A 66-year-old man presents with vertigo triggered by using his left arm. Duplex ultrasound shows monophasic antegrade flow in the left common carotid artery and reversal of flow direction in the left vertebral artery throughout systole. Which finding on the same study best explains these results?

• A High-grade stenosis at the origin of the left subclavian artery ✓
• B Occlusion of the left internal carotid artery
• C Arteriovenous fistula of the left arm
• D Dissection of the left vertebral artery

Explanation

Subclavian steal syndrome is caused by a proximal subclavian stenosis or occlusion that lowers pressure distal to the lesion, so the ipsilateral vertebral artery flows retrogradely to supply the arm. Arm exercise provokes the vertigo. Vertebral flow reversal is the defining Doppler sign. Internal carotid occlusion would not reverse vertebral flow, and vertebral dissection produces irregular stenosis or occlusion of the vertebral artery itself rather than reversed direction throughout the vessel.

Reference: Brant and Helms Fundamentals of Diagnostic Radiology, 5th ed.

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Written and medically reviewed by the StethoPrep medical team.