Subclavian Steal Syndrome
Key Points at a Glance
Section titled “Key Points at a Glance”1. What is Subclavian Steal Syndrome?
Section titled “1. What is Subclavian Steal Syndrome?”Subclavian steal syndrome (SSS) is a condition characterized by stenosis or occlusion of the subclavian artery proximal to the origin of the vertebral artery. To compensate for blood flow to the distal subclavian artery, retrograde flow occurs in the ipsilateral vertebral artery, causing blood to be “stolen” from the brain to the upper limb.
The prevalence varies by report, ranging from 0.6% to 6.4% 2). Atherosclerosis is the most common cause, and it occurs predominantly in men in their 50s–60s with a history of smoking 2). The left subclavian artery is affected 2–3 times more often than the right.
Rare congenital and acquired causes include the following:
- Congenital aortic arch anomalies: Right aortic arch with aberrant left subclavian artery (RAA-ALSA). This occurs in less than 0.1% of the population, and only 11 cases of SSS associated with RAA-ALSA have been reported 1).
- Takayasu arteritis: Inflammatory stenosis of large vessels 1).
- Post-radiation therapy: Accelerated atherosclerosis and fibrosis after neck irradiation can occlude the subclavian artery. The median time from treatment to onset of stenosis is approximately 21 years, and the median low-neck radiation dose in patients who developed subclavian artery stenosis is reported as 4400 cGy 4).
- Thoracic outlet syndrome (TOS): Vascular compression in the clavicle-first rib space 2).
- After repair of coarctation of the aorta, after coronary artery bypass grafting (coronary-subclavian steal syndrome when using the internal thoracic artery), dialysis shunt: Hemodynamic changes associated with the creation of an extracorporeal shunt 4).
The prevalence is reported to range from 0.6% to 6.4%, but many cases are asymptomatic and are often discovered incidentally during ultrasound examination or blood pressure measurement in both arms. Only a small proportion become symptomatic, and it is particularly problematic in patients with advanced systemic atherosclerosis.
2. Main Symptoms and Clinical Findings
Section titled “2. Main Symptoms and Clinical Findings”Subjective Symptoms
Section titled “Subjective Symptoms”Most cases of SSS are asymptomatic and are discovered incidentally through blood pressure differences between the arms or ultrasound examination. When symptomatic, symptoms mainly result from reduced blood flow to the vertebrobasilar system.
Symptoms of vertebrobasilar insufficiency
- Dizziness and vertigo: The most common symptoms.
- Syncope and lightheadedness: Easily triggered by sudden changes in posture or exercise of the affected upper limb.
- Diplopia: Due to ischemia of the brainstem nuclei that control eye movements 3).
- Dysarthria: Due to ischemia of the swallowing and vocalization centers in the brainstem 3).
- Blurred vision and transient visual loss: Caused by ischemia of the visual cortex in the occipital lobe. May be monocular.
Upper limb symptoms
- Upper limb claudication: Exercise-induced arm pain or fatigue. Worsens with vigorous activity of the affected upper limb 2).
- Numbness, cold sensation, paresthesia: Due to peripheral circulatory insufficiency in the affected upper limb 4).
Triggers for symptoms include vigorous exercise of the affected upper limb or sudden rotation of the head toward the affected side.
Clinical Findings (Findings Confirmed by Physician Examination)
Section titled “Clinical Findings (Findings Confirmed by Physician Examination)”Blood Pressure Difference
The systolic blood pressure difference between both arms is the most important physical finding. A systolic blood pressure difference of 15 mmHg or more suggests significant subclavian artery stenosis4). Case reports may show larger differences (e.g., left arm 79 mmHg vs. right arm 108 mmHg, difference 29 mmHg2)).
Other Findings
- Bruit: Heard on auscultation over the supraclavicular fossa or suboccipital region4).
- Upper extremity arterial insufficiency findings: Weak pulse in the radial artery on the affected side, atrophic nail changes.
Ophthalmic Findings
Damage to the occipital lobe or optic radiation due to vertebrobasilar ischemia can cause homonymous hemianopia or higher visual dysfunction. Additionally, medullary damage (Wallenberg syndrome) may be accompanied by ocular motility disorders, nystagmus, and Horner syndrome. OCT examination may reveal thinning and loss of retinal layers associated with retinal artery occlusion or ischemia.
