Explain the pathway of the internal carotid artery.

Question

The answer to this question will include the four different classifications of the internal carotid artery, as well as the different spaces/bony landmarks that will indicate which section of the internal carotid artery you are dealing with.

Answer 1

This is a very good question regarding the anatomy of the ICA. I would only add to the previously posted expert answer that looking at the structure/function correlate of the ICA, my thinking is to understand the ICA once it passes through the foramen lacerum into the brain.

This final distal route of the ICA is its communicating segment that becomes the posterior communicating arteries and then dividing into the anterior and middle cerebral arteries.

The middle cerebral arteries (MCA) supply most of the lateral surface of the cerebral hemispheres, except the medial/superior contours of the frontal lobe and superior contour of the anterior parietal lobe which are supplied by the anterior cerebral artery (ACA) and the inferior contour of the temporal/occipital lobes supplied by the posterior cerebral artery (PCA).

Study of the ACA is significantly relevant for understanding saccular and dissecting aneurysms, called berry aneurysms (BA). The important anatomical correlate here is the anterior communicating artery that connects the two ACAs. This communicating artery is relatively small and permits collateral blood flow into the contralateral hemisphere if the ICA is occluded or stenotic on either side. Because this is a collateral communicating and connecting artery, it is also not uncommon for arteriovenous malformations (AVM) to occur.

  

The clinical significance of BA/AVM of the anterior communicating artery where it joins the ACA is quite important in the construct sequelae of cerebral ischemic and/or thrombotic events in stroke, presenting as a lightning bolt headache, visual disturbances, unilateral facial paresthesia/weakness, loss of balance, difficulty speaking, and memory problems.

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Answer 2

We will start in the neck and head superiorly. This is where the common carotid artery, located in the carotid sheath, bifurcates into the external carotid artery and the internal carotid artery (ICA).

1. From here, the ICA travels up the remainder of the neck, where it is denoted as the cervical portion of the ICA.
2. Once the cervical ICA reaches the base of the skull, it travels through the carotid canal in the temporal bone. While it is traveling through this canal, the cervical ICA changes its name to the "petrous" portion of the ICA. An easy way to remember this is because the temporal bone is one of the densest and hardest bones in your body. Petrosus in Latin means "rock-like", meaning that the ICA is traveling through a stone like structure. To recap, the ICA enters the base of the skull through the carotid canal, which is in the petrous part of the temporal bone.
3. Next, the petrous ICA continues to travel superiorly and anteriorly once in the cranial cavity. From here, it travels along the body of the sphenoid in what is called the cavernous sinus. Remember, sinuses in the skull are sort of tunnel like structures, where the roof is made of dura mater. So to sum it up, once the ICA leaves the carotid canal, it travels along the body of the sphenoid where it is denoted as the "cavernous" portion of the ICA.
4. As the cavernous ICA continues to travel along the body, it makes a sharp 180 degree turn from heading anteriorly to heading posteriorly and superiorly. Once it leaves the cavernous sinus which is indicated as it passes through the dural layer, it continues superiorly passing the optic chiasm and heading towards the brain. It is this portion between the it leaving the cavernous sinus and before it branches into the anterior and middle cerebral arteries (parts of the circle of Willis) that is denoted as the "cerebral" portion of the ICM.