DIAGNOSIS Extraaxial anaplastic ependymoma
For a patient of this age, a supratentorial, extra-axial mass with contrast enhancement is most likely to be a meningioma, but given the cystic appearance and lack of peri-tumoral edema, an exophytic pilocytic astrocytoma might also be considered. In older patients, the radiological differential diagnosis would include hemangiopericytoma, solitary fibrous tumor, and dural metastasis. However, pathologic examination showed the tumor to be an extra-axial anaplastic ependymoma.
Supratentorial ependymomas are reported to be 30 to 50 % of all intracranial ependymomas. About the 50% of the supratentorial ependymomas are hemispheric, demonstrating no connection to the ventricular system (7). Some hemispheric tumors may extend to the cortex but pure cortical ependymomas are rare entity (6). To our knowledge, there have been 15 cortical supratentorial ependymomas reported in literature including our case. Previous supratentorial ependymomas reported are sub-pial masses without ventricular connection. This case is the first extraaxial ependymoma with no obvious involvement of the cortex. For the anaplastic ependymomas in supratentorial cortical region, this marks the 5th case in the world (4). Vernet et al suggested the origin of the supratentorial cortical ependymoma to be 1) intraparenchymal or subarachnoid ependymal cysts due to the migration disorders from germinal matrix, 2) extensive differentiated tumors from primitive neuroectodermal tumor, or 3) neoplastic growth from the ectopic ependymal cells from migrational errors (10).
Ependymoma is still considered to be a surgical disease, especially in pediatric patients (1). For low grade tumors, surgical gross total resection is the most common treatment. Ependymomas are known to be insensitive to radiation therapy. Since most of the intracranial ependymomas are local at diagnosis, craniospinal irradiation is not used anymore (8). 5 year overall survival rate for pediatric intracranial ependymoma with adjuvant radiation therapy was 74.8% in recent report by Pediatric Oncology Group (1). Histologic grade was considered not affecting the outcome of the patients but with increasing rate of gross total resection with improved imaging studies and intraoperative monitoring methods, higher grade tumors seem to be related to the higher rate of recurrence (3). There are still debates on whether the extent of resection and histology has any effect on the outcome (1). The use of adjuvant chemotherapy on ependymoma is still debated. For childhood ependymomas, adjuvant chemotherapy may result in a transient response, but additional chemotherapy has not proven to extend overall survival (5). A randomized trial by Children's Oncology Group will evaluate this further.
Ependymomas occurring in different regions have the same histological features but the incidence differs by age. In a recent study by Taylor et al, different genetic alterations were found in ependymomas from different locations (supratentorial, posterior fossa and spinal cord) (9). In addition, distinct populations of radial glial stem cells are described as candidate stem cells for the different subgroups of ependymoma by anatomic location. These findings may correlate with the appearance of different subgroup of ependymomas at different age groups (2).
Supratentorial cortical ependymomas are suggested to be less aggressive than other subgroups of ependymomas (6). However, anaplastic subgroups are prone to recur and one case progressed to a glioblastoma-like high grade lesion despite total resection with adjuvant focal radiation therapy (4). Therefore, anaplastic supratentorial cortical ependymomas warrant close follow-up. In summary, we report a rare care of supratentorial cortical anaplastic ependymoma that is progression-free three years after total resection with focal radiation therapy.
Contributed by Eun Kyung Park, Yun-Ho Lee, Dong-Seok Kim, Joong-Un Choi, Tae-Seung Kim, Kyu-Won Shim