Simultaneous Occurrence of Well-Differentiated Papillary Mesothelial Tumor and Multicystic Mesothelioma

Our plain-English summary of Simultaneous Occurrence of Well-Differentiated Papillary Mesothelial Tumor and Multicystic Mesothelioma, by D. Miličić, S. Tomić, B. Delić, et al (Diagnostics, 2026).

The study

• Authors: D. Miličić, S. Tomić, B. Delić, M.D. Mimica
• Journal: Diagnostics
• Published: 2026;16(14)
• Read it: PubMed · Publisher · Free full text

Abstract

We report a rare case of simultaneous well-differentiated papillary mesothelial tumor (WDPMT) and multicystic mesothelioma. The concurrent occurrence of these entities is exceptionally uncommon and may pose challenges during surgical intervention. Both lesions are rare mesothelial proliferations that are often identified incidentally during surgery. Well differentiated papillary mesothelial tumor (WDPMT) is a neoplastic mesothelial proliferation of low malignant potential, which predominantly involves the peritoneum of young women. Microscopically it is composed of branching plump papillae lined by a single layer of bland cuboidal mesothelial cells. Cytologic atypia is minimal, and mitoses usually absent (or at most 1 mitosis per 10 high power fields). Differential diagnosis includes: 1. diffuse malignant peritoneal mesothelioma, 2. localized malignant peritoneal mesothelioma, 3. serous borderline tumors. A 41-year-old patient was admitted for laparoscopic surgery due to a tumor mass localized near the left ovary. Ultrasound examination revealed solid lesion adjacent to the left ovary, exhibiting central vascularization. The patient was diagnosed with the solid tumor mass during routine gynecological examination. The mass was extraovarian and positioned between the left ovary and the uterus. Over the course of the next 18 months, the tumor increased 5 cm in size. Given the fact that the patient presented with no symptoms, such as abdominal pain, distension or ascites, and that the tumor markers were not elevated, additional radiological imaging such as CT or MRI of the abdomen and pelvis was not performed. Intraoperatively, the mass appeared as an extraovarian solid tumor of soft consistency positioned between the left ovary and the uterus. Extirpation of the tumor was performed. Frozen section analysis of the extirpated tumor mass confirmed the diagnosis of WDPMT. During the laparoscopic procedure, a left adnexectomy was also performed and multiple biopsies of white nodules were found dispersed in the peritoneal cavity. Final patohystological analysis concluded that these nodules were peritoneal inclusion cysts. Almost three years after the procedure, the patient is without symptoms and regular clinical and ultrasound examinations were performed every six months, which showed no signs of recurrence or dissemination of the primary tumor. Recognizing well-differentiated papillary mesothelial tumor and multicystic mesothelioma is critical for accurate differential diagnosis from malignant mesothelioma. Awareness of these entities informs appropriate surgical management and follow-up protocols.

In plain English

This is a single case report from the University Hospital of Split, Croatia. A 41-year-old woman had a solid mass between the left ovary and the uterus, found at a routine gynecological examination. Over 18 months it grew from 3 cm to 5 cm in diameter. Tumor markers were not elevated and the patient had no symptoms. At laparoscopic surgery the mass was removed with the left adnexa (ovary and tube). It was identified as a well-differentiated papillary mesothelial tumor (WDPMT), without cell atypia, mitotic activity or stromal invasion. Multiple white nodules under 1 cm were scattered on the ovaries, uterus and peritoneum. Biopsies showed multiloculated peritoneal inclusional cysts, previously termed multicystic mesothelioma. Complete removal of the nodules was not possible. The authors listed supposed risk factors for WDPMT, including asbestos exposure. Of these, the patient had only previous abdominal surgery (caesarean section). Almost three years later the patient was well, with no sign of recurrence on six-monthly checks. The authors concluded that recognizing these entities is critical for distinguishing them from malignant mesothelioma.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Case report (single patient), published as an 'Interesting Images' article
• Who was studied: One 41-year-old female patient (gravida 1, para 1) admitted for laparoscopy at the Department of Gynaecology and Obstetrics, University Hospital of Split, Croatia; the mass had been diagnosed 18 months before admission
• Exposure: No asbestos exposure is reported for this patient. Of the supposed risk factors the authors list for WDPMT (smoking, asbestos exposure, previous abdominal surgeries, family history, endometriosis, trauma), the patient had only previous abdominal surgery (caesarean section).
• Main results:
  • On repeated transvaginal ultrasound over 18 months, the mass near the left ovary grew in diameter from 3 cm to 5 cm, with central vascularization
  • The patient's tumor markers were not elevated (CEA 1.08 µg/L, CA19-9 less than 2 kIU/L, CA125 26.8 kIU/L)
  • Frozen section analysis of the removed mass gave the diagnosis of well-differentiated papillary mesothelial tumor (WDPMT)
  • In the removed tumor, cells stained positive for calretinin, WT1 and podoplanin and negative for CK5/6, and no stromal invasion was detected
  • Multiple white nodules were found on both ovaries, the pelvic peritoneum, the uterus, the vesicouterine fold and other peritoneal surfaces; they were less than one cm in size
  • Biopsies of the nodules were diagnosed as multiloculated peritoneal inclusional cyst, the term the WHO prefers, previously termed multicystic mesothelioma; no mitoses were identified
  • Complete debulking was not possible because of the extent of the lesions
  • Almost three years after surgery the patient was well and without symptoms, and six-monthly clinical and ultrasound examinations showed no suspicion of recurrence or dissemination
• The authors' conclusion: The authors concluded that recognizing well-differentiated papillary mesothelial tumor and multicystic mesothelioma is critical for accurate differential diagnosis from malignant mesothelioma, and that awareness of these entities informs surgical management and follow-up

Topics

Medical terms in this study, explained in our Lexicon: Well-Differentiated, Multicystic Mesothelioma (MCM), Peritoneum, Papillae, Mesothelial Cells, Differential Diagnosis, Peritoneal Mesothelioma, Ultrasound.

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