Morphometric Study of the Extradural Middle Cranial Fossa for Transpetrosal Surgery

Kim, Bum Tae; Shin, Won Han; Choi, Soon Kwan; Byun, Bark Jang

Abstract

As an attempt to better understand the microanatomy during transpetrosal surgery and to determine the limitation of extradural middle fossa approach, 16 adults human cadaveric skull base speciments were dissected at the region of petroclivus and posterior cavernous sinus. The important landmarks chosen for this study included the following: a petrosigmoid intersection, arcuate eminence, foramen spinosum, foramen ovale, hiatus of greater superficial petrosal nerve (GSPN), porus acousticus internus, geniculate ganglion, cochlea and petrous portion of internal carotid artery(ICA). The resultant data are as follows: the length between the petrosigmoid intersection and the arcuate eminence was 23.1mm+/-1.9(20.1-26.5). The depth covering geniculate ganglion was 1.3mm+/-0.3(0.8-1.8). The length between the geniculate ganglion and the hiatus of GSPN as well as cochlea were 4.6mm+/-1.1(3.5-7.1) and 0.9mm+/-0.2(0.7-1.2) respectively. The whole length of the GSPN exposed the middle cranial fossa was 11.0mm+/-0.8(9.3-12.5). The diameter f the petrous portion of ICA was 5.9mm+/-0.2(5.5-6.4). The length of the horizontal segment of the petrous ICA that can be exposed for anastomosis was 10.8mm+/-0.9(9.0-12.3). The distance between geniculate ganglion and porus acousticus showed a sighificant difference in all measurements to be compared with right and left side(p<0.05). The angle between the internal acoustic meatus and GSPN correlated inversely to the length of horizontal segment of pertrous ICA(r=-0.54, p<0.05). Morphometric analysis and their correlation between bony landmarks and structures within the pyramid helped to decide the angle and direction from which bone removal could be accomplished more safely during transpetrosal surgery, including the middle fossa approach.