a 35-year - old man presented with a 7.0 cm anterior mediastinal mass on a chest radiograph during a routine medical evaluation at an outside hospital .
the patient was transferred to the department of thoracic and cardiovascular surgery for further evaluation and treatment .
the patient did not present with any specific medical problems or symptoms and had no family history of cancer or prior surgeries except for an operation due to a pneumothorax that was performed 12 years prior to presentation .
fluorodeoxyglucose ( fdg)-positron emission tomography / computed tomography ( ct ) revealed two heterogenic hypermetabolic foci in the anterior mediastinum , with standard uptake values of 3.3 and 3.4 .
no significant fdg uptake was observed in the lymph nodes or anywhere else in the body to suggest distant metastasis , except for physiological uptake in both testes ( fig .
contrast - enhanced chest ct images showed multiple tumors in the anterior mediastinum . specifically , a 5.0 cm mass compressing the superior vena cava , a 1.5 cm nodule , and a 1.0 cm nodule were observed ( fig .
ultrasonography of the testes revealed a normal shape and echogenicity without focal mass or infiltrative lesions .
the serum levels of  human chorionic gonadotropin ( 0.1 iu / l ) and -fetoprotein ( 12.8 ng / ml ) were in the normal range .
a biopsy was performed in the operating room , and the diagnosis of thymoma was determined based on frozen tissue sections .
the largest mass ( 5.05.0 cm in size ) showed a lobulated , homogeneous , firm , cut surface with a partial hemorrhage . in the normal thymic tissue surrounding the largest tumor , two smaller masses ( 1.51.2 cm and 1.00.5 cm in size ) were seen , which had a well - defined , round , homogeneous , soft appearance .
the medium - sized mass was located 1.5 cm from the largest tumor , and the smallest mass was 0.5 cm away ( fig .
, low - power magnification of the largest mass showed a well - circumscribed , thick - walled capsule with a partially incomplete area , lobular architecture , and perivascular spaces containing proteinaceous fluid and lymphocytes .
the tumor was composed of a dual population of lymphocytes and epithelial cells in equal proportions . under high - power magnification , the epithelial cells had a bland nuclear appearance with small inconspicuous nucleoli .
the lymphocytes that were intermixed with the epithelial cells were small and mature - appearing .
the two small masses without a capsule revealed clusters or islands of large epithelioid cells with prominent nucleoli and pale cytoplasm that were intermingled with small , infiltrating lymphocytic cells .
interestingly , these two small tumors revealed a prominent lymphoid follicular hyperplasia with the formation of germinal centers , some microscopic cysts , and hassall s corpuscles in the surrounding area of the seminomatous component ( fig .
, the epithelial cells of the thymoma showed diffuse positive reactions for cytokeratin 19 and p63 and negative reactions for placental - like alkaline phosphatase , cd5 , cd117 , and d2 - 40 ( fig .
in contrast , the epithelial cells of the seminoma - like tumors showed diffuse positive reactions for cd117 , partially strong positive reactions for placental alkaline phosphatase ( plap ) and d2 - 40 , and negative reactions for -fetoprotein , cytokeratin 19 , and p63 ( fig .
epithelial membrane antigen staining was observed in hassall s epithelial cells of the thymoma and in microcystic epithelial cells of the seminomas . in summary ,
histological and immunohistochemical analyses of the anterior mediastinal masses revealed a type b2 invasive thymoma and two seminomas .
the simultaneous occurrence of a thymoma and seminoma in the thymus has not yet been reported except for two cases described by weissferdt et al .   in 2014 .
however , they reported a thymoma with a component of a thymic seminoma combined within a single tumor .
the seminomatous component showed seminoma - like epithelioid cells with distinct hyalinization adjacent to the area of the conventional thymoma .
our case included one large thymoma and two small seminomas in the anterior mediastinum , with distances of 1.5 cm and 0.5 cm between the thymoma and the seminomas .
because multiple thymic masses containing a thymoma and small seminomas are very rare , the possibility of metastasis from another organ or a morphological transformation of the thymic epithelial tumor cells into thymic carcinoma should be considered .
the two small masses showed negative reaction for cd5 and pan - cytokeratin and positive reaction for plap and d2 - 40 by immunohistochemical staining .
