Subclavian steal syndrome

INTRODUCTION — The term "subclavian steal" refers to a phenomenon of flow reversal in the vertebral artery (figure 1) ipsilateral to a hemodynamically significant stenosis or occlusion of the prevertebral subclavian artery (subclavian, innominate) [1-3]. This represents an appropriate physiologic response to proximal arterial disease. Most individuals who exhibit this phenomenon are asymptomatic. Subclavian steal syndrome implies the presence of significant cerebrovascular symptoms due to arterial insufficiency in the brain.

The physiology, diagnosis, and treatment of subclavian steal syndrome are reviewed. Asymptomatic presentations and upper extremity ischemia associated with upper extremity atherosclerotic disease are reviewed separately. (See "Upper extremity atherosclerotic disease".)

General considerations for patients with symptoms of vertebrobasilar ischemia are discussed in detail elsewhere. (See "Posterior circulation cerebrovascular syndromes".)

DEFINITION AND PHYSIOLOGY — Subclavian steal syndrome refers to the presence of significant cerebrovascular symptoms ipsilateral to a hemodynamically significant stenosis or occlusion of the prevertebral subclavian (or innominate) artery (figure 2). Neurologic symptoms can be caused by vertebrobasilar ischemia of the brainstem and cerebellum. (See 'Clinical features' below.)

●Hemodynamic changes – Subclavian artery occlusion or a hemodynamically significant stenosis proximal to the origin of the vertebral artery results in lower pressure in the subclavian artery distal to the obstruction [4,5]. As a result, blood flow in the ipsilateral vertebral artery may be reversed, supplying collateral blood flow to the arm. Blood flow in the basilar artery may be reversed in some cases (figure 1) [6-8]. Reversed vertebral artery flow, although serving as an important collateral artery for the arm in this setting, may concurrently have deleterious neurovascular or coronary effects. Although patients with documented subclavian steal physiology have a very low incidence of vertebrobasilar circulation ischemic events, they are more likely to develop symptoms as the blood pressure differential between the upper limbs increases [9].

●Importance of collateral flow – The presence of collateral blood supply and the capacity to increase collateral flow may be the principal determinants of which patients with steal physiology develop symptoms. Cerebrovascular symptoms tend to develop in the context of concurrent cerebrovascular lesions. Anomalies of the circle of Willis (figure 2), the most important collateral route in the cerebrovascular circulation, occur with increased frequency in patients with subclavian steal syndrome [10]. (See "Upper extremity atherosclerotic disease", section on 'Collateral circulation'.)

●Retrograde basilar blood flow – Bilateral vertebral flow reversal is very uncommon and indicative of retrograde collateral basilar artery flow from the carotid system via one or both posterior communicating arteries. Such a persistent pattern of retrograde flow in the basilar artery has been reported in patients without any overt neurovascular or upper extremity symptoms [11]. However, upper limb exercise may precipitate neurovascular symptoms that may differ in magnitude and duration [12].

ETIOLOGY

Atherosclerotic disease — Atherosclerosis is by far the most common cause of subclavian (or innominate) artery stenosis or occlusion [13,14]. The risk factors associated with atherosclerosis are discussed elsewhere. (See "Overview of established risk factors for cardiovascular disease" and "Upper extremity atherosclerotic disease".)

Among individuals with documented peripheral atherosclerotic disease, the prevalence of upper extremity atherosclerotic disease is much lower than in the lower extremities. Approximately 30 percent of such patients have subclavian artery stenosis; however, only a minority develop symptoms, predominantly because of the extensive collateral network of vessels around the shoulder (figure 3) [8].

Most individuals referred for noninvasive vascular imaging who have incidentally identified subclavian steal physiology are asymptomatic [9]. In a review that identified subclavian stenosis/occlusion in 432 of 7881 patients presenting for ultrasound exam of the extracranial neck vessels, only 38 (8.8 percent) experienced symptoms (32 with vertebrobasilar circulation symptoms) [9].

Subclavian stenosis and therefore subclavian steal syndrome occurs more commonly on the left side (>75 percent), possibly due to a more acute origin of the left subclavian artery, resulting in accelerated atherosclerosis from increased turbulence [4,9,15-18]. However, right-sided subclavian steal syndrome can occur and may indicate innominate artery stenosis [19-21].

