MRI findings of malignant transformation of epidermoid cyst: case report.

Malignant transformation of epidermoid cysts into squamous cell carcinoma (SCC) rarely occurs. A 67-year-old man initially presented with an 8-year history of right trigeminal neuralgia. His symptoms had changed into right facial anesthesia with right-ear hearing impairment 8 months before first consulting a neurosurgeon at our hospital. Results obtained using MRI suggested an epidermoid cyst in the right cerebellopontine angle, but showed atypical findings of a small enhancing nodule in the periphery and surrounding edema in the cerebellum and pons. Surgery was performed to remove the mass, but a small nodule was not reached. Despite stereotactic radiosurgery, the patient's clinical course deteriorated; he died 13 months after the first MRI examination. Autopsy revealed SCC originating from the epidermoid cyst. We present serial MRI and pathologic findings in the early and terminal phases of this patient.