The basilar artery and internal carotid arteries contribute to the ring-shaped anastomosis.
The ICA ascends within the cavernous sinus after entering the skull base through the carotid canal in the petrous region of the temporal bone. It passes over the anterior clinoid process and divides into the middle cerebral artery and ACA (MCA).
According to Bouthillier, the seven ICA segments are classified as C1-cervical, C2-petrous, C3-lacerum, C4-cavernous, C5-clinoid, C6-ophthalmic, and C7-communicating (Bouthillier, van Loveren, & Keller, 1996). But when talking about ICA pathology, anatomical and microsurgical landmark-based ICA subdivisions are most frequently used.
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