Two fans in middle cranial fossa: microsurgical anatomy of middle cranial fossa through subtemporal-transpetrosal extradural approach

Abstract

Objective To study the anatomy of the middle cranial fossa through subtemporaltranspetrosal extradural approach. Methods Fixed in formalin, 20 sides of 10 Chinese adult cadaveric heads were filled with red and blue silica gel. Followed the subtemporal transpetrosal extradural approach,the manipulation was done. The extradural trajectory in middle fossa was exposed laterly to the arcuate eminence (AE) and posteriorly to the superior petrosal sinus. The petroclival region was seen after drilling the bone of Day quadrilateral while preserving the internal auditory canal (IAC), cochlea and internal carotid artery (ICA). The anatomy of middle cranial fossa was studied. Results (1) According to the shape and gasification, the arcuate eminence was classified to there types:Smooth-type, terrace-type and gravel-type. The relationship between arcuate eminence and superior semicircular canal was clear in the former two types. (2) The related structures in middle cranial fossa and petrosal bone could be described and linked systematically by two associated fans:anterior fan centered around the gasserian ganglion, posterior fan centered around the geniculater ganglion.(3)The internal auditory canal was in the posterior fan. The angle between GSPN and AE was 122.7°±7.6°(108.1°～137.5°). The angle between GSPN and interior border of IAC was 46.6°± 4.9°(35.0°～55.2°). Cochlea was located in the angle of GSPN and IAC.Conclusion Easier to be understood and momerized, all structures in the middle cranial fossa through subtemporal-transpetrosal extradural approach could be generalized by two fans.Identification of the interior border of IAC is more important in drilling of petrosal apex than that of the axis of IAC. Key words: Microanatomy; Middle cranial fossa; Extradural approach