title: Proposed clinical internal carotid artery classification system.
abstract: BACKGROUND
  Numerical classification systems for the internal carotid artery (ICA) are available, but modifications have added confusion to the numerical systems. Furthermore, previous classifications may not be applicable uniformly to microsurgical and endoscopic procedures. The purpose of this study was to develop a clinically useful classification system.
  
  
  METHODS
  We performed cadaver dissections of the ICA in 5 heads (10 sides) and evaluated 648 internal carotid arteries with computed tomography angiography. We identified specific anatomic landmarks to define the beginning and end of each ICA segment.
  
  
  RESULTS
  The ICA was classified into eight segments based on the cadaver and imaging findings: (1) Cervical segment; (2) cochlear segment (ascending segment of the ICA in the temporal bone) (relation of the start of this segment to the base of the styloid process: Above, 425 sides [80%]; below, 2 sides [0.4%]; at same level, 107 sides [20%]; P < 0.0001) (relation of cochlea to ICA: Posterior, 501 sides [85%]; posteromedial, 84 sides [14%]; P < 0.0001); (3) petrous segment (horizontal segment of ICA in the temporal bone) starting at the crossing of the eustachian tube superolateral to the ICA turn in all 10 samples; (4) Gasserian-Clival segment (ascending segment of ICA in the cavernous sinus) starting at the petrolingual ligament (PLL) (relation to vidian canal on imaging: At same level, 360 sides [63%]; below, 154 sides [27%]; above, 53 sides [9%]; P < 0.0001); in this segment, the ICA projected medially toward the clivus in 275 sides (52%) or parallel to the clivus with no deviation in 256 sides (48%; P < 0.0001); (5) sellar segment (medial loop of ICA in the cavernous sinus) starting at the takeoff of the meningeal hypophyseal trunk (ICA was medial into the sella in 271 cases [46%], lateral without touching the sella in 127 cases [23%], and abutting the sella in 182 cases [31%]; P < 0.0001); (6) sphenoid segment (lateral loop of ICA within the cavernous sinus) starting at the crossing of the fourth cranial nerve on the lateral aspect of the cavernous ICA and located directly lateral to the sphenoid sinus; (7) ring segment (ICA between the 2 dural rings) starting at the crossing of the third cranial nerve on the lateral aspect of the ICA; (8) cisternal segment starting at the distal dural ring.
  
