benign cystic mesothelioma ( bcm ) is a very rare disease characterized by proliferative lesions of the peritoneal mesothelial cells mainly in the pelvic or abdominal cavity . however , it can also develop in the pleura , pericardium , tunica vaginalis , and spermatic cord . in the past , it has also been named multicystic peritoneal mesothelioma , multilocular cysts of the peritoneum , multicystic mesothelioma , and multicystic peritoneal inclusion cysts [ 1 , 2 ] . it was first described by mennemeyer and smith   in 1979 as a possible diagnosis in a case that resembled intra - abdominal cystic hygroma . its etiology is still not definite and its pathogenesis , which is reactive or neoplastic change , is controversial . there is a case report of a patient who died from the disease 12 years after the diagnosis without treatment . although intraperitoneal chemotherapy after resection is reported as treatment in a large series of patients with peritoneal dissemination of appendiceal malignancy , there still is controversy about chemotherapy . bcm is often observed in women , particularly those in their childbearing age and with a history of endometriosis , pelvic inflammation , and abdominal surgery . the rate of bcm in men is 17% . the disease is sometimes found in patients without any typical symptoms ; however , in most cases , large masses are palpable in the abdomen and abdominal pain often accompanies the disease . the authors report the case of a bcm in a 52-year - old middle - aged male patient who showed a unique pattern in that he had ascites and had first been misdiagnosed with peritoneal carcinomatosis based on radiological examination . a 52-year - old man was admitted to our hospital due to ascites found during a medical checkup performed in a private clinic . at the time of admission , his health status was normal : blood pressure 139/86 mm hg , pulse rate 73 beats / min , respiratory rate 20/min , and temperature 36.5c . there was a little abdominal distension , but there seemed to be no increase in the abdominal circumference and no tenderness . in the course of the previous few months , he presented no change in weight or peripheral edema of the limbs . the peripheral blood examination showed normal findings , i.e. leukocytes 7,820/mm , hemoglobins 14.8 g / dl , and platelets 220,000/mm . the biochemical test results were as follows : c - reactive protein ( crp ) 0.08 mg / dl , bun 13.2 mg / dl , creatinine 0.87 mg / dl , ast 30 iu / l , alt 38 iu / l , total bilirubin 0.56 mg / dl , and albumin 4.3 g / dl . the tumor marker test showed normal findings , i.e. -fetoprotein 1.8 ng / ml , carcinoembryonic antigen ( cea ) 2.0 ng / ml , and carbohydrate antigen 199 ( ca 199 ) 11.5 u / ml . abdominal computed tomography ( ct ) scans presented ascites of a moderate amount . the irregularly thickened peritoneum across the abdomen and the reticular membrane in the upper left abdomen formed a mass ( fig . positron emission tomography of the whole body showed no increase in the f - fluorodeoxyglucose uptake . the paracentesis conducted after the hospitalization resulted in an erythrocyte count of 171/mm , leukocyte level of 288/mm ( lymphocytes 74% ) , albumin level of 2.0 g / dl , protein level of 2.7 g / dl , and adenosine deaminase level of 9.5 iu / l , and there was no mtb pcr and afb stain . as the abdominal ct findings strongly suggested peritoneal cancer , diagnostic laparoscopy was conducted . the laparoscopic examination showed several cystic masses in the paracolic gutter forming a large mass ( fig . there was much yellowish ascites , and multiple nodules of a size of 23 mm were widely spread in the abdominal cavity ( fig . biopsy was performed providing tissue of the size of 2  1.5 mm from the reticular membrane . the biopsy result showed several cysts of various sizes , which were surrounded by flat cubic epithelial cells ( fig . strongly stained for calretinin and d240 , the patient was diagnosed with bcm ( fig . the patient was informed about the possible progression to malignancy and was recommended to have radical excision performed , but he preferred to wait since the symptoms were not yet apparent . as there was no change in the lesion and there still was ascites , we recommended surgical treatment . however , he kept refusing it , and thus , we decided to continue monitoring the development . although bcm was first referred to by plaut   in 1928 , it was suggested to have its origin in the mesothelial cells due to the observations made by mennemeyer and smith   using electron microscopy . afterwards the disease could be diagnosed as soon as it had been distinguished from other diseases . after the introduction of immunohistochemistry , bcm was diagnosed when it was stained both for calretinin and d2 - 49 at the same time . a report on the analysis of 37 patients with bcm showed that 83.8% of the patients were female and their average age was 38 years . as the disease is found in 37.8% of subjects in their 50s , in 5.3% of subjects in their 60s and in 10.8% of subjects in their 70s , as well as in infants , it is suggested that bcm may occur in patients at all ages . it is known to be more frequent in patients with a history of endometriosis , pelvic inflammation , and abdominal surgical treatment , particularly in patients having had hysterectomy and cesarean section . bcm is a tumor originated from mesothelial cells in the peritoneum , pleura and pericardium . it can also appear in the groin and scrotum , which is the extension of the peritoneum . in the case of bcm in the groin and scrotum , the patients can detect palpable masses by themselves and therefore present themselves to the hospital earlier . on the other hand , bcm in the abdominal or pelvic cavity bcm in our case is also not easy to be detected because it is rare in a middle - aged man , and there were no specific symptoms such as palpable mass or abdominal distension . worldwide , only 5 cases of bcm accompanied by ascites have been described so far . paracentesis results showed that his serum - ascites albumin gradient ( saag ) was 2.3 g / dl and the protein level was 2.7 g / dl , showing that the disease may be caused by cardiac ascites . thus , when more data about bcm with ascites are available in the future , the specific features of ascites in bcm could be analyzed . bcm can be classified into three types depending on its shape : ( 1 ) the solitary type when the boundary is clear , ( 2 ) the localized type when the multiple masses are found in the localized part of the abdominal membrane , and ( 3 ) the diffuse type when the masses are widely spread across the abdominal membrane . surgical removal is the best treatment . to prevent possible recurrence and transformation to the malignancy worldwide , there were only 2 cases where bcm developed into the malignancy : a baby at the age of 6 months and a female at the age of 36 years [ 9 , 10 ] . accordingly , as the rate of transformation to the malignancy is very low , re - excision is often performed even for local recurrence . in a few studies , there have been attempts to use heated intraperitoneal chemotherapy in the abdominal cavity , but this still is at an experimental stage . bcm is a very rare disease , which is often observed in women in their childbearing age . we presented a male patient with bcm of the diffuse type accompanied by ascites and who had first been misdiagnosed with peritoneal carcinomatosis . the published research is compliant with the guidelines for human studies and animal welfare regulations .
benign cystic mesothelioma ( bcm ) is a rare benign disease that forms multicystic masses in the abdomen , pelvis , and retroperitoneum . 
 it occurs predominantly in young to middle - aged women . 
 the majority of cases were associated with a history of abdominal or pelvic operation , a history of endometriosis , and pelvic inflammatory disease . 
 we present a unique case of bcm which is different to the previous cases . 
 the patient was a 52-year - old man showing features of peritoneal carcinomatosis accompanied by ascites on abdominal computed tomography scans . 
 we herein report a case of bcm misdiagnosed with peritoneal carcinomatosis .