Atherosclerosis of Intracranial Internal Carotid Artery Causing Embolic Ocular Events

Embolic disease to the eye often indicates carotid artery disease. Although most of the time the culprit is atherosclerotic disease in the common carotid arteries in the neck, we describe 2 cases where the embolic source was intracranial carotids. CASE 1 A 55-year-old man with past medical history of Type 2 diabetes, hypertension, and hyperlipidemia noticed gradually worsening vision in the right eye (RE) for the past 2 months. Examination demonstrated one peripapillary hemorrhage and several plaques in the retinal circulation RE. Carotid Doppler ultrasound was interpreted as normal. Referral to his family physician for evaluation of thromboembolic source was made on an elective basis. He subsequently developed ocular pain and was referred to our service. Visual acuity was hand motions RE and 20/30 left eye (LE) with right relative afferent pupillary defect (RAPD). Intraocular pressures were 28 and 11 mmHg. There was iris neovascularization visible on biomicroscopic examination RE. Funduscopy demonstrated pale right optic nerve with associated retinal whitening, box-carring of the retinal arterioles and several peripapillary hemorrhages (Fig. 1A). Diagnosis of central retinal artery occlusion (CRAO) and ocular ischemic syndrome (OIS) complicated by neovascular glaucoma was made. Echocardiogram, Holter monitor and brain MRI were unrevealing, but brain and neck computed tomography angiography (CTA) and magnetic resonance angiography (MRA) demonstrated high-grade stenosis of the right intracavernous internal carotid artery (ICA) and moderate stenosis of the distal right ICA (Fig. 1B).FIG. 1.: A. Fundus photo of the right eye demonstrating optic nerve pallor and severe arteriolar attenuation and nonperfusion. B. Computed tomography angiography image, coronal view through cavernous sinus, demonstrating severe stenosis of the right intracavernous carotid artery (blue arrows).CASE 2 A 58-year-old man complained of transient vision loss 3 times in the previous 2 months in his RE only. The peripheral visual field tunneled down to a small central island surrounded by complete blackness over the course of seconds and returned after approximately 5 minutes. He denied pain, headache, jaw claudication, weight loss, anorexia, and arthralgias. Past medical history was significant for depression, migraine with aura, systemic lupus erythematosis, coronary artery disease status post-triple bypass, hypertension, hypercholesterolemia, obstructive sleep apnea, idiopathic thrombocytopenia, and chronic kidney disease. On examination, central vision was 20/20 in each eye. There was no RAPD. Fundoscopy demonstrated no plaques or other retinal pathology. Automated perimetry was normal. Brain MRI was unremarkable; however, brain and neck MRA showed normal cervical carotid arteries, but >80% narrowing of the right intracavernous ICA. Cerebral angiography confirmed these findings and did not show evidence of vasculitis (Fig. 2A). ESR and CRP were normal. Three months after initial presentation, patient awoke with persistent tunneling of his visual field RE. Acuity was 20/40 RE, but fundus examination demonstrated CRAO with the plaque visible in the CRA and cilioretinal sparing (Fig. 2B).FIG. 2.: A. Digital subtraction angiography of the right carotid artery demonstrating severe stenosis of its intracavernous portion (blue arrow). B. Fundus photo demonstrating general retinal whitening with the sparing of cilioretinal artery with the thrombus visible in the central retinal artery at the optic nerve head.These 2 cases demonstrate the importance of evaluating the entire carotid tree, including the intracranial circulation, in patients with evidence of thromboembolic disease (amaurosis fugax, CRAO, OIS). Doppler ultrasonography of the neck is the main recommended diagnostic modality when evaluating patients with signs of OIS; however, the stenosis or complete blockage of carotid circulation could occur anywhere from the bifurcation of ICA to the ophthalmic artery (1,2). Although atherosclerosis of the carotid arteries in the neck is the most common cause of thromboembolic disease affecting the brain (and the eye), ICAS deserves consideration in the absence of significant stenosis of the neck vessels in all patients with OIS and/or thromboembolic complications in the ocular circulation (2). Doppler ultrasound of the neck is the most common modality used when thromboembolic and/or ischemic complications in the ocular circulations are encountered with other less commonly used modalities including CTA and MRA and occasionally digital subtraction angiography (DSA) of the brain and neck (1). Several studies compared the accuracy of these modalities in detecting atherosclerotic disease in the neck. When compared with histological specimens, CTA was found to have the strongest correlation with atherosclerotic disease, but underestimated the stenosis by 2.4%, whereas MRA overestimated it by 2.6% (3). Bash et al (4) compared sensitivity of DSA to CTA and MRA in detecting ICAS and found that CTA had a higher sensitivity than MRA for intracranial stenosis, a higher positive predictive value and higher interoperator reliability. The treatment for extracranial carotid artery stenosis is based on the findings of North American Symptomatic Carotid Endarterectomy (NASCET) trial recommending carotid endarterectomy (CEA) in symptomatic carotid artery stenosis of 70%–90% and in asymptomatic stenosis Aggressive medical treatment with or without stenting in high-risk patients with intracranial artery stenosis (SAMMPRIS) trial and VISSIT (Vitesse Intracranial Stent Study for Ischemic Stroke Therapy) trials compared aggressive medical management (antiplatelet therapy, management of vascular risk factors and lifestyle modification) against aggressive medical management and Wingspan/Vitesse stents in patients with high-grade stenosis of intracranial circulation. Both trials were prematurely terminated and demonstrated increase risk of stroke or death in patients treated with stenting compared with the medically treated group (5).The most recent recommendation from a meta-analysis of all recent trials concluded that stenting should be considered only in symptomatic ICAS patients that are hemodynamically unstable or have repeatedly failed best medical management (6). Although it is well known that CRAO and OIS are associated with extracranial carotid artery stenosis, their association with ICAS is not well appreciated. These 2 cases underline the importance of investigating the entirety of the internal carotid blood supply, because the stenosis or occlusion may occur in the intracranial portions of carotid circulation rather than the extracranial ICA. Although Doppler ultrasound has high sensitivity for picking up extracranial stenosis, if it is normal in patients demonstrating evidence of ocular thromboembolic disease or ocular hypoperfusion such as CRAO or OIS, CTA or MRA of the brain and neck should be obtained to evaluate the patency of the intracranial circulation as the source of thromboembolic disease and ocular hyperperfusion. Although treatment of intracranial carotid stenosis is mostly medical, selected patients may benefit from stenting of the sites of intracranial stenosis. STATEMENT OF AUTHORSHIP Category 1: a. Conception and design: E. Margolin and M. Lee; b. Acquisition of data: E. Margolin and M. Lee; c. Analysis and interpretation of data: E. Margolin and M. Lee. Category 2: a. Drafting the manuscript: L. Tong, E. Margolin, and M. Lee; b. Revising it for intellectual content: E. Margolin, M. Lee, and L. Tong. Category 3: a. Final approval of the completed manuscript: E. Margolin, M. Lee, and L. Tong.

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