The trinity of the internal carotid artery: Unifying terminologies of the main classifications to improve its surgical understanding.

Background: The internal carotid artery (ICA) has multiple classification systems; it is essential for brain blood supply, which has bone/neurovascular relationships of wide neurosurgical interest; its anatomy must be known in detail, its angiographic-imaging aspect (endovascular), its ventral aspect (endoscopic endonasal approaches); and its lateral aspect (anterolateral skull base surgery). Our objectives were to identify coincidences/differences between the main classifications of the ICA to improve its surgical-anatomical understanding, unify the terminology of ICA segments, avoid confusion, and carry out a simple description. Methods: There are differences between classifications; however, these may overlap each other and determine the correspondence between segments, regardless of their purpose. Literature on ICA classifications was reviewed; a cadaver endonasal endoscopic and anterolateral skull base dissection was performed, obtaining representative images of the ICA, as well as angiography. The main terminology of ICA segments was collected, and artistic-anatomical illustrations were created to facilitate the study of ICA. Results: We compared the endoscopic roadmap to the ICA by Labib/Kassam, the extradural ICA at its lateral aspect by Cherian, and the classic classification by Bouthillier (as well as a small reference to the classification by Gibo/Rhoton). We found the shared characteristics and differences between classifications, with a total of 17 interrelated segments, with a variety of nomenclature and anatomical extension. Initially, we except the extradural ICA by Cherian because it uses almost the same nomenclature that Labib, varying in one segment, which coincides with the nomenclature of Bouthillier and does not change the total summary. The initial and terminal segments were nominative/anatomically equivalent, and there is anatomical nominal variation in the intermediate segments and its relation/correspondence has been easily demonstrated. Conclusion: Anatomical knowledge of all aspects of ICA using its main classifications, the relation between them, and its diversity of nomenclature is essential to improve its anatomical-surgical understanding and avoid anatomical nominal confusion. It can be achieved through our comparative tables/illustrations.