Pulmonary cysts in smoking-related interstitial fibrosis: a form of pseudocyst secondary to pulmonary interstitial emphysema.

Smoking-related interstitial fibrosis is a distinct form of fibrosis, found in smokers, which has striking histopathological features. We present a case of pulmonary interstitial fibrosis with cysts in a 58-year-old woman who was a significant active smoker, presenting with a 7 month history of progressive dyspnea. TAC revealed thin-walled pulmonary cysts. An open lung biopsy was performed and the histopathological study showed hyaline fibrous thickening of the alveolar septa, respiratory bronchiolitis and cysts in the thickness of the interlobar septa. Immunohistochemically, the absence of an epithelial, vascular or lymphatic endothelial lining of the cysts would suggest that the cysts had been caused by pulmonary interstitial emphysema. Immunohistochemistry is essential in the differential diagnosis that includes, in this case, true cysts, pseudocysts and pulmonary lymphangiectasia.