Applied Anatomy Of Endoscopic Resections Of Vestibular Schwannomas Through The Transcanal Vestibular Approach

Objective The aim of this study was to explore the possibility of endoscopic resections of vestibular schwannomas(VS)through the transcanal vestibular approach from imaging and applied anatomy,and to observe and record the safety limits,anatomical landmarks and the anatomical relations of the nerves in the IACfor this approach.Methods1.Retrospective analysis of CT of the temporal bone in 100 patients(200 sides)from the first affiliated hospital of shenzhen university,to observe and record the morphology of the internal auditory canal(IAC)and the anteroposterior diameter and the superoinferior diameter of IAC fundus.2.Five(10 sides)fresh frozen adult cadaver heads were scanned in CT of temporal bone,then exposed to IAC by the endoscopic transcanal vestibular approach.The safety limits,some key anatomical landmarks and the anatomical relations of the nerves in the IAC of this approach was recorded.Results1.The IAC morphology of 100 patients(200 sides)can be characterized as cylinder(n=155),ampulla(n=40),trumpet(n=2)and irregular(n=3).The anteroposterior diameter of IAC fundus was 4.23±0.80 mm,and the superoinferior diameter was5.07±0.93 mm.The anteroposterior diameter and superoinferior diameter of the left IAC fundus were 4.19±0.73mm、5.02±0.88 mm,of the right IAC fundus were 4.27±0.86mm、5.12±0.98 mm.There was no statistically significant difference in these measures between the left and right IAC fundus.The anteroposterior diameter and superoinferior diameter of the male IAC fundus were 4.39±0.82mm、5.13±1.01 mm,of the female IAC fundus were 4.01± 0.76 mm 、 5.02 ± 0.87 mm.The anteroposterior diameter of IAC fundus has statistically significant difference between sexes.But was not noticed in the superoinferior diameter of IAC fundus between sexes.2.The IAC morphology of Five(10 sides)fresh frozen adult cadaver heads can be characterized as cylinder(n=9),ampulla(n=1).The anteroposterior diameter of IAC fundus was 4.31±0.34 mm,and the superoinferior diameter was 5.44±0.15 mm.3.The safety limits of this approach were the tympanic segment of the facial nerve superiorly,the mastoid segment of the facial nerve posteriorly,the jugular bulb inferiorly,and the medial turn and partial basal turn of the cochlea anteriorly.The oval window,round window,cochleariform process,finiculus and the tympanic segment of the facial nerve were the key landmarks of this approach.4.The anatomical relations of the nerves in the IAC: At first,the superior vestibular nerve was exposed under this approach,the inferior vestibular nerve is inferiorly,the facial nerve is anteriorly,and the cochlear nerve is under in the facial nerve.Conclusion This approach is feasible both on imaging and applied anatomy.From the view of endoscopic anatomy,this approach can not only fully expoxe the contents of the IAC,complete the resection of the lesions of the IAC,but also preserve the cochlear nerve,the medial,apical and partial basal turn of the cochlea,which provides a possibility to the patients for the implantation of cochlear implants in the simultaneous or later.This approach is one of the best choice for those patients with VS who have residual hearing and whose VS in Koos stage Ⅰ or Ⅱ.