Discussion
We reported a 17-year-old male presented with a large pulmonary hydatid cyst (PHC). Spontaneous rupture of the cyst led to acute respiratory distress syndrome requiring mechanical ventilation. Echinococcus granulosus, a parasitic tapeworm is the pathogenic organism of hydatid disease. This infectious disease is endemic in many parts of the world such as Iran and it is considered a health concern in these countries. While hydatid cysts could be produced in different organs, the liver and lungs are the most frequently affected sites. The definite hosts of the disease are carnivores such as dogs. Humans are defined as the incidental intermediate host who is infected by direct contact with dogs or ingestion of food contaminated by their feces. Echinococcal embryos are released in the gastrointestinal lumen and reach the blood vessels or lymphatics by penetrating the intestinal wall. Then they reach different organs including the liver and lungs through the bloodstream or lymphatics where they form hydatid cysts. As we mentioned in the case presentation section our patient was a vegetable farmer and he might have been infected by the ingestion of contaminated vegetables [3, 4].
Hydatid cyst remains asymptomatic during the first few years. Clinical presentation depends on the location and size of the cysts. The most frequently reported symptoms of pulmonary hydatid disease are cough, chest pain, dyspnea, and hemoptysis. Rupture of the cysts or secondary bacterial infection may occur. Rupture of the cysts either iatrogenic or spontaneous may cause cough, chest pain, hemoptysis, emesis, pneumothorax, pleural effusion, or empyema. Fever and hypersensitivity reactions including anaphylaxis may occur as a consequence of cyst rupture [3, 4].
Chest X-ray and chest CT scan are diagnostic tools for pulmonary hydatid cysts. Similar to our case, on chest CT scans, PHCs are smooth-walled cysts with variable thickness and contain soft tissue with the density of water or near water. Leukocytosis, eosinophilia, and elevated ESR are nonspecific laboratory features. The coexistence of pulmonary and liver cysts is prevalent. Therefore, when PHC is diagnosed, additional imaging like ultrasonography should be done to investigate possible liver cysts. Surgery and medical treatment are two major therapeutic options. Surgery is the treatment of choice. Medical treatment includes benzimidazoles like mebendazole or albendazole which are administered orally and used for specific indications such as disseminated disease, contraindication for surgery, recurrent cysts, multiple cysts, or leakage of hydatid fluid during operation [5, 6].
Fanne et al reported a 21-year-old female presented with productive cough, dyspnea, and fever. Two cavitary lesions with air-fluid levels were found on the chest X-ray. Five days after hospitalization she developed eosinophilia, ARDS, and anaphylactic shock and was intubated. Albendazole, praziquantel, and high doses of intravenous steroids were administered. She improved after four weeks and underwent cyst resection and lobectomy after discharge [7].
In conclusion, acute respiratory distress syndrome could be a possible complication of a pulmonary hydatid cyst. Physicians should be aware of this life-threatening complication for appropriate diagnosis and treatment.