Other vascular causes — Other conditions that can result in subclavian obstruction and may lead to subclavian steal include:

●Takayasu arteritis – These patients typically present at a younger age compared with patients with atherosclerotic disease [22,23]. The prevalence of Takayasu arteritis is highest in Asia. (See "Clinical features and diagnosis of Takayasu arteritis".)

●Giant cell arteritis – This is a rare cause of subclavian stenosis [24,25]. (See "Clinical manifestations of giant cell arteritis", section on 'Large vessel involvement'.)

●Arterial thoracic outlet syndrome – Compression of the subclavian artery in the thoracic outlet can result from variant anatomy including an anomalous rib or aberrant musculotendinous attachments (figure 4). The site of arterial compression in thoracic outlet syndrome is most often distal to the origin of the vertebral artery. Therefore, the potential for symptomatic steal is overall low. These patients can have posterior circulation strokes due to retrograde propagation of thrombus. Athletes, such as baseball pitchers, cricket bowlers, and swimmers, are the most likely to be affected due to neurovascular compression as the subclavian artery crosses over the first rib. (See "Overview of thoracic outlet syndromes", section on 'Arterial TOS'.)

●Congenital anomalies – Congenital abnormalities that can cause subclavian steal syndrome include anomalies of the aortic arch (eg, right aortic arch with isolation of the left subclavian artery, Kommerell diverticulum) and anomalies of the brachiocephalic arteries [26-32]. (See "Vascular rings and slings" and "Overview of aneurysmal disease of the aortic arch branches or upper extremity arteries in adults", section on 'Kommerell diverticulum (aneurysm of aberrant proximal subclavian artery)'.)

●Consequence of corrective surgery – Subclavian steal syndrome can also occur following:

•Surgical repair of coarctation of the aorta [33]. (See "Management of coarctation of the aorta", section on 'Surgery'.)

•Surgical repair of tetralogy of Fallot with a Blalock-Taussig anastomosis [34]. (See "Tetralogy of Fallot (TOF): Management and outcome".)

●Hemodialysis vascular access associated – The creation of a hemodialysis arteriovenous access distal to a previously unknown prevertebral stenosis can precipitate symptoms of subclavian steal syndrome due to the alterations in flow induced by the fistula [35-37]. Vertebrobasilar and coronary symptoms in those with vascular access and prior coronary artery bypass grafting can also occur without significant subclavian/innominate stenosis. (See "Hemodialysis access-induced distal ischemia" and "Arteriovenous fistula creation for hemodialysis and its complications", section on 'Coronary steal'.)

EPIDEMIOLOGY — The prevalence of subclavian steal syndrome has not been well defined, although subclavian steal physiology has been reported in 1.3 to 2.6 percent of general populations of patients with extracranial atherosclerosis [38,39], as well as within subsets of those presenting with acute ischemic stroke [40]. The prevalence increases with age in parallel with the increased prevalence of atherosclerosis. (See "Upper extremity atherosclerotic disease", section on 'Chronic upper extremity ischemia'.)

CLINICAL FEATURES — Neurologic symptoms are uncommon manifestations of subclavian or innominate artery stenosis/occlusion. Patients who manifest cerebrovascular symptoms may or may not also exhibit symptoms of upper limb ischemia or evidence of coronary ischemia (ie, those with internal mammary grafts). (See "Upper extremity atherosclerotic disease", section on 'Chronic upper extremity ischemia' and "Upper extremity atherosclerotic disease", section on 'Coronary-subclavian steal'.)

Cerebrovascular manifestations — Neurologic symptoms can be caused by vertebrobasilar ischemia of the brainstem or the cerebellum. Ischemic neurologic symptoms associated with subclavian steal syndrome can include dizziness/vertigo, binocular double vision, incoordination, dysarthria, syncope, or drop attacks (sudden fall without loss of consciousness) [13]. Symptoms are clustered into transient, paroxysmal, and stereotypical (ie, like each other in semiology) episodes that may be precipitated by exercise of the ischemic arm. The latter, when present, constitutes a very good indicator of the diagnosis of subclavian steal, while its absence does not exclude it.