  
  CONCLUSIONS
  The classification may be applied uniformly to all skull base surgical approaches including lateral microsurgical and ventral endoscopic approaches, obviating the need for 2 separate classification systems. The classification allows extrapolation of relevant clinical information because each named segment may indicate potential surgical risk to specific structures.
authors.affiliation: Department of Neurological Surgery, Saint Louis University, Saint Louis, Missouri, United States of America.
authors.forename: Saleem I
authors.initials: SI
authors.lastname: Abdulrauf
authors.affiliation: Department of Neurological Surgery, Saint Louis University, Saint Louis, Missouri, United States of America.
authors.forename: Ahmed M
authors.initials: AM
authors.lastname: Ashour
authors.affiliation: Department of Neurological Surgery, Saint Louis University, Saint Louis, Missouri, United States of America.
authors.forename: Eric
authors.initials: E
authors.lastname: Marvin
authors.affiliation: Department of Neurological Surgery, Saint Louis University, Saint Louis, Missouri, United States of America.
authors.forename: Jeroen
authors.initials: J
authors.lastname: Coppens
authors.affiliation: Department of Neurological Surgery, Saint Louis University, Saint Louis, Missouri, United States of America.
authors.forename: Brian
authors.initials: B
authors.lastname: Kang
authors.affiliation: Department of Neurological Surgery, Saint Louis University, Saint Louis, Missouri, United States of America.
authors.forename: Tze Yu Yeh
authors.initials: TY
authors.lastname: Hsieh
authors.affiliation: Department of Neurological Surgery, Saint Louis University, Saint Louis, Missouri, United States of America.
authors.forename: Breno
authors.initials: B
authors.lastname: Nery
authors.affiliation: Department of Neurological Surgery, Saint Louis University, Saint Louis, Missouri, United States of America.
authors.forename: Juan R
authors.initials: JR
authors.lastname: Penanes
authors.affiliation: Department of Neurological Surgery, Saint Louis University, Saint Louis, Missouri, United States of America.
authors.forename: Aysha K
authors.initials: AK
authors.lastname: Alsahlawi
authors.affiliation: Department of Neurological Surgery, Saint Louis University, Saint Louis, Missouri, United States of America.
authors.forename: Shawn
authors.initials: S
authors.lastname: Moore
authors.affiliation: Department of Neurological Surgery, Saint Louis University, Saint Louis, Missouri, United States of America.
authors.forename: Hussam
authors.initials: H
authors.lastname: Abou Al-Shaar
authors.affiliation: Department of Neurological Surgery, Saint Louis University, Saint Louis, Missouri, United States of America.
authors.forename: Joanna
authors.initials: J
authors.lastname: Kemp
authors.affiliation: Department of Neurological Surgery, Saint Louis University, Saint Louis, Missouri, United States of America.
authors.forename: Kanika
authors.initials: K
authors.lastname: Chawla
authors.affiliation: Department of Neurological Surgery, Saint Louis University, Saint Louis, Missouri, United States of America.
authors.forename: Nanthiya
authors.initials: N
authors.lastname: Sujijantarat
authors.affiliation: Department of Neurological Surgery, Saint Louis University, Saint Louis, Missouri, United States of America.
authors.forename: Alaa
authors.initials: A
authors.lastname: Najeeb
authors.affiliation: Department of Radiology, Saint Louis University, Saint Louis, Missouri, United States of America.
authors.forename: Nadeem
authors.initials: N
authors.lastname: Parkar
authors.affiliation: Department of Radiology, Saint Louis University, Saint Louis, Missouri, United States of America.
authors.forename: Vilaas
authors.initials: V
authors.lastname: Shetty
authors.affiliation: Department of Neurological Surgery, Saint Louis University, Saint Louis, Missouri, United States of America.
authors.forename: Tina
authors.initials: T
authors.lastname: Vafaie
authors.affiliation: Department of Head and Neck Surgery, Saint Louis University, Saint Louis, Missouri, United States of America.
authors.forename: Jastin
authors.initials: J
authors.lastname: Antisdel
authors.affiliation: Department of Head and Neck Surgery, Saint Louis University, Saint Louis, Missouri, United States of America.
authors.forename: Tony A
authors.initials: TA
authors.lastname: Mikulec
authors.affiliation: Department of Neurology, Saint Louis University, Saint Louis, Missouri, United States of America.
authors.forename: Randall
authors.initials: R
authors.lastname: Edgell
authors.affiliation: Department of Neurological Surgery, Saint Louis University, Saint Louis, Missouri, United States of America.
authors.forename: Jonathan
authors.initials: J
authors.lastname: Lebovitz
authors.affiliation: Department of Neurological Surgery, Saint Louis University, Saint Louis, Missouri, United States of America.
authors.forename: Matt
authors.initials: M
authors.lastname: Pierson
authors.affiliation: Department of Neurological Surgery, Saint Louis University, Saint Louis, Missouri, United States of America.
authors.forename: Paulo Henrique
authors.initials: PH
authors.lastname: Pires de Aguiar
authors.affiliation: Center for Outcomes Research, Saint Louis University, Saint Louis, Missouri, United States of America.
authors.forename: Paula
authors.initials: P
authors.lastname: Buchanan
authors.affiliation: Department of Neurological Surgery, Saint Louis University, Saint Louis, Missouri, United States of America.
authors.forename: Angela
authors.initials: A
authors.lastname: Di Cosola
authors.affiliation: Department of Neurological Surgery, Saint Louis University, Saint Louis, Missouri, United States of America.
authors.forename: George
authors.initials: G
authors.lastname: Stevens
keywords: Aneurysms; endoscopy; internal carotid artery skull base; tumors