Proposed clinical internal carotid artery classification system
Saleem I Abdulrauf1, Ahmed M Ashour1, Eric Marvin1, Jeroen Coppens1, Brian Kang1, Tze Yu Yeh Hsieh1, Breno Nery1, Juan R Penanes1, Aysha K Alsahlawi1, Shawn Moore1, Hussam Abou Al-Shaar1, Joanna Kemp1, Kanika Chawla1, Nanthiya Sujijantarat1, Alaa Najeeb1, Nadeem Parkar2, Vilaas Shetty2, Tina Vafaie1, Jastin Antisdel3, Tony A Mikulec3, Randall Edgell4, Jonathan Lebovitz1, Matt Pierson1, Paulo Henrique Pires de Aguiar1, Paula Buchanan5, Angela Di Cosola1, George Stevens1
1 Department of Neurological Surgery, Saint Louis University, Saint Louis, Missouri, United States of America
2 Department of Radiology, Saint Louis University, Saint Louis, Missouri, United States of America
3 Department of Head and Neck Surgery, Saint Louis University, Saint Louis, Missouri, United States of America
4 Department of Neurology, Saint Louis University, Saint Louis, Missouri, United States of America
5 Department of Center for Outcomes Research, Saint Louis University, Saint Louis, Missouri, United States of America
Saleem I Abdulrauf
Department of Neurosurgery, Saint Louis University, 3635 Vista Avenue, 5-FDT, Saint Louis, MO
United States of America
Source of Support: None, Conflict of Interest: None
Introduction: 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.
Materials and 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.