usually encapsulated, mucin-containing tumors that may hemorrhage and calcify. On MR they are usually isointense on T1WI, high intensity on T2WI, and enhance (see Fig. 17-20). However, as a result of calcification or hemorrhage they may be high or low intensity on T1WI and T2WI. They can grow out neural foramina and simulate neurogenic tumors.

Hemangioblastoma

Hemangioblastomas are vascular lesions that may involve the cervical and thoracic spinal cord. They are the third most common primary intramedullary spinal neoplasm (1% to 7% of all spinal cord neoplasms). The tumor is composed of a dense network of capillary and sinus channels. They diffusely widen the spinal cord and may have both a cystic and solid component, with the solid component enhancing intensely. These tumors are associated with considerable edema (Fig. 17-21). Hemangioblastomas may be solid in 25% of cases.

Figure 17-21 Hemangioblastoma of the spine. A, Sagittal T1-weighted image (T1WI) demonstrates multiple enhancing nodules (arrows) along the thoracic spinal cord. The cord is enlarged and there is low intensity centrally. B, Axial T1WI at the cervicomedullary junction shows enhancement of multiple masses (arrows) representing other hemangioblastomas in this region. Note that in this case the lesions are solid.

Hemorrhagic components may be seen in the tumor nodule. There may be multiple lesions (20% of the time) in the spine and they may be eccentric, at times appearing extramedullary or pial based, and they can occur on the nerve roots. With this presentation, the question of dropped hemangioblastoma seeds from a cerebellar lesion versus primary spinal cord or nerve root lesions is always raised. Spinal angiography shows dilated arteries, a tumor stain, and draining vein. On MR, intratumoral flow voids can be identified when the lesion is reasonably sized, and prominent posterior draining veins can also be seen. They are of variable intensity on T1WI due to hemorrhage and high intensity on T2WI. Edema can be noted surrounding the lesions. Avid homogeneous enhancement is visualized in the solid portion of the tumor. The fractional anisotropy values of hemangioblastomas are significantly higher than those of other spinal cord tumors.

Spinal cord hemangioblastomas may present as isolated lesions (80%), but one third of cases are associated with von Hippel-Lindau disease and are multiple (see Chapter 9). Von Hippel-Lindau disease has been isolated to a germline mutation of the VHL gene on chromosome 3. Hemangioblastomas are more commonly thoracic than cervical, and 43% have associated cysts.

Intradural Metastatic Disease

Metastases can deposit on the dura, pia-arachnoid region, and rarely in the cord itself (Fig. 17-22 ; see Fig. 17-18). The incidence of leptomeningeal and intramedullary metastases (up to 3% of patients with metastatic disease) is increasing as patients with cancer live longer. Patients may have nonspecific symptoms (headache, back pain) or focal neurologic symptoms. Intramedullary lesions result from tumor growth along the Virchow-Robin spaces because of CSF spread. Spinal cord metastases may also occur as a result of hematogenous dissemination. Intramedullary metastases enlarge the cord, are associated with edema, and enhance (see Fig. 17-18). The most common locations are the thoracic and cervical cord. They are usually solitary lesions involving two to three vertebral body segments. Box 17-8 lists lesions that commonly metastasize to the spinal cord or its coverings.

Figure 17-22 A, Subarachnoid seeding from metastatic melanoma. Enhanced T1-weighted image (T1WI) shows diffuse linear and nodular enhancement (arrows) on posterior and anterior surface of the spinal cord. B, This man with lung cancer had an intramedullary metastasis (arrow) in the thoracic cord, but he also had subarachnoid spread seen on the T2WI (C) and on the postcontrast T1WI (D).

Box 17-8 Lesions that Commonly Metastasize to the Spinal Cord or Leptomeninges

CHILDREN

Lymphoma, leukemia

Medulloblastoma

Pineal region tumors (e.g., germinoma, pineoblastoma)

Choroid plexus tumors

Ependymoma

Glioblastoma

Neuroblastoma

Retinoblastoma

ADULTS

Lymphoma, leukemia

Glioblastoma multiforme

Hemangioblastoma

Melanoma (primary or metastasis)

Metastases from lung > breast > melanoma > colorectal > renal > gastric carcinomas

Oligodendroglioma

Intraspinal metastases are usually low intensity on T1WI and high intensity on T2WI (prominent edema surrounding the tumor nodule) with avid homogeneous enhancement of the tumor nodule.

Cerebrospinal fluid spread of tumor in the leptomeninges is most often diagnosed by enhanced MR, but findings on lumbar puncture in carcinomatous meningitis are abnormal, with positive cytology on serial punctures in 90% of cases. MR reveals enhancement of the metastatic nodules, producing an irregular cord margin rather than its usual smooth contour. The entire subarachnoid space can enhance (sugar-coated appearance), and tumor nodules can be seen on nerve roots or in the cauda equina (Christmas balls). Pial metastases reveal linear enhancement on the surface of the cord (see Fig. 17-22A); however, this can be observed in nonmalignant disease, including sarcoidosis and infection. The CSF on T1WI can be more intense than normal, and the conspicuity between CSF and cord may be diminished. Cerebral MR is necessary in this situation because leptomeningeal metastases may be the result of CSF seeding from brain parenchymal metastases.

Parameningeal masses (termed chloromas) are a preferred presentation for leukemia and can grow through the intervertebral foramina, a mode of spread also noted in both Hodgkin and non-Hodgkin lymphoma. CNS lymphoma rarely occurs as an intramedullary lesion (3%). Leukemic cell spread to the CSF may be invisible on MR and is better diagnosed by lumbar puncture.