A systolic blood pressure difference of 15 mmHg or more suggests significant subclavian artery stenosis4). However, this finding alone does not confirm SSS; additional tests such as ultrasound evaluation of vertebral artery blood flow are necessary. Measuring blood pressure in both arms routinely can be a clue for early detection.
3. Causes and Risk Factors
Section titled “3. Causes and Risk Factors”The most common cause of SSS is atherosclerosis. The following risk factors increase the progression of arteriosclerosis and the risk of subclavian artery stenosis.
- Hypertension: Sustained mechanical stress on the arterial wall
- Dyslipidemia: Promotion of plaque formation3)
- Diabetes: Promotes systemic vascular damage 3)
- Smoking: One of the largest modifiable risk factors for atherosclerosis 2)
- Advanced age: Cumulative progression of atherosclerosis
SSS is also a marker of systemic atherosclerosis and suggests an increased risk of major adverse cardiovascular and cerebrovascular events (MACE) such as myocardial ischemia and stroke.
4. Diagnosis and Examination Methods
Section titled “4. Diagnosis and Examination Methods”Blood Pressure Measurement and Screening
Section titled “Blood Pressure Measurement and Screening”Simultaneous blood pressure measurement in both upper limbs is the first step in screening. A systolic blood pressure difference of 15 mmHg or more suggests significant subclavian artery stenosis and requires further investigation 4).
Ultrasound (Color Doppler)
Section titled “Ultrasound (Color Doppler)”Confirmation of retrograde blood flow in the vertebral artery is a key noninvasive test for diagnosing SSS. A peak systolic velocity (PSV) in the subclavian artery exceeding 240 cm/s suggests significant stenosis. An inter-arm pressure difference greater than 10 mmHg is also suggestive of SSS 3).
CT Angiography (CTA) and MR Angiography (MRA)
Section titled “CT Angiography (CTA) and MR Angiography (MRA)”Both CTA and MRA can noninvasively visualize the location and degree of subclavian artery stenosis or occlusion. CTA has a short acquisition time and allows evaluation of vascular wall calcification and plaque. MRA is noninvasive but may overestimate the severity of stenosis. 3D reconstruction is useful for assessing anatomical abnormalities and aortic arch anomalies 1).
Catheter cerebral angiography
Section titled “Catheter cerebral angiography”Although invasive, it provides high-resolution images and is excellent for visualizing collateral circulation. Therapeutic interventions (such as stent placement) can be performed simultaneously.
Differential diagnosis
Section titled “Differential diagnosis”Symptoms of SSS overlap with the following conditions:
| Differential diagnosis | Key differentiating features |
|---|---|
| Peripheral artery disease (PAD) of the upper extremity | No neurological symptoms |
| Posterior circulation stroke | Infarct confirmed on imaging |
| Aortic stenosis | Differentiated by heart sounds and echocardiography |
| Diabetic neuropathy | History of glycemic control |
| Thoracic outlet syndrome (TOS) | If symptoms persist after SSS treatment, consider concomitant TOS2) |
5. Standard Treatment
Section titled “5. Standard Treatment”Overview of Treatment Strategy
Section titled “Overview of Treatment Strategy”For asymptomatic cases, medical management (management of arteriosclerosis risk factors and antiplatelet therapy) is the standard. For symptomatic cases, drug therapy, endovascular treatment, or surgery is selected based on severity. Spontaneous improvement has also been reported 4).
Medical Treatment
Section titled “Medical Treatment”Antiplatelet therapy is performed to prevent cerebral infarction. Active cardiovascular risk management with aspirin, statins, and antihypertensive drugs forms the basis of medical treatment.
Endovascular Treatment (First Choice)
Section titled “Endovascular Treatment (First Choice)”According to the 2018 ESC guidelines, percutaneous balloon stent placement is the first choice for most symptomatic SSS cases. Percutaneous transluminal angioplasty (PTA) is also recommended for localized proximal subclavian artery occlusion.
