[Endoscopic anatomy of the middle ear]

To provide a detailed anatomic description of middle ear endoscopy via different approaches.

Using 0, 30 and 90 degree rigid endoscopes, 6 dry temporal bones and 11 temporal bone blocks were examined to define the average range of view obtained by three approaches: 1. via the external ear canal approach; 2. via a retroauricular incision: including two subdivided routes, the mastoid-tympanic antrum route and mastoid-retrotympanum route; 3. via the middle ear cranial fossa. Each region of the middle ear was chosen for inspection.

1. via the external ear canal approach, all sites of the tympanic cavity structures were seen with 0, 30 and 90 degree rigid otoendoscopes, including the hidden areas such as the tympanic sinus, facial recess, anterior epitympanic recess, orifice of eustachian tube et al. 2. via the mastoid-tympanic antrum route, the structures of the mastoid cavity, tympanic antrum, epi-mesotympanum were clearly defined; via the mastoid-retrotympanum route, the structures of the mastoid cavity and meso-hypotympanum were also observed; 3. via the middle cranial fossa approach, the structures of the epitympanum, tympanic antrum, mastoid cavity and lateral wall were inspected, most mesotympanic structures were evaluated.

Middle ear endoscopy through the different approaches provides the otosurgeons a clear view field of the middle ear structures, can therefore decrease the incidence of cholesteatoma recurrence and evaluate the state of the postoperative middle ear cavity. The 30 degree otoendoscope can provide a better visualization of the middle ear structures, via the three approaches, the 90 degree otoendoscope is suited for the inspection of the posterior epitympanum via the transmeatal approach and retrotympanum via mastoid cavity-tympanic antrum route.