solitary fibrous tumor ( sft ) is a rare neoplasm that typically presents as a well - defined lobulated soft tissue mass commonly arising from the visceral pleura . on ct , small sfts typically appear as well - defined , homogeneous , lobular , soft - tissue masses . large sfts are frequently appear heterogeneous before and after contrast injection due to myxoid change , hemorrhage , necrosis , or cystic degeneration ( 1 - 3 ) . however , to the best of our knowledge , no cases of sfts containing air have been reported in the literature . herein , we report an extremely rare case of an sft manifesting as an air - containing cystic mass arising from the posterior visceral pleura enveloping the right upper lobe within the right major fissure . a 58-year - old woman was transferred to our hospital due to an incidentally identified lung mass at an outside hospital . 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 ( fig . chest ct demonstrated a 4.5 cm - sized , spindle - shaped cystic mass containing air within the superior portion of the right major fissure ( fig . 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 ( fig . 1d , e ) . 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 ( fig . f18-fluorodeoxyglucose ( fdg ) pet / ct demonstrated mild fdg uptake with a maximum standard uptake value ( suvmax ) of 2.3 ( fig . 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 ( fig . 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 ( fig . 1j ) . 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 ( fig . there was cleft - like cystic air space surrounding the solid nodule , which was partially lined by cuboidal cells ( fig . 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 ( fig . antibodies for actin , desmin , s100 , and cd117 ( c - kit ) were nonreactive in the tumor cells . solitary fibrous tumor is a rare mesenchymal neoplasm that can be either benign or malignant . the tumors typically affect the pleura but can develop in a number of other locations including the mediastinum , lung , tracheobronchial tree , abdomen , head , neck , and central nervous system ( 1 , 4 ) . the tumors most commonly present during the fifth and sixth decades of life and occur equally in men and women ( 5 ) . although sfts of the pleura are asymptomatic in up to 50% of patients , they can be associated with chest pain , dyspnea , cough , hypoglycemia , and clubbed finger ( 6 ) . sft of the pleura is suspected to be derived from the submesothelial connective tissues that originate from the differentiation of a primitive multipotent mesenchymal cell . tumors are typically highly vascular with vessels of varying sizes , and approximately 50% of sfts of the pleura have a pleura - based pedicle , approximately 1 cm in length , and contain hypertrophic arteries and veins ( 6 ) . chest radiographs of a patient with sft of the pleura characteristically demonstrate a peripheral , well - defined , solitary nodule or mass , occupying the lower hemithorax , which may mimic diaphragmatic elevation or eventuration ( 1 ) . ct images of small sfts typically show homogeneous , well - defined , lobular , noninvasive , soft - tissue nodules or masses . sfts usually enhance strongly after contrast injection , which can be heterogeneous , particularly for large tumors . heterogeneous attenuation of the tumor after contrast enhancement is correlated with hemorrhage , necrosis , or cystic change , and tumoral calcification occurs in 7% to 25% of patients , typically in those with larger tumors , and is often related to necrosis ( 1 - 3 , 6 ) . however , several cases of pulmonary sclerosing hemangioma surrounded by slit - like air space have been described ( 7 , 8) . in these reports , proliferation and hyalinization of alveolar mesenchymal cells around the bronchus can lead to airway narrowing and distention of distal air space ( 7 ) . air meniscus may also be induced by disparate rates of contraction between the tumor and capsule , possibly after tumor hemorrhage ( 7 ) or by airway communication after peritumoral hemorrhage ( 8) . in rare cases , benign metastasizing leiomyomas can also present as fluid- or air - filled cysts . cleft formation within the tumor caused by entrapment of the surrounding alveolar lining epithelial cells may eventually progress to cysts or bullae ( 9 , 10 ) . in the present case , immunohistochemically stained pneumocytes were present in the cystic portion of the tumor , representing the entrapped lung tissue , which can serve as the best explanation of air collection within the tumor . peripheral lung tissue entrapped by the tumor may have resulted in air trapping within the tumor through the communicated bronchioles , and eventually , the air space may have enlarged through both the check - valve mechanism and tumor growth . to the best of our knowledge , this is the first case of an sft containing a large amount of air within the tumor , and we speculate that entrapment of peripheral lung tissue by the growing tumor with eventual air - trapping over time may have resulted in the large air space within the tumor . although this finding is extremely uncommon , radiologists should not exclude the possibility of sft in the diagnosis of a pleural or subpleural nodule containing intra - tumoral air .
solitary fibrous tumor ( sft ) is a rare mesenchymal neoplasm that typically presents as a well - defined lobular soft tissue mass commonly arising from the pleura . 
 we report an extremely rare case of an sft containing air arising from the right major fissure in a 58-year - old woman . 
 chest ct showed an ovoid air - containing cystic mass with an internal , homogeneously enhancing solid nodule . to our knowledge , this is the first case in the literature . 
 the histopathologic findings were correlated with the radiologic findings , and the mechanism of air retention within the tumor is discussed .