Balancing Thrombosis and Bleeding: A Case of Massive Haemothorax Complicating Anticoagulation for Pulmonary Embolism.

Massive haemothorax is a life-threatening condition most commonly associated with thoracic trauma, malignancy, or iatrogenic injury. Anticoagulation, while essential for thromboembolic disease management, may precipitate or exacerbate occult bleeding complications. We report the case of a 69-year-old woman who presented with pleuritic chest pain, productive cough, and progressive dyspnoea following a recent fall and long-haul travel. CT pulmonary angiography confirmed segmental and subsegmental pulmonary emboli with bilateral consolidation, and therapeutic low-molecular-weight heparin was initiated. On the third hospital day, she developed sudden hypoxia, left-sided chest pain, and a significant haemoglobin decline. Repeat imaging demonstrated a massive left haemothorax with lung collapse and mediastinal shift, together with previously unrecognised right-sided rib fractures. Anticoagulation was immediately discontinued and reversed, and the patient underwent blood transfusion and chest drainage, yielding over 2.4 L of blood. Residual loculated haemothorax was successfully managed using image-guided catheter drainage without surgical intervention. This case highlights the rare occurrence of delayed contralateral haemothorax complicating anticoagulation and underscores the importance of recognising atypical bleeding presentations and balancing thrombotic and haemorrhagic risk through multidisciplinary decision-making.