The accessory hemiazygos vein is an infrequently visualized channel that normally drains the posterior intercostal veins of the left midthorax, but can maintain critical venous return following innominate occlusion. In a 47-year-old woman, severe left innominate vein stenosis (Fig 1, arrow) occurred after an ipsilateral central venous catheter had been in place for 7 months. A peculiar garland-shaped venous configuration resulted from a grossly dilated accessory hemiazygos vein maintaining jugular and subclavian flow into the right atrium via the azygos vein, enabled by a tortuous hemiazygos-subclavian anastomosis (course demonstrated by guide wire in Fig 2, arrows). Such an anastomosis does not always exist: compensatory venous return following innominate occlusion instead commonly occurs via multiple smaller superficial and deep veins of the neck and thorax into the jugular, subclavian, and innominate veins contralaterally, or via collateral flow into the hemiazygos or inferior epigastric veins through intercostal and internal mammary veins.
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