Grading of the Position of the Mastoid Tegmen in Human Temporal Bones - A Surgeon's Perspective

To establish a new surgically relevant classification system of the anatomic variations of the temporal bone tegmen plate as well as to perform a comparative analysis, with respect to the pneumatization patterns in the cadaveric temporal bones.

Microdissection of the human cadaveric temporal bones was performed after obtaining ethical approval from the Institutional Ethical Committee (F.8-522/A-522/2017/RS). The pneumatization pattern of the temporal bones was noted as "under-pneumatized" or "well-pneumatized." The tegmen mastoid (TM) was classified into two grades as per the position of the tegmen plate and the visibility of the superior semicircular canal (SSCC) and the aditus. The latter two structures were well visualized in Grade A and poorly visualized in Grade B. The data were analyzed using Stata 14.0 (Stata Corp, 4905, Lakway drive, College Station, Texas, USA).

Ninety-three temporal bones were dissected under microscope. Fifty-eight bones were well-pneumatized and 35 were under-pneumatized. The tegmen plates were classified as Grade-A in 49 bones (well-pneumatized -37 and under-pneumatized -12), and as Grade-B in 44 bones (well-pneumatized-21, poorly-pneumatized-23). Grade-A classification was significantly more common in well-pneumatized temporal bones, while Grade-B was more common in under-pneumatized bones (p=0.0057).

We propose a surgically relevant classification for TM positioning. A well-pneumatized temporal bone is associated with a significantly higher position of the tegmen plate (Grade-A TM).