Results of Treatment of Medulloblastomas

M EDULLOBLASTOMAS are common tumors of the posterior cranial fossa in children, although they may also occur in young adults. They comprise about 7% of all brain tumors of neuro-epithelial origin. 1~ In children their incidence is about 10% of all malignant disease, comprising about 80 cases per year in the whole of Great Britain. It is well recognized that they metastasize or seed themselves very rapidly via the cerebrospinal fluid to involve the whole cerebrospinal axis, and without treatment the average life expectancy of the patient is around 9 months. Radical surgery of the primary tumor is rarely possible, and even if it were this would not deal with the metastases or potential spread of the tumor. However, if the intracranial pressure is very high at the time of the initial craniotomy, decompression and removal of the main mass of tumor, or a by-pass procedure using a Spitz-Holter valve, may be of value. Fortunately, these tumors are very radiosensitive, 9 and treatment should be given by irradiating the whole cerebrospinal axis homogeneously over a period of 4 to 5 weeks. Although I have seen marked tumor regression after a dose of 1750 R one should aim for a much higher dose; usually a minimum of 3000 R is recommended, and 3500 to 4000 R is preferred, at least to the primary tumor site. One long continuous field to the spinal cord and posterior portion of the skull is preferable to a number of smaller matched fields, since in the latter method there is the danger of over or under dosage at the junctional points. The anterior portion of the brain should be irradiated simultaneously by one or more fields, the former being preferred. Some authors advocate that, if the patient's general condition is very poor, then only the brain should be treated, leaving irradiation of the spinal cord to a later date. 1~