Transmastoid encephaloceles. A case report.

Encephaloceles are uncommon abnormalities occurring in the pediatric age group. For the otolaryngologist they are usually encountered in the nasopharynx or nose, but may also be found in other sites adjacent to the brain. Encephaloceles usually develop as a result of prior mastoid surgery, trauma, or infections; but it is extremely rare for large encephaloceles to occur congenitally in the mastoid. It is even more uncommon for there to be a second mastoid defect which would allow the brain to present as a subcutaneous postauricular mass. The case history of a child with congenital subcutaneous transmastoid encephalocele is presented and the management discussed. In this child, the right temporal lobe of the brain herniated through a congenital defect in the tegmen and then through the mastoid cavity to exit through a lateral wall defect in the mastoid cortex. It then presented as a postauricular subcutaneous mass. The initial diagnosis was a subperiosteal abscess. The correct diagnosis was not made until surgery despite a normal preoperative CT evaluation. The world literature is reviewed and similar diagnostic and therapeutic problems are discussed.