Locations of primary cholesteatoma.

Primary cholesteatomas (PCs) are embryologic residual nests in the middle ear cleft. Based on a study of 56 cases (48 of them from the literature), a new classification is suggested: tympanic cavity PC (71% of the cases), and temporal bone PC (29%). Among the tympanic cavity cases a significant number (63%) were found in the anterosuperior quadrant. The findings support the embryologic theory for the origin of PC.