Solitary Fibrous Tumor of the Pleura Manifesting as an Air-Containing Cystic Mass: Radiologic and Histopathologic Correlation
A 58-year-old woman was transferred to our hospital due to an incidentally identified lung mass at an outside hospital. She was a never smoker and was asymptomatic. Chest radiography showed an ovoid, thick-walled, air-containing cystic mass in the right upper lung zone where the mass was located eccentrically and surrounded by crescent-shaped air on the medial aspect (). Chest CT demonstrated a 4.5 cm-sized, spindle-shaped cystic mass containing air within the superior portion of the right major fissure (). This mass had an irregular thin wall with a thickness of several millimeters. A well-defined soft tissue nodule was eccentrically located within the lesion and measured approximately 3 cm. The nodule had a homogeneous density of 25 Hounsfield units (HU) on pre-contrast CT and was relatively homogenously enhanced after intravenous contrast administration, with a density of 50 HU (). Her previous chest CT images, performed at the outside institution approximately 2 years prior, revealed a same-sized cystic mass containing a much smaller internal soft tissue nodule compared to the lesion on the present CT images (). F18-fluorodeoxyglucose (FDG) PET/CT demonstrated mild FDG uptake with a maximum standard uptake value (SUVmax) of 2.3 ().\nVideo-assisted thoracoscopic surgery was performed to resect the tumor. An encapsulated ovoid cystic mass was shown in the pleural space, with a broad short pedicle and prominent blood vessels over the thin serosal lining of the tumor (). The stalk arose from the posterior portion of the visceral pleura enveloping the right upper lobe within the upper portion of the right major fissure. Cut sections of a gross specimen revealed an air-containing cystic mass with an eccentrically yellow-gray-colored solid nodule (). Histopathologic examination with hematoxylin-eosin (HE) staining revealed spindle-shaped tumor cells mixed with collagen fibers in the tumor and its cystic wall without evidence of mitosis or nuclear pleomorphism, representing a benign SFT (). There was cleft-like cystic air space surrounding the solid nodule, which was partially lined by cuboidal cells (). Immunohistochemical studies of the tumor showed diffuse staining for CD34 and vimentin, and the cells lining the cystic portion of the tumor stained positively for TTF1 and CK7, suggesting that they were pneumocytes originating from alveoli or terminal respiratory epithelium (). Antibodies for actin, desmin, S100, and CD117 (c-kit) were nonreactive in the tumor cells.