[High-resolution computed tomography of posterior tympanum]

A complex set of sinuses, eminences and ridges lies in the posterior border of the tympanic cavity (posterior tympanum). The facial nerve canal is located between the facial sinus and the sinus tympani. The posterior limit is the posterior semicircular canal. The posterior tympanum is often the site of residual collection of granulation tissue or cholesteatoma, and is not directly visualized by the usual surgical approaches. Thus preoperative knowledge of cholesteatoma in these area is of obvious importance. It has been accepted that high-resolution computed tomography (HRCT) has the significant advantage to provide specific information of the middle ear. Contribution of the HRCT for diagnosis of posterior tympanum was examined by three temporal bone specimens and one hundred subjects with normal middle ear. In the experiments using the temporal bone specimens, each structure in the posterior tympanum was labeled by a fine needle. HRCTs were subsequently obtained to confirm the labeled structure. In one hundred subjects, it was examined whether each structure was also confirmed by the routine HRCT. Results are as follows: (1) Axial HRCT sections provided essential informations for the preoperative evaluation of the posterior tympanum. (2) Such bony structures as the pyramidal eminence and the pyramidal ridge were the most prominent structures on the posterior wall. (3) Laterally close to the pyramidal eminence lies one sinus which was marked by the needle placed in the facial sinus proper or in the lateral tympanic sinus; It is the facial sinus in a wide sense.(ABSTRACT TRUNCATED AT 250 WORDS)