Estimated prevalence at < 1.106. The absence of the internal carotid artery may result from agenesis or aplasia. The term 'agenesis' is used when the internal carotid artery and its bony canal are absent (there are remnants of the bony carotid canal in case of aplasia).

*        total agenesis of an internal carotid artery translates into the total absence of both the internal carotid artery and its bony  canal: it predominates in women and on the left side. The substitutive supply comes from the posterior communicating artery for the middle cerebral artery and from a large anterior communicating artery for the anterior cerebral artery. The precommunicating segment of the anterior cerebral artery (or A1 segment in the Fisher's classification) homolateral to the anomaly is often hypoplastic. Other anatomical variations are sometimes associated such as the presence of an accessory middle cerebral artery, a suboptic pathway of the precommunicating segment of the anterior cerebral artery or an ophthalmic artery originating from the middle cerebral artery or from the middle meningeal artery.

*        partial agenesis can affect any segment of the internal carotid artery with a predilection for the cervical segment. This anomaly, when it is unilateral, is located indefferently to the right or left side and preferentially affects men. The absence of the cervical segment of the internal carotid artery is defined by the existence of a substitutive blood supply by a large intercarotid artery vascularizing the carotid siphon and all the carotid branches, with the exception of the anterior cerebral artery. The topography of the anastomosis is variable: intrasellar, intra or retroclival. Other anomalies frequently coexist, such as an aneurysm of the anterior communicating artery or hypoplasia of the homolateral precommunicating segment of the anterior cerebral artery.

This anomaly is associated with an increased risk of intracranial aneurysm (24-34 % of cases compared to an incidence of 2-4 % in the general population).

It is usually asymptomatic and discovered by chance. When symptoms are present, they are related to cerebral ischemia, pressure exerted by the compensatory dilatation of the other intracranial vessels, or the presence of an aneurysm. Sometimes: transitory ischemic attacks, stroke.

The cerebral arterial blood supply is ensured via the polygon of Willis and small collateral arteries surrounding the homolateral internal jugular vein.

Anesthetic implications:

risk of intra- or extracranial aneurysm; puncture of the jugular vein and supraclavicular blocks of the brachial plexus should be echoguided.

References : 

-        David H, Dubayle P, Girodeau A, Sarrazin JL, Boyer B.
Agénésie de l’artère carotide interne: à propos de deux cas.
J Radiol 2000; 81: 147-50.

-        Rambhia MT, Kamenetsky E.
Perioperative clinical considerations in a patient with carotid agenesis : a case report.
A&A Practice 2019; 12:388-9.

Updated: July 2019