Anomalous Origin of Left Internal Mammary Artery

Origin of the internal mammary artery from sites other than the inferior surface of the first part of the subclavian artery is not uncommon. We describe the case of a left internal mammary artery (LIMA) originating from the third part of the left subclavian artery and its clinical relevance. Case Report. A 65-year-old man gave a two-week history of unstable angina seven years after successful coronary artery bypass (CABG) surgery. He had required two admissions to the hospital with typical angina at rest associated with ST segment depression in leads V4-V6, I and AVL and raised Troponin I and MBCPK levels but no Q-waves. Cardiac catheterization showed good left ventricular function with inferior hypokinesia.The left main coronary artery had a 95% distal stenosis, the left anterior descending (LAD) and left circumflex coronary arteries were occluded and the dominant right coronary artery (RCA) had a 95% mid-third stenosis. The saphenous vein grafts to the obtuse marginal and diagonal arteries were patent without significant disease, but the LIMA which had been grafted to the LAD could not be demonstrated and was assumed to be occluded. He was referred for percutaneous coronary intervention (PCI) to the ungrafted RCA. However, prior to PCI it was felt necessary to be certain that the LIMA was occluded. Using a 5 French LIMA diagnostic catheter (JoMed Inc., Rancho Cordova, California), the LIMA was not found in its usual position on the inferior surface of the first part of the subclavian artery. On advancing the catheter progressively more distally, hand injection of contrast media demonstrated the LIMA to originate from the third part of the subclavian artery (Figure 1). The LIMA was selectively engaged and angiography demonstrated patency with good run-off down the LAD. PCI with stent implantation was then performed to the RCA stenosis without complication and produced an excellent angiographic and clinical result. Discussion. The subclavian artery is anatomically divided into three parts. The first part extends from the arch of the aorta to the medial border of the scalenus anterior. The second segment lies behind scalenus anterior and the third part from the lateral border of this muscle to the outer border of the first rib.1 The internal mammary artery (IMA) arises most commonly from the inferior aspect of the first part of the subclavian artery just beyond the curve in the vessel and the origin of the vertebral artery. However, little awareness exists of the anomalous origins of the IMA. In a detailed post-mortem study, Henriquez-Pino et al.2 found that the IMA arose directly from the subclavian artery in only 70% of cases and from a common arterial trunk (e.g. thyrocervical or costocervical trunk) in 30%. The IMA arose from the first part of the subclavian artery in 92%, in 7% from the second part, and in 1% from the third part. In their study, the IMA originated from the third part of the left subclavian artery, whereas Vorster et al.3 described a similar anomalous origin from the right subclavian artery. An earlier study of 769 cadavers also reported IMAs originating from the third part of the subclavian artery in 0.78% of cases.4 In a single cadaveric report, Omar et al.5 described bilateral IMAs originating from the third parts of the respective subclavian arteries and discuss the developmental embryology of the IMAs. Finally, Chavez and Osborne6 reported a LIMA originating from the junction of the left subclavian artery and aorta. In an angiographic study of IMAs in 262 patients,7 a common origin of the IMA with another large artery was found in 11% and a lateral origin in 1.5%, the latter being consistent with the post-mortem study of Dr. Henriquez-Pino and colleagues.2 The possibility of these unusual anomalous origins should be remembered when restudying patients after CABG surgery, since proven patency may have important implications when considering repeat CABG or the need for a high-profile surgical cover for percutaneous coronary intervention in what may be assumed to be a “last-remaining vessel” scenario. Moreover, an anomalous origin of the IMA from the third part of the subclavian artery and its proximal course anterior to the distal attachment of the scalenus anterior may render it susceptible to trauma or entry in patients undergoing percutaneous subclavian vein catheterization. Anomalies of the left internal mammary artery are uncommon and routine identification of the LIMA by selective angiography prior to coronary artery bypass surgery is not recommended unless clinical features suggest subclavian artery stenosis.

1. Gray’s Anatomy. 34th Edition. DV Davies and RE Coupland (Eds). Published by Longmans, Green and Co Ltd., London, 1967: pp. 808–811. 2. Henriquez-Pino JA, Gomes WJ, Prates JC, Buffolo E. Surgical anatomy of the internal thoracic artery. Ann Thorac Surg 1997;64:1041–1045. 3. Vorster W, Du Plooy PT, Meiring JH. Abnormal origin of the internal thoracic and vertebral arteries. Clin Anat 1998;11:33–37. 4. Daseler CJ, Anson BJ. Surgical anatomy of the subclavian artery and its branches. Surg Gynecol Obstet 1959;108:147-9. 5. Omar Y, Lachman N, Satyapal KS. Bilateral origin of the internal thoracic artery from the third part of subclavian artery: A case report. Surg Radiol Anat 2001;23:127–129. 6. Chavez J, Osborn LA. Anomalous origin of left internal mammary artery from the lateral junction of the left subclavian artery and aorta. Cathet Cardiovasc Diagn 1996;37:168–169. 7. Bauer EP, Bino MC, von Segesser LK, et al. Internal mammary artery anomalies. Thorac Cardiovasc Surg 1990;38:312–315.