Epidermoid cyst of the frontal bone masquerading as frontal sinusitis.

Epidermoid cysts occur whenever two epidermal surfaces fuse together during early intrauterine life and an ectodermal implant is retained deep to the surface. They are very slow growing and symptoms may not occur till middle age. The authors present a patient whose symptoms of frontal headache were mistaken for frontal sinusitis for over 10 years. The patient's symptoms were completely relieved by surgical excision of an epidermoid cyst of the frontal bone.