title: Distinction between paraclinoid and cavernous sinus aneurysms with computed tomographic angiography.
abstract: OBJECTIVE
  To examine the reliability of using the optic strut as a landmark in computed tomographic (CT) angiography, to differentiate between intradural and extradural (cavernous sinus) aneurysms involving the paraclinoid segment of the internal carotid artery (ICA).
  
  
  METHODS
  Microanatomic dissections were performed with five cadaveric heads (10 sides), to establish the relationships of the optic strut to the cavernous sinus and the ICA. Results from these anatomic studies were compared with intraoperative and CT angiographic findings for four patients with nine intracranial aneurysms involving the paraclinoid segment of the ICA.
  
  
  RESULTS
  The inferior boundary of the optic strut accurately localized the point at which the ICA pierced the oculomotor membrane (proximal dural ring) and exited the cavernous sinus. The optic strut and its relationship to the ICA could be well observed on CT angiograms. During surgery, six of six aneurysms that arose distal to the optic strut were identified intradurally and were successfully clipped. Conversely, all aneurysms that arose proximal to the optic strut were observed to lie within the cavernous sinus. An aneurysm at the optic strut was within the clinoid segment or interdural, between the proximal and distal rings.
  
  
  CONCLUSIONS
  The optic strut, as identified with CT angiography, provided a reliable anatomic landmark for accurate discrimination between intradural and extradural (cavernous sinus) aneurysms.
authors.affiliation: Division of Neurological Surgery, Barrow Neurological Institute, St. Joseph's Hospital and Medical Center, Phoenix, Arizona 85013, USA.
authors.forename: L Fernando
authors.initials: LF
authors.lastname: Gonzalez
authors.forename: Matthew T
authors.initials: MT
authors.lastname: Walker
authors.forename: Joseph M
authors.initials: JM
authors.lastname: Zabramski
authors.forename: Shahram
authors.initials: S
authors.lastname: Partovi
authors.forename: Robert C
authors.initials: RC
authors.lastname: Wallace
authors.forename: Robert F
authors.initials: RF
authors.lastname: Spetzler
mesh_terms: D000328:Adult; D002343:Carotid Artery, Internal / Q000000981:diagnostic imaging* / Q000601:surgery; D002426:Cavernous Sinus / Q000000981:diagnostic imaging* / Q000601:surgery; D002533:Cerebral Angiography; D003937:Diagnosis, Differential; D005260:Female; D006801:Humans; D002532:Intracranial Aneurysm / Q000000981:diagnostic imaging* / Q000601:surgery; D008297:Male; D008875:Middle Aged; D019635:Neurosurgical Procedures; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013100:Sphenoid Bone / Q000000981:diagnostic imaging / Q000601:surgery; D014057:Tomography, X-Ray Computed