Feasibility of an Endoscopic-Assisted Retrolabyrinthine Approach for Intracanalicular Vestibular Schwannoma-A Radiographic Morphometric Study.

OBJECTIVE

To analyze radiographic characteristics that predict adequate internal auditory canal (IAC) access through retrolabyrinthine corridor for potential removal of vestibular schwannoma (VS).

STUDY

DESIGN

Retrospective imaging analysis of the retrolabyrinthine corridor (RLC) and fundal fluid cap (FC) were measured and multiple linear regression models were used to examine the relationship between RLC width and FC and their impact on extent of IAC access as well as logistic regressions to analyze the likelihood of tumor exposure achievable with both 0 and 30-degree endoscopic views.

SETTING

Single-institution radiology analysis of patients undergoing MRI IAC with diagnosis of VS (ICD-10 D33.3).

RESULTS

The predicted IAC exposure was 68.6% and 42.2% with 30 and 0-degree views, respectively ( P <0.05, CI: 17.1%-35.6%). For every 1 mm increase in RLC width, the 30-degree IAC access increases by ∼1.54 mm ( P <0.001) and the 0-degree IAC access increases by 1.45 mm ( P <0.001), while FC did not significantly impact IAC access. When predicting the impact on tumor exposure with a 0-degree view, each 1 mm increase in RLC width increases the odds of complete exposure by 153% (OR=2.53, P =0.043), while each 1 mm increase in FC corresponds to 109% higher odds (OR=2.09, P =0.012). With a 30-degree view, each 1 mm increase in RLC increases the odds of complete exposure by nearly 300% (OR=3.99, P <0.001). FC has less impact on tumor exposure when utilizing a 30-degree view compared with a 0-degree view with each 1 mm increase in FC increasing odds of complete exposure by 56% (OR=1.56, P =0.011). In addition, the use of a 30-degree endoscope over a 0-degree endoscope is associated with 4,336% higher odds of achieving complete tumor exposure (OR=44.35, 95% CI: 8.46-232.52, P <0.001), highlighting the importance of angled visualization and exposure in skull base surgery.

CONCLUSION

Greater retrolabyrinthine corridor and fundal cap measurements are correlated with improved IAC access and VS exposure. These radiographic characteristics may be used as tools to predict candidacy for a retrolabyrinthine approach to VS.