A unique variant of abducens nerve duplication in a case of a large vestibular schwannoma

Vestibular schwannomas (VS) are slow-growing benign tumors commonly found in the cerebellopontine angle, potentially compressing brain structures and cranial nerves, including the abducens nerve (AN), responsible for lateral gaze. Although large VSs may compress the AN, postsurgical AN palsy is rare, and the clinical significance of AN variations, particularly in VS cases, remains unclear. We report a unique case of a 29-year-old female with a large left vestibular schwannoma. The patient underwent a left-sided microsurgical two-stage excision with an uneventful recovery (House-Brackmann facial grade I). During surgery, a rare variant of the AN was identified. This AN originated as two separate trunks and merged 3 mm distal to its origin in the same segment. To the best of our knowledge, arising and merging in the cisternal segment of AN variation has not been reported previously. Recognizing AN variations is vital for successful skull base surgeries, especially in preserving both branches during vestibular schwannoma surgery and ensuring ocular function.