A micro-CT study of the sinus tympani variation in humans.

The posterior part of the tympanic cavity comprises a depression called the sinus tympani (ST). The said structure is of outmost importance, e.g., in surgical procedures involving the middle ear, as apathology (microbial biofilm or cholesteatoma) present in this difficult to access location might hinder its effective treatment. The aim of the study was to evaluate anatomical variants of the sinus tympani in human adult petrous bones. For this purpose, 3D models of the ST were recreated from micro-CT scans of 44 dry petrous bone samples (19 female, 25 male), applying 3D Slicer, Meshmixer and MeshLab softwares. Anatomical variants of the ST were classified in terms of both shape and surface configuration. The internal configuration of the ST was classified as heterogeneous - containing small bony trabeculae and crests up to 1.0 mm in size, contrasting to homogeneous ST that characterizes a relatively smooth interior, or mere presence of minor depressions and mild folds. Female STs were more bowl-shaped (57.9%) than saccular (42.1%), and had heterogeneous surface configuration (52.6%) compared to homogeneous (47.4%). On the contrary, male STs were more saccular (52.0%) rather than bowl-shaped (48.0%), and predominantly had a heterogeneous surface (84.0%) over homogeneous (16.0%). A complex combination of ST features comprised of a saccular shape and heterogeneous surface occurred in 52.0% of males and in 15.8% of females (a statistically significant difference; p=0.0254, Fisher's exact test) seems to be clinically important because of its potential negative implication on health outcomes after surgery in case of e.g., cholesteatoma, and it may also favor chronic pathological processes.