Sinus Tympani: A Practical Classification

Abstract

Objectives: (1) Describe a classification for the sinus tympani (ST) different types based on their otoendoscopic and surgical anatomy in relation to their development theories. (2) Evaluate possible approaches to each of its types. (3) Eliminate the discrepancy between the various methods used to describe it in literature. Methods: Fifty-five temporal bones were dissected, and the anatomic details were studied using an operating microscope and otoendoscopes of different angles. In addition, the ST anatomy and relations were studied in 200 temporal bones’ computed tomography scans. Results: Four distinct types of ST could be observed. Type 1, the most common type, was pneumatized and consisted of an orifice and cavity. In Type 2, the well-pneumatized type, the cavity was deep enough posteriorly to exceed the level of the mastoid segment of the facial nerve in any direction. In Type 3, the common posterior tympanic sinus, ST communicated with the upper posterior tympanic sinus proper or with a retro-ponticulus up-ward extension. Type 4, the nonpneumatized type, was shallow with no true orifice and cavity. Types 1 and 4 were mainly approached via the transcanal route. Types 2 and 3 required a combined transcanal and transmastoid approach. Endoscopic transcanal approach alone was satisfactory for types 1 and 4 but to a lesser extent in type 3. Conclusions: ST shape and extension both depend mainly on the extent of its pneumatization, which in turn influences its relation to the surrounding structures in the retrotympanic area. Extensively or unusually pneumatized types need special or combined approaches.