Endoscopic anatomy of the posterior tympanum

This study aims to describe anatomical variations in the posterior tympanum. Different configurations which influence surgical decisions in middle ear surgery are described. Surgical access to the sinus tympani remains a challenge for otologic surgeons. Usually, the retrotympanum is approached through the middle ear in the anterior-posterior direction during chronic ear surgery. An endoscopic approach is necessary to detail all reliefs of the middle ear and control the total removal in a cholesteatoma surgery.

Our study included 120 ears with otosclerosis that were operated on. We have performed an intra-operative endoscopic examination with different endoscopes from the Storz company (3.0 mm diameter 45 and 70 degrees). Its rigid endoscopes have been used to obtain a detailed inspection of the entire middle ear cavity. Three main anatomical configurations increase difficulty for the otologic surgeons.

One hundred and twenty ears were included in this retrospective study. We described 44 shallow sinus tympani of type I (36.6%), and 46 intermediary sinus tympani of type II which account for 38.4% of the ears. In these two groups, a disease such as cholesteatoma is quite easy to control. In 30 ears we observed a deep sinus tympani of type III (25%). This type of sinus is a real difficulty for the surgeon, which means that a total exploration without an endoscope is not possible and entails intraoperative risks. Some anatomical variations were noted: indeed, six high jugular bulbs were described in the middle ear (5%). In 4 other ears (3.3%), there was a posterior extension which passes under the pyramidal eminence and the fallopian canal.

For 8.3% of the ears, some important intraoperative risks are involved, which can cause damage to the facial nerve or the jugular bulb. Moreover a quarter of the ears have deep sinus tympani which can not be explored with a microscope. This makes the endoscope an essential complement to the microscope in otologic surgery.