Sinus tympani endoscopic anatomy.

Objective: The sinus tympani has been the focus of clinical interest because of its tendency to be invaded by cholesteatoma, its visual obscurity, and the lack of a straightforward surgical approach by which it can be addressed. This study was undertaken to describe the microscopic as well as the endoscopic anatomy of the sinus tympani.

Study Design And Setting: Thirty temporal bones harvested from cadavers were dissected using an operating microscope and telescopes with different angles and 2.7- and 4-mm diameters, fitted with a videocamera. Images were transmitted to a computer screen. Precise measurements were made after scaling the distances with the digital image processing.

Results: Marked variation in size and shape was the rule. It was found that the sinus tympani is bounded laterally by a constant ledge of bone anterior to the facial nerve. It was deep, extending posterior to the facial nerve in 6 specimens. The telescopes (30 degrees to 70 degrees ) enabled the surgeon to see this region clearly because the orifice plane was more or less perpendicular to the axis of the external auditory canal.

Conclusion: The study emphasizes the importance of removal of this lateral lip of bone to expose the orifice of the sinus tympani. This should be complemented with the use of a 30 degrees endoscope (1.7 mm in canal-up and 4.0 mm in canal-down technique) for better visualization and cleaning of this hidden area.