Cholesteatomata of the Temporal Bone

A Cholesteatoma of the mastoid requires two conditions for its formation: firstly, a lowgrade, chronic infection and, secondly, a diplœtic or poorly pneumatised mastoid. The condition is associated with a long-standing history of a copious and foul aural discharge. Almost all middle-ear infections commence in the naso-pharynx and spread up the Eustachian tube into the middle ear. The accompanying diagram, though not intended to be anatomically correct, shows the path which these infections take (Fig. 1). In a cellular mastoid, the infection spreads from the middle ear, through the aditus ad antrum into the mastoid antrum and, thence, into the mastoid cells. In an acellular mastoid, if the infection is of some virulence, the diplœtic bone is infiltrated by the organisms and diffuse bone infection takes place; but if the invasion of the acellular mastoid is by an organism of low virulence, then a much slower process takes place. The normal mucosa of the middle ear is destroyed and gradually replaced by epidermal cells, either by extension of the epidermis from the external auditory canal through the ruptured drum, or by cellular metaplasia. These epidermal cells are continually being desquamated by the infection and replaced, and they collect in a slow, but constantly enlarging mass in the epitympanic recess, the aditus as antrum or the mastoid antrum. The organism is not sufficiently virulent to infiltrate to any extent the surrounding acellular bone, but it gradually softens it by infection and erodes it by the pressure of the constantly enlarging mass of dead cells.