Phenotypical Variability of the Internal Acoustic Canal in the Middle Cranial Fossa Surgery

Abstract

Introduction: The wide range of anatomical variability of the structures of the middle cranial fossa and the lack of reliable surgical landmarks contribute to a high level of complications in the surgical treatment of vestibular schwannomas. We hypothesized that the cranial phenotype influences the shape of the middle cranial fossa, the orientation of the pyramid of the temporal bone, and the relative topography of the internal acoustic canal. Materials and Methods: The skull base structures were studied on 54 embalmed cadavers and 60 MR images of the head and neck by photo modeling, dissection, and 3D analysis techniques. By the value of the cranial index, all specimens were subdivided into dolichocephalic, mesocephalic, and brachycephalic groups for comparison of variables. Results: The length of the superior border of the temporal pyramid, the apex to squama distance, and the width of the middle cranial fossa all peaked in the brachycephalic group. The value of the angle between the superior border of the pyramid and the axis of the acoustic canal varied from 33 to 58 º; it peaked in the dolichocephalic group and showed its smaller value in the brachycephalic one. The pyramid to squama angle had reversed distribution and dominated in the brachycephalic group. Conclusions: The cranial phenotype influences the shape of the middle cranial fossa, temporal pyramid, and internal acoustic canal. Presented in this paper data help specialists operating on the vestibular schwannoma to localize the internal acoustic canal based on the individual shape of a skull.

Phenotypical variability of the sigmoid sinus in translabyrinthine and retrosigmoid surgeries

“…The authors analyzed neither the diameters of the cranial fossae nor the orientation of the pyramid of the temporal bone but measured only the distances from the surface of the skull to the apex, however. The results of our early research showed that the length of the superior border of the pyramid of the temporal bone and the distance from the apex of the pyramid to the squama is larger in brachycephalic specimens due to the positive correlation of the laterolateral diameter of the middle cranial fossa with the transverse diameter of the skull [1]. The orientation of the temporal pyramid varied between the phenotypes significantly, with a half the size of the angle between the superior border of the pyramid and the squama in dolichocephalic specimens.…”

“…After the dissection of the superficial tissues of the head and craniotomy, the brain and meninges were removed from the cranial cavity exposing the skull base. Then, the cadaveric specimens were digitized using the Photo Modeler (2021) software and technique, as previously described [1].…”