[Malignant Transformation of Cerebellopontine Angle Epidermoid Cyst:A Case Report].

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.