Subclavian steal: An interesting imaging scenario

Saranya Manickavasagam¹, Rajarajan Rajendran², Arunagiri Viruthagiri³, Senthivel Murugan V¹

¹Department of Radiodiagnosis, Kauvery Hospital, Trichy, India

²Department of Neurology, Kauvery Hospital, Trichy, India

³Department of Vascular and Endovascular Surgery, Kauvery Hospital, Trichy, India

Background

Subclavian steal phenomenon refers to steno occlusive disease of proximal subclavian artery with subsequent reversal of flow in the ipsilateral vertebral artery. The cerebral ischemic symptoms or upper limb claudication constitutes the Subclavian Steal Syndrome (SSS). Here we present a case of SSS who had dysarthria and upper limb weakness and numbness for a short duration.

Case presentation

A 61-year-old male came with sudden onset of difficulty in speaking which lasted for ten minutes three days before the date of admission. He had left upper limb weakness and numbness the next day which lasted for fifteen minutes and resolved spontaneously.

He was a chronic smoker with history of coronary artery disease. His vitals were stable at the time of presentation. GCS was 15/15, power was 5/5 in all four limbs and no facial asymmetry.

Imaging

MRI Brain was done which showed lacunar infarcts in posterior cerebral artery territory and internal border zone in the left side (Fig. 1).

Fig. 1. Small acute infarcts showing diffusion restriction in the left parietal lobe and centrum semiovale region. Non-contrast MR angiogram showed narrowed intracranial segment of left vertebral artery and left internal carotid stenosis.

Carotid and vertebral doppler were requested which revealed normal doppler spectrum in bilateral carotids and right vertebral artery. The left vertebral doppler showed bidirectional flow and the spectrum revealing forward systolic flow with mid systolic reversal and restoration of forward flow in diastole. This suggested the possibility of left subclavian stenosis /occlusion with partial subclavian steal [1].

During doppler study, blood pressure cuff maneuver was done by inflating the cuff for a while followed by rapid deflation. This can induce reactive hyperemia leading to complete reversal of flow in the left vertebral artery. Thus, partial steal can be converted to complete steal by doing this BP cuff manoeuvre or arm exercise (Fig. 2).

Fig. 2a. Left vertebral doppler depicting nadir of mid systolic cleft falling below the baseline signifying systolic flow reversal with forward diastolic flow. Fig 2b. After doing BP cuff manoeuvre, partial subclavian steal got converted to complete steal with flow reversal.

Subsequently, CT angiogram of carotid and cerebral arteries was done for the confirmation and to quantify the stenosis. CT Angiogram showed short segment near total occlusion of left subclavian artery at its origin and focal stenosis of left internal carotid (Segment) (Fig. 3).

Fig. 3. CT Angio showing diffuse atherosclerotic wall thickening with near total occlusion of left subclavian artery at its origin.

Detailed clinical examination was done which showed blood pressure of 100/80 mmHg in the right arm and 70/60 mmHg in the left arm.

Vascular surgeon’s opinion was sought. Clinical examination revealed left subclavian bruit and absent peripheral pulses in bilateral lower limbs. The diagnosis of left subclavian stenosis with steal syndrome and peripheral arterial disease was made. The need for left subclavian stenting on follow up was explained to the patient and discharged.

Discussion

Subclavian stenosis is mostly due to atherosclerosis and risk factors include smoking, dyslipidemia, hypertension, diabetes etc. Rare causes are aortic dissection, Takayasu arteritis and Blalock Taussig shunt. Subclavian steal phenomenon can be clinically diagnosed when there is pulse deficit or systolic pressure difference of >20 mm Hg between the arms. Doppler is the initial modality to investigate in suspected cases as it not only assesses the degree of stenosis with hemodynamic changes related to occlusion but also the direction of blood flow which is a key finding to detect subclavian steal. Severity of steal is classified into three grades (2):

Grade I: Pre-steal (antegrade flow)

Grade II: Partial steal (bidirectional flow)

Grade III: Complete subclavian steal (retrograde flow)

CT/MR Angiography or Digital subtraction Angiography is the confirmatory imaging for any suspected case of subclavian steal which is found on doppler.

Management includes mainly conservative treatment with cessation of smoking, good control of hypertension, diabetes and dyslipidemia. Carotid-subclavian bypass, endovascular procedures including angioplasty and stenting are reserved for significant clinical symptoms like posterior circulation stroke or limb threatening ischemia.

Conclusion

Subclavian steal is a benign condition as it rarely poses significant risk of brain damage or death. New imaging techniques has helped in both diagnosis and intervention. It should be considered in the differential diagnosis in patients who present with transient ischemic attack. Surgical or endovascular intervention is based on clinical symptoms and not only on imaging findings.