A Rare Presentation of a Giant Hepatic Hydatid Cyst Mimicking Massive Pleural Effusion: A Case Report

Background: Hydatid disease, caused by Echinococcus granulosus, commonly affects the liver and lungs. Complications such as transdiaphragmatic extension are rare and may mimic primary pulmonary conditions. Case Presentation: A 72‑year‑old female with long‑standing Type 2 Diabetes Mellitus and recently diagnosed Hypertension presented with acute worsening breathlessness and right upper quadrant abdominal pain. Clinical findings revealed a stony dull percussion note and complete absence of breath sounds over the right hemithorax, suggestive of massive pleural effusion. Laboratory investigations showed marked eosinophilia and an exudative eosinophilic pleural fluid. Ultrasound and CT imaging identified a large hepatic hydatid cyst measuring 15.3 × 10.7 cm with associated massive right‑sided pleural effusion. Discussion: The respiratory‑dominant symptoms led initially to a misdiagnosis of primary pleural effusion. However, the presence of eosinophilic pleural fluid and a palpable hepatic mass redirected suspicion towards hydatid disease. Transdiaphragmatic extension and immunologically mediated sympathetic effusion are known but uncommon complications. Conclusion: Hydatid disease should be considered in elderly patients presenting with combined hepatic and thoracic symptoms, particularly in the presence of eosinophilic pleural effusion. Early recognition and multidisciplinary management are essential.