Pneumothorax due to perforated pulmonary hydatic cyst with bronchial fistula.

Cystic echinococcosis (CE) is a zoonotic disease caused by Echinococcus granulosus, with a high prevalence in Iran, particularly in Mazandaran province. This case report presents a 24-year-old male with pneumothorax resulting from ruptured pulmonary hydatid cysts with bronchial fistulization. The patient presented with persisted dyspnea, productive cough, fever, and mild right thoracoabdominal pleuritic pain, alongside a history of occupational exposure as a sheep keeper. Imaging revealed large cystic masses in lungs and a severe right pneumothorax. Despite initial stabilization with chest tube insertion, surgical intervention was aborted due to intraoperative instability, necessitating pulmonary rehabilitation. The hydatid serology ELISA test was negative, however the cell-free DNA (cfDNA) based PCR biomarker confirmed the diagnosis. This report highlights the diagnostic value of cfDNA in pulmonary CE, particularly when serological tests yield negative results. Early detection and multidisciplinary management are critical for optimal outcomes in pulmonary hydatid cysts complicated by pneumothorax.