Origin of congenital cholesteatoma from a normally occurring epidermoid rest in the developing middle ear.

The sites of involvement of congenital cholesteatoma, a lesion which has recently become more frequently recognized, are reviewed from literature sources. There is a propensity for its occurrence, especially when small, in the anterior superior part of the middle ear. The same situation is the precise location of an epidermoid cell rest, the epidermoid formation (EF). This is seen in most fetal ears at the junction of the Eustachian tube with the middle ear near the anterior limb of the tympanic ring, until 33 weeks gestation, when it disappears. Its origin is traced to early fetal life from the ectoderm of the first branchial groove. In embryonic and early in fetal life it seems to act as an organizer in the development of the tympanic membrane and middle ear. It is likely that congenital cholesteatoma is derived from the EF by its continued growth instead of regression. Congenital cholesteatomas show a thinner and flatter matrix than acquired cholesteatomas, probably because the former are most frequently 'closed' and therefore subject to pressure effects from the keratin within the cyst. 'Open' forms also occur in smaller numbers. It is possible that a screening program for congenital cholesteatoma in infants might reduce the incidence of the severe, extended form of the disease.