Lung cyst caused by centrally located bronchogenic carcinoma.

A 45-year-old smoker was referred for evaluation of recent onset streaky hemoptysis and a large cystic lesion in the left lower lobe (LLL). Presence of air trapping in LLL was observed on computed tomography scan of thorax. Prior to completion of diagnostic evaluation, the patient was lost to follow up. On return after a two-month gap, 'disappearance' of the cyst was observed along with complete collapse of LLL. A fibreoptic bronchoscopy revealed presence of a tumor completely occluding the LLL main bronchus and biopsy confirmed presence of squamous cell carcinoma of lung. The temporal clinico-radiological profile suggested a check-valve mechanism resulting from endobronchial obstruction as the primary mechanism for cyst formation. This case highlights the need to consider malignant endobronchial obstruction as the likely etiology among heavy smokers presenting with symptomatic solitary lung cysts.