The sonographic pitfall of carotid collateralisation via the vasa vasorum.

A 52-year-old man with obesity, type 2 diabetes mellitus and hypertension was admitted because of sudden onset of left hemiparesis and somnolence. Brain MRI disclosed a recent right thalamic stroke and multiple encephaloclastic lesions, suggestive of vascular sequelae. Carotid ultrasound demonstrated occlusion of the right internal carotid artery (ICA) and residual flow in the periphery of the left ICA lumen (fig 1A, B). Subocclusive stenosis was suspected. Carotid arteriography confirmed atherosclerotic occlusion of both bulbar ICAs. On the left side, however, filiform collateralisation with a spiral configuration was seen, extending from the ICA bulb to the cavernous segment (fig 1C). The patient was offered medical treatment.