A carotid artery aneurysm (CAA) is a section of the carotid artery that is swollen towards the outside, due to a weakness in the wall. These aneurysms can be found in all three branches, the common, internal and external carotid artery, and can occur both extracranially and intracranially.
The carotid artery is divided into three segments: the common carotid artery and the internal and external carotid artery. The latter two, the internal and external are the two branches into which the common carotid artery is divided, at the level of the 4th cervical vertebra (carotid bifurcation). Anyone of these segments can be affected with an aneurysm; the internal carotid artery is the one most prone to aneurysms. Based on their location, CAAs are divided into intracranial and extracranial and lead to different symptoms. Very small aneurysms or larger aneurysms that do not exert pressure or influence adjacent structures in any way may remain asymptomatic in both cases.
It has been reported that, on average, 2,5% of the population is affected by an intracranial carotid artery aneurysm, most of which lead to no significant clinical manifestations . The symptoms greatly depend on the specific location of the aneurysm and indicate a neurological, cerebral pathology. Intracranial CAAs may manifest with diplopia, persistent headaches, and cranial nerve palsy, such as a palsy of the abducens nerve (VI cranial nerve) . An aneurysmal rupture is a medical emergency and patients present with complaints related to a hemorrhagic stroke or subarachnoid hemorrhage; death may even ensue . A hemorrhagic stroke will manifest with focal deficits, such as a facial droop, visual impairment or aphasia, alongside a decreased level of consciousness, nausea, and vomiting. Subarachnoid hemorrhage usually causes photophobia, intense headache, meningismus signs or fainting. Aneurysms that have a diameter of over 2,5 cm have a 50% chance of rupturing .
Extracranial CAAs are a rare medical occurrence. Affected cases are expected to exhibit symptoms related to a transient ischemic attack (TIA), as transient strokes are caused by aneurysmal emboli  . A transient ischemic attack is a stroke whose symptoms last for a brief period of time and may involve a variety of deficits, including loss of orientation and confusion, lightheadedness, ataxia, numbness of one body side, memory disturbances and other symptoms . Although a TIA stops producing signs after minutes or a few hours, patients have an augmented risk of stroking severely in the near future. Extracranial aneurysms located in the common carotid artery may also present as a mass in the neck area.
Carotid artery aneurysms may be asymptomatic or symptomatic. Asymptomatic ones may be incidentally diagnosed during evaluation carried out for another cause, by means of a brain or cervical computerized tomography scan (CT) or magnetic resonance imaging scan (MRI) . Other imaging modalities that may be employed to diagnose symptomatic carotid artery aneurysms include a CT or MRI scan as well as diffusion-weighted imaging (DWI), magnetic resonance angiography (MRA) and T2-weighted imaging (T2WI). The final precise diagnosis is rendered possible by means of an arteriography, which allows for the comprehensive assessment of the cerebral and cervical vessels .