- Sustained resolution of ischemic symptoms is achieved in over 95% of patients.
- The restenosis rate is highest in cases of complete occlusion, reported as 7–41% over 5 years 4).
Surgical Treatment
Section titled “Surgical Treatment”Surgery is selected when endovascular treatment is difficult (severe occlusion, calcification, fibrosis, congenital anomalies). Complete occlusion and fibrosis after radiation therapy are difficult to treat endovascularly, and surgical bypass is recommended 4).
- Carotid-subclavian bypass: The most common surgical procedure 4).
- Carotid-axillary bypass: A procedure selected for cases of congenital aortic arch anomalies. A case has been reported in which a 6 mm PTFE graft was used, the patient was discharged 2 days after surgery, and preoperative symptoms almost completely disappeared 15 days after surgery 1).
- Subclavian artery transposition (carotid-subclavian transposition) 1).
- The 5-year failure rate of surgical bypass is reported as 0–4% 4).
Management of Concomitant Conditions
Section titled “Management of Concomitant Conditions”When SSS and thoracic outlet syndrome (TOS) coexist, first treat SSS to improve blood flow at the origin of the subclavian artery. If symptoms persist, evaluate for TOS and consider first rib resection 2).
If symptoms persist despite improved subclavian artery flow after SSS treatment (e.g., stenting), concomitant thoracic outlet syndrome (TOS) should be considered 2). Evaluation with arm-elevated CTA may be useful. Once TOS is confirmed, surgical treatments such as first rib resection and scalenectomy may be effective.
6. Pathophysiology and Detailed Mechanisms
Section titled “6. Pathophysiology and Detailed Mechanisms”Basic Hemodynamics
Section titled “Basic Hemodynamics”Normally, the vertebral artery arises from the subclavian artery and supplies blood to the brain in an antegrade direction. In SSS, stenosis or occlusion of the subclavian artery proximal to the origin of the vertebral artery reduces distal subclavian artery pressure. This creates a retrograde pressure gradient in the vertebral artery, causing blood intended for the brain to be “stolen” to the upper limb.
Hemodynamic Severity Classification of Steal
Section titled “Hemodynamic Severity Classification of Steal”- Mild: Only reduced systolic flow in the vertebral artery (no complete reversal)
- Moderate: Retrograde flow during systole and antegrade flow during diastole (alternating flow)
- Severe: Complete retrograde flow in the vertebral artery
Association with Aneurysm Formation
Section titled “Association with Aneurysm Formation”Retrograde blood flow in the vertebral artery increases hemodynamic stress at the vertebrobasilar junction and may contribute to aneurysm formation. A case has been reported in which left vertebral artery flow loss due to calcification and occlusion of the left subclavian artery led to compensation by the right vertebral artery, resulting in the formation of a saccular aneurysm at the junction 3).
Congenital mechanisms
Section titled “Congenital mechanisms”Right aortic arch with aberrant left subclavian artery (RAA-ALSA) results from abnormal development of the aortic arch during the 4th to 8th week of gestation. Various malformations arise depending on the regression and persistence patterns of the fourth pharyngeal arch artery and the dorsal aorta. ALSA originates from a Kommerell diverticulum and can take three courses: retroesophageal, between the esophagus and trachea, or pretracheal. Congenital SSS occurs due to occlusion or stenosis of ALSA along this course 1).
Perfusion territories and patterns of impairment in the vertebrobasilar system
Section titled “Perfusion territories and patterns of impairment in the vertebrobasilar system”The vertebrobasilar system supplies the brainstem and occipital lobes. The main syndromes of impairment by region are listed below.
- Medulla oblongata: Wallenberg syndrome (vertigo, dysphagia, Horner syndrome, alternating sensory disturbance)
- Pons: MLF syndrome, Foville syndrome, Millard-Gubler syndrome
- Midbrain: Weber syndrome, Benedikt syndrome, Parinaud syndrome
- Posterior cerebral artery ischemia: Homonymous hemianopia, higher visual dysfunction
Radiation-induced mechanisms
Section titled “Radiation-induced mechanisms”Radiation-accelerated atherosclerosis and fibrosis are presumed to cause subclavian artery occlusion. Most reports are after treatment for Hodgkin lymphoma, with a median interval of about 21 years from treatment to subclavian or carotid artery stenosis 4).
