peritoneal inclusion cysts ( pic ) are uncommon mesothelium - lined abdominopelvic cysts seen in perimenopausal women . it presents as pelvic mass or with pelvic pain and may be misdiagnosed as an ovarian tumor . we report a case of pic , which was diagnosed clinically as benign mucinous cystadenoma of ovary ; however , it turned out to be pic on histopathology . a multiparous premenopausal woman presented to our outpatient department with progressively increasing dull ache and abdominal swelling for 2 years , with no anorexia , weight loss , bowel , bladder or menstrual complaint . she had bilateral tubal ligation 20 years back and had mental illness for which she was taking some ayurvedic medicine . a large multiseptated cystic lesion in pelvis extended into the pouch of douglas and retroperitoneum with left ovary unidentified separately , suggesting an ovarian neoplasm . ct scan showed multiple fibroids in uterus and a large multiseptate cystic mass in pelvis , separate from uterus and extending into retroperitoneum , with no solid area / calcification or , no free fluid in abdominal cavity suggesting benign ovarian neoplasm . nearly 15 - 18 discrete uniloculated thin walled , smooth surfaced , clear fluid filled and variably sized cysts ( 2 - 10 cm ) studded utero - vesical fold , broad ligament , pelvis and retroperitoneal spaces [ figure 1a ] . cut section confirmed absent papillae or solid areas . ( a ) intraoperative picture showing multiple cysts , ( b ) h  e  20  , photomicrograph showing cyst wall with smooth muscle bundles , thick walled blood vessels and stromal edema histopathology showed multiple cysts lined by flattened to indistinct mesothelium with interspersed loose fibrocollagenic tissue , scattered smooth muscle bundles and intervening stroma showing congested vessels diagnostic of pic with chronic endometritis , chronic salpingitis and oophoritis [ figure 1b ] . pic , also called benign ( multi ) cystic peritoneal mesothelioma , inflammatory cysts of the peritoneum , postoperative peritoneal cyst , benign papillary peritoneal cystosis , are mesothelium - lined cysts classically presenting in perimenopausal woman and are diagnostic dilemmas for gynecologists and radiologists . usual presentation is progressive abdominal or pelvic pain or palpable mass as present in our patient . rarely there can be backache , dyspareunia , constipation , tenesmus , urinary frequency or incontinence , anorexia , dysfunctional uterine bleeding , or infertility . risk factors include previous intraperitoneal surgeries performed 6 months to 20 years earlier by any route , intraperitoneal inflammation , pelvic inflammatory disease , peritoneal tuberculosis , leiomyoma , tubo - ovarian abscess , etc . pic may be misdiagnosed as mucinous cystadenoma of ovaries for similar presentation and slightly raised ca125 derived from coelomic epithelium in both conditions . usg features are non - specific , with smooth thin walled multiseptate cysts containing liquid of different attenuation . ct scan similarly give cobweb appearance of loculated fluid with septations within , conforming to the peritoneal space with ipsilateral ovary within it or in the wall . unaware of the entity , we only entertained the differential diagnosis of hydatid cyst . postulated pathology for pic includes inability to absorb physiological secretions of active ovaries by diseased , inflamed or fibrosed peritoneum forming cysts within peritoneal adhesions . we missed the diagnosis of this uncommon entity possibly because of similar age , symptoms , signs and usg features mimicking benign mucinous cystadenoma of ovary . management varies from observation with serial imaging , hormones , image - guided aspiration with or without sclerotherapy , and surgical excision to complete resection . usg /fluoroscopy - guided sclerotherapy with 10% iodine or absolute ethanol reported 90% success rate . pic consciousness particularly in patients with predisposing condition may help suspect and diagnose this uncommon entity . this may permit conservative management in selected case with close follow - up for possible recurrence .
peritoneal inclusion cysts are uncommon abdominopelvic cysts seen in perimenopausal women . 
 it is often misdiagnosed clinically as an ovarian tumor due to similar presentation and mimicking findings on radiology . 
 we describe a perimenopausal woman presenting with pelvic mass . 
 her clinical finding on radiology suggested an ovarian tumor ; however , biopsy revealed it as peritoneal inclusion cysts . 
 we discuss the possible ways to avoid such mistakes .