Some of the symptoms of vertebrobasilar ischemia, such as headaches and dizziness (by far the most common neurologic symptom of subclavian steal syndrome), can be vague and difficult to interpret. In this context, dizziness always warrants some diagnostic consideration regardless of whether it represents lightheadedness (ie, presyncope) from poor overall brainstem perfusion (ie, hemodynamic compromise of the reticular activating system) or bona fide vertigo (ie, ischemia of the labyrinthine apparatus or its brainstem connections). In fact, isolated vertigo has been known to herald vertebrobasilar insufficiency under a variety of clinical contexts [41-43]. Other more specific neurovascular symptoms such as binocular double vision, decreased vision, oscillopsia, or incoordination (ie, equilibratory or appendicular), with or without accompanying physical findings, increase the likelihood of the patient having vertebrobasilar ischemia. (See "Posterior circulation cerebrovascular syndromes".)

Neurovascular symptoms can be precipitated by certain head movements capable of inducing vertebral artery compression (eg, "bow hunter" syndrome), such as rotation toward the opposite side or extension while reaching for items on a top shelf [44-50].

Atypical neurologic presentations — There is also increasing recognition that patients with vertebrobasilar insufficiency can present with other types of symptoms not directly attributable to brainstem or cerebellar ischemia but that merit diagnostic consideration:

●Subarachnoid hemorrhage – The hemodynamic changes that accompany subclavian steal syndrome have been reported to have the potential to induce the development and growth of vertebrobasilar junction cerebral aneurysms, with their corresponding risk of rupture and the development of subarachnoid hemorrhage [51-54]. These patients may not have any specific symptoms unless the aneurysm was to rapidly expand or rupture. (See "Aneurysmal subarachnoid hemorrhage: Clinical manifestations and diagnosis".)

●Cognitive and mood abnormalities – In the author's clinical experience, subclavian steal syndrome may be associated with neuropsychologic (eg, visuospatial and executive) and mood abnormalities (eg, depression), detectable by bedside testing (ie, Montreal Cognitive Assessment or Hamilton Depression Rating Scale), which are potentially reversible by revascularization. These abnormalities are analogous to those reported with chronic vertebrobasilar ischemia [55,56]. This is an important departure from the historically "classic" interpretation of cerebrovascular ischemic events and constitutes a fertile field for further study.

EVALUATION — Although neurovascular symptoms associated with subclavian steal physiology occur in only a minority of patients, symptoms of vertebrobasilar ischemia demand critical evaluation [57-61]. Stroke risk reduction in these patients may require preemptive intervention and correction of the underlying hemodynamic derangement [62-66]. (See 'Vascular intervention' below.)

When to suspect subclavian steal — The diagnosis of subclavian steal syndrome should be considered in patients with a measurable upper extremity blood pressure differential who develop episodic neurologic symptoms attributable to brainstem or cerebellar ischemia (eg, dizziness/vertigo); suspicion is increased if the episodes are provoked by arm exercise, especially if accompanied by ischemic arm symptoms [13].

Physical examination — All major pulses should be palpated, and blood pressure should be checked in both arms. Bruits may originate from the anterior (carotid) or posterior (subclavian/vertebral) circulation. It is important to examine the subclavian arteries in the supraclavicular fossa using palpation (pulse character and thrills) and auscultation for paraclavicular bruits. The carotid arteries should also be carefully examined, using palpation and auscultation, for evidence of occlusive arterial disease. Auscultation over the suboccipital region for vertebral artery bruits should also be performed.

On examination, there may be a significant decrease in brachial blood pressure on the affected side with a pulse delay appreciated when palpating the radial arteries simultaneously (waveform 1). The presence of concurrent pulse deficits (subclavian and carotid) raises the possibility of Takayasu disease. (See "Clinical features and diagnosis of Takayasu arteritis".)

The skin of the hands and nail beds of the affected extremity should also be thoroughly examined for evidence of atheroembolism. (See "Embolism to the upper extremities".)

Initial vascular imaging — We use duplex ultrasound (combined two-dimensional ultrasound and pulsed-wave Doppler) as the initial screening study for patients with suspected subclavian steal. A difference in upper extremity blood pressure in a patient with appropriate cerebrovascular symptoms suggests subclavian steal syndrome; however, vascular imaging is necessary to confirm the vascular lesion. Noninvasive imaging of the cerebrovascular and upper extremity arterial circulation demonstrates the lesion and appropriate physiology. Whether the vascular lesion is the cause of the cerebrovascular symptoms is a matter of judgment and is discussed below. (See 'Management' below.)

