A 42-year-old woman presented with worsening angina. Electrocardiography showed ST-segment elevation in lead aVR. Coronary angiography showed 80% ostial left main coronary stenosis (A, Online Video 1) and 90% ostial right coronary stenosis (B, Online Video 2). An intraaortic balloon pump was placed, and urgent coronary artery bypass surgery was performed. Intraoperatively, the patient had a “shield-like” infiltrative whitish mass involving the aortic root, ascending aorta, and pulmonary arteries, and extrinsically compressing both coronary arteries (C). Despite extensive involvement of the aortic root and arch, cannulation of the aortic arch was feasible, and saphenous vein grafts were placed. Biopsies showed necrosis with chronic inflammatory cells, mainly lymphocytes and neutrophils with fibroblasts and extensive collagen deposition (D and E). The cause of the mass remains idiopathic despite extensive workup.

Fibrosing mediastinitis is commonly idiopathic and related to autoimmune processes, such as retroperitoneal fibrosis, Riedel's thyroiditis, orbital pseudotumor, and Hodgkin's disease. Histoplasmosis, Mycobacterium tuberculosis, aspergillosis, blastomycosis, Nocardia, and Wuchereria bancrofti have been identified as potential causes.