Metastatic Gastric Adenocarcinoma Presenting With Pleuropericardial Effusions and Cardiac Tamponade: A Diagnostic Challenging Case Report.

Metastatic gastric adenocarcinoma rarely manifests initially with massive pleuropericardial effusions and life-threatening cardiac tamponade. Identifying the primary tumour source in such acute and complex clinical presentations represents a significant diagnostic challenge. A 44-year-old man with a history of heavy tobacco smoking and chronic opium use presented with acute-onset dyspnea and chest pain. Imaging revealed massive pleural and pericardial effusions causing cardiac tamponade, necessitating urgent pericardial drainage. Initial investigations, including pleural and pericardial fluid analyses, were non-diagnostic and demonstrated lymphocyte-predominant exudative effusions. Definitive diagnosis was achieved through video-assisted thoracoscopic surgery (VATS) with pleural biopsy, revealing metastatic adenocarcinoma. Immunohistochemical profiling (CK7+/CK20+/TTF-1-) supported a primary origin of gastric carcinoma. The patient's clinical course was complicated by ventilator-associated pneumonia and septic shock, ultimately resulting in death before initiation of systemic therapy. This case highlights the diagnostic challenge of occult gastric adenocarcinoma presenting with pleuropericardial effusions and tamponade. In unexplained lymphocyte-predominant effusions, malignancy should be considered, and early VATS-guided pleural biopsy may be required when noninvasive tests are inconclusive. Prognosis remains poor in advanced disease.