Rare case of congenital absence of left internal carotid artery.

Sir,

We present a rare case of congenital absence of left internal carotid artery and its possible implications.

A 42-year-old male with no significant past medical history, presented to the ED with a chief complaint of a dull, throbbing pain on the right side of the face, temple, and neck for 3 weeks. He denied any visual symptoms, numbness, or weakness in the extremities. His physical exam was unremarkable except for bounding carotid pulsations on the right side and no palpable pulse on the left. He did not have any elevation of inflammatory markers.

He underwent magnetic resonance imaging (MRI) of the brain that was unremarkable and MR angiogram of the head and neck that showed rare developmental anomaly with absence of the left internal carotid artery [Figure 1]. Absence of the carotid canal confirmed agenesis of the left internal carotid artery (ICA). Left hemispheric flow now was provided via collateralization by the right internal carotid artery and left posterior cerebral artery. There was mild enhancing soft tissue surrounding the right carotid bifurcation suggestive of an inflammatory process, likely the cause of his symptoms. He was started on an NSAID with subsequent resolution of his symptoms.

Figure 1

Absence of left internal carotid artery

Discussion

Absence of internal carotid artery is a rare congenital anomaly, occurring in less than 0.01% of the population. Congenital absence may be unilateral or bilateral, although the unilateral variant is more common.[1] Causes of unilateral absence are thought to be related to mechanical and hemodynamic stresses on the embryo in utero, with folding of the embryo toward one side or constriction by amniotic bands. No explanation for bilateral absence has been proposed thus far.[2]

While many patients remain asymptomatic due to robust collateral pathways, problems can arise later in life, particularly with progression of atherosclerotic disease. The absence of the carotid artery has also been associated with an increased incidence of cerebral aneurysms, which are reported to be 24-34%, compared to 2-4% in the general population. This is thought to be related to increased and altered flow dynamics though the collateral vessels.[3]

Although the exact etiology of the patient's symptoms remains unclear, we postulate that inflammation of the right carotid artery could be related to turbulent and shear forces on the arterial wall because of supplying the left hemisphere and compensating for the absence of the left anterior circulation system. Early recognition of the developmental abnormalities of the carotid circulation may have important implications, particularly in setting of thromboembolic disease, cerebral aneurysms, during carotid endarterectomy and risk stratification during carotid endarterectomy or transsphenoidal hypophyseal surgery.

Early recognition of developmental abnormalities of the carotid circulation may have important implications, particularly in the setting of thromboembolic disease, cerebral aneurysms, and risk stratification during carotid endarterectomy or transsphenoidal hypophyseal surgery.

Future prospective studies are needed to investigate whether carotid developmental anomalies are associated with higher risk of stroke and neurological complications.