●Duplex ultrasound – Duplex ultrasound can suggest the presence of subclavian artery stenoses and demonstrate reversal of flow, if present, in the ipsilateral vertebral artery (image 1). A subclavian artery peak systolic velocity >240 cm/second is predictive of a significant (>70 percent) subclavian artery stenosis [67]. Duplex ultrasound is limited in the evaluation of the origin of the subclavian artery for evidence of occlusive disease due to its intrathoracic location. Duplex is also extremely accurate for the assessment and identification of significant extracranial carotid artery occlusive disease, which may occur in conjunction with subclavian lesions. (See "Upper extremity atherosclerotic disease", section on 'Duplex ultrasound'.)

When severe stenosis (>80 percent narrowing) of the proximal subclavian artery is present, 65 percent of patients have permanent flow reversal in the ipsilateral vertebral artery, and 30 percent have intermittent flow reversal (ie, "to-and-fro" waveform pattern on duplex) [57,68]. In patients with moderate subclavian artery stenosis (approximately 50 percent narrowing), flow reversal in the vertebral artery is constant in 56 percent and intermittent in 36 percent. Some vascular laboratories use provocative testing in patients with to-and-fro vertebral flow, but this more often encountered in patients without symptoms and is reviewed separately. (See "Upper extremity atherosclerotic disease", section on 'Duplex ultrasound'.)

●Transcranial Doppler ultrasound – When flow reversal of the vertebral artery is identified, some authors have suggested the use of transcranial Doppler to evaluate the direction of flow in the basilar artery [58]. A finding of reversed flow at the level of the basilar artery has been shown to correlate with clinical symptoms more than reversal of flow in the isolated vertebral artery only. In one study of patients with flow reversal of the vertebral artery ipsilateral to a subclavian stenosis/occlusion, 76 percent had antegrade flow in the basilar artery [68]. Patients with antegrade flow in the basilar artery are less likely to have symptoms.

Confirmatory vascular imaging — In most cases, the diagnosis can be confirmed with angiographic imaging, using either noninvasive methods (ie, computed tomographic angiography [CTA] or magnetic resonance angiography [MRA]) [13,14,37] or catheter-based digital subtraction angiography (DSA). While duplex ultrasound is the first-line imaging modality for the detection of subclavian stenosis causing subclavian steal syndrome, it cannot reliably evaluate the origin of the aortic branches or the intracranial vessels.

●CTA – Multidetector CTA provides excellent imaging of the thoracic, cervical, and cerebral vessels and provides precise measurement of the severity of stenosis. In addition, it can reveal concurrent pathology involving the extracranial and intracranial arteries. Its main drawback is the absence of dynamic flow information. CTA is indicated for patients with subclavian steal syndrome who have abnormal or nondiagnostic findings on duplex ultrasound to identify and characterize the underlying pathology and any anatomic abnormalities [9,69]. It can also help to identify not only stenoses, but thrombosis, occlusion, aneurysm formation, and vasculitic changes within the subclavian artery [70].

●MRA – Gadolinium-enhanced phase-contrast MRA provides excellent image quality for the supra-aortic arteries [71]. Its sensitivity for the detection of arterial stenoses is comparable with that of CTA and catheter-based angiography, although it lacks equivalent specificity [72,73]. Since MRA does not depict images of arterial anatomy but rather the behavior and speed of flowing protons within the vessels, there is a general tendency to overestimate the degree of hemodynamic compromise caused by arterial lesions, which becomes particularly significant under conditions of very low flow (ie, occlusion versus near occlusion).

Flow reversal in the vertebral artery ipsilateral to a subclavian stenosis is inferred from presence of vertebral artery patency on three-dimensional contrast-enhanced MR, but absence of flow on time-of-flight localizer images [74]. In addition to evaluation of the extracranial vessels, MRA also provides information of the intracranial cerebrovascular circulation and, since it can be carried out sequentially with brain imaging, it allows interrogation of brain parenchyma and the identification of relevant ischemic injury, or alternative diagnoses.

