Comparison of subtemporal versus presigmoidal approaches for exposing petrous apex utilizing virtual reality technique

Abstract

Objective To perform quantitative comparison of microanatomical features between subtemporal and presigmoidal minimally invasive approaches for exposing petrous apex on the basis of virtual reality image model.  Methods CT and MRI were performed on 15 adult cadaver heads (30 sides) to establish virtual reality three-dimensional anatomical model of petrous apex. The superior edge of the root of temporal bone zygomatic process and the mastoidale on the calvaria were selected as landmark points of craniotomy through subtempral and presigmoidal approaches. Petrous apex was selected as exposure landmark point on the skull base. The lines between craniotomy and exposure landmark points were used as axis to outline a cylinder simulating surgical routes of subtemporal and presigmoidal approaches. Anatomical exposures in two surgical routes were observed and measured. Statistical comparison was launched by paired t test.  Results Surgical route of subtemporal approach passed through middle skull base and temporal lobe, and then reached petrous apex. Petrous bone drilling was performed to expose internal acoustic meatus, facial nerve and labyrinth. Then, trigeminal nerve, superior petrous sinus and cavernous sinus were exposed. Surgical route of presigmoidal approach was performed by drilling petrous bone through mastoid and passing vertical segment of facial nerve. Then, glomus jugulare, the lower cranial nerves, ossicular chain, labyrinth and internal carotid artery (ICA) were exposed in turn. Reaching internal acoustic meatus, the route exposed anterior inferior cerebellar artery (AICA) and facial-acoustic nerve complex. Reaching petrous apex, the route involved superior cerebellar artery, superior petrous sinus, inferior petrous sinus, cavernous sinus, trigeminal nerve and partial temporal lobe. The volumes of route, osseous structures, facial-acoustic complex, labyrinth and vein involved in presigmoidal approach were more than those in subtemporal approach (P = 0.000, for all). Volumes of temporal lobe, trigeminal nerve and ossicular chain involved in subtemporal approach were more than those in presigmoidal approach (P = 0.000, for all). Volume of lower cranial nerve and artery involved in presigmoidal approach was (32.38 ± 2.86) mm³ and (262.74 ± 16.93) mm³ respectively, but above structures were not involved in subtemporal approach.  Conclusions Exposure of structures in and around petrous bone in presigmoidal approach is more than that in subtemporal approach. Thus, more attention should be paid to protect critical structures in presigmoidal approach. Subtemporal approach can reach petrous apex through temporal lobe, thus it is suitable to treat lesions in middle skull base which implicate petrous bone and push temporal lobe upward.

DOI: 10.3969/j.issn.1672-6731.2016.07.008