Mesothelial Cyst of Uterine Corpus Misdiagnosed as Leiomyoma
A 46-year-old woman, gravida 3, para 1, presented at West China Second Hospital with complaints of a space-occupying lesion in the uterus. Two years prior, she had been diagnosed with a uterine cyst at the same hospital. At that time, B-ultrasonography revealed a cystic mass with a compartmentalized structure measuring 10.3 × 5.4 × 8.8 cm on the left side of the pelvic cavity. Laparoscopic exploration identified a cystic mass on the posterior uterine wall, which was initially diagnosed as “leiomyoma with cystic degeneration” based on pathology analysis of flash-frozen surgical tissues. A laparoscopic myomectomy was performed, and subsequent pathology analysis of paraffin-embedded tissue confirmed the diagnosis of “leiomyoma with degeneration.” Immunohistochemistry results showed the lesion was positive for caldesmon but negative for CD10. The Ki67 positivity rate was less than 1%, indicating a benign lesion. The patient recovered well postoperatively.
Follow-up ultrasonography three months after the surgery identified a uterine cystic mass measuring 3.0 × 2.5 × 1.7 cm. At the current admission, two years after the initial surgery, ultrasonography indicated that the mass had grown to 6.2 × 4.7 × 9.3 cm. The patient reported no abdominal pain or distention, and both her menstrual cycle and blood volume were regular. A bi-manual examination revealed an enlarged palpable uterus, equivalent to what might be expected for a 4-month pregnancy. Laboratory tests showed mild anemia (hemoglobin, 91 g/L) and negative results for cancer antigens 125 and 19-9. Given the unusual situation, senior pathologists were consulted to review the paraffin-embedded sections from the initial surgery. They concluded that the lesion was “leiomyoma combined with mesothelial cyst,” not “leiomyoma with degeneration” as originally determined.
A second operation involving hysterectomy was suggested, which the patient accepted. Laparoscopy under general anesthesia revealed an enlarged, irregularly shaped uterus. Total hysterectomy and bilateral salpingectomy were performed, and all specimens were carefully examined. The right myometrium of the uterus contained a thin-walled, 9-cm cyst filled with clear liquid. Analysis of paraffin-embedded sections from this repeat surgery showed a single-layer cystic structure lined with flat mesothelial cells on the myometrial wall. The revised pathology classification of “mesothelial cyst of uterine corpus” was confirmed by positive immunostaining for the mesothelial markers calretinin, mesothelin, and cytokeratin 5/6. The patient recovered well after the operation, and her hemoglobin levels were normal one month later. Follow-up at three months after surgery did not reveal any abnormal signs or complaints.
Mesothelial cysts are single or multiple, thin-walled inclusion cysts derived from benign mesothelioma. These cysts can occur at any abdominal peritoneal surface, such as the round ligament, mesentery, and peritoneum. Uterine mesothelial cysts are exceedingly rare. A search of PubMed entries since 1985 failed to identify a single case of a mesothelial cyst in the uterine myometrium. Instead, seven reports describing 19 patients with mesothelial cysts on the round ligament were found, 17 of whom were women of reproductive age. The triggers for the growth of mesothelial cysts are unknown, although developmental disorders are generally suspected. Past abdominal surgery, pelvic inflammation, or endometriosis may be associated with mesothelial cysts of the round ligament. Some studies have explored a potential relationship between sex hormones and mesothelial cysts, but this remains controversial, especially given that mesothelial cysts on round ligaments do not immunostain for estrogen or progesterone.
Mesothelial cysts share similar appearance and histopathology characteristics with benign cystic mesothelioma. Both conditions can present as inclusion cysts in the pelvic cavity. Mesothelial cysts are usually solitary and benign, containing 1 to 3 cavities, with well-differentiated flat mesothelial tissue on the cyst wall. Benign cystic mesothelioma, in contrast, often presents as multi-cavity cysts, which are considered to be a reactive tumor or a neoplastic tumor with negligible potential for recurrence and malignancy. If a patient is asymptomatic, serial ultrasonography can be used to assess cyst size and monitor changes in benign cystic mesothelioma. Surgical excision is the definitive treatment.
Uterine mesothelial cysts are not associated with specific clinical manifestations. Some patients may have a palpable abdominal mass or experience lower abdominal discomfort. Menorrhagia may also be detected in some women. Ultrasonography may reveal a cyst in the uterus. Diagnosis of uterine mesothelial cysts is particularly challenging because of the similarities between leiomyomas with cystic degeneration and congenital uterine cysts. Indeed, the patient in this case was initially misdiagnosed as having leiomyoma with cystic degeneration after the first operation. Only after consultation with senior pathologists was the diagnosis revised to “leiomyoma combined with mesothelial cyst.” The typical microscopic appearance of a single layer of cuboidal cells lining the cyst wall and positive staining for specific markers such as calretinin may help diagnose mesothelial cysts in the pelvic cavity. This case highlighted the need to be aware of the possibility of uterine mesothelial cysts in women of reproductive age.
No definitive treatment has been established for uterine mesothelial cysts, reflecting their rarity. Ultrasonography-guided aspiration of mesothelial cysts of the round ligament can offer temporary relief from symptoms, but it leads quickly to fluid re-accumulation and symptom recurrence. Cyst removal may be an option, but the thinness and multi-cystic appearance of cyst walls make complete removal challenging, which leads to a high recurrence rate. The best way to eliminate lesion recurrence, at least in older women and women without childbearing plans, is total or partial hysterectomy.
The authors certify that they have obtained all appropriate patient consent forms. The patient has given her consent for her images and other clinical information to be reported in the journal. The patient understands that their names and initials will not be published, and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.
doi.org/10.1097/CM9.0000000000000291
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