RESUMO
Lung cysts in children are usually of congenital origin. Necrotising pneumonias, trauma, cystic fibrosis and kerosene poisoning may be the cause of acquired cysts in the lungs during childhood. We describe a child who presented with pneumothorax and was later discovered to have a cyst in his right lung. The cyst was resected and on histology found to be of inflammatory origin with no epithelial cell lining i.e. a pseudo-cyst. The immuno-histochemical staining of the inflammatory cells from the pseudo-cyst wall showed them to be predominantly histiocytes i.e:, CD68 antigen positive. The cells showed negative staining for S-100 (marker for Langerhans cells), cytokeratins (epithelial markers) and smooth muscle actins excluding the possibility of histiocytosisX, epithelial and congenital cysts respectively. This case illustrates the occurrence of acquired pulmonary pseudocysts unrelated to known etiologic agents which should be considered in the work-up for pneumothoraces.