Epidermoid cyst with perforation of the skull.

A rare case of an epidermoid cyst associated with a skull defect is reported. The patient was a 59-year-old healthy woman from Japan who exhibited an elastic, soft, subcutaneous tumor on the left side of the parietal scalp for approximately 10 years without a history of trauma. On radiographic findings, a punched-out lesion was shown. Computed tomography of the cranium revealed a mass on the left parietal side that adhered to the cerebrum through the bone defect. Surgical excision resulted in remission. The tumor was peridurally located and showed no adhesion to the dura mater encephali. Histopathologically, a hybrid epidermoid cyst with no malignant features was seen. We hypothesized that long-term continuous pressure by the cyst resulted in a bone defect called scalloping.