Bulky brachial plexus trunks showing interstitial oedema of the surrounding fat. The middle scalene muscle shows a tapering posteroinferior end denoting medialized insertion into the 1st rib. The subclavian artery shows a normal wave pattern in the neutral position.
However, on raising the patient's arm above the head with the face to the contralateral side, the waveform displays a sharp systolic upstroke (staccato wave) with increased peak systolic velocity (nearly doubled) denoting significant stenosis. The left side shows a normal calibre of the brachial plexus trunks compared to the affected right side.