although cd5 loss in thymic carcinoma is known , the other immunohistochemical findings favor seminoma rather than thymic carcinoma
. we could not find a case of a thymic carcinoma with a positive reaction for plap or d2 - 40 in the literature .
our case showed site - associated features such as the presence of multiple cysts , reactive remnant thymic epithelium , epithelioid granulomatous reaction , fibrosis , and follicular lymphoid hyperplasia . in the seminomatous tumor
fortunately , site - associated morphologic features of mediastinal masses are rare in gonadal tumors .
although a biopsy of the testes was not performed , metastatic seminoma in the mediastinum from an intratubular germ cell neoplasia is unusual in the absence of retroperitoneal lymph node metastasis .
these clinical and histological findings support the conclusion that these seminomas are of mediastinal origin rather than due to metastasis .
primary mediastinal seminomas were first described in 1955 by woolner et al .   and have been well recognized for over 50 years .
however , it is believed that mediastinal seminomas originate from extragonadal germ cells in the thymic gland due to chromosomal abnormalities .
chromosome 12p abnormalities , which are specific genetic alterations found in testicular seminomas , are also present in mediastinal seminomas .
specifically , przygodzki et al .   reported a unique pattern of a kit exon 17 mutations in mediastinal seminomas , which are rare in testicular seminomas .
this may imply that the mediastinal seminoma develops through different pathways than that of its gonadal counterpart .
regardless of the tumor location , seminomas show kit protein expression , which is also seen in thymic carcinomas but not in thymomas .
histopathological analyses show that thymomas have heterogeneous morphological features such as spindle cells , lymphocytic infiltrate , and rhabdomyomatous components .
additionally , cytokeratin expression in seminoma tumor cells , which reflects the differential potential or the morphological transformation of the seminoma into another nonseminomatous gcts , has been reported . moreover
, a thymic carcinoma or seminoma may occur in combination with a thymoma within a single tumor .
therefore , we cautiously hypothesize that thymoma , thymic carcinoma , and seminoma occur from cells of the same origin , such as embryonic stem cells or primordial germ cells , which have the ability to differentiate into a diverse population of cells .
they obtain chromosomal and molecular abnormalities such as chromosome 12p abnormalities and kit mutations and transform from thymic epithelial tumors into gcts ( seminoma ) or from seminomas into thymic epithelial tumors .
the etiology and pathogenesis of thymomas and seminomas in the thymus are unknown , and further research is required in this area .
follicular lymphoid hyperplasia of the thymus can be seen in reactive , autoimmune diseases like myasthenia gravis
, follicular lymphoid hyperplasia may be associated with specific antigens produced by the microenvironment of the seminoma .
weissferdt and moran   postulated that the specific distribution of antigen - presenting dendritic cells in mediastinal seminomas is related to the pathogenesis of follicular lymphoid hyperplasia . in short ,
we report a case of one thymoma and two mediastinal seminomas that developed simultaneously in the thymus of a young adult . the seminomas revealed florid follicular lymphoid hyperplasia and microcystic changes that do not appear in testicular seminomas . in addition , no clinical or radiological evidence of gcts was found elsewhere . therefore ,
even though multiple masses were present , we considered these tumors to be synchronous primary thymic tumors rather than metastases from an occult tumor of the testis . to our knowledge , this is the first description of a synchronous occurrence of a separate thymoma and mediastinal seminomas within the thymus .
 thymoma is the most common neoplasm of the anterior mediastinum and has malignant potential . 
 germ cell tumors ( gcts ) found in the anterior mediastinum are usually benign , and malignant gcts , such as seminomas , are rare . 
 histologically , mediastinal seminoma is indistinguishable from testicular seminoma except for site - associated morphological features such as lymphoid follicular hyperplasia . 
 therefore , excluding metastasis is very important . 
 recently , we treated a young adult patient with multiple thymic masses that occurred simultaneously . 
 the patient underwent a thymectomy for the removal of the mediastinal masses , one of which was diagnosed as type b2 invasive thymoma , and two of which were diagnosed as primary mediastinal seminomas with massive follicular hyperplasia . 
 the patient received adjuvant chemotherapy after surgical resection . 
 to our knowledge , this is the first description of a thymoma and a mediastinal seminoma occurring simultaneously in the thymus . 
 we present this case along with a literature review . 
CASE REPORT
DISCUSSION