Revised: Feb. 2004
Medulloblastomas or posterior fossa primitive neuroectodermal tumors are aggressive tumors characterized histologically by small dark cells with scanty cytoplasm. They constitute 20 – 25% of all pediatric brain tumors but are rare in adults. In the BCCA, only 22 cases were identified between 1978 & 1995(1). Because of their rarity, management has been mainly guided by knowledge derived from pediatric medulloblastomas.
Presentation & Investigations
With its posterior fossa location, symptoms of a medulloblastoma are those of increased intracranial pressure and those related to the cerebellar tracts and brainstem long tracts. Medulloblastomas are well known for their propensity for spread through the craniospinal axis. In the series from B.C., 5 out of the 13 patients who were worked up for craniospinal axis disease had positive CSF dissemination (1). Metastasis outside of the CNS is possible but rare at presentation. All patients diagnosed with medulloblastomas should have an MRI of the craniospinal axis +/- CSF cytology to rule out CSF dissemination.
Treatment
Medulloblastomas are treated with surgical resection, followed by craniospinal radiation with or without chemotherapy.
An attempt should be made to excise as much as possible the gross tumor. Although data in adults are rare, pediatric series have consistently shown significantly better survival in patients with minimal postoperative disease compared to those with gross residual disease (2,3).
Because of the propensity of metastasis through the spinal axis, postoperative radiotherapy to the entire craniospinal axis is the standard treatment in patients with medulloblastomas. Hair loss and general fatigue are common during craniospinal radiation. In addition, patients may have hematological toxicity, particularly lymphopenia, during the 5 – 6 weeks of treatment. Their blood picture will be monitored and prophylactic antibiotics started as indicated.
The role of chemotherapy is not well defined for adult medulloblastomas. Whether chemotherapy can improve the cure rate after optimal surgery and craniospinal radiation is not clear because of the rarity of the disease. Nevertheless, chemotherapy is often given for high risk patients based on the results of adjuvant chemotherapy in the pediatric age group. Patients considered high risk for recurrence are those with gross residual disease and spinal axis dissemination. This definition of high risk group is again an extrapolation from the pediatric literature. CCNU, vincristine and cisplatinum are commonly used. If chemotherapy is given, it is usually started after surgery and radiation is completed.
Outcome of Treatment
The 2 largest published series of adult medulloblastoma patients are from the Royal Marsden Hospital (4) and the Princess Margaret Hospital (5). Both include about 50 patients treated over a 30-year period from the 1950's to the 1980's. The 5-year survival is about 50 – 60% and 10-year survival is about 40%. The 22 patients treated in BCCA from 1978 – 1995 did better, with a 5 year disease specific survival of over 80%. Even among patients with proven spinal dissemination, only 1 out of 5 failed (1). The reason for this better outcome is not clear, but it may just reflect the different time periods in which patients are treated.
References:
- Kwan W, Agranovich A, Rheaume D et al: Adult medulloblastomas, the B.C. experience. Unpublished data, presented at the 8th Biennial Canadian Neuro-Oncology Meeting, Niagara-on-the-Lake. May 1998.
- Bourne JP, Geyer R, Berger M et al: The prognostic significance of post-operative residual contrast enhancement on CT scan in paediatric patients with medulloblastoma. J Neuro-Oncology 14: 263-270, 1992.
- Jenkin D, Goddard K, Armstrong D, et al: Posterior fossa medulloblastoma in childhood: Treatment results and a proposal for a new staging system. Int J Radiation Oncology Biol Phys 19: 265-274, 1990.
- Bloom HJG, Bessell EM: Medulloblastoma in adults: a review of 47 patients treated between 1952 and 1981. Int J Radiation Oncology Biol Phys 18: 763-772, 1990.
- Frost PJ, Laperriere NJ, Wong CS et al: Medulloblastoma in adults. Int J Radiation Oncology Biol Phys 32: 951-957, 1995.