62 year-old male with past medical history significant for ischemic heart disease and coronary bypass graft (CABG) surgery 5 years ago, now presenting with new onset angina and a mediastinal mass on chest radiograph.

Figure 1: Axial DB HASTE image demonstrates a mass lesion protruding into the lateral aspect
of the right atrial wall which is surrounded by a thin smooth wall. This mass measured 8.2
(craniocaudal) x 4.2 (oblique transverse) x 3.3 (oblique AP) cm.

Figure 2: Coronal DB HASTE image demonstrates a smooth bilobed mass protruding into the lateral
aspect of the right atrial wall.

Figure 3: Coronal thin MIP image demonstrates a coronary bypass graft originating from the ascending
aorta and coursing through the bilobed right atrial wall mass. The anastomosis of the coronary
graft to the aorta appears patent. There is an area of extraluminal contrast collection (yellow arrow) adjacent to the mass surrounded by non-enhancing thrombus. The distal coronary graft anastomosis is obscured by overlying adjacent metal artifact (red arrow), presumably from a vascular clip.

Coronary artery bypass graft aneurysm with extensive mural thrombus.

Coronary artery revascularization (coronary artery bypass graft surgery (CABG)) with saphenous vein grafts is a surgical standard for treatment of coronary artery disease. Aneurysmal dilatation of saphenous vein grafts (SVG) is a rare complication, with only 78 cases reported in the English literature since 1975. Saphenous vein graft aneurysms can be either true or false (pseudo) aneurysms. They can occur as an early or late complication of CABG surgery, with most occurring at a mean of 10 years after surgery (range 2 months to 21 years). True aneurysms involve all 3 layers of the vessel wall, whereas pseudoaneurysms represent a dilatation of the vessel with disruption of one or more layers of the vessel wall. True aneurysms, which usually develop in the body of the graft, are most commonly associated with progression of atherosclerosis and remodeling the bypass grafts. Hypertension, hypercholesterolemia, hyperlipidemia and elevated triglycerides have been implicated in atherogenesis of SVGs. Other contributing factors for the development of true aneurysms include vein graft necrosis, hypertension, fibrosis, intimal thickening, loss of elasticity varicosities, venous valves, weakness at branch points, and trauma. Although most true aneurysms occur in the late postoperative period secondary to atherosclerosis and intimal hyperplasia, they can develop early in the postoperative period due to preexisting vein wall weakness, vein graft necrosis, or hypertension. Pseudoaneurysms are caused by graft necrosis, suture breakage, faulty suture placement, infection of vein graft, suture line dehiscence, and shear stress. Staphylococcus aureus infection is the most common infection of the vein graft in pseudoaneurysms. Pseudoaneurysms occur at the aortotomy site, at the site of the ligated tributaries of the graft, or at the graft and coronary anastomotic site. The average size of a SVG graft aneurysm at diagnosis is 5.5 cm. Pseudoaneurysms tend to be larger than true aneurysms. True aneurysms tend to be fusiform and symmetric as opposed to pseudoaneuryms, which are usually saccular and asymmetric.

Saphenous vein graft aneurysms are more common in men than in women, probably because more men undergo CABG surgery. Men are twice as likely to have true rather than pseudoaneurysms, whereas, women develop true and pseudoaneurysms in equal distribution. At the time of diagnosis, the average age of patients is 59 years (range 23-80 years). Women tend to be older than men at presentation, most likely because of the later development of coronary artery disease and treatment with coronary artery vascularization. Of cases reported in literature, 61% of patients present with ischemic symptoms, such as unstable angina or acute myocardial infarction, caused by either occlusion of the graft or embolic phenomenon. Other signs and symptoms can include a painful pulsatile retrosternal mass, superior vena cava syndrome, pleuritic chest pain, and worsening dyspnea. Many saphenous vein graft aneurysms may be asymptomatic and remain subclinical, often presenting as an incidental finding of a mediastinal mass on chest radiograph. Potential complications of vein graft aneurysms and pseudoaneurysms include bleeding, embolization, thrombosis, myocardial infarction, rupture with hemothorax, fistula formation between the aneurysm in the graft and one of the chambers of the heart, and sudden death.

The radiologist should always suspect the presence of a coronary graft aneurysm whenever a patient presents with the following triad: a history of previous CABG surgery, new onset angina, and a chest radiography remarkable for a mediastinal mass. Various diagnostic modalities have been used for the diagnosis of saphenous vein graft aneurysms include including subtraction angiography, transesophageal echocardiography, coronary angiography, and computed tomography (CT).

Magnetic resonance imaging (MRI) is a very useful noninvasive diagnostic tool for evaluating coronary artery bypass grafts. On MR reverse saphenous vein and internal mammary grafts are relatively easy to image because of their relatively stationary position, less convoluted and more predictable course, and larger lumen in comparison to native coronary vessels. MR images can also accurately identify coronary graft pathology including graft occlusion less frequently encountered complications such as graft aneurysm. Because MR imaging has the ability to image in more than one plane, MR allows for excellent definition of a SVG aneurysm. MR images can localize the aneurysm to the graft and delineate the extent of graft vessel involvement. In addition, dynamic MR imaging has the ability to gather functional data on blood flow through the graft and aneurysm. On contrast enhanced dynamic MR images, the graft aneurysm demonstrates enhancement simultaneously with the descending aorta and later than the pulmonary artery. MR imaging is hindered by the presence of sternal wires, graft markers or surgical clips that create local field inhomogeneities and susceptibility artifacts.

The distinction between true and false aneurysms does not impact treatment. Although the recommendations for saphenous vein graft aneurysms are not well established, the significant morbidity and mortality associated with both true and pseudoaneurysms advocates early surgical intervention on detection of a SVG aneurysm. Surgical correction involves resection of the aneurysm with replacement of the diseased graft. Other treatment options for SVG aneurysm include coil implantation and embolization procedures. Mortality rate is high, with up to 28% of patients dying within 90 days of initial presentation of symptoms.

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