Neovascularization of Thymoma From Left Internal Mammary Artery Bypass Graft Jordan Y. Dubique, BS, Harma Turbendian, MD, and Danny Chu, MD University of Pittsburgh School of Medicine, Department of Cardiothoracic Surgery, and Division of Cardiac Surgery, University of Pittsburgh Medical Center Heart and Vascular Institute, Pittsburgh, Pennsylvania
We present the case of a type AB thymoma in a 69-yearold man with previous coronary artery bypass grafting (CABG) in whom angiography revealed a left internal mammary artery graft supplying blood flow to a thymic neoplasm, which simultaneously occluded the graft. This required a redo sternotomy, lysis of pericardial adhesions, complete thymectomy, and redo one vessel off-pump CABG. This case seeks to sensitize physicians to the possibility of coronary adverse events in patients with a previous CABG in the setting of management of mediastinal neoplasms, and it presents the novel findings on cardiac imaging associated with this case. (Ann Thorac Surg 2017;103:e247–8) Ó 2017 by The Society of Thoracic Surgeons
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hymomas are defined as low-grade epithelial neoplasms that arise from the thymus and are most commonly located in the anterosuperior mediastinum. The majority of thymomas exist as encapsulated wellcircumscribed firm masses and can range from microscopic to over 30 cm in diameter. The interior typically has a lobulated appearance, with bands of fibrous stroma. Thymomas can also occasionally be invasive and encase other mediastinal structures [1]. Thymomas represent 20% of all mediastinal masses and affect patients typically between the ages of 40 and 60 years. Internal mammary grafts are widely acknowledged in the cardiac-related health professions as being superior to other methods of cardiac revascularization and the left internal mammary artery (LIMA) to the left anterior descending artery (LAD) is seen as the gold standard in coronary artery bypass grafting (CABG). This status is attained in part because the patency rates are higher at 10 years compared with saphenous vein grafts (SVG) (90% of LIMA grafts patent vs 57% of SVG in a study of 4,333 patients) [2]. Furthermore, reoperative cardiac surgical procedures represent a significant challenge to surgeons because of the well-documented increased risk of cardiac injury and hemorrhage, which increase perioperative morbidity and mortality [3]. These risks are the result of a myriad of factors that complicate redo cardiac operations. These factors include adherence of grafts, the aorta and
right ventricle to the sternum, making sternal entry more complicated. In addition, the dissection of the heart required in redo cardiac surgical procedures leads to an increased risk of thromboembolism, hemorrhage, or both caused by the manipulation of previously grafted vessels and the presence of native disease in those vessels [4]. A 69-year-old white man presented for evaluation of a mediastinal mass and coronary artery disease (CAD). The patient had experienced progressive dyspnea on exertion and a chronic nonproductive cough. His medical history was significant for CAD, and for three-vessel CABG performed in 2002 with LIMA to LAD, SVG to diagonal artery, and radial artery graft to posterior descending artery. The result of physical examination was unremarkable. Computed tomography (CT) demonstrated a 5.8 5.5 5 cm anterior mediastinal mass that was abutting the ascending aorta and left internal mammary bypass graft (Fig 1). Cardiac catheterization revealed a patent radial artery graft, ostial occlusion of the saphenous vein graft, and an atretic LIMA that was occluded within the area of the mediastinal mass (Fig 2), likely from a compressive effect. There were also several small perforating vessels to the mass that arose from the left internal mammary. Histologic examination of a CT-guided biopsy specimen confirmed a type A thymoma. After initial outpatient surgical evaluation and preoperative planning, the patient came to the emergency department with reproducible chest pain and dyspnea on exertion. No ST segment changes were noted at the time, and troponins were within normal limits. He was taken to the operating room a few days later for a median sternotomy, thymoma excision, and off-pump CABG. The previously placed LIMA graft was occluded by the tumor and was removed. A skeletonized in-situ pedicle right internal mammary artery (RIMA) to LAD graft was placed. The pathologic appearance was notable for a 6 7 cm encapsulated type AB thymoma, which was completely resected with grossly negative margins, and no signs of invasive properties (Masaoka stage I).
Accepted for publication Aug 14, 2016. Address correspondence to Dr Chu, Department of Cardiothoracic Surgery, UPMC Presbyterian Hospital, 200 Lothrop St, C-700, Pittsburgh, PA 15213; email:
[email protected].
Ó 2017 by The Society of Thoracic Surgeons Published by Elsevier
Fig 1. Noncontrast computed tomographic chest scan demonstrating thymoma abutting left internal mammary artery graft. 0003-4975/$36.00 http://dx.doi.org/10.1016/j.athoracsur.2016.08.047
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CASE REPORT DUBIQUE ET AL LIMA GRAFT SUPPLYING BLOOD TO THYMOMA
Fig 2. Coronary angiogram demonstrating left internal mammary artery graft neovascularization of thymoma (arrow).
Comment Thymomas are defined as anterior mediastinal tumors that can be categorized into three main groups according to histologic appearance and behavior. They are categorized as low-grade neoplasms in the absence of macroscopic and microscopic invasion but as high-grade malignant neoplasms in the presence of capsular invasion. The third category, thymic carcinoma, includes tumors that have undifferentiated malignant epithelial features [2]. Complete surgical resection through a median sternotomy is the standard of care for encapsulated thymomas [5, 6]. This patient’s previously grafted LIMA supplied the thymoma by means of neovascularization and had its flow to the LAD occluded by the neoplasm from mass effect. The thymus is an encapsulated structure that exists as two lobes supplied by the thymic arteries, which are typically branches of the internal thoracic arteries. This natural anatomic relation likely played a role in the angiogenesis that arose from the internal mammary graft. In addition, the compromised cardiac blood flow partially induced by the thymoma required a careful and well-planned surgical approach in which we managed to completely resect the thymoma and to restore perfusion to the myocardium through the RIMA graft. Various
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strategies helped make this reoperative surgical procedure successful. Preoperative imaging allowed the selection of an optimal approach. Performance of the procedure off pump minimized the postoperative risks typically associated with cardiopulmonary bypass. Minimizing the manipulation of previous venous grafts decreased the risk of thrombosis or hemorrhage. A previous account of an SVG encased in a thymoma was treated with resection of the mass around the vein. There was also a case of a patent LIMA partially encased in a thymoma and perfusing it treated solely with tumor resection. Furthermore, although a LIMA encased in a thymoma has been described, to the best of our knowledge we have not found any cases in which flow from the LIMA to the LAD was compromised by a thymoma and vascularization of the tumor occurred through the occluded vessel [7, 8]. In summary, this case highlights a unique and rare case of a type AB thymoma in a patient with CAD and a previous three-vessel CABG with the LIMA graft compressed by the neoplasm, occluding flow and raising concern about severe cardiac adverse events. Mitigation of these concerns required the performance of a challenging redo sternotomy, lysis of pericardial adhesions, complete thymectomy, and redo one-vessel off-pump CABG of RIMA to LAD. Furthermore, this case report serves to sensitize physicians to one of the rare potential adverse events of mediastinal masses and contributes to the body of medical knowledge our unique findings.
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