[Cystic pulmonary metastasis simulating a diagnosis of histiocytosis X]

A case of cystic pulmonary metastases from a renal origin simulating lung histiocytosis on high-resolution CT is presented. This diagnosis was suggested because of the presence of cystic lung lesions, micronodules and recurrent pneumothoraces in a male smoker. The diagnosis was reviewed after lung biopsy and demonstration of a renal mass.