Involution of diencephalic pilocytic astrocytoma after partial resection. Report of two cases in adults.

Spontaneous involution of pilocytic astrocytoma has been reported in children, particularly in those with neurofibromatosis Type 1. However, this rare occurrence has not been documented in adults. In this report the authors describe two cases of adults with pilocytic astrocytoma. One patient had a tumor in the thalamus and the other in the hypothalamus and optic chiasm; both patients underwent partial resection of the tumor. The initial magnetic resonance (MR) images demonstrated reduction in size of the tumors, and subsequent MR images obtained several months later revealed marked further involution with reduction in size and enhancement. The possible mechanisms for this uncommon occurrence are discussed.