BRAIN, RIGHT PARIETAL, "TUMOR", EXCISION
ANAPLASTIC EPENDYMOMA (WHO GRADE III/IV)
CLINICAL FOLLOW UP:
The patient underwent surgical resection and radiation therapy. The follow-up radiology examination showed no evidence of recurrence (Figures 21, 22).
Ependymomas are slowly growing tumors of children and young adults, typically arising within or adjacent to the ependymal lining of the ventricular system, occasionally within the brain parenchyma. They account for less than 10% of central nervous system lesions and 25% of spinal cord tumors. Ependymomas arise in different locations in children and adults. Infratentorial ependymomas are most common in children with an age range of 2 months to 16 years. Supratentorial ependymomas affect pediatric as well as adult patients, whereas spinal tumors predominantly occur in the adults.
Typical ependymomas span a histologic appearance from low grade (WHO grade II) differentiated lesions to anaplastic (WHO grade III) tumors. In addition, the myxopapillary ependymoma of the caudal spinal cord and the subependymoma are histologically distinct, benign neoplasms (WHO grade I). Classical ependymomas are well-demarcated, moderately cellular gliomas with perivascular pseudorosettes, sometimes displaying true ependymal rosettes or canals, and rare or absent mitotic figures. Anaplastic ependymomas usually show increased cellularity and brisk mitotic activity, often associated with microvascular proliferation necrosis. Perivascular pseudorosettes form a histological hallmark, that is not always prominent, but ependymal rosettes are rare or absent. Anaplastic ependymomas still tend to remain well demarcated, and extent of resection may be more prognostically significant than tumor grade. Ependymal neoplasms can exhibit regions of clear cell change with perinuclear halos and nuclear uniformity, creating a distinctly oligodendroglioma-like appearance. This is more frequently observed in the supratentorial compartment in young patients. The differential diagnosis between ependymoma and oligodendroglioma would be very important, because standard therapy for ependymoma consists of complete surgical resection, sometimes followed by adjuvant radiotherapy; whereas oligodendrogliomas would be treated with chemotherapy.
Oligodendrogliomas occur most frequently in the frontal lobe with a diffuse and infiltrative growth pattern. The most frequent genetic alterations are LOH on chromosomes 1p and/or 19q, and anaplastic oligodendrogliomas bearing these changes respond well to certain chemotherapeutic regimens. As demonstrated in this case, ependymomas are grossly and microscopically discrete lesions that, at least focally, exhibit perivascular pseudorosette formation. Genetic alterations on chromosome 22q and 6q have been reported. In poorly differentiated ependymomas, ultrastructural studies are typically more useful than immunohistochemical stains in providing definitive evidence of ependymal differentiation in the form of cell junctions, microvilli and cilia.
One unique feature of this case is the location of the tumor: right parietal/occipital lobe, which is rare for ependymomas. Molina et al. (1999) reported the largest series of 34 consecutive patients diagnosed with extraventricular cerebral anaplastic ependymomas over 13 year period in Venezuela. 10 cases occurred in the 31-40 year age range. All 34 patients harbored supratentorial growths in frontal or parietal lobes. Thus, supratentorial anaplastic ependymomas can occur in the locations distant from the ventricular system, probably at a greater frequency than generally expected.
Contributed by Xiaoyan Wang, MD, PhD; Charleen T. Chu, MD, PhD