a 21-year - old woman was referred to our hospital due to a mediastinal mass that was incidentally detected on a chest x - ray performed during health screening . chest computed tomography scan revealed a densely - enhanced , round to oval - shaped mass in the right cardiophrenic angle of the anterior inferior mediastinum . the specimen was a relatively well - demarcated solid mass with a rubbery consistency , measuring 5.3 4.0 cm . the cut surface of the tumor was tan yellow and had a nodular appearance without a necrotic or hemorrhagic area ( fig . microscopically , the tumor was enveloped by a variable , thickened fibrous capsule with no evidence of infiltration into adjacent tissue . a solid growth pattern was evident , with prominent vascular structures composed of small- to medium - sized blood vessels . medium - sized vessels occasionally appeared with staghorn features and myxoid changes in their walls ( fig . the high cellular areas appeared in vague nodular configuration , and the low cellular area had edematous and myxoid change and was present between high cellular areas ( fig . high - powered examination revealed that the tumor was composed of round epithelioid cells , which had clear to eosinophilic cytoplasm with sharply defined borders . the centrally - located vesicular nuclei were round to polygonal , with a mild convoluted contour of nuclear membranes . immunohistochemical staining for smooth muscle actin and vimentin showed diffuse and focal positivity , respectively . tumor cells were not immunoreactive for cd34 , calretinin , cytokeratin , desmin , or neuroendocrine markers , including synaptophysin and chromogranin ( fig . 2e , f ) . based on the histology and immunohistochemical results , glomus tumors are unusual benign smooth muscle neoplasms that comprise fewer than 2% of all soft tissue tumors . these tumors are preferentially located in the subungal area of extremities and have a characteristic clinical triad that includes pain , pinpoint tenderness and hypersensitivity to cold temperatures . clinically , this type of tumor is usually benign , and malignant cases have rarely been reported . additionally , mediastinal glomus tumors , first described in 1949 , are extremely rare ; only five cases have been described in the english literature [ 1 - 3,8,9 ] . the pathologic differential diagnoses of mediastinal glomus tumor include carcinoid tumor , hemangiopericytoma , epithelioid leiomyoma , primitive neuroectodermal tumor , and paraganglioma . characteristic morphologic features that are helpful for distinguishing these tumors include uniform , round tumor cells with centrally - located nuclei , a well - defined cell membrane and immunohistochemial results that are positive for actin and equivocal or negative for cd34 , neuroendocrine markers ( chromogranin a , synaptophysin , neuron specific enolase ) and cd99 . a previous article reported that mediastinal glomus tumors tend to have atypical histologic appearance with cytologic pleomorphism and infiltrate into surrounding tissue . however , clinicopathologic features or distinct classification of glomus tumors in the mediastinum or visceral organs have not been established due to their infrequency . we comprehensively reviewed the clinicopathologic data of mediastinal glomus tumors ; this data and the current case are presented in table 1 . compared with previous cases , our patient was young and did not present with any symptoms . in addition , although previous mediastinal glomus tumors were frequently found in the posterior superior area , this case was noted in an unusual location , the anterior inferior mediastinum . to investigate the clinicopathologic characteristics in malignant mediastinal glomus tumors , we searched for histologic descriptions in former reports . a previous report indicated that , in a fatal mediastinal glomus tumor case , advanced age , extensive local invasion , and brisk mitotic activity were significant and correlated with poor prognosis in mediastinal glomus tumors . glomus tumors with atypical features should be evaluated for variable clinicopathologic features , based on recently - defined classifications . these classifications include tumor location and size , nuclear atypia , and mitosis including atypical ones . the tumors can be categorized into four groups ( table 2 ) . since glomus tumors that arise in visceral organs , including the mediastinum , can be considered deeply - located tumors , they should be classified as malignant glomus tumor or glomus tumor of uncertain malignant potential . however , only one of six such reported patients died , and the remainder had no evidence of recurrence or metastasis during follow - up . therefore , we collected and analyzed glomus tumor cases in visceral organs to define and outline characteristics for increased diagnostic accuracy , based on prognosis and adequate treatment . we described an extremely rare case of mediastinal glomus tumor with no subject symptoms and reviewed the clinicopathologic features of previously reported cases . considering the unpredictable prognosis of mediastinal glomus tumor , we suggest the need for histopathologic assessment parameters through collection and observation of glomus tumors that originate in the visceral organs .
a glomus tumor in the mediastinum is very uncommon , and only five cases have been reported in the english literature . 
 we recently encountered a 21-year - old woman with an asymptomatic mediastinal mass that measured 5.3  4.0 cm . 
 surgical excision was performed , and the tumor was finally diagnosed as mediastinal glomus tumor with an uncertain malignant potential . after reviewing this case and previous reports , we analyzed the clinicopathologic features associated with progression of such a tumor .