When Constriction Is Not Just the Pericardium: Extrinsic Cardiac Encasement by Thymic Squamous Cell Carcinoma.

Constrictive pericarditis (CP) typically primarily involves pericardial pathology, but mediastinal malignancies can create an identical hemodynamic profile through direct extrinsic encasement. We report a 58-year-old male patient with metastatic thymic squamous cell carcinoma presenting with refractory right-sided heart failure and anasarca. Although his history initially suggested radiation-induced or post-COVID-19 pericarditis, right heart catheterization and echocardiography revealed classic constrictive physiology, including a "septal bounce" and ventricular interdependence with a preserved ejection fraction. A four-month trial of corticosteroids and colchicine failed to improve his hemodynamics. Positron emission tomography-computed tomography (PET/CT) subsequently confirmed that the thymic mass had directly infiltrated the mediastinal pleura and pericardium, creating a rigid shell encasing the heart and compressing the inferior vena cava. Due to the tumor's surgical inaccessibility and the failure of medical treatment, the patient was transitioned to palliative care. This case of "malignant pseudo-constriction" emphasizes the diagnostic challenge of distinguishing reversible inflammatory pericarditis from irreversible malignant encasement. In patients with advanced mediastinal tumors, persistent constrictive symptoms despite anti-inflammatory therapy should raise high clinical suspicion for direct tumor infiltration. This condition, which can be diagnosed utilizing advanced imaging modalities, carries a poor prognosis and typically precludes surgical intervention.