Hydatid disease, attributed to the tapeworm Echinococcus granulosus, poses a significant health threat in regions where it is endemic. Here, we present a case involving a 15-year-old boy from rural Pakistan who initially sought medical attention due to a persistent cough and hemoptysis. Despite initially testing negative for serological markers, imaging studies revealed well-defined cysts in both lungs. Confirmation of the diagnosis was achieved through histopathological examination. Management includes albendazole therapy and surgical excision of the cyst. Our case underscores the diagnostic challenges associated with seronegative cases and underscores the importance of considering hydatid disease in endemic regions, irrespective of typical serological markers. This report enhances understanding regarding the clinical presentation, diagnostic approach, and management strategies for pulmonary hydatid cysts.

Echinococcosis is caused by tapeworms belonging to the Echinococcus genus. The most common site of infection is the liver although it may involve almost any organ. Symptoms of pulmonary echinococcosis vary depending on the location and structure of the cyst. While uncomplicated cysts usually appear at imaging as well-defined homogeneous lesions with fluid content and smooth walls of variable thickness, complicated lesions may have a more heterogeneous content with higher density making more difficult the distinction from malignancies or other infections. Hereby we describe the case of a 61-year-old Northern African male admitted to our tertiary center for left upper chest pain who then underwent a chest computed tomography (CT) scan which demonstrated a large hypodense lesion, with smooth and thick walls, in the upper left lobe. The following magnetic resonance confirmed the homogeneous fluid content, and the 18 F- fluorodeoxyglucose-positron emission tomography/CT demonstrated a mild uptake of the walls. According to these findings, the main differential diagnoses at imaging included bronchogenic cyst, synovial sarcoma, and pulmonary hematoma although the patient denied any recent trauma. Given the large size and clinical symptoms he underwent surgery. Intra-operative frozen section, supported by imprint cytology, excluded the presence of malignancy while suggested an echinococcal laminar exocyst. The final pathological examination confirmed the diagnosis of echinococcosis (i.e., Echinococcus Granulosus protoscolex). After surgery he was treated with albendazole and at the six-month follow-up he was in good clinical conditions. Our case highlights the importance of considering rare infections, particularly in individuals from endemic areas. Frozen tissue analyses can be a diagnostic challenge and often require ancillary tools such as imprint cytology and serial sections for more sensitive and accurate diagnosis.