https://orcid.org/0000-0003-4367-6230
Abstract
Benign multicystic peritoneal mesothelioma is a rare mesothelial neoplasm with fewer than 200 reported cases, typically arising on peritoneal or pelvic surfaces in premenopausal women. We describe a 21-year-old woman with a 2-week history of left lower abdominal pain. Magnetic resonance imaging showed a multiloculated cystic retroperitoneal mass adherent to the sigmoid colon, with normal ovaries and uterus. CA-125 was mildly elevated. At laparotomy, the mass was confirmed to be retroperitoneal without ovarian involvement, requiring en-bloc excision with sigmoid colectomy and primary anastomosis. Histopathology showed flat-to-cuboidal mesothelial cells with a hobnailing pattern in fibromyxoid stroma; immunohistochemistry was positive for calretinin and WT-1, and negative for SALL4, GATA3, and CD31, confirming benign multicystic peritoneal mesothelioma. At 6-month follow-up she remained asymptomatic with no recurrence on imaging. This case highlights BMPM as a mimicker of primary retroperitoneal neoplasms and the potential need for bowel resection to achieve complete excision.
Introduction
Benign multicystic peritoneal mesothelioma (BMPM) is a rare mesothelial neoplasm of the peritoneal cavity, first characterized by Mennemeyer and Smith in 1979 [1]. Fewer than 200 cases have been reported, predominantly in premenopausal women, with an estimated incidence of 0.15 per 100 000 [2, 3]. BMPM typically mimics other pelvic and retroperitoneal cystic lesions on imaging, and preoperative diagnosis is rarely achieved; histopathology and immunohistochemistry remain the diagnostic cornerstone [4]. We report a case presenting as an isolated retroperitoneal mass without ovarian involvement, requiring sigmoid colectomy for complete excision.
Case report
A 21-year-old previously healthy woman presented with a 2-week history of progressive left lower abdominal pain, without constitutional, urinary, or bowel symptoms, and no prior surgical or gynaecological history. Examination revealed left lower abdominal tenderness and a palpable fixed pelvic mass. Routine bloods were unremarkable.
Transabdominal ultrasound showed a complex left pelvic mass measuring approximately 8 × 8 × 10 cm. Contrast-enhanced magnetic resonance imaging (MRI) demonstrated a multiloculated cystic lesion in the left hemipelvis, measuring 6.3 × 10.7 × 10 cm, appearing retroperitoneal in origin with thin enhancing septations and adherence to the sigmoid colon (Fig. 1). The uterus and bilateral ovaries were normal and separate from the mass. Tumour markers showed AFP 2.91 ng/ml (normal), CA-125 83.4 U/ml (mildly elevated; normal <35 U/ml), inhibin A 26.11 pg/ml, inhibin B 9.41 pg/ml, and 17-β oestradiol 251 pg/ml, all interpreted as nonspecific.
Contrast-enhanced MRI of the abdomen and pelvis demonstrating a multiloculated cystic lesion in the left hemipelvis, measuring 6.3 × 10.7 × 10 cm, with thin enhancing septations and adherence to the sigmoid colon. The uterus and bilateral ovaries are normal and separate from the mass.
Following multidisciplinary review, the patient underwent exploratory laparotomy. A 10 × 8 cm retroperitoneal mass adherent to the lateral wall of the sigmoid colon was identified, with normal uterus, ovaries, fallopian tubes, omentum, and peritoneal surfaces (Fig. 2). En-bloc resection with segmental sigmoidectomy and primary anastomosis was performed, together with omental biopsies. Recovery was uneventful, and she was discharged on postoperative day five.
Intraoperative photographs. (A) The retroperitoneal mass adherent to the lateral wall of the sigmoid colon. (B) The en-bloc resection specimen comprising the cystic mass with the adherent sigmoid colon segment.
Gross pathology showed a multiloculated cystic mass, 9 × 6.5 × 3.5 cm, with a sponge-like cut surface containing yellow gelatinous and clear serous fluid (Fig. 3A). Microscopy revealed variably sized cystic spaces lined by flat-to-cuboidal cells with a hobnailing pattern, set within loose fibromyxoid stroma containing a mild chronic inflammatory infiltrate and occasional Touton giant cells (Fig. 3B). Immunohistochemistry was positive for calretinin (Fig. 4A), WT-1 (Fig. 4B), and weakly positive for inhibin (Fig. 4C), with negativity for SALL4, GATA3, and CD31—confirming BMPM and excluding lymphangioma, germ cell tumour, and urothelial malignancy, respectively.
(A) Gross pathology: Cut surface of the resection specimen showing a multilocular, sponge-like cystic architecture containing yellow gelatinous and clear serous fluid. (B) Photomicrograph showing variably sized cystic spaces within loose fibromyxoid stroma (haematoxylin and eosin, ×20).
Immunohistochemistry of the tumour. (A) Calretinin positivity in cyst-lining cells (×40). (B) WT-1 nuclear positivity (×40). (C) Weak cytoplasmic inhibin positivity (×40).
At 6-month follow-up the patient remained asymptomatic, with no recurrence on pelvic MRI. She has been enrolled in structured surveillance with imaging every 6 months for 2 years, then annually.
Discussion
BMPM characteristically arises on peritoneal or pelvic surfaces in women of reproductive age; presentation as an isolated retroperitoneal mass without peritoneal or ovarian involvement, as in this case, is distinctly uncommon and contributed to the diagnostic difficulty [4, 5]. Three pathogenic hypotheses have been proposed: a reactive mesothelial response to chronic inflammation, a true neoplastic process, and a hormonally driven mechanism, though no single mechanism is universally accepted [2, 6]. Unlike malignant mesothelioma, BMPM has no association with asbestos exposure [6].
The differential diagnosis of a multiloculated retroperitoneal cystic mass in a young woman includes cystic lymphangioma, peritoneal inclusion cysts, and extragonadal germ cell tumours. Cystic lymphangioma typically occurs in male children, contains chylous fluid, and is CD31-positive but calretinin-negative—features excluded here by CD31 negativity [4]. Extragonadal germ cell tumours were excluded by normal AFP, normal ovaries on imaging and at surgery, and SALL4 negativity, a highly sensitive germ cell marker [7, 8]. Malignant mesothelioma was excluded by the absence of cytological atypia, invasion, and asbestos history [6].
Complete surgical resection is the treatment of choice, and may require resection of adherent bowel, as in this case, to achieve clear margins [5, 9]. The principal management challenge is the high recurrence rate, reported in up to 50% of cases even after apparently complete resection, with late recurrences described more than a decade after surgery [10]. Long-term surveillance is therefore mandatory. Cytoreductive surgery with HIPEC has been used for multifocal or recurrent disease, though evidence is limited to small series [9, 11]. Malignant transformation is exceedingly rare [6].
BMPM should be considered in the differential diagnosis of any multiloculated retroperitoneal cystic mass in a young woman with normal ovaries, even in the absence of overt peritoneal disease. Bowel resection may be required for complete excision, and long-term surveillance is essential given the substantial recurrence risk.
Conflicts of interest
The authors declare no conflicts of interest.
Funding
No funding was received for this work.
Patient consent
Written informed consent was obtained from the patient for publication of this case report and accompanying images. A copy of the consent is available for review by the Editor-in-Chief on request.
