Malignant change in an intradiploic epidermoid cyst.

We describe a unique case of an intra-diploic epidermoid cyst of the parietal and occipital right bone in a 43 year-old man. The tumor remained quiescent for 12 years and then spontaneously showed malignant changes with intra-cerebral involvement. Fatal outcome occurred one year after surgery, radiation therapy and chemotherapy because of a recurrence. Malignant transformation of the epithelium in epidermoid cyst is very rare. Our case is the first one where this transformation occurred spontaneously without previous surgery.