Nonatherosclerotic Subclavian Steal Syndrome Due to Brachiocephalic Trunk Kinking in an Elderly Woman: A Case Report

Introduction

The brachiocephalic trunk (BCT), historically termed the innominate artery, is the first and largest branch of the aortic arch, essential for the blood supply to the right upper limb, head, and neck. Subclavian steal syndrome (SSS) is a hemodynamic phenomenon characterized by the reversal of blood flow in the ipsilateral vertebral artery to supply the upper-limb circulation due to a stenosis or occlusion proximal to the origin of the artery [1].

Historically, the first angiographic observation of subclavian flow reversal was documented by Contorni in 1960 [2]. In 1961, Reivich et al reported cases of patients with signs of cerebrovascular insufficiency associated with vertebral artery flow reversal due to subclavian obstruction [3]. Shortly thereafter, Fisher introduced the official term “subclavian steal” to describe this syndrome [4].

Estimates indicate an overall prevalence between 0.6% and 6.4% in the population [5,6]. Labropoulos et al conducted a large-scale study on the prevalence of SSS, demonstrating its presence in 5.4% of 7881 patients undergoing arterial Doppler ultrasound of extracranial vessels [7]. In patients with suspected carotid artery disease, the identified prevalence is approximately 2.3%, reinforcing the need for systematic vascular surveillance [7].

The pathophysiology of SSS is based on an inverted hydrodynamic pressure gradient. Under physiological conditions, aortic pressure is higher than distal circulation; however, a significant stenosis in the BCT or proximal subclavian artery generates a pressure drop that recruits retrograde flow from the vertebral artery [8,9]. This phenomenon can be classified via Doppler into latent steal (Stage I), intermittent (Stage II), or complete (Stage III) [10,11].

While atherosclerosis is the primary cause, SSS can be triggered by congenital anomalies, arteritis, or extrinsic compressions. Currently, it is recognized that mechanical distortions, such as arterial kinking or twisting, can reduce distal systolic pressure enough to invert the flow gradient, even in the absence of classic obstructive plaques [12,13]. It is a differential diagnosis in patients presenting with a pulse deficit or a systolic blood pressure difference greater than 20 mmHg between the upper limbs [5].

The classification of SSS is based on the analysis of the spectral Doppler waveform morphology in the vertebral artery, which reflects the degree of stenosis or occlusion in the subclavian artery proximal to the vertebral origin [10]. This hemodynamic progression is divided into 3 main stages:

Doppler evaluation is crucial not only for diagnosis but also for cardiovascular risk stratification, as the presence of atherosclerosis in cervical vessels is a marker of systemic risk [15]. In cases of latent or partial steal, reactive hyperemia maneuvers can be used to unmask or exacerbate the steal pattern on Doppler imaging [11]. This report presents the case of a 66-year-old woman with partial subclavian steal syndrome due to kinking in the proximal portion of the brachiocephalic trunk.

Case Report

A 66-year-old woman with a history of a previous ischemic stroke and permanent atrial fibrillation (CH2DS2-VASc score of 5) was referred to the vascular laboratory for carotid and vertebral artery Doppler ultrasound evaluation. She was clinically stable, and the examination was part of a routine vascular follow-up.

During the ultrasound assessment, spectral Doppler imaging of the right vertebral artery revealed a bidirectional flow pattern, characterized by retrograde flow during systole and antegrade flow during diastole, consistent with a Stage II (intermittent) subclavian steal pattern (Figure 1) [10]. Notably, no significant atherosclerotic plaques or flow velocity changes were detected in the visualized segments of the proximal right subclavian artery.

To investigate the etiological origin of the hemodynamic alteration, computed tomography angiography (CTA) of the aortic arch and supra-aortic trunks was performed. The CTA excluded significant atherosclerotic obstructive disease or signs of vasculitis. However, it revealed a marked 90-degree mechanical angulation (kinking) at the origin of the brachiocephalic trunk (BCT) (Figures 2, 3). This sharp angulation created a localized hemodynamic resistance sufficient to drop the distal systolic pressure, thereby recruiting retrograde flow from the right vertebral artery to maintain perfusion in the right upper limb territory (Figure 4).

