The so-called cholesteatoma of the middle ear is the result of an ingrowth of the stratified squamous epithelium of the external auditory meatus into the middle ear. There are several ways in which a cholesteatoma may develop, the cholesteatoma always being characterized by an accumulation of concentric layers of horny epithelial lamellas within a cystlike sac which communicates through a perforation in the tympanic membrane with the external canal. The wall of the sac, the "matrix" of the cholesteatoma, is formed by an inner layer of stratified, squamous epithelium with abundant superficial keratinization and an outer layer of connective tissue.
In rare instances similar formations are found in the external canal.
For a long time it was doubted that a cholesteatoma could occur in the external canal without the simultaneous presence of a cholesteatoma of the middle ear; but lately it has been histologically shown by Mayer1 that isolated cholesteatoma-like