The introduction of the ability to provide flow quantification using MR imaging techniques has improved the ability to assess the impact of steno-occlusive pathology of the vertebrobasilar system [75,76]. In addition, it has created a framework to improve risk stratification, and may at some point in the future allow a more precise treatment allocation, even in patients with subclavian steal [77,78].

●DSA – DSA (image 2) is generally not necessary to establish a diagnosis of subclavian steal syndrome. However, it is used in planning and performing therapeutic procedures, particularly endovascular interventions. The demonstration of subclavian steal on DSA requires injection of the contralateral subclavian and/or vertebral arteries while imaging the ipsilateral proximal subclavian, which fills with contrast a few frames later via retrograde vertebral artery opacification. Once this pattern is identified, it is then imperative to follow with another contralateral vertebral artery injection while imaging the distal vertebrobasilar system in orthogonal planes. This is bound to demonstrate the dynamics of basilar artery contrast opacification and will uncover the presence of vertebrobasilar junction aneurysms.

DIAGNOSIS

Diagnostic criteria — The presence of subclavian steal physiology with demonstration of a subclavian (or innominate) artery stenosis/occlusion proximal to the origin of the vertebral artery and demonstration that the lesion causes sufficiently severe hemodynamic compromise of downstream flow, resulting in:

●Measurable reduction in the ipsilateral brachial artery blood pressure.

●Reversal of the direction of blood flow in the ipsilateral vertebral artery.

●Neurologic symptoms referrable to the vertebrobasilar circulation (ie, cerebellum, brainstem, thalamus, and occipital regions) that may be explained by the presence of the hemodynamic derangement.

However, establishing a causative connection between the presence of subclavian stenosis or occlusion and the symptoms that bring the patient for evaluation is not an easy task, and requires a critical assessment of the clinical data available. The likelihood that the presence of subclavian steal physiology will lead to subclavian steal syndrome increases as the brachial pressure differential between the two upper limbs becomes more pronounced, particularly >40 mmHg [9]. Despite all these considerations, several observations cast some doubt in the diagnosis of these patients, as follows:

●Retrograde flow in the vertebral arteries is commonly identified with duplex ultrasound and is infrequently associated with neurovascular symptoms [57].

●Concurrent steno-occlusive pathology in other cerebral arteries is often present, thereby confounding the etiopathogenic diagnosis.

●Exercise does not invariably precipitate neurovascular symptoms.

●Reestablishment of antegrade blood flow may not relieve symptoms.

Differential diagnosis — The differential diagnosis of subclavian steal includes other conditions that lead to symptoms related to ischemia in the vertebrobasilar circulation. These include all potential causes of vertebrobasilar embolism. However, it is unlikely that any of these would lead to repetitive, stereotypical (ie, like each other in semiology) paroxysmal, transient episodes resembling those of subclavian steal syndrome, or be precipitated by arm exercise.

Atherosclerotic lesions of the extracranial or intracranial vertebral artery and/or the basilar artery are also capable of producing ischemic symptoms by virtue of hemodynamic compromise, without any evidence of steal. (See "Posterior circulation cerebrovascular syndromes".)

MANAGEMENT — The treatment of subclavian steal syndrome is individualized and varies with type and severity of symptoms but also the etiology of subclavian steal syndrome.

Atherosclerotic subclavian steal syndrome

Approach — For most patients with atherosclerosis as the etiology for subclavian steal syndrome, conservative medical management is the preferred as initial therapy.

Because subclavian steal syndrome carries a relatively low risk of ischemic stroke referable to the subclavian or innominate lesion, the primary purpose of treatment has historically focused on symptom control and optimizing of quality of life. Revascularization may be warranted for patients with severe disabling or refractory symptoms such as repetitive posterior circulation transient ischemic attacks (TIAs; causing syncope, falls) [13].

Conversely, frail patients or those with minimal symptoms may be monitored for progression of symptom severity, particularly since, in many instances, symptoms remain stable or improve over time without vascular intervention. In one review of 55 patients with subclavian steal syndrome followed for one to six years, no patient had a stroke involving the vertebrobasilar circulation, but four patients (4.8 percent) had a transient vertebrobasilar ischemia [79].

