59-year-old woman presented with a pulsatile lump in the neck after carotid artery stenting for symptomatic focal stenosis (50-69%) of the left carotid bulb (Fig. 1A). Cervical duplex ultrasonography and computed tomography-angiography revealed a large lobulated pseudoaneurysm (measuring 2.6 × 2.4 × 2.1 cm) involving the left common and internal carotid artery (Fig. 1B and C). Swirling motion of blood flow, referred to as the "yin-yang sign", was observed within the pseudoaneurysm (Supplementary movie 1).1) During surgical exploration, the tissue surrounding the pseudoaneurysm was noted be infected involving left internal carotid artery, vagus nerve and the internal jugular vein (Fig. 1D). She unfortunately sustained a left hemispheric stroke post-operatively. Fig. 1 Neck X-ray showing a long left carotid stent (arrow) (A). Cervical duplex showing the pseudoaneurysm originating from distal common carotid artery (straight arrow, B). Computed tomography angiography of the neck (C). The lobulated pseudoaneurysm (arrow, ...