Primary cysts of the mastoid process.

Two patients with primary mastoid cysts are presented. These examples stress the importance of regular follow-up of patients with chronic serous otitis media so that the complications or associated abnormalities may be treated early prior to extensive destructive erosion. The formation of these cysts may be due to changes brought about by chronic serous otitis media, or they may be of congenital origin with middle ear effusion as a sequela.