First Presentation With Impending Cardiac Tamponade Leading to a New Diagnosis of Mediastinal Lymphoma: A Shared Learning Case on the Atypical Presentation of Pericardial Effusion and Cardiac Tamponade

Cardiac tamponade is a life-threatening emergency classically associated with Beck's triad of hypotension, muffled heart sounds, and elevated jugular venous pressure; however, incomplete or atypical presentations may delay diagnosis.We report the case of a previously healthy 28-year-old woman who presented with progressive dyspnoea, pleuritic chest pain, orthopnoea, peripheral oedema, fever, and fatigue.Examination revealed mild tachycardia, soft heart sounds, reduced basal air entry, and ankle oedema, while the patient remained normotensive.Initial investigations demonstrated cardiomegaly with pleural effusions on chest radiograph, low-voltage QRS complexes on electrocardiogram, and markedly raised inflammatory markers.Computed tomography pulmonary angiography identified a large anterior mediastinal mass encasing the great vessels, a significant pericardial effusion with features of cardiac tamponade, and bilateral pleural effusions.Emergency pericardiocentesis resulted in immediate clinical improvement.Histopathological analysis confirmed high-grade B-cell lymphoma, most consistent with primary mediastinal B-cell lymphoma.The patient was treated with immunochemotherapy, achieving complete metabolic remission on end-of-treatment PET-CT.This case highlights the importance of recognising atypical presentations of cardiac tamponade and considering mediastinal malignancy in young patients presenting with unexplained cardiorespiratory symptoms.