Within the past few years there has been a revival of interest in the cholesteatomatous material which is sometimes found within the middle ear cleft. Its source, its structure, its peculiar power of eroding bone, its association with mastoid pneumatization, and its relationship to middle ear infection, have been reexamined in a number of recent papers (Diamant, 1953; Fernández, 1959; Friedmann, 1959; Rüedi, 1958; Tumarkin, 1958).
"Epidermoids" or "primary cholesteatomata" are terms used to describe a particular form of cholesteatomatous matter which accumulates within the temporal bone and is thought to arise from epithelial cell rests, as opposed to the more frequently discussed cholesteatoma which arises within the middle ear cleft and the origin of which is considered to be associated with pathological changes therein. Each of these writers on cholesteatomata has mentioned epidermoids or primary cholesteatoma only to exclude them from consideration on account of their supposed rarity.
CAWTHORNE T, GRIFFITH A. Primary Cholesteatomata of the Temporal Bone. Arch Otolaryngol. 1961;73(3):252-261. doi:10.1001/archotol.1961.00740020260002