Aberrant left internal thoracic artery origin from the extrascalenic part of the subclavian artery

The internal thoracic artery (ITA) is considered to be the optimal conduit for surgical coronary artery revascularization. Variations in ITA anatomy are relatively common and may impact surgical results. The ITA usually arises from the intrascalenic (first) part of the subclavian artery (SCA) and, occasionally, from the interscalenic (second) part. Origination from the extrascalenic (third) part of the SCA is rare, with a reported incidence rate of 0.5% to 1.0% in anatomical studies, and 1.5% in one angiographic study. Such an aberrant ITA descends inferomedially, anterior to the distal attachment of the scalenus anterior muscle, passes posterior to the first rib and enters the thorax, from where it follows its usual course. A patient with a five-year history of in situ grafting of the left ITA to the anterior interventricular artery is presented. Coronary angiography performed because of anterior wall ischemia revealed an aberrantly arising ITA from the extrascalenic part of the SCA. The implications of this ITA variant with regard to bypass surgery, postoperative angiography and subclavian vein catheterization are discussed.