a 48-year - old man presented with a complaint of scrotal pain and swelling that had been gradually increasing for a period of 6 months . physical examination revealed an enlarged left hemiscrotum . testicular ultrasonography showed a left hydrocele consisted of three nodules measuring 2 cm , 1.4 cm , and 0.9 cm ( fig . the patient has done well with no signs of residual disease 3 years after surgery . these were found to be pedunculated masses with 2 cm , 1.5 cm , and 1 cm in diameter . microscopically , the masses were composed of multiple branching , papillary structures with a fibrovascular core ( fig . negative results were found with carcinoembryonic antigen ( cea ) , cancer antigen 125 , and cd10 . additionally , we searched for simian virus 40 ( sv40 ) by polymerase chain reaction ( pcr ) amplification . two sets of primers ( 5'-gaa - tgg - gag - cag - tgg - tgg - aat - gc-3 ' and 5'-tct - ctt - ctt - ttt - tgg - agg - agt - aga-3 ' ) were used for sv40 detection.12 no sv40 was detected in this case . mesotheliomas can arise from the pleura , peritoneum , or paratesticular areas , in decreasing order of frequency . paratesticular mesothelioma can arise from the tunica vaginalis , formed by an outpouching of the abdominal peritoneum . mesothelial lesions of this area include reactive mesothelial hyperplasia , mesothelial cysts , adenomatoid tumor , wdpm , and mm . wdpm is a rare type of mesothelioma that mostly arises from the peritoneum or pleura.13,14 barbera and rubino9 reported the first case of wdpm in 1957 . to the best of our knowledge only 18 cases of paratesticular wdpm have been published to date in the english literature . the majority of these cases have been presented as case reports , except for one series of 8 cases that was published by brimo et al.8 recently . all cases also had bland appearing cells which lack significant atypia , pleomorphism , and stromal invasion . only trpkov et al.6 mentioned a small focus of coagulative necrosis . one of the cases in the series by brimo et al.8 showed osteoclast - like giant cells . mesothelial hyperplasia can also be composed of papillary structures , but often do not contain a fibrovascular core like wdpm . one major clinical concern is differentiating wdpm from mm , as they can have overlapping histologic features . the presence of invasion , marked cytologic atypia , atypical mitosis , and a bulky mass are the major features that should be considered in making a diagnosis.15,16 the etiology of wdpm has not been clearly elucidated . it has been suggested that proliferative lesions might be related to local trauma , herniorrhaphy , or a long - term hydrocele.17 a relationship between asbestos exposure and mesotheliomas of the tunica has been postulated . only one case of wdpm of the tunica vaginalis in the literature had a history of asbestos exposure7 and one had a history of a household contact with exposure.4 our case had no asbestos exposure like the rest majority of reported cases . in addition to asbestos , potassium bromate in drinking water has been shown to increase the risk of mm of the tunica vaginalis in an animal model.15 sv40 is a dna monkey virus that has been associated with mm and has been implicated in mesotheliomas of the pleura . sv40 contaminated polio vaccines produced between 1955 and 1978 are postulated to have been the route of virus transmission from monkeys to humans . many studies have demonstrated the presence of sv40 in pleural mesotheliomas through the use of various techniques , and animal studies have demonstrated a clear association of up to 60% of developing mesothelioma.15,16,18 however sv40 dna has not been as well studied in mesotheliomas of the tunica vaginalis as it has been in its pleural counterpart . xiao et al.1 applied pcr for sv40 dna in their wdpm case and found it to be negative . we also performed pcr , but did not find sv40 in our case . in taking into consideration all reported cases , hydrocele seems to be the major risk factor for developing wdpm of the tunica vaginalis . non - mesothelial tumors of diverse histology must also be kept in mind in the differential diagnosis . this group includes papillary cystadenoma of the epididymis . features that distinguish papillary mesothelioma from papillary cystadenoma include the absence of clear cells and the presence of calretinin positivity . papillary serous neoplasms may also be difficult to differentiate from wdpm . however , serous tumors tend to have broader papillae and stratification , budding , and occasional cilia of tumor cells . additionally , papillary serous tumors express cea and ber - ep4 , both of which are usually negative in wdpm.19,20 the current case had a focal area of consisting of only superficial , entrapped tubules in the underlying tissue . given that the stroma exhibited no evidence of hypercellularity , storiform growth or desmoplastic response , we did not consider the tumor to be invasive . only one previous report mentioned a small focus of coagulative necrosis.6 this area was considered coagulative necrosis in the current case due to torsion or infarct , as mentioned in the previous report . currently , the main limitation in differentiating wdpm from mm with dominant papillary growth is limited experience , with only 18 known cases in the literature . although our case had no invasion , cytologic atypia , infiltrative growth , or mitotic activity we recommended close patient follow - up because of the areas of focal necrosis and complexity . the biologic behavior of paratesticular wdpm is not well - known because of such a limited number of cases .
well - differentiated papillary mesothelioma is an uncommon tumor of the testes that usually presents as a hydrocele . here , we present the case of one patient who did not have a history of asbestos exposure . 
 the tumor was localized in the tunica vaginalis and was composed of three pedunculated masses macroscopically . 
 microscopically , branching papillary structures with focal coagulative necrosis were present . 
 in addition to immunohistochemistry , simian virus 40 dna was also tested by polymerase chain reaction . 
 this report presents one case of this rare entity , its clinical and macroscopic features , and follow - up results .