The Impact of Tumor Elongation on Facial Nerve Outcome after Surgery for Koos Grade 3 and 4 Vestibular Schwannomas in the Semi-Sitting Position via the Retrosigmoid Approach

<b>Background:</b> Facial nerve paralysis is a severe dysfunction after vestibular schwannoma (VS) surgery. <b>Methods:</b> This monocentric study analyzed 61 patients who underwent sporadic VS surgery in a standardized manner. The primary endpoint was the facial nerve outcome (FNO) at 3 months after VS surgery. FNO was dichotomized into "good" (House-Brackmann (HB) score ≤ 2) and "poor" (HB > 2). <b>Results:</b> Poor FNO was observed in 11 patients (18.0%) at 3 months after VS surgery. Radiomic tumor shape features were analyzed, and the AUC of elongation in the prediction of a poor HB at 3 months was 0.70 (95% CI: 0.56-0.85, <i>p</i> = 0.03) and the optimum threshold value (≤/>0.35) yielded a sensitivity and specificity of 64.0% and 75.4%, respectively. Multivariable logistic regression analyses considering the extent of resection (</≥93.4%), preoperative tumor volume (</≥2.6 cm³), age (</≥55), sex (female/male), and elongation (≤/>0.35) revealed that more elongated VSs (≤0.35; OR: 5.8; 95%CI: 1.2-28.2; <i>p</i> = 0.03) and those with an increased EoR (≥93.4%; OR: 6.5; 95%CI: 1.0-42.5; <i>p</i> = 0.05) are independently associated with poorer FNO at 3 months after surgery. <b>Conclusions:</b> Highly elongated VS shape seems to be a risk factor for worsened facial nerve outcome at 3 months after surgery for Koos grade 3 and 4 tumors.