CASE 11671 Published on 17.03.2014
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Left subclavian artery occlusion: a cause of subclavian steal syndrome

Section

Cardiovascular

Case Type

Clinical Cases

Authors

Horta M1, Fernandes O2, Costa N2, Leal C2,Figueiredo L2

1Serviço de Radiologia
Centro Hospitalar Lisboa Ocidental
Lisbon/Portugal
Email:mariana_horta@hotmail.com
2Serviço de Radiologia
Hospital de Santa Marta
Centro Hospitalar Lisboa Central
Lisbon/Portugal
Connected authors
Mariana Horta PORTUGAL
Patient

62 years, male

Categories
Area of Interest Vascular ; Imaging Technique CT-Angiography, Ultrasound-Spectral Doppler, Catheter arteriography
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Clinical History
A 62-year-old man complaining of recurrent episodes of dizziness and uncontrolled hypertension was referred to our hospital.
Physical examination revealed upper extremity blood pressure differences (right arm = 210/105 mm-Hg; left arm = 180/100 mm-Hg) and asymmetric brachial arterial pulses.
Physical and laboratory assessments were otherwise negative.
Imaging Findings
The patient was referred to a carotid triplex ultrasonography that depicted reverse flow in the left vertebral artery (LVA), showing a retrograde waveform during systole and absent flow during diastole (Fig.1 a, c).
Proximal left subclavian artery (LSA) could not be assessed, however, spectral study of the homolateral axillary artery showed an unusual monophasic tardus waveform. In this hypertensive patient, peak systolic velocity was abnormally asymmetric when compared with the right artery (Fig. 2 a, b). These findings were suggestive of a subclavian steel syndrome (SSS).
Meanwhile, a CT angiography was performed showing the occlusion 12.9 mm after LSA origin (Fig.3 e), depicting flow distal to the origin of LVA, thyrocervical trunk and of internal thoracic artery (Fig. 5 a). Left internal thoracic artery calibre was considerably smaller than the contra-lateral one (Fig. 5 b).
Conventional angiography confirmed the diagnosis, demonstrating a proximal LSA occlusion causing the SSS (Fig. 6).
Discussion
Subclavian steal syndrome is defined by the presence of reverse blood flow in the vertebral artery due to proximal ipsilateral subclavian or innominate arteries stenosis or occlusion [1].
The vertebral artery is usually the most proximal collateral of the subclavian artery [1]. An occlusion/stenosis proximal to its origin will determine lower pressure in the distal subclavian artery, which will be responsible for the stealing of blood from the vertebrobasilar system which in turn is filled from the contralateral vertebral artery via the basilar artery [1, 2].
A large number of patients are asymptomatic, therefore the prevalence of this phenomenon is unknown [2].
Other patients develop neurological symptoms of vertebral insufficiency that are exacerbated by ipsilateral arm exercise [3]. These include symptoms such as syncope, vertigo, dizziness, visual changes, confusion, ataxia and weakness [2, 4].
A significant inter-arm pressure difference is usually present in this context [5]. A study conducted by English et al., suggests that brachial systolic pressure difference of ≥ 15 mm Hg has a high specificity (90%) and a sensitivity close to 50% for diagnosing subclavian stenosis [6, 7].
Weakened or absent pulses and ipsilateral arm claudication symptoms are other findings that may be encountered [4].
SSS is mostly caused by atherosclerosis (>90%), which affects predominantly LSA due to its turbulent flow caused by the acute inclination of its origin [2].
Other less frequent causes are aortic dissection, congenital malformations (e.g. aortic coarctation), vasculitides (e.g. Takayasu and giant cell arteritis) as well as a sequela of trauma and of surgical and radiation procedures [2, 5, 8-14].
Carotid duplex ultrasound is the standard clinical screening imaging modality for SSS [2, 15].
The pre-steal phenomenon is characterized by a systolic flow deceleration in the vertebral artery. Partial subclavian steal is defined by a transient reversal of flow during systole. In a complete subclavian steal, a permanent retrograde waveform is seen [15].
CT and MR angiography confirm the diagnosis by detecting delayed enhancement in the vertebral artery, showing the cause of the SSS, which in the majority of cases cannot be accessed by ultrasound.
Conventional angiography is still the gold standard for detecting subclavian artery stenosis/occlusion [2, 5, 7].
In highly symptomatic patients the therapeutic approach includes endovascular stenting, angioplasty and surgical bypass [2, 3, 15].
Conservative management with anti-platelet and anti-coagulation therapies and risk factor modification are generally recommended in asymptomatic patients or with isolated symptoms [2, 15].
Differential Diagnosis List
Subclavian steal syndrome caused by atherosclerotic left subclavian occlusion
Atherosclerosis
Aortic dissection
Congenital malformations
Vasculitides
Post-surgical and post-radiation procedures
Post-trauma
Final Diagnosis
Subclavian steal syndrome caused by atherosclerotic left subclavian occlusion
Case information
URL: https://www.eurorad.org/case/11671
DOI: 10.1594/EURORAD/CASE.11671
ISSN: 1563-4086
Figure 1

Colour/Spectral Doppler

Colour/Spectral Doppler
Colour/Spectral Doppler shows a retrograde waveform in LVA (A) and cephalad flow in the right vertebral artery (B). Note the opposite direction of flow of left common carotid artery and of LVA (C)
Figure 2

Colour/Spectral Doppler

Colour/Spectral Doppler
Colour/Spectral Doppler images show an unusual monophasic tardus waveform of left axillary artery with peak systolic velocity abnormally asymmetric when compared with the contralateral artery.
Figure 3

MIP reformatted images

MIP reformatted images
Sagittal oblique (A), coronal (B) and sagittal (E) MIP reformatted images of CT-angiography show proximal left subclavian occlusion (blue arrows). Axial images show the patent LVA (C) and the occluded segment of LSA (D).
Figure 4

Volume rendered technique

Volume rendered technique
Volume rendered technique (VRT) images (A and B) showing the proximal occlusion of left subclavian artery.
Figure 5

Axial CT-angiography

Axial CT-angiography
Axial CT-angiography image demonstrates flow distal to the origin of LVA, thyrocervical trunk and of internal thoracic artery (A). Left internal thoracic artery calibre was considerably smaller than the contralateral one (B, orange arrow).
Figure 6

Angiography

Angiography
Conventional aortic arch angiography (A) and selective left subclavian angiography (B) show the occluded proximal left subclavian artery (blue arrows). Blood flows from left vertebral artery to the upper left limb (C, orange dashed-arrows).