Ependymomas are rare brain tumors that arise from the cells that line CSF containing structures such as the central canal of the spinal cord, or the surface of the cerebral ventricles. They are rare, with an incidence of only about 2-4/million. They occur in all age groups.
There are several varieties. Subependymomas mainly occur within the ventricles, and are almost benign, slowly growing tumors with a very good prognosis. According to Ernestus and Schroder (1993), these tumors mainly occur in middle aged and elderly males, and are most common in the fourth ventricle.
Myxopapillary ependymomas mainly occur at the bottom of the spinal cord. There are also more aggressive tumors called anaplastic ependymomas or ependymoblastomas.
Ependymoma of the fourth ventricle typically produce vague, nonspecific symptoms until they obstruct. Then they cause headache, vomiting, papilloedema and ataxia. Compression of the roof of the fourth ventricle causes nausea. (Gandolfi et al, 1981). According to Ernestus and Schroder, the median symptomatic period is 12 months (1993). As these tumors occur within CSF containing spaces, it seems implausible that they should regularly cause brain symptoms, other than those related to spinal fluid pressure shifts.
|Fourth ventricular mass presumed to be a subependymoma.|
Contemporary diagnosis is presently based on neuroradiological tests. MRI scans commonly documents a structure mainly within the ventricle, as shown above. The less aggressive subependymomas are reported to show homogeneous signal intensities, while ependymomas have a more heterogeneous signal intensity (Spoto et al, 1990).
Ependymomas of the fourth ventricle are rarely diagnosed on anything other than imaging studies (e.g. MRI or CT scan) prompted by symptoms of hydrocephalus, but Kim et al (2011) reported a case with premature reversal of caloric nystagmus on one side, and "perverted nystagmus" after cold stimulation on the other side. In our opinion, this is an unusual "once-off" type event.
In our clinical practice in Chicago, we have seen several patients thought by our radiology service to have ependymoma of the fourth ventricle, with the common feature being positional nystagmus. Often the nystagmus resembles anterior canal BPPV.
Surgery is the standard treatment for ependymoma of the fourth ventricle. It confirms the diagnosis, may relieve obstruction of spinal fluid flow, and may allow for total removal. 100% resection is common for ependymomas of the fourth ventricle. Maximal surgical resection is said to be desirable, but incomplete resection is the rule for ependymomas in other locations because ependymomas usually grow in relatively inaccessible parts of the nervous system. As fourth ventricular ependymomas are reportedly not very aggressive and unlikely to have drop metastases, a good neurosurgeon will use frozen section and clinical judgement as to whether or not surgery should be extensive.
Spinal drop metastases was not reported in subependeymomas as of 1993 (Ernestus and Schroder, 1993), but a case was reported in 2001 (Nakasu et al).
Postoperative radiation treatment is standard for the more malignant ependymomas, but a clear response has so far not been established. Radiation may be delayed after surgery until it is clear that there is residual growing tumor.
Little is known about chemotherapy for ependymomas, and at this writing (2012), it is considered investigational.
Operative mortality is about 25-50% for ependymomas of the posterior fossa, but this statistic is largely drawn from older literature as these tumors are rare.
The prognosis depends on age. The 1 year survival is about 82% for adults. Five year survival is 79% in younger adults, but only 44% in patients 75 and older.