Excerpt from Ependymoma, Spine

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Background

Ependymomas are believed to account for 60% of all primary neoplasms of the spinal cord and filum terminale (Slooff, 1964). Intraspinal ependymomas are most easily grouped into 3 classes: intramedullary lesions, myxopapillary ependymomas, and metastases from an intracranial origin.

Pathophysiology

Most intraspinal ependymomas arise de novo. Although intramedullary and cauda equina tumors may arise from an intramedullary source, these origins are uncommon. Intraspinal ependymomas are believed to arise from the ependymal cells lining the central canal, from the ventriculus terminalis of the conus, from within the filum terminale, or from cerebrospinal fluid (CSF) dissemination (Moser, 1992).

Intramedullary ependymomas most commonly occur in the cervical and cervicothoracic part of the spinal cord (McCormick, 1990; Hoshimaru, 1999). Their arterial supply is most often derived from the anterior spinal artery.

Myxopapillary ependymomas arise almost exclusively in the region of the conus and filum terminale. They account for as many as 90% of tumors in the conus (Moelleken, 1992; Celli, 1993). Rarely, they may arise in an extradural postsacral location, presumably from the coccygeal medullary vestige (Morantz, 1979) (see Anatomy).

Mortality/Morbidity

Both intramedullary and myxopapillary ependymomas tend to grow slowly, without infiltration of the surrounding neural tissue. Metastasis from myxopapillary ependymomas in adults is rare; however, several cases of intracranial seeding from conus and/or filum myxopapillary ependymomas are reported (Woesler, 1998; al Moutaery, 1996). These tumors are more aggressive in children than in adults; the tumors may spread via the subarachnoid space, invade locally, or result in extraneural metastases (Graf, 1999).

In 1996, Rezai et al examined 140 patients with ependymomas and found that the following were significant risk factors for tumor metastasis: a location in the spine rather than in the brain (12.5% vs 9.6%), a young patient, a myxopapillary histologic finding, a high proliferative index, and incomplete resection. In 1994, Cervoni et al found that the duration of symptoms before surgery, the degree of resection, and the appearance of the tumor are closely related to the likelihood of recurrence.

Sacral ependymomas may behave aggressively, with direct bony invasion, and they may spread to the lymph nodes and distant organs (Schweitzer, 1992).

Sex

Myxopapillary ependymomas has a predilection for males. This observation is in contrast to a slight preponderance of females who have intramedullary ependymomas.

Age

The myxopapillary variant appears in patients who are younger than those with intramedullary ependymomas.

Anatomy

Intramedullary ependymomas most commonly occur in the cervical and cervicothoracic parts of the spinal cord (McCormick, 1990; Hoshimaru, 1999). The tumors are centrally located and well circumscribed and cause symmetric expansion of the cord. Their arterial supply is most often derived from the anterior spinal artery.

Ependymomas generally appear as reddish or purple-gray masses with numerous, small, superficial blood vessels. Sometimes, the tumors are encapsulated. Although cystic ependymomas are infrequently reported, associated reactive cysts occur with most intramedullary ependymomas (Fine, 1995). Hemorrhage often occurs at the outer margins of these tumors (McCormick, 1990).

Myxopapillary ependymomas arise almost exclusively in the region of the conus and filum terminale. Rarely, they may arise in an extradural postsacral location, presumably from the coccygeal medullary vestige (Morantz, 1979). Unlike the discrete fusiform intramedullary variety, myxopapillary ependymomas primarily appear as lobulated discrete masses adherent to the filum and secondarily appear in the nerve roots of the cauda equina and in the conus. Grossly, they appear moderately vascular, reddish to purplish, sausage shaped, and encapsulated. They frequently have peripheral hemorrhage and cystic degeneration.

Clinical Details

Intramedullary ependymomas have a clinical manifestation of neck or back pain and, less often, numbness or paresthesias (McCormick, 1990). Myxopapillary ependymomas typically cause nonspecific symptoms, most commonly low back pain and lower extremity radiculopathy and, much less frequently, lower extremity weakness or bladder dysfunction. Given the slow growth and well-circumscribed quality of these tumors, symptoms generally progress slowly, and patients often have a long history prior to diagnosis.

Complete surgical resection is the treatment for intraspinal ependymomas (McCormick, 1990; Epstein, 1993; Lee, 1998; Hoshimaru, 1999). Total resection is generally curative, without the need for postoperative irradiation. Preoperative imaging is essential in planning care beyond identification of the tumor.

Tumor dissemination precludes surgical cure and makes continued aggressive resection in the setting of waning intraoperative electrophysiologic recordings unwarranted. Likewise, in the presence of hydrocephalus or a large intracranial mass, the intracranial pathologic condition should be addressed before the spinal lesion is resected.

In 1999, Hoshimaru et al found that the degree of preoperative cord atrophy and arachnoid scarring, particularly in the case of thoracic tumors, is closely correlated with surgical morbidity. Epstein (personal communication) reported similar risk factors and additionally noted that very large or very small tumors may be associated with an outcome poorer than that of other tumors.

Preferred Examination

The initial imaging evaluation likely includes plain radiography of the spine. The images may demonstrate erosion of the pedicle or scalloping of the dorsal vertebral body surface. However, the yield of plain radiography is limited, and when clinical suspicion exists, MRI of the spine with and without gadolinium enhancement is the study of choice. MRI permits evaluation of the cord substance itself for masses and associated findings such as edema, hemorrhage, cyst, syringomyelia, and cord atrophy.

For myxopapillary tumors, both the brain and spine should be evaluated at MRI with and without gadolinium enhancement. Solitary intramedullary lesions are less frequently associated with intracranial spread; thus, cerebral imaging is less important.

Limitations of Techniques

The radiographic diagnosis of intraspinal tumors is indirect and nonspecific. Changes induced by the tumor may be observed in the adjacent tissues. The pedicles may appear flattened or concave, with an increased interpedicular distance as a result of chronic pressure resulting in bony atrophy. Similarly, scalloping of the posterior part of the vertebral bodies or thinning of the lamina with a widened spinal canal may be observed (McCormick, 1990). Scoliosis may be visible on plain radiographs. Finally, in rare cases, intratumoral calcification may be observed on radiographs.

Myelography may assist in localizing an intraspinal mass to the extradural, intradural extramedullary, or intradural intramedullary compartments. A centrally situated, regularly fusiform cord may be suggestive of an intramedullary ependymoma, whereas fusiform swelling in the cauda equina, particularly when it is large enough to result in bony erosion, and a blockage of contrast enhancement may be consistent with an ependymoma of the filum.

With a yield similar to those of plain radiography or myelography, CT findings are not conclusive for ependymoma. Nonspecific findings of canal widening, bony erosion, and a thickened cord or filum are suggestive of but not diagnostic for ependymoma.

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