Recurrence of acoustic neurilemoma as a malignant spindle-cell neoplasm. Case report. A 75-year-old man presented with a right cerebellopontine angle tumor 11 months after complete macroscopic resection of a right acoustic neurilemoma. Histological examination of the recurrent tumor showed a malignant spindle-cell neoplasm with positive staining for S-100 protein. The patient had no stigmata of von Recklinghausen's disease. It is proposed that this recurrence represents progression from a benign to a malignant acoustic nerve-sheath tumor, an event that is extremely rare outside the clinicopathological context of neurofibromatosis. 