Primary Mediastinal Pleural Hydatid Cyst Mimicking Tuberculous Pleuritis: A Case Report.

Hydatid disease, caused by various Echinococcus species, is endemic in developing countries and most commonly affects the liver and lungs. Approximately 7.4% of cases involve intrathoracic extrapulmonary locations, with pleural involvement usually resulting from rupture of adjacent hepatic or pulmonary cysts. However, primary pleural hydatid cysts are extremely rare, representing less than 1% of extrapulmonary cases, and may cause compressive symptoms depending on size and location. Diagnosis is guided by serologic testing and imaging, while surgical excision remains the mainstay of treatment. A 26-year-old Middle Eastern female presented to the emergency department with exertional dyspnea, right-sided pleuritic chest pain, low-grade fever, and night sweats. Physical examination revealed decreased breath sounds, dullness to percussion, and increased tactile fremitus on the right side, while imaging confirmed a moderate-to-large right pleural effusion with adhesions and fibrinous strands. Laboratory tests showed a lymphocytic exudative effusion with elevated adenosine deaminase, initially suggesting tuberculous pleuritis. However, negative cultures and positive anti-Echinococcus antibodies redirected the diagnosis to hydatid disease. Video-assisted thoracoscopic surgery (VATS) revealed dense adhesions and granulomatous inflammation on biopsy. Due to restricted lung expansion, right thoracotomy was performed, excising a cystic mass from the mediastinal pleura. Histopathology confirmed a hydatid cyst. The patient recovered well and was discharged on oral Albendazole. This case emphasizes the rarity of primary pleural hydatid cysts, the diagnostic challenges they pose, and the importance of considering parasitic infections in pleural effusions for timely surgical and medical management.