The carotid canal is an important route within the temporal bone (temple) of the head. This canal provides a passage for the internal carotid artery (ICA) that circulates blood mainly to the brain, along with some autonomic nerves that are attached to the artery. Lower opening of the canal is referred to as the carotid foramen. The canal has a slightly zigzag path which finally opens into the cranial cavity; the middle cranial fossa in particular. Some exceptional conditions are also associated with carotid canal that are discussed later.
Two main structures pass through the carotid canal:-
- Internal Carotid Artery (ICA): ICA is a major artery that arises from the division of common carotid artery and transmits blood mainly to the brain and eyes.
- Internal Carotid Plexus (Sympathetic Nerves): This network of nerve fibers is attached with the internal carotid artery, largely inside the carotid canal. Internal carotid plexus communicates with other nerves to carry out its autonomic functions.
Clinical Importance – Associated Conditions & Diseases
Some conditions arise from complications related to the canal. Most important, yet not so common conditions are discussed below:-
Moyamoya disease is characterized by one-sided weakness of the body, blurry vision, slurring of speech, seizures and headache, and caused by constriction of arteries supplying blood to the brain. It is a rare disease and occurs most frequently in early childhood when the carotid canal is still developing, although developing abnormally in Moyamoya disease. Latest research suggests an origin associated with abnormally developed narrow canal which constricts the internal carotid artery, hence producing the symptoms.
Carotid Canal Fracture
Fractures of the canal following head trauma, usually linked with cranial fractures of the base of skull by serving as their extension. This can rupture or occlude the internal carotid artery (ICA) which can result in hemorrhage and finally stroke (cerebral infarction). It has been found that head injuries involving carotid canal fractures are more severe in nature.
Compression of Carotid Canal by Cochlea
Cochlea is a part of inner ear concerned with hearing and lies in close proximity with the carotid canal. Cochlea can cause compression of carotid canal and ultimately the occlusion of internal carotid artery (ICA). Although the chances of this situation are very low, still it can be clinically relevant where it can cause stroke in worst cases, or at least loss of consciousness, due to reduced blood supply to the brain.
Congenital Absence of Carotid Canal
Rarely it happens that carotid canal fails to develop (agenesis) during fetal life in one or both sides. This also directly results in the absence of internal carotid artery (ICA), hence causing abnormalities of the Circle of Willis, which is the main arterial network of supplying blood to the brain, with aneurysm being the most common complication. Branches of internal carotid artery (ICA) contribute numerous branches to form Circle of Willis. Congenital absence of carotid canal is typically caught on a CT scan while investigating an unrelated abnormality.
Clinical Anatomy by Regions – Richard S. Snell, 9th Ed, The Head And Neck
Gray’s Anatomy, 40th Ed, Section IV, Head And Neck