Understanding cystic lung lesions in smokers with interstitial lung disease: radiologic-pathological correlation.

Due to destructive, fibrotic, and remodeling mechanisms, we can find a varied constellation of aerated and cystic lung lesions in smoker patients with interstitial lung disease that pose a diagnostic challenge for both radiologists and pathologists. Radiologic terminology used for cystic lung lesions in smokers is varied and sometimes confusing, and the same applies to their pathologic correlation, with different names for similar findings. Moreover, there is substantial overlap among different cystic lesions in both radiology and pathology. Ultimately, the diagnosis of a given type of cyst may lead to a wrong diagnosis with important clinical implications. In this setting, the goals of this article are to present a diagnostic approach to these lesions by correlating radiologic findings with pathology and describing a series of radiologic characteristics of these lesions, which we have called "the four S of cystic lung lesions in smokers" for size, site, shape, and surrounding of the lesions. We will define the clue radiological findings of centrilobular emphysema, paraseptal emphysema, thin-walled cysts, traction emphysema, honeycombing, smoking-related diffuse cystic lung disease, cysts in Langerhans cell histiocytosis, and cystic lesions appearing in desquamative interstitial pneumonia and we will try to show a correlation of each of these lesions with pathology for a better understanding of radiological findings. Finally, we will deal with fibrosing lung diseases and cystic lung lesions in smokers, specifically with smoking-related interstitial fibrosis and its pathological variants, and with usual interstitial pneumonia, whose prognosis is strikingly different. CRITICAL RELEVANCE STATEMENT: Knowledge of the pathological correlation of the different cystic lesions that appear in smokers with interstitial lung disease permits a better understanding of their radiological manifestations. KEY POINTS: Interstitial lung disease in smokers is characterized by varied cystic lung lesions. Cystic lesions are characterized by their size, site, shape, and surroundings. Cystic lesions in smokers may help to characterize the underlying fibrosing disease.