Pitfall of electron beam computed tomography angiography in diagnosis of subclavian steal syndrome.

A patient presented with vertebrobasilar insufficiency during exertion. Vertebral duplex and transcranial Doppler ultrasonography showed reversal of flow in both intracranial and extracranial vertebral and basilar arteries, suggesting bilateral subclavian and vertebrobasilar steal. Electron beam computed tomography angiography (CTA) showed no evidence of subclavian artery stenosis including normal vertebral artery origin on both sides. However, digital subtraction angiography revealed complete occlusion of both subclavian arteries with retrograde flow from both vertebral and basilar arteries to reconstitute both subclavian arteries. This false-negative finding on CTA in detection of subclavian steal syndrome (SSS) is due to inappropriate contrast administration technique and postprocessing method, inability to differentiate flow direction, and lack of hemodynamic time sequences. This study demonstrates a pitfall of CTA in diagnosis of SSS compared to more reliable hemodynamic information obtained by duplex and transcranial Doppler ultrasonography, and digital subtraction angiography.