Optimal medical management — Management of atherogenic risk factors with intensive medical treatment and multifactorial risk reduction should be the mainstay of care. In one review, patients were more likely to experience events involving the carotid circulation (39 of 55, 71 percent) compared with vertebrobasilar events (4 of 55, 7 percent) [79]. Progression of disease in the carotid arteries was associated with stroke, TIA, and the need for carotid revascularization in 18 patients (46 percent).

Prevention of ischemic stroke and TIA due to extracranial large artery stenosis includes the use of antiplatelet agents, antihypertensive drugs, low-density lipoprotein cholesterol-lowering therapy, and lifestyle modification. (See "Overview of secondary prevention of ischemic stroke".)

Prescribing low-dose aspirin (eg, 81 mg daily) is a reasonable general proposition since this regimen carries a relative beneficial stroke risk reduction that approximates 20 to 25 percent in patients with atherosclerosis. However, the addition of other antiplatelet agents or the use of anticoagulants does not seem justified since this condition is, strictly speaking, a hemodynamic derangement. On the other hand, once a decision to proceed with surgical or endovascular intervention has been made, additional antithrombotic regimens are required.

Optimal blood pressure management requires careful attention as to which arm is used to monitor the effects of treatment, since the ipsilateral brachial artery will have spuriously low blood pressure readings. In addition, any increase in antihypertensive dosage must carefully monitored, with particular attention to an increase in magnitude or duration of the original symptoms. An inability to properly optimize blood pressure control should be considered a potential indication for intervention.

Vascular intervention — Patients with disabling neurologic symptoms should be considered for vascular intervention. This may include patients whose symptoms may cause them to experience harm (eg, recurrent loss of consciousness, recurrent falls, recurrent loss of vision).

Approach to revascularization — When intervention is selected for subclavian steal syndrome, the approach is based on the underlying etiology, location of the lesion, and patient-specific anatomy. The approach to innominate and subclavian artery revascularization is reviewed separately. (See "Upper extremity atherosclerotic disease", section on 'Intervention for proximal disease' and "Surgical and endovascular techniques for aortic arch branch and upper extremity revascularization".)

For atherosclerotic subclavian lesions associated with subclavian steal syndrome, an endovascular approach is often preferred unless it will jeopardize the integrity of the vertebral artery, in which case, surgical revascularization (eg, carotid-subclavian bypass or subclavian-carotid transposition) may be the better option. (See "Upper extremity atherosclerotic disease", section on 'Intervention for proximal disease' and "Surgical and endovascular techniques for aortic arch branch and upper extremity revascularization", section on 'Proximal occlusive lesions'.)

Following intervention for atherosclerotic subclavian lesions, freedom from reintervention and sustained resolution of ischemic symptoms is observed in most patients (>95 percent) and appears to be independent of the revascularization approach [80-89]. Recurrent symptoms due to significant (>70 percent) recurrent stenosis or obstruction occur in approximately 10 percent of patients and are typically treated with repeat angioplasty; however, surgery may be required in up to 5 percent of patients [80]. Patients with a continuous (compared with intermittent) subclavian steal syndrome may have a higher risk of subclavian artery restenosis following endovascular intervention [90].

Special clinical scenarios

•Concomitant carotid disease – The best approach to revascularization in patients with subclavian steal syndrome and coexisting severe carotid atherosclerosis has not been well studied. Clearly, if the patient's carotid pathology is symptomatic, revascularization should be offered first, before addressing the subclavian steal. An added benefit of this approach is that improving carotid artery flow in the presence of adequate posterior communicating arteries may also relieve any potential symptoms from subclavian steal. (See "Management of symptomatic carotid atherosclerotic disease" and "Carotid endarterectomy" and "Overview of carotid artery stenting".)

•Bilateral steal – Bilateral subclavian steal syndrome is rare. The presence of bilateral subclavian artery stenoses, if sufficiently severe, would invariably lead to a steal phenomenon from the carotid system, a hemodynamic derangement that is likely to be poorly tolerated by patients. A careful analysis of the semiology should guide the need and prospect of revascularization. There are no clear guidelines governing the preferred sequence of treatment.

Nonatherosclerotic subclavian steal syndrome — For nonatherosclerotic etiologies, the primary cause of subclavian/innominate artery stenosis/occlusion needs to be addressed. Treatment is tailored to the specific etiology and may include medical therapy or surgery. The management of other potential causes of nonatherosclerotic subclavian steal is discussed separately:

●Takayasu arteritis (See "Treatment of Takayasu arteritis".)

