Cholesteatomas extending toward the lateral sinus. Associated lesions of adjacent structures.

A systematic radiological investigation to include tomographic studies in the axial, lateral, and Poschl projections has been devised to study all cholesteatomas. Erosions and fistulae of the lateral, vertical, and posterior semicircular canal can be shown on tomographic sections in the axial projection. Fistulae of the lateral and vertical semicircular canal, as well as lytic processes of the facial canal, were also demonstrated on tomographic studies in Poschl projection. Lateral tomographic sections have shown erosions of the cortical line in between the facial canal and the canalis musculi stapedius as well as lytic processes of the tegmen tympani. Fistulae of the semicircular canal and denudation of the facial canal are specifically associated with cholesteatomas extending toward the lateral sinus. In some cases, such diagnostic features may also have a definite bearing on the surgical approach.