A Heart Under Pressure: Anesthetic Management of a Large Ascending Aortic Aneurysm Mimicking Mediastinal Mass Physiology.

Large ascending aortic aneurysms (AscAAs), defined as exceeding 8 cm, are exceedingly rare and carry high mortality due to the combined risks of rupture and mediastinal compression. Their management demands precise anesthetic, surgical, and perfusion coordination to prevent hemodynamic collapse and neurologic injury. We report an 83-year-old woman with an 8.9 × 7.7 cm AscAA producing marked right ventricular and pulmonary artery compression. Perioperative management emphasized advanced monitoring, preservation of venous return during induction, and readiness for immediate cardiopulmonary bypass (CPB). Given the aneurysm's proximity to the sternum and high rupture risk, CPB via right axillary cannulation was established prior to sternotomy, followed by deep hypothermic circulatory arrest and complex aortic reconstruction. Intraoperative transesophageal echocardiography (TEE)-guided cannulation assessed ventricular filling under dynamic compression and confirmed graft and valve function. The patient recovered without major complications. This case underscores the physiologic overlap between giant aneurysms and anterior mediastinal masses, where loss of spontaneous ventilation or preload reduction may precipitate cardiovascular collapse. Our report additionally provides multimodal imaging that demonstrates the degree of anatomic distortion caused by a giant AscAA and includes a concise review of previously published cases. Effective management of these rare, life-threatening aneurysms relies on anticipating dynamic obstruction physiology, preparing for rapid bypass initiation, and maintaining continuous interdisciplinary coordination throughout the perioperative course.