●Arterial thoracic outlet syndrome (See "Overview of thoracic outlet syndromes", section on 'Arterial TOS'.)

●Congenital anomalies (See "Vascular rings and slings" and "Overview of aneurysmal disease of the aortic arch branches or upper extremity arteries in adults", section on 'Kommerell diverticulum (aneurysm of aberrant proximal subclavian artery)'.)

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Occlusive carotid, aortic, renal, mesenteric, and peripheral atherosclerotic disease".)

SUMMARY AND RECOMMENDATIONS

●Subclavian steal syndrome – Subclavian steal syndrome refers to the presence of significant vertebrobasilar symptoms ipsilateral to a hemodynamically significant stenosis or occlusion of the prevertebral subclavian (or innominate) artery (figure 1). (See 'Definition and physiology' above.)

●Etiology – Atherosclerosis is by far the most common etiology of subclavian steal syndrome; however, other conditions can cause a subclavian/innominate artery stenosis or occlusion leading to subclavian steal syndrome. These include Takayasu arteritis, giant cell arteritis, arterial thoracic outlet syndrome, congenital anomalies, and postsurgical changes. (See 'Etiology' above.)

●Clinical features – Neurologic symptoms as a manifestation of subclavian or innominate artery stenosis/occlusion are uncommon but are more likely in the context of concurrent cerebrovascular lesions. Symptoms result from ischemia of the brainstem, cerebellum, or occipital region and present as short-lived episodes that may be precipitated by upper extremity exercise. Associated peripheral ischemia or coronary syndromes may or may not be present (see 'Clinical features' above):

•Dizziness (lightheadedness, vertigo) is a commonly reported symptom. Other symptoms include binocular double vision, decreased vision, oscillopsia, and incoordination. Vertebrobasilar junction cerebral aneurysm and cognitive and mood abnormalities may also be consequences of hemodynamic changes in the vertebral artery.

•On physical examination, a difference in the upper extremity pulses may be appreciated and correlates with a differential in blood pressure. Evidence of distal embolization can be present.

●Evaluation – When subclavian steal syndrome is suspected based on clinical features, comparison of upper extremity arm blood pressures and duplex ultrasound are first-line studies. Duplex can suggest proximal subclavian artery stenosis and demonstrate reversal of flow in the ipsilateral vertebral artery if it is present. The diagnosis of subclavian steal must be confirmed by angiography. In most cases, this can be accomplished with noninvasive imaging using computed tomographic angiography (CTA) or magnetic resonance angiography (MRA). (See 'Evaluation' above.)

●Diagnosis – The diagnosis of subclavian steal syndrome relies on the following (see 'Diagnosis' above):

•Presence of a subclavian steal physiology – This requires demonstration of a hemodynamically significant stenosis or occlusion proximal to the origin of the vertebral artery (eg, subclavian, innominate artery) inducing reversal of flow in the ipsilateral vertebral artery.

•Presence of neurovascular symptoms – Symptoms must be referable to the brainstem, cerebellum, or occipital region.

●Management – Management of patients with subclavian steal syndrome is individualized depending on etiology, type, and severity of symptoms and their impact on quality of life (see 'Management' above):

•Atherosclerotic subclavian steal syndrome – For most patients, atherosclerosis is the cause of subclavian/innominate artery stenosis and is initially managed conservatively. (See 'Atherosclerotic subclavian steal syndrome' above.)

-Conservative management – Conservative management includes intensive medical treatment and multifactorial risk reduction. (See 'Optimal medical management' above.)

-Vascular intervention – Revascularization can be considered for patients with severe disabling or refractory symptoms such as repetitive posterior circulation transient ischemic attacks (TIAs; causing syncope, falls). (See 'Vascular intervention' above.)

•Nonatherosclerotic subclavian steal syndrome – For nonatherosclerotic causes of subclavian/innominate artery stenosis (eg, Takayasu arteritis, congenital vascular lesions), treatment is tailored to the specific etiology and may include medical therapy or surgery.

ACKNOWLEDGMENT — The editorial staff at UpToDate acknowledges Peter C Spittell, MD, who contributed to an earlier version of this topic review.