Predictors of Improved Abducens Nerve Palsy following Endoscopic Endonasal Approach to Skull Base Lesions

Introduction: Endoscopic skull base surgery frequently brings surgeons near the course of the abducens nerve. We sought to characterize the relative frequency, rates of improvement and associated factors related to postoperative abducens nerve palsy.

Methods: We reviewed patients undergoing endoscopic endonasal resection of skull base lesions from 2011 to 2017. New postoperative abducens nerve palsies and their severity were recorded. Palsies that developed after the first postoperative day were defined as delayed. Demographic characteristics, past medical history, operative duration, tumor pathology, and radiographic involvement of different segments of CN VI (prepontine cistern, Dorello’s canal, and cavernous sinus) were determined. Univariate analysis comparing immediate palsy versus delayed palsy was performed using Chi-squared, Fisher’s exact, and Mann–Whitney tests as appropriate. Values with a p < 0.2 were included in multivariate analysis via logistic regression comparing immediate palsy versus delayed palsy. A p-value < 0.05 was considered significant. Long-term palsies were defined at a minimum of 6 months of follow-up.

Results: A total of 74 patients developed postoperative abducens palsies, of which 36 (48.6%) were complete. At most recent follow-up (mean: 34 months, median: 25 months), 53 of these 74 (72%) patients had persistent palsies. Resolution of the palsy was identified in 15/38 (39.5%) partial palsies and 6/36 (16.7%) complete palsy (p = 0.029). Sixty-three (85.1%) patients had an immediate abducens nerve palsy. Resolution of the palsy was identified in 15/63 (23.8%) immediate palsies, and 6/11 (54.5%) delayed palsies (p = 0.037). Involvement of all three zones and increased tumor size were associated with immediate compared with delayed development of abducens palsy on univariate analysis. Prepontine cistern involvement (OR: 2.72, p = 0.041) was associated with immediate palsy and obesity was associated with a delayed abducens nerve palsy (OR: 16.9, p = 0.037) on multivariate analysis.

Conclusion: Following endoscopic endonasal resection of high-risk tumors, partial and delayed abducens nerve palsies were substantially more likely to improve. Immediate abducens nerve palsy was associated with prepontine cistern tumor involvement and may also be linked to increased tumor size and involvement across a large portion of the abducens nerve territory. Obesity was associated with delayed abducens nerve palsy, possibly reflecting a less aggressive surgical approach in patients with significant comorbidities.

No conflict of interest has been declared by the author(s).