Imaging in Spine Ependymoma 

Ependymomas are believed to account for 60% of all primary neoplasms of the spinal cord and filum terminale.^[1] Intraspinal ependymomas are most easily grouped into 3 classes: intramedullary lesions, myxopapillary ependymomas, and metastases from an intracranial origin. See the images below.

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 with MRI, with and without gadolinium enhancement. Solitary intramedullary lesions are less frequently associated with intracranial spread; thus, cerebral imaging is less important.

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, computed tomography (CT) scan findings are not conclusive for ependymoma. Nonspecific findings of canal widening, bony erosion, and a thickened cord or filum are suggestive but not diagnostic of ependymoma.

The radiographic diagnosis of intraspinal tumors is indirect and nonspecific. Changes induced by the tumor may be observed in the adjacent tissues on plain films. The pedicles may appear eroded, 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. Scoliosis may be visible on plain radiographs. Finally, in rare cases, intratumoral calcification may be observed on radiographs. Because of the limited yield of plain radiography, when clinical suspicion exists, MRI of the spine with and without gadolinium enhancement is the study of choice.

On T1-weighted images, ependymomas generally appear isointense relative to the normal cord, although they may appear hypointense (a less common finding). Heterogeneity and hyperintensity on T1-weighted images may indicate a hemorrhagic component of the mass. On T2-weighted images, ependymomas are generally hyperintense relative to the normal cord. Ependymomas are homogeneously and intensely enhancing with the administration of a gadolinium-based contrast material (see the following images).^[2] With contrast enhancement, the tumor often is seen to have well-defined borders.

Hemosiderin

Hemorrhage or hemosiderin in or at the cranial or caudal margin of ependymomas is a common imaging finding. T2-weighted MRIs may demonstrate a low-signal-intensity rim around some tumors; this finding represents the hemosiderin (see the image below). In 1995, Fine et al noted this finding in only 20% of tumors^[2] ; this percentage is far lower than the 64% Nemoto et al reported in 1992.^[3] This hemosiderin cap is fairly suggestive of ependymomas.^[4] With filum ependymomas, hemorrhagic products may be seen within the filum.

Cysts

In 1995, Fine et al observed that 1 of 25 tumors evaluated was cystic, but 14 had associated reactive cysts: 11 cysts were rostral to the tumor; 10, caudal to the tumor; and 7, both rostral and caudal.^[2] All reactive cysts had signal intensity similar to that of CSF (see the image below). The cysts were hypointense on T1-weighted MRIs and hyperintense on T2-weighted MRIs. These cysts did not enhance with the administration of contrast material. In 1995, Wippold et al examined 20 patients with myxopapillary ependymomas; of these, 3 had cystic tumors, and 2 had a syrinx.^[5] Rarely do the tumors themselves have a cystic appearance.

Tumor size and location

Cervical lesions average 4.2 vertebral segments in length, thoracic lesions average 3.1 segments, and filar tumors average 4.0 segments.^[2] Most often, intramedullary ependymomas occur in the cervical cord; fewer lesions are thoracic, and fewer still occur at the conus.^[2] About 50% of intraspinal ependymomas occur at the cauda equina (see the image below); these are predominantly of the myxopapillary subtype.^[6] Multiple lesions occur much more often in this region, with a frequency of 15%.^[5]

Differential Diagnosis

The chief intramedullary lesions from which ependymomas must be distinguished are astrocytomas and hemangioblastomas.

Ependymomas of the filum must be distinguished from schwannomas, hemangioblastomas, and astrocytomas. Astrocytomas of the cord are infiltrative and have margins that are less sharp than those of the other lesions. Astrocytomas are less prone to hemorrhage and infrequently result in a hemosiderin cap. More often, astrocytomas are eccentric in location. Schwannomas may demonstrate a central area of poor enhancement.

Hemangioblastomas have prominent vascularity, as well as large reactive cysts, which are consistent with their intracranial appearance. With MRI, signal intensity characteristics of hemangioblastomas are similar to those of ependymomas. The tumor nodule, which is situated on a pial surface, may have more intense enhancement than that of ependymomas. Local edema of the cord is more impressive around hemangioblastomas than ependymomas. Flow voids are often visible in hemangioblastomas.

It may be impossible to distinguish schwannomas from filum ependymomas; their signal intensity characteristics are very similar. In fact, the signal intensity characteristics of schwannomas and ependymomas are nearly identical on T1-weighted, T2-weighted, and gadolinium-enhanced MRIs. Schwannomas more often assume a dumbbell configuration and result in an enlargement of the adjacent neural foramina. When the tumors are small, the observation of an origin from a root in the cauda equina, rather than the filum, may aid in distinguishing schwannomas from myxopapillary ependymomas. The distribution of the roots of the cauda equina in the thecal sac may help in distinguishing the tumors: An ependymoma of the filum pushes the roots to the periphery of the thecal sac, whereas a schwannoma of the cauda more often pushes the roots together in an eccentric fashion.

Compared with ependymomas, schwannomas infrequently appear multilobulated. The periphery of schwannomas is strongly enhancing, but the tumors may have central areas with poor enhancement.

Note on gadolinium

Gadolinium-based contrast agents (gadopentetate dimeglumine [Magnevist], gadobenate dimeglumine [MultiHance], gadodiamide [Omniscan], gadoversetamide [OptiMARK], gadoteridol [ProHance]) have been linked to the development of nephrogenic systemic fibrosis (NSF) or nephrogenic fibrosing dermopathy (NFD). For more information, see the eMedicine topic Nephrogenic Fibrosing Dermopathy. The disease has occurred in patients with moderate to end-stage renal disease after being given a gadolinium-based contrast agent to enhance MRI or MRA scans.

NSF/NFD is a debilitating and sometimes fatal disease. Characteristics include red or dark patches on the skin; burning, itching, swelling, hardening, and tightening of the skin; yellow spots on the whites of the eyes; joint stiffness with trouble moving or straightening the arms, hands, legs, or feet; pain deep in the hip bones or ribs; and muscle weakness. For more information, see FDA Information on Gadolinium-Based Contrast Agents or Medscape.

Additional MRIs of spine ependymomas are provided below.