A lot of focus has been placed on the vertebrobasilar artery, due to its perceived anatomical vulnerability, but proper pre-manipulative screening has to include the internal carotid artery as well.
Reason being is that it supplies 80% of our blood flow to the brain andpathological changes are very common and blood flow in the internal carotid arteries is known to be influenced by movement of the neck.
The internal carotid artery arises from around level C3 where it bifurcates with the external carotid artery from the common carotid artery.
The course of the ICA runs through contractile structures, such as the sternocleidomastoid, longus capitis, stylohyoid, omohyoid and diagastric muscles.
The ICA is tethered to the anterior body of C1, which explains why mainly extension of the head and -less so- rotation will decrease blood flow through the artery.
The ICA supplies blood to the brain and the retina. The natural onset and progress of an ICA dissection usually begins with non-ischemic local signs and symptoms, which can precede cerebral or retinal ischemia from less than a week to beyond 30 days.
Early symptoms that you need to look for during your patient history-taking and physical assessment include:
- mid/upper cervical pain
- pain around the ear and the jaw and tenderness of the carotid artery, also called carotidinia
- head pain in the fronto-temporo-parietal area
- ptosis, which is a drooping or falling of the upper eyelid
- lower cranial nerve dysfunction of the nerves 8 till 12
- an acute onset of pain described like ‘unlike any other’.
These early signs and symptoms are followed by later ones which are:
- transient retinal dysfunctions, such as scintillating scotoma, which is an aura in the visual field
- amaurosis fugax, which is transient monocular blindness
- transient ischemic attacks
- cerebral vascular accidents
To sum it up:
It’s important to look for risk factors during patient history-taking and to be aware that early signs can mask as usual neck pain with headache. Physical examination of the cranial nerves, blood pressure measurement and sustained extension with or without rotation of the neck, like in the Extension-Rotation Test, can help you to categorize a patient into different risk profiles.
At last make a risk-benefit analysis to decide whether a cervical manipulation is indicated and refer the patient back to the GP immediately, if internal carotid artery dissection is suspected.