Dermoid cysts located laterally in the posterior fossa are rare. The authors report the case of a dermoid cyst in the cerebellar hemisphere presenting with hemifacial spasm (HFS) caused by multiple vascular attachments due to remote compression effects.
A 48-year-old man presented with left HFS. Computed tomography showed a mass lesion in the left cerebellar hemisphere with calcification and erosion of skull bone. Magnetic resonance imaging showed no contrast enhancement of the lesion and a dural defect. The lesion compressed the brainstem and cerebellopontine cistern, but no vascular attachments to the facial nerve were seen. Tumor removal and microvascular decompression were performed. The lesion was composed of soft tissue containing oil-like liquid and hairs, and the border of the cerebellar arachnoid was clear. There were multiple vascular attachments to the root exit zone, facial nerve, and brainstem. After displacing these arteries, the intraoperative abnormal muscle response disappeared. Histopathological findings showed stratified squamous epithelium, keratin flakes, calcifications, and hairs. The HFS disappeared completely and has remained absent for 27 months.
The dermoid cyst originating from occipital bone compressed the cerebellar hemisphere, displacing multiple vessels and leading to HFS. Tumor removal and the removal of all vascular factors can completely resolve HFS.