Sclerosing Pneumocytoma: a Carcinoma Mimicker. A Case Report and Literature Review

Sclerosing pneumocytoma (SP) is a rare entity. Diagnosis of SP can be problematic especially on biopsy specimens, in particular, when the sample is obtained from the papillary component.

An asymptomatic 33 year-old female with no smoking history was incidentally found to have a lung mass. She was diagnosed to have well-differentiated adenocarcinoma with papillary features on biopsy. A lobectomy was performed.

The circumscribed mass was composed predominately of papillary structures, with the "surface cuboidal cells" located on the surface of the papillae and "round cells" in the stalks of the papillae. Immunohistochemical staining demonstrated nuclear reactivity for TTF-1 in both cell types and Napsin A positivity only in "surface" cells.

In evaluation of a lung biopsy from a mass with a predominantly papillary pattern, sclerosing pneumocytoma (sclerosing hemangioma in previous classifications) should always be in the differential diagnoses.