Position and Course of Facial Nerve and Postoperative Facial Nerve Results in Vestibular Schwannoma Microsurgery

OBJECTIVE: To investigate the variation in the position and course of the facial nerve (FN) in patients undergoing vestibular schwannoma (VS) microsurgery by the keyhole retrosigmoid approach and the relationship between FN position and postoperative facial results. METHODS: The series consists of 100 patients who underwent VS microsurgery during a 5-year period in whom the position and course of the FN could be confirmed by direct stimulation. The course of the FN was classified into 4 patterns according to its position: anterior (ventral) surface of the tumor (A), anterior-superior (AS), anteriorinferior (AI), and dorsal (D). RESULTS: The distribution of patterns was as follows: AS in 48 cases, A in 31, AI in 21, and D in zero. For tumors <1.5 cm, the AS pattern was most common (68.4%). For tumors >= 1.5 cm, the proportion of A and AI positions increased (31.4% and 25.5%). Significant differences were observed between position and course patterns of the FN and postoperative nerve results. Patients with AS and AI patterns had better House-Brackmann FN function compared with patients with the A pattern (P < 0.05). Moreover, in tumors > 3.0 cm, the FN tended to adhere strongly to the tumor capsule, and postoperative facial deficits were more frequent (P < 0.05). CONCLUSIONS: The AS pattern was most common for smaller VSs. The A position and course and adhesion of the FN to the tumor capsule were the 2 factors most strongly associated with worse postoperative FN result.