Prognostic significance of preoperative geometric changes in the internal acoustic canal for hearing preservation in vestibular schwannoma surgery

Abstract Object We focused on the changes in the internal acoustic canal (IAC) caused by vestibular schwannomas and their prognostic significance for postoperative hearing outcome. Methods 125 consecutive cases of VS were included. We used a neuronavigation software to perform the following measurements on both tumor and healthy side: volume (VIAC), maximal diameter of the IAC (DIAC) and length of the IAC (LIAC). A statistical analysis was realized using Spearman’s correlation to test the correlation of the morphometric measure of the IAC and the postoperative hearing. Multivariate analysis was performed to test the impact of measurements of the IAC and the preoperative hearing on the postoperative hearing. Results The mean VIAC on tumor and on healthy side were respectively 0.271 cm3 and 0.169 cm3. The mean DIAC was 9.438 mm on tumor side and 7.034 mm contralateral. The correlations tests showed significant correlations of both postoperative hearing deficit and degree of hearing loss with: 1) VIAC on the tumor side; 2) the difference between VIAC on tumor and healthy side; 3) DIAC on the tumor side; 4) the difference between the DIAC on the tumor and healthy side. The multivariate analysis showed significant impact of the maximal diameter of the IAC (p=0.01) and the preoperative hearing status (p=0.02) on the postoperative hearing. Conclusions Enlargement of IAC volume and diameter are negative prognostic factors for hearing preservation. Reasons may be long-standing compression of the auditory nerve and an increased vulnerability of the inner ear structures during the drilling of IAC.