Continued Flow in the Internal Carotid Artery Post Occlusion Due to an Aberrant Distal Branch
Article Outline
Abstract
We present the case of a patient who exhibited continued flow in the distal internal carotid artery (ICA) despite complete occlusion at the carotid bifurcation. Patency was maintained by the presence of an aberrant branch distal to the occlusion.
Keywords: Aberrant, Carotid, Occlusion
Introduction
The ICA is the major paired artery of the head and neck, supplying blood to the brain, eye and intracranial structures. It is a terminal branch of the common carotid artery, arising at the level of the third cervical vertebra when the common carotid artery (CCA) bifurcates to form the ICA and the external carotid artery (ECA), which supplies the face and scalp.
Unlike the ECA, the ICA gives off no branches in the neck.1 It traverses the skull base within the bony carotid canal and does not give rise to named branches until it finally divides within the cranial cavity to form the anterior and middle cerebral arteries.
Acquired atherosclerotic disease is the cause of ninety percent of extracranial carotid lesions.2 Embolisation from ulcerated atherosclerotic plaques is one of the mechanisms known to cause ischaemic strokes. Thrombosis and low cerebral flow rate are other possible aetiologies of stroke. Stroke is therefore a serious and potentially devastating complication of carotid stenosis and patients with such disease warrant consideration for carotid artery intervention. This decision is dependent on the degree of stenosis and the risk of future strokes.
ICA occlusion does not necessarily lead to complete disruption of cerebral flow due most commonly to cross circulation via the circle of Willis. An alternative is the shunting of blood from the ECA to the ICA by collateral pathways. Previous studies have reported that this alternative route may arise from one of several major branches of the ECA3, 4 with the occipital artery most commonly identified.5 Consequently, patients with complete occlusion of the ICA may present with different symptoms dependent on the condition of the collateral pathways for cerebral blood flow.
Report
A 49-year-old male whilst overseas suffered collapse associated with a right sided headache, dysarthria and left hemiparesis. He was a lifelong smoker (30 pack years) and moderate drinker with a family history of CVA. On admission his cholesterol was raised. CT scan at the time revealed a right middle cerebral artery infarct with mass effect necessitating an emergency craniectomy. The event was thought to be associated with an acute occlusion of the right ICA. The patient made a partial neurological recovery and returned to the UK.
In our hospital carotid duplex scan showed complete right carotid occlusion and no flow in the left ICA. Both CT and MRA scans confirmed complete right carotid occlusion extending from the skull base to the arch of the aorta and severe atheroma at the left carotid bifurcation. No lumen could be demonstrated at the left ICA origin, despite which contrast filling was detected distally (Fig. 1). Both vertebral arteries showed stenosis at their origin.
Figure 1
Magnetic resonance angiography of the carotid arteries. a. Left common carotid artery, b. Left external carotid artery, c. Left internal carotid artery occluded at bifurcation, d. Flow in left internal carotid artery distal to occlusion, e. Aberrant vessel feeding distal left internal carotid artery.
The images were discussed at a multidisciplinary meeting with input from surgeons, interventional radiologists and neurologists. Because there was evidence of precarious patency of the ICA, it was decided to proceed directly to surgical exploration on the next available list rather than await angiography.
At operation the left ICA was found to be completely occluded for two centimetres from the carotid bifurcation. Distal to this occlusion patency seemed to be maintained by flow in an anomalous extracranial branch arising three centimetres from the origin of the ICA. In retrospect, this was visible faintly on the MRA (Fig. 1e). A carotid endarterectomy and vein patch was performed and the patient made a good post-operative recovery. He was subsequently transferred for neurological rehabilitation.
Discussion
It is unusual for an apparently occluded ICA to be repaired with a good clinical outcome. This case demonstrates an anatomic rarity, an extracranial branch of the ICA providing a collateral pathway for ICA flow. This branch may have arisen from the occipital artery (Fig. 2) although this was not identified at operation.
Figure 2
Possible anatomy of aberrant branch of the internal carotid artery. a. Superior thyroid artery, b. Lingual artery, c. Facial artery, d. Posterior auricular artery, e. Occipital artery, f. Lower sternocleidomastoid branch, g. Aberrant ICA branch.
Anomalous extracranial branches of the ICA have been reported previously. Benson and Hamer4 describe a case similar to ours where an anomalous vessel arising from the ICA two centimetres from the carotid bifurcation preserved distal cerebral flow, shown to be antegrade on duplex scanning. Angiography showed this branch to arise from the occipital artery. Verbeeck et al. discuss the importance of accurate depiction of patency in the distal ICA since evidence of flow suggests a collateral supply which may permit surgical repair.6
Most anomalies of the carotid vasculature are asymptomatic and they may be more common than is documented in anatomical texts.1 Pre-operative detection by duplex ultrasonography has been reported.3, 6 This case underlines their potential importance in maintaining ICA patency in the presence of proximal occlusion.
Despite advances in carotid imaging, distinguishing occlusion, “trickle flow” or patency in the ICA may be problematic, particularly in the presence of advanced calcific atheroma at the bifurcation. This remains a grey area.7, 8 Whenever imaging provides some evidence of continued patency of the cervical ICA, operative exploration should be considered. Anomalous collaterals which can make reconstruction feasible may have been overlooked.
References
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- . Anomalous origin of the occipital artery from the cervical internal carotid artery. J Vasc Surg. 1988;8:643–645
- . The anatomy and clinical significance of the collateral circulation between the internal and external carotid arteries through the ophthalmic artery. Ital J Anat Embryol. 1993;98(1):23–29
- . Patent internal and external carotid arteries beyond an occluded common carotid artery: report of a case diagnosed by color Doppler. JBR-BTR. 1999;82(5):219–221
- Detection of total occlusion, string sign, and preocclusive stenosis of the internal carotid artery by color-flow duplex scanning. Am J Surg. 1995;170(2):154–158
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PII: S1533-3167(08)00022-8
doi:10.1016/j.ejvsextra.2008.09.002
© 2008 European Society for Vascular Surgery. Published by Elsevier Inc. All rights reserved.
