Middle Cranial Fossa Approach: Anatomical Study on Skull Base Triangles as a Landmark for a Safe Anterior Petrosectomy.

The Kawase approach provides access to the petroclival and posterior cavernous sinus regions, cerebellopontine angle, and upper basilar artery territory. Nevertheless, it remains one of the most challenging approach for neurosurgeons, due to the considerable related morbidity and mortality. The goal of this study was to evaluate the relationship between anatomical landmarks and their possible variations, and to measure the extension of the Kawase space, to define the reliability of these landmarks while performing an anterior petrosectomy.  Using eight cadaveric specimens (15 sides), an anatomical dissections and extradural exposure of the Kawase area were performed.  A two-step analysis of the distances between the mandibular branch of the trigeminal nerve (V3) and the structures at risk of iatrogenic damage was performed.  We measured the distance between V3 and the basal turn of the cochlea, and between V3 and the internal acoustic canal (IAC), analyzing the limits of bone resection without causing hearing damage.  We analyzed eight cadaveric (15 sides) formalin-fixed heads injected with colored silicone: four males and four females of Caucasian race (mean age: 73.83 years). We found a mean distance of 10.46 ± 1.13 mm between the great superficial petrous nerve (GSPN) intersection with V3 and the basal turn of the cochlea, and of 11.92 ± 1.71 mm between the origin point of V3 from the Gasserian ganglion and the fundus of the IAC.  The knowledge of the safe distance between the most applicable anatomic landmarks and the hearing structures is a practical and useful method to perform this approach reducing related comorbidity.