title: Avoiding injury to the abducens nerve during expanded endonasal endoscopic surgery: anatomic and clinical case studies.
abstract: BACKGROUND
  Understanding the course of the most medially located parasellar cranial nerve, the abducens, becomes critical when performing an expanded endonasal approach.
  
  
  OBJECTIVE
  We report an anatomoclinical study of the abducens nerve and describe relevant surgical nuances to avoid its injury.
  
  
  METHODS
  Ten anatomic specimens were dissected using endoscopes attached to an high-definition camera. A series of anatomic measurements and relationships of the abducens nerve were noted. Illustrative clinical cases are described to translate those findings into practice.
  
  
  RESULTS
  Cisternal, interdural, gulfar, and cavernous segments of the abducens were identified intracranially. The mean distance from the vertebrobasilar junction (VBJ) to the pontomedullary sulcus (PMS) was 4 mm; horizontal distance between both abducens nerves at the PMS was 10 mm, and between both abducens at the interdural segment was 18.5 mm. The upper limit of the lacerum segment of the internal carotid artery was at the same level of the dural entry point of the sixth cranial nerve posteriorly. The sellar floor at the sphenoid sinus marks the level of the gulfar segment in the craniocaudal axis. At the superior orbital fissure, the abducens nerve and V2 were at an average vertical distance of 11.5 mm.
  
  
  CONCLUSIONS
  Anatomic landmarks to localize the abducens nerve intraoperatively, such as the VBJ for the transclival approach, the lacerum segment of the carotid, and the sellar floor for the medial petrous apex approach, and V2 for Meckel's cave approach, are reliable and complementary to the use of intraoperative electrophysiological monitoring.
authors.affiliation: Department of Neurological Surgery, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, USA.
authors.forename: Juan
authors.initials: J
authors.lastname: Barges-Coll
authors.forename: Juan Carlos
authors.initials: JC
authors.lastname: Fernandez-Miranda
authors.forename: Daniel M
authors.initials: DM
authors.lastname: Prevedello
authors.forename: Paul
authors.initials: P
authors.lastname: Gardner
authors.forename: Victor
authors.initials: V
authors.lastname: Morera
authors.forename: Ricky
authors.initials: R
authors.lastname: Madhok
authors.forename: Ricardo L
authors.initials: RL
authors.lastname: Carrau
authors.forename: Carl H
authors.initials: CH
authors.lastname: Snyderman
authors.forename: Albert L
authors.initials: AL
authors.lastname: Rhoton
authors.forename: Amin B
authors.initials: AB
authors.lastname: Kassam
mesh_terms: D000010:Abducens Nerve / Q000033:anatomy & histology* / Q000601:surgery; D020222:Abducens Nerve Injury / Q000209:etiology / Q000503:physiopathology / Q000517:prevention & control*; D000328:Adult; D002102:Cadaver; D035301:Cranial Fossa, Middle / Q000033:anatomy & histology* / Q000601:surgery; D004724:Endoscopy / Q000009:adverse effects / Q000379:methods*; D005260:Female; D006801:Humans; D007431:Intraoperative Complications / Q000209:etiology / Q000503:physiopathology / Q000517:prevention & control*; D008297:Male; D019291:Skull Base / Q000033:anatomy & histology* / Q000601:surgery; D055815:Young Adult