抄録
The middle ear space is divided into the anterior and posterior tympanic cavities. In the former are included the eustachian tube, protympanum, meso-, hypo-, and retrotympanum, and in the latter are included the epitympanum and mastoid antrum with mastoid air cells. The border line between the two cavities is the tympanic diaphragm which is composed of the malleus head and incus body with their related mucosal folds and the anterior attic bony plate with the anterior attic mucosal fold.
In the well-pneumatized ear, the epitympanum communicates not only with the mesotympanum via the tympanic isthmus (posterior route), but also with the protympanum via the supratubal recess (anterior route), in which the anterior attic bony plate is vestigial and the mucous fold is broad and perforated. This is called the membranous tympanic diaphragm type which allows ventilation of the epitympanum even if the tympanic isthmus is closed.
On the other hand, in the poorly pneumatized ear like the cholesteatomatous ear, the supratubal recess is small and the bony plate is long and thick and the mucous fold is vestigial. This type is called the bony tympanic diaphragm type which does not allow ventilation of the epitympanum if the isthmus is closed. The bony tympanic diaphragm in cholesteatoma can be classified into the plate type, pyramidal type, anterior type, and membranous types. These differences in the bony tympanic diaphragm are caused by difference in pneumatization of the pyramidal bone after birth. The bony tympanic diaphragm must be removed for the prevention of recurrence of cholesteatoma treated by the canal up technique.
