Ruling Out Internal Carotid Artery Agenesis in a Patient with Chronic Occlusion: A Case Report

Background/Objectives: This study presents a case of chronic internal carotid artery [ICA] occlusion initially misinterpreted as ICA agenesis on magnetic resonance angiography (MRA). The report underscores the importance of retrospective review of prior imaging, particularly computed tomography angiography [CTA], in establishing the correct diagnosis. Case Report: A 70-year-old man presented with persistent headache, pulsatile tinnitus, and intermittent dizziness. Neurological examination and laboratory results were unremarkable. Initial cranial MRA demonstrated absence of flow in the left ICA, raising suspicion of congenital agenesis. However, retrospective evaluation of a CTA performed nine years earlier revealed a well-formed left carotid canal without ICA opacification, confirming the diagnosis of chronic ICA occlusion. Results: Current imaging again showed lack of enhancement in the left ICA, with adequate cerebral perfusion supplied via the contralateral ICA and vertebrobasilar system. Recognition of the preserved carotid canal on earlier CTA clarified the diagnosis as chronic occlusion rather than agenesis. Although surgical or endovascular revascularization was recommended, the patient opted for conservative management. At three months of follow-up, symptoms had improved and clinical monitoring continues. Conclusions: This case underscores the importance of distinguishing ICA agenesis from chronic occlusion, particularly by evaluating the carotid canal on CT. The presence of a carotid canal strongly indicates prior patency of the ICA and supports a diagnosis of occlusion. Careful differentiation is critical to avoid misinterpretation and to guide appropriate clinical management. In addition, reviewing prior imaging can be valuable when current findings are inconclusive or potentially misleading. Since this is a single case report, these observations should be regarded as hypothesis-generating rather than definitive, and further studies are needed to validate their broader applicability.