Cases have been reported in which retrograde blood flow in the vertebral artery continuously applies hemodynamic stress to the vertebrobasilar junction, leading to the formation of a saccular aneurysm 3). Advanced imaging techniques such as 4D flow MRI enable real-time visualization of retrograde flow dynamics, and are expected to contribute to future diagnostic and therapeutic strategies.
7. Latest research and future perspectives (reports at the research stage)
Section titled “7. Latest research and future perspectives (reports at the research stage)”Combined case of SSS and thoracic outlet syndrome
Section titled “Combined case of SSS and thoracic outlet syndrome”Kageyama et al. (2024) reported a 59-year-old woman with residual symptoms after SSS treatment 2). Stent placement improved blood flow at the origin of the subclavian artery, but dizziness and numbness persisted. CTA in arm elevation revealed subclavian artery stenosis at the costoclavicular space, leading to a diagnosis of neurogenic TOS. Endoscopic-assisted subclavian approach with first rib resection and scalenotomy was performed, and symptoms improved immediately after surgery. At 12 months, there was no recurrence, grip strength improved from 12 to 23 kg on the left, and the DASH score improved from 90 to 4.
SSS due to congenital aortic arch anomaly
Section titled “SSS due to congenital aortic arch anomaly”Nakata et al. (2023) reported a 74-year-old woman with congenital SSS due to RAA-ALSA 1). Her chief complaints were recurrent rotational vertigo-induced falls and right-sided ataxia over 6 years. CTA showed occlusion of the left subclavian artery origin and a 2.4 cm stenotic segment. Left carotid-axillary artery bypass (6 mm PTFE graft) was performed. She was discharged 2 days postoperatively, and symptoms almost completely resolved by postoperative day 15.
Association between vertebrobasilar aneurysm and SSS
Section titled “Association between vertebrobasilar aneurysm and SSS”Castañeda Aguayo et al. (2024) reported an SSS-related vertebrobasilar junction aneurysm in a 66-year-old woman presenting with Wallenberg syndrome 3). They suggested that blood flow loss in the vertebral artery due to left subclavian artery occlusion and hemodynamic stress from retrograde flow contributed to aneurysm formation. 4D flow MRI enables real-time visualization of retrograde flow dynamics, which is expected to contribute to future diagnostic and treatment strategies. Additionally, advanced technologies such as preoperative simulation using 3D printing to replicate patient-specific vascular anatomy and intraoperative real-time overlay of vascular position using augmented reality (AR) are also anticipated.
SSS after radiotherapy
Section titled “SSS after radiotherapy”Woo et al. (2022) reported SSS leading to posterior circulation TIA and cerebral infarction in a 67-year-old man who had received radiotherapy (6000 cGy/30 fractions) to the left cervical lymph nodes for tonsillar cancer 12 years earlier 4). CTA showed complete occlusion of the proximal left subclavian artery, and Doppler ultrasound confirmed retrograde flow in the left vertebral artery. MRI revealed a subacute infarction in the left occipital lobe. Although the dose-effect curve for radiotherapy and large vessel disease has not been established, the median low-neck radiation dose in patients who developed subclavian artery stenosis has been reported as 4400 cGy.
8. References
Section titled “8. References”- Nakata J, Stahlfeld KR, Simone ST. Subclavian steal syndrome in a right aortic arch with aberrant left subclavian artery atresia. SAGE Open Med Case Rep. 2023;11:2050313X231180045.
- Kageyama A, Suzuki T, Kiyota Y, et al. A case of concomitant subclavian steal syndrome and thoracic outlet syndrome. J Vasc Surg Cases Innov Tech. 2024;10(5):101617.
- Castañeda Aguayo F, Aguirre AJ, Garcia I, et al. Wallenberg syndrome secondary to vertebrobasilar aneurysm associated with subclavian steal syndrome. Cureus. 2024;16(10):e72108.
- Woo JD, Markowitz JE. A great heist: subclavian steal syndrome causing posterior transient ischemic attack and stroke. Perm J. 2022;26(4):148-153.