Stereotactic gamma knife surgery (GKS)-induced
brain tumors are extremely rare, and no ependymal
tumors induced by GKS have been reported. Therefore, little is known about their clinical, pathologic, and genetic features. In addition, a regimen of
adjuvant chemotherapy for
anaplastic ependymoma (AE) has not been established. A 77-year-old man presented with a gait disturbance and left-side
cerebellar ataxia more than 19 years after GKS performed for a cerebellar
arteriovenous malformation. Imaging studies demonstrated an enhancing mass in the irradiated field with signs of intraventricular dissemination. Surgical resection confirmed the diagnosis of AE.
Temozolomide (TMZ) was administrated postoperatively because the methylated promoter region of
O(6)-methylguanine-DNA methyltransferase (MGMT) and 1p36 deletion were observed. Surprisingly, images 16 days after TMZ initiation demonstrated a complete resolution of the
residual tumor that was maintained after three cycles of TMZ. This first case report of GKS-induced AE emphasizes the importance of genetic evaluation of MGMT and chromosomal deletion of 1p36 that are not commonly performed in primary ependymal
tumors. In addition, it is speculated that a GKS-induced
tumor may have a different genetic background compared with the primary
tumor because the pathogenesis of the
tumors differed.