Subclavian Steal Phenomenon

The term SSS should be reserved for retrograde vertebral artery flow associated with transient neurologic symptoms related to cerebral ischemia. SSP refers to retrograde flow in the vertebral artery only. First diagnosed angiographically in the early 1960s, SSS is now most commonly diagnosed during Doppler ultrasound (US) examination of the neck arteries.

Color Doppler US is the preferred examination for subclavian steal syndrome, but it is operator dependent. In addition, direct examination of the proximal subclavian artery is compromised by the overlying clavicle, ribs, and sternum.

• Etiology: Severe subclavian artery (SCA) stenosis or occlusion with collateral flow of blood to the arm via the vertebral artery (VA)
• With proximal SCA occlusion, blood flow is "stolen" from the ipsilateral VA with hyperdynamic flow through the contralateral VA as it is supplying the vertebrobasilar system and collateral blood flow to the contralateral arm.
• Causes: By far the most common is atherosclerotic disease (>70% stenosis). Other less likely causes are vasculitis, neoplasm with mass effect, or dissection.
• Clinically often asymptomatic. May cause arm claudication during exercise. Decreased upper extremity blood pressure on ipsilateral side of occlusion/stenosis
• Very rarely causes vertebrobasilar infarct of the brainstem or cerebellum due to collateralization of the anterior circulation
• Predominantly occurs on the left side (85%)
• Treatment:
  • Angioplasty or stenting
  • Bypass graft such as common carotid to subclavian bypass
  • Address atherosclerotic risk factors
• CT findings: Occlusion or severe stenosis of the proximal SCA on contrast-enhanced study
• MR findings:
  • T2WI � absence of flow voids if severely stenotic SCA or occluded
  • MRA � can determine degree of SCA stenosis. Phase contrast MRA can confirm vessel patency and direction of flow
• Angiography: reversal of flow in the ipsilateral vertebral artery with high grade proximal SCA stenosis
• Ultrasound: Gold standard
  • Reversal of flow in the VA ipsilateral to the proximal SCA occlusion/severe stenosis
  • Moderate steal can appear as to-and-fro flow in the ipsilateral VA
  • Increased blood flow velocity in the contralateral VA
  • Doppler evidence of SCA stenosis such as turbulence or high velocity
  • Early subclavian steal physiology identified on Doppler waveforms include transient sharp deceleration of blood flow after the first systolic peak. As disease state progresses, the second systolic peak broadens and diminishes until reversal of flow during systole with return of antegrade flow during diastole.