類表皮囊胞の悪性転化と診断した小脳橋角部扁平上皮癌の1例

Malignant Transformation of Cerebellopontine Angle Epidermoid Cyst:A Case Report

Ⅰ．はじめに

　類表皮囊胞は小脳橋角部や鞍上部に好発する良性囊胞性病変であり，典型的にはその増大は緩徐で手術による摘出にて良好な転機をたどるが，文献上ごく少数の悪性転化が報告されている．今回，急速な経過で増大を来し，類表皮囊胞の悪性転化と診断した頭蓋内扁平上皮癌の症例を経験したため，文献上の考察をまじえ報告する．

　Intracranial epidermoid cysts are benign cystic lesions that typically exhibit slow growth. Their malignant transformation into squamous cell carcinoma is rare. We report a 77-year-old woman who was admitted to our hospital because of a near-drowning incident due to a seizure sustained in her bathtub. Magnetic resonance imaging（MRI）revealed an extra-axial tumor occupying the right cerebellopontine angle. The lesion appeared hyperintense in diffusion-weighted images and exhibited contrast enhancement after gadolinium injection. Cerebrospinal fluid examination revealed noninfectious meningitis, presumably due to the ruptured epidermoid cyst. Tumor resection was performed and histopathological examination revealed squamous cell carcinoma, which was indicative of malignant transformation of the cyst. The patient underwent adjuvant radiotherapy and has no signs of recurrence 9 months postsurgery. Rapid neurological deterioration and contrast enhancement on MRI are key signs of malignant transformation of epidermoid cysts.