C63-23 Acquired Right Ventricular Outflow Tract Obstruction From Anterior Mediastinal Thymoma

Abstract Introduction Thymomas are the most common anterior mediastinal tumors, often found incidentally or in association with myasthenia gravis. Rarely, they can present with symptoms of compression on adjacent structures. Only a few cases describe right ventricular outflow tract (RVOT) or pulmonary artery compression leading to acquired pulmonic stenosis. We report a patient with an asymptomatic thymoma presenting solely with a new ejection murmur due to RVOT obstruction. Case Description A 58-year-old man with prior prostate cancer (post-prostatectomy, 2015) was found to have a new holosystolic ejection murmur during routine examination. He denied dyspnea, chest pain, or syncope. Transthoracic echocardiography revealed subpulmonic and pulmonic valve stenosis from external compression by an anterior mediastinal mass, with a peak pulmonic valve gradient of 55 mmHg. Chest computed tomography demonstrated a 12 × 9×13 centimeters anterior mediastinal mass compressing the main pulmonary artery, invading the left upper lobe, and abutting the pericardium and aortic arch. Mediastinoscopy with biopsy confirmed Type AB thymoma. Given the tumor’s invasion and high surgical risk, a multidisciplinary team recommended neoadjuvant chemotherapy with cisplatin, doxorubicin, and cyclophosphamide (CAP regimen). Due to risk of hemodynamic compromise, treatment was initiated under continuous inpatient monitoring. After two cycles, repeat echocardiography showed improvement in the peak pulmonic valve gradient (from 55 to 35mmHg) and partial decompression of the pulmonary artery. The patient continues systemic therapy with planned surgical resection. Discussion Thymomas constitute about 20 percent of anterior mediastinal neoplasms. Although often indolent, invasive tumors can compress the RVOT or pulmonary artery, increasing right ventricular afterload and potentially causing right heart failure or obstructive shock. Echocardiography defines the hemodynamic impact, while CT delineates anatomical relationships. Management requires multidisciplinary coordination. Neoadjuvant chemotherapy can reduce vascular compression, improve pulmonary pressures, and enhance surgical resectability. In our patient with severe RVOT obstruction, we were concerned that initiation of chemotherapy might lead to hemodynamic instability due to tumor necrosis, inflammation, volume shifts, or systemic complications such as tumor lysis and capillary leak syndromes. These risks prompted initiation of therapy in an inpatient monitored setting, with early intervention strategies in place and consideration of extracorporeal membrane oxygenation (ECMO) if decompensation occurred. Awareness of thymoma as a rare cause of acquired pulmonic stenosis expands the differential diagnosis for RVOT obstruction. Prompt recognition and timely therapy can prevent hemodynamic compromise and improve outcomes. This abstract is funded by: None