Recurrence of medulloblastoma after homogeneous field radiotherapy. Report of three cases.

Three cases are reported of posterior fossa medulloblastoma in children. In each case metastatic spread occurred despite homogeneous field radiotherapy to the whole neuraxis; the secondary tumor was located in the subfrontal region. In the two cases in which operative removal of the metastasis was carried out, the tumor was found to be extracerebral and was attached to the dura in the region of the cribiform plate. The "face-down" position of patients during operations on the posterior fossa makes this area the most dependent part and therefore the most likely recipient of tumor cells shed at operation. This area has not previously been included in the field of maximum dosage for radiotherapy, but as a result of these findings a modification in technique of radiotherapy has been suggested.