Treatment Surgical excision followed by radiation therapy has been the conventional treatment for oligodendroglioma. However, because of uncertainty as to the histologic classification of many of the reported cases, it is not clear whether radiation therapy is attended by longer survival. Well-differentiated oligodendrogliomas should probably not receive radiation if seizures are well controlled and there are no neurologic deficits. As mentioned earlier, in the discovery by Cairncross and MacDonald of considerable importance is that many oligodendrogliomas, especially anaplastic ones and those with IDH mutations and 1p/19q codeletion, respond impressively to chemotherapeutic agents. This has been studied with the PCV regimen (procarbazine, cyclophosphamide, and vincristine) given in approximately 6 cycles, but also applies to the better-tolerated temozolomide, which has become the preferred treatment.
Mixed oligodendrogliomas and astrocytomas should generally be treated like astrocytomas, but temozolomide probably suffice to treat both components. An adequate direct comparison between temozolomide and PCV is awaited.
Ependymoma (See Also “Patients Who Present Primarily With Signs of Increased Intracranial Pressure” Further on)
Correctly diagnosed by Virchow as early as 1863, the origin of this tumor from ependymal cells was first suggested by Mallory, who found the typical blepharoplasts (small, darkly staining cytoplasmic dots that are the basal bodies of the cilia as seen by electron microscopy). Two types were recognized by Bailey and Cushing: one was the ependymoma, and the other, with more malignant and invasive properties, the ependymoblastoma, now recognized as an anaplastic ependymoma. Fewer than 10 percent of all intracranial gliomas are ependymomas, the percentage being slightly higher in children. Approximately 40 percent of the infratentorial ependymomas occur in the first decade of life, a few as early as the first year. The supratentorial ones are more evenly distributed among all age groups, but in general the age incidence is lower than that of other malignant gliomas.
There is also a myxopapillomatous type of ependymoma, localized exclusively in the filum terminale of the spinal cord as discussed further on. The latter gives rise to a special syndrome that variably combines symptoms and signs of the conus medullaris and the cauda equina such as sciatica or femoral pain, bladder difficulty, saddle anesthesia, and spastic leg weakness.
Ependymomas are derived from ependymal cells, that is, the cells lining the ventricles of the brain and the central canal of the spinal cord; this is the most common glioma of the spinal cord. These cells have both glial and epithelial characteristics. As one might expect, the tumors grow either into the ventricle or adjacent brain tissue. The most common cerebral site is the fourth ventricle; less often they occur in the lateral or third ventricles. Grossly, those in the fourth ventricle are grayish pink, firm, cauliflower-like growths; those in the cerebrum, arising from the wall of the lateral ventricle, may be large (several centimeters in diameter), reddish gray, and softer and more clearly demarcated from adjacent tissue than astrocytomas, but they are not encapsulated. The tumor cells tend to form rosettes with central lumens or, more often, circular arrangements around blood vessels (pseudorosettes). Some ependymomas are densely cellular; others form papillae. Some of the well-differentiated fourth ventricular tumors are probably derived from subependymal astrocytes (see later in this chapter).
Anaplastic ependymomas are identified by their high mitotic activity and endothelial proliferation, nuclear atypia, and necrosis. However, correlations between histopathologic features and clinical outcomes have not been well defined.