Malignant transformation in benign cerebellar astrocytoma. Case report.

The authors give follow-up information on Case 59 of Cushing's 1931 series of cerebellar astrocytomas. The patient died with a malignant cerebellar astrocytoma 48 years after partial removal of a previously benign astrocytoma at the same site. Including the present one, there have been only five reported cases in which this has occurred. Ordinarily, juvenile pilocytic astrocytomas are of extremely genign character, and it is well established that even with incomplete resections patients have survived for years without progression of the tumor. Not all of the cases so reported can be wholly accepted as respresenting malignant transformation of the tumor, but may instead be instances of recurrence of an inherently benign glioma since the presence of features such as endothelial hyperplasia or nuclear atypicality in a juvenile pilocytic astrocytoma does not warrant is being classified as malignant. Features truly suggestive of malignancy are hypercellularity, frequent mitoses, necrosis, and, in some instances, a diffusely infiltrative growth pattern; all of these features were found in the present case.