Factors Associated with Abducens Nerve Recovery in Patients Undergoing Surgical Resection of Sixth Nerve Schwannoma: A Systematic Review and Case Illustration

BACKGROUND: Limited or no literature exists identifying factors associated with functional nerve recovery in patients undergoing resection of sixth cranial nerve (CN VI) schwannomas. METHODS: A systematic review of literature was performed on CN VI schwannomas that were treated surgically. Synthesizing the findings pooled from the literature, we investigated associations of patient demographics and clinical characteristics with postsurgical CN VI functional recovery in multivariable regression models. In addition, we present the findings of an adolescent woman surgically managed for intracavernous CN VI schwannoma. Complete encasement of the cavernous segment of the internal carotid artery is unique to our case. RESULTS: We synthesized data of 32 patients from 29 studies, and our index case. Overall, the mean age of the patients was 44.0 +/- 16.5 years, and approximately 52% (n = 17) were female. Most tumors were left-sided (n = 18; 54.5%), with an average size of 3.46 +/- 1.71 cm. The most common location was cisternal (n = 11; 33%), followed by cavernous sinus (CS) proper (n = 9; 27%), cisterocavernous (n = 8; 24%), orbital (n = 4; 12%) and caverno-orbital (n [1; 3%). CN VI recovery was reported in less than half the cohort (n = 14; 45%). Tumor extension in the CS was significantly associated with lesser likelihood (odds ratio [OR], 0.07; 95% confidence interval [CI], 0.01-0.98; P = 0.048) of postsurgical CN VI recovery. Although female gender (OR, 0.86; 95% CI, 0.07e 10.09; P = 0.906), large tumor size (> 2.5 cm) (OR, 0.45; 95% CI, 0.07-2.89; P = 0.397), and solid consistency (OR, 0.37; 95% CI, 0.03-4.19; P = 0.421) were associated with lesser odds for recovery, these were not statistically significant. Likewise, although gross total resection (OR, 6.28; 95% CI, 0.33-118.25; P = 0.220) was associated with higher odds of nerve recovery, the estimates were statistically insignificant. CONCLUSIONS: CS involvement is associated with lesser odds for functional nerve recovery in patients undergoing surgical resection for CN VI schwannoma.