Dr. Merchant provides a comprehensive overview of intracranial ependymoma in children. As he points out, most of the current information regarding childhood intracranial ependymoma has come from single-institution retrospective reviews. Of the prognostic indicators mentioned in the article, both young age and subtotal resection are widely accepted. Children less than 3 years old have a worse prognosis than older children, possibly because of more aggressive tumor biology, reluctance to give postoperative radiotherapy, or use of lower doses of radiotherapy. Regarding the degree of surgical resection, assessment by postoperative imaging is more important than the neurosurgeon’s perspective on whether a gross total or subtotal resection has been performed.[1,2]
Tumor grade is a controversial prognostic factor. Our experience and that of others indicate a worse outcome for high-grade or anaplastic ependymomas[3,4]; however, cooperative group studies and other single-institution reviews have not verified this finding.[2,5] One problem concerning tumor grade is the lack of agreement among individual pathologists. In a study from the Children’s Cancer Group, 22 (69%) of 32 cases had a discrepancy in the diagnosis on central review.
Perhaps one of the more controversial topics in ependymoma until recently has been the volume of irradiation. Studies from the 1970s to early 1980s reported a better outcome among patients receiving wide-field irradiation (craniospinal and whole-brain radiotherapy). With the advent of better imaging and surgical techniques, current evidence indicates that the predominant pattern of failure is local, regardless of tumor grade or location.[2-3,5] For infratentorial ependymomas, the entire posterior fossa does not need to be treated.
Our current recommendation for a nondisseminated ependymoma is local radiotherapy. Craniospinal irradiation has more toxicity and may protract treatment duration, which can affect eventual outcome.[8,9] Craniospinal radiotherapy is reserved for the less than 10% of children with neuraxis dissemination.
Studies that have shown a dose response level for ependymoma indicate a dose threshold of 45 to 50 Gy.[10,11] More recent studies suggest that dose escalation in subtotally resected tumors may be beneficial. As Dr. Merchant correctly points out, the Pediatric Oncology Group (POG) study 9132 used hyperfractionated radiotherapy to a total dose of 69.6 Gy (1.2 Gy twice daily). The 4-year event-free survival rate was 50%, compared to 24% in an earlier POG study that used a lower total dose of conventional radiotherapy.