Mesothelial Inclusion Cyst of Uterus in a Primary Infertility Patient

INTRODUCTION

Uterine cysts can either be congenital or acquired. Mesothelial inclusion cysts are rarely found and reported lesions. They originate from mesothelial cells. The origin of congenital uterine cystic lesions can be from mesonephric or paramesonephric ducts.^[1] Acquired uterine cystic lesions have been reported in humans to be commonly associated with cystic degeneration of fibroids, adenomyosis, serosal inclusion cysts, and cystic endometrial hyperplasia.^[2] As there are very few relevant reports, diagnosing uterine mesothelial cysts can be difficult for clinicians. Thus, we present a case of a mesothelial cyst of the uterus that is misdiagnosed as hydrosalpinx and review the relevant literature.

CASE REPORT

A 31-year-old woman with primary infertility presented in the infertility OPD in December 2024. When she visited our hospital, she had stable vital parameters. Her abdominal examination had normal findings. During per vaginum examination, a cystic mass of about 5 cm was felt behind the uterus. Ultrasound revealed a large left adnexal (measuring 7.24 cm × 3.3 cm) convoluted tubular cystic lesion separate from the left ovary. The lesion had incomplete septations, and its lumen appeared anechoic; therefore, a diagnosis of left hydrosalpinx was made preoperatively [Figures 1 and 2].

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Figure 1:

2D transvaginal scan showing a cystic mass behind the uterus

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Figure 2:

3D picture of the lesion

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A Hysterolaparoscopy was planned for her. When the laparoscopic surgery was performed, a unilocular, smooth, globular, cystic lesion was detected on the surface of the posterior uterine wall during surgery, and it contained clear, straw-coloured fluid. The uterine cyst was unilocular and did not indent the endometrial layer of the uterus [Figure 3]. The cyst wall was smooth, and there were no nodules on the surface. It was aspirated, and then the residual cyst wall was cauterised and excised without opening the endometrium. There was no complication, and the patient was discharged post-completely recovered on the same day. Routine histological analysis was done to exclude malignancy. The analysis confirmed that it was a mesothelial cyst, which was the final diagnosis. Microscopically, the cyst was lined by a single layer of flattened cuboidal epithelial cells. There was no obvious necrosis, mitosis or atypia; thus, these features suggested a mesothelial cyst [Figure 4].

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Figure 3:

Intraoperative photograph showing a mesothelial cyst originating from the posterior wall of uterus

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Figure 4:

High-resolution microscopic findings confirming mesothelial cyst. Stain used: Haematoxylin and eosin (H&E) at a magnification of 400x

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Immunohistochemistry was done to further confirm the diagnosis. There are no definite criteria for the immunohistochemical diagnosis of uterine myometrial cysts. Currently, HBME-1, thrombomodulin, calretinin, WT1 gene product, and cytokeratin 5/6 are considered the best antibodies for identifying mesothelial differentiation.^[3] To further differentiate them from other diagnoses, negative markers are also important. PAX8 and GATA3 are the immune markers that differentiate between paramesonephric and mesonephric neoplasms, respectively.^[4]

In the immunohistochemical test, CK 5/6 and WT1 tests were positive, and PAX8 and GATA3 tests were negative, thus further establishing the diagnosis of uterine mesothelial cyst [Figures 5 and 6].

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Figure 5:

Immunohistochemistry test for CK5/6- positive. Stain used: Diaminobenzidine (DAB), at a magnification of 400X.

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Figure 6:

Immunohistochemistry test for WT1 - positive. Stain used: Diaminobenzidine (DAB), at a magnification of 400X

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DISCUSSION

Most mesothelial cysts are benign, but their characteristics are a topic for debate. Mesothelial cysts have been defined as benign cystic mesothelioma, inflammatory cysts of the peritoneum and peritoneal inclusion cysts and also as post-operative peritoneal cysts.^[5] There are only a few reported cases of mesothelial cysts. In a thorough search on PubMed, only 4 cases of mesothelial cysts of the uterus were found.^[6–9] Chronic inflammation of the peritoneum is a common underlying reason for the formation of a mesothelial cyst, as it may promote the proliferation and migration of mesothelial cells in underlying peritoneal tissues.^[10] Mesothelial cysts may be associated with pelvic inflammatory disease, previous abdominal surgery or endometriosis.^[10] However, further detailed studies are needed to prove this. Preoperative diagnosis of mesothelial cysts is very difficult and challenging due to nonspecific signs and symptoms, and also nonspecific radiological findings. A specific diagnosis can only be made intraoperatively, followed by histopathology. Even immunohistochemical diagnostic criteria are not definitive for the diagnosis of the uterine mesothelial cyst.

Large uterine mesothelial cysts should be managed surgically, preferably by the laparoscopic method. It can be a difficult surgery, as the cyst is generally embedded in the myometrium.

CONCLUSION

Thus, we conclude that uterine mesothelial cysts are a rare finding, most probably post-inflammatory in origin. They have a vague presentation with non-specific signs and symptoms. Sonography is not specific. A definitive diagnosis can be made intraoperatively, followed by histopathology. Awareness of this lesion can prevent misdiagnosis and mistreatment.