Given the patient’s high thromboembolic risk profile and the absence of disabling vertebrobasilar insufficiency symptoms (such as drop attacks, syncope, or severe vertigo), a multidisciplinary team opted for a conservative management strategy. The therapeutic plan focused on optimized medical therapy, including systemic anticoagulation for atrial fibrillation and strict control of cardiovascular risk factors. The patient remains under periodic clinical and imaging surveillance, showing no recurrence of neurological events to date. The stability of flow in the basilar artery, confirmed by the absence of retrograde flow beyond the vertebral confluence, was a key determinant for the safety of this conservative approach.

Discussion

The brachiocephalic trunk (BCT) is an infrequent location for the development of hemodynamically significant stenoses compared to the left subclavian artery. The pathophysiology of SSS in this context is analogous to that observed in subclavian pathology: a reduction in systolic pressure distal to the obstruction that inverts the vertebrobasilar pressure gradient, forcing retrograde flow through the ipsilateral vertebral artery [10]. In the present case, the etiology was nonatherosclerotic, which is a clinical rarity. The kinking (sharp angulation) of the BCT without evident plaques suggests a mechanical/positional origin for the pressure drop.

Modern diagnostic evaluation requires a multi-modal approach. While cervical Doppler imaging is the initial screening tool, computed tomography angiography (CTA) plays a crucial role in anatomical definition, allowing precise visualization of variations such as kinking and the exclusion of calcified plaques or adjacent soft tissues that might cause extrinsic compression [16]. Complementarily, magnetic resonance angiography (MRA), specifically the time-of-flight (TOF) technique, is extremely sensitive to flow alterations. In patients with SSS, MRA can demonstrate a signal loss in the intracranial vertebral artery due to slow and turbulent retrograde flow, which aids in confirming the proximal hemodynamic impact before any intervention [17].

Intracranial hemodynamic repercussion is best evaluated by transcranial Doppler (TCD) imaging. TCD findings in patients with vertebral steal reveal that the reversal of flow in the extracranial vertebral artery may not necessarily translate into reversal in the basilar artery, depending on the competence of the circle of Willis. However, in severe cases, TCD can identify retrograde or alternating flow in the basilar artery, which significantly increases the risk of neurological symptoms and vertebrobasilar insufficiency [18]. In our case, the stability of flow in the basilar artery was a key determinant for the safety of conservative management.

Although subclavian steal is often an incidental finding, its clinical management in patients with multiple comorbidities requires cautious analysis [8]. The physiological impact of this phenomenon was further elucidated by Smith et al [19], who demonstrated that regional cerebral blood flow can be significantly affected during arm exercise in patients with SSS, potentially exacerbating symptoms of vertebrobasilar insufficiency. The decision to use conservative management in this patient aligns with evidence that the risk of isolated stroke due to SSS is relatively low [1]. However, the CHA2DS2-VASc score of 5 and the history of ischemic stroke increased the complexity. Although atrial fibrillation was the predominant embolic source, the turbulence generated at the site of BCT kinking could, theoretically, constitute an additional thrombogenic niche, exacerbating the risk of recurrence.

Endovascular or surgical intervention, while effective, carries risks; studies indicate that the periprocedural stroke risk can reach 2% [20]. For a patient with Stage II (partial) steal and an absence of disabling vertebrobasilar insufficiency symptoms, optimized medical treatment focused on systemic anticoagulation and rigorous risk factor control is the safest strategy [16,17].

As illustrated in Figure 4, this kinking resulted in a significant reduction in pressure in the right subclavian artery. To compensate, blood was “stolen” from the cerebral circulation: it flowed anterogradely through the left vertebral artery and then reversed direction (as shown by the blue arrow) to maintain perfusion in the distal right subclavian artery territory. This mechanism highlights an unusual yet important anatomical variation causing the subclavian “steal” phenomenon. No similar cases of subclavian steal caused by kinking in the brachiocephalic trunk were found in the literature.

Conclusions

This case demonstrates that mechanical kinking of the brachiocephalic trunk is a rare but functionally significant cause of partial subclavian steal syndrome. Diagnosis requires a high index of suspicion when Doppler ultrasound reveals flow inversion in the absence of proximal atherosclerotic stenosis.

The integration of multi-modal imaging is mandatory; while Doppler imaging defines the hemodynamic phenomenon, CTA provides the definitive etiological diagnosis. In patients with high cardiovascular complexity and elevated risk scores, management should prioritize clinical stability and systemic protection, avoiding invasive interventions for stable anatomical variations in asymptomatic patients.