Abducens Nerve Duplication: Novel Intraoperative and Radiographic Observation of a Rare Anatomical Variant.

 The abducens nerve has a long, serpentine subarachnoid course with complex topographical relationships, rendering abducens nerve palsy the most common ocular motor cranial nerve palsy in adults and second most common in pediatric patients, with anatomical variants reported in the literature. Preoperative awareness of abducens nerve variant anatomy may help prevent inadvertent intraoperative injury.  This study is a case report with a review of the abducens nerve anatomy and variants.  The study setting included outpatient, inpatient, and operating room in the neurosurgery department of a quaternary referral center.  The study included a woman in her early 30s with a diagnosis of petrous meningioma.  In vivo documentation of a type 3 abducens nerve duplication was carried out.  A left extended retrosigmoid craniotomy was recommended for the petroclival meningioma resection. Intraoperatively, a complete duplication of the left abducens cisternal segment was encountered and photographed. The left unilateral abducens nerve duplication was confirmed with postoperative volumetric magnetic resonance imaging using the FIESTA (fast imaging employing steady-state acquisition) sequence, revealing the union of the duplicated cisternal abducens nerves into a single trunk from Dorello's canal distally.  Abducens nerve variants are uncommon, and although reported in the setting of cadaveric dissection, in vivo documentation of them is limited. This case report of an in vivo type 3 abducens nerve duplication with intraoperative photographic and radiographic images highlights the need for clinical awareness to avoid inadvertent intraoperative injury.