- Case report
- Open Access
A rare case of perivascular epithelioid cell tumor (PEComa) of the greater omentum
© The Author(s). 2018
- Received: 7 March 2018
- Accepted: 6 June 2018
- Published: 19 June 2018
A tumor composed exclusively or predominantly of human melanin black 45 (HMB45)-positive epithelioid cells is called a perivascular epithelioid cell tumor (PEComa). We report a very rare case of a PEComa of the greater omentum.
MRI conducted to examine the orthopedic disease of the patients, a 49-year-old Japanese woman, also identified a tumor in her pelvis. A CT scan revealed a tumor mass on the right side of the pelvic floor and clear nutrient vessels originating from the splenic and celiac arteries. An omental primary tumor or accessory spleen was thus suspected, and tumor resection was performed. The tumor was a light brown solid tumor with a smooth margin, measuring 5.2 × 3.8 × 3.5 cm. Histopathologically, the tumor was composed mainly of spindle and epithelioid cells, and large and small blood vessel formation was observed. In the immunohistochemical staining, tumor cells were positive for human melanin black 45 (HMB-45) and Melan-A and partially positive for alpha-smooth muscle actin. The final diagnosis was PEComa of the greater omentum.
Although omental PEComa is very rare, it should be considered as a differential disease of an omental primary tumor.
- Perivascular epithelioid cell tumor
- Human melanin black 45
- Omental primary tumor
- Omental PEComa
A perivascular epithelioid cell tumor (PEComa) is a rare mesenchymal tumor composed of epithelioid cells characterized by histological and immunohistochemical evidence of both smooth muscle and melanocytic differentiation . In immunohistochemical staining, the melanocyte marker HMB-45 (human melanin black 45) is the most sensitive (92% positive); Melan-A is the next most sensitive. The smooth muscle marker smooth muscle actin (SMA) is found in 80% of PEComas . PEComas have been reported to occur at various sites such as gynecologic sites, ureter, intestinal tract, bone, and skin [2–6]. However, there are few reports of primary omental PEComa.
Although primary tumors of the greater omentum are rare, there are several reports of malignant tumors of this type . Therefore, in the treatment of an omental primary tumor, the preoperative differential diagnosis is important, and it is necessary to consider PEComa as one of the differential diagnoses. Here, we describe a rare case diagnosed as an omental PEComa postoperatively.
Based on the above results, the tumor was diagnosed as an omental PEComa. There has been no recurrence at 16 months after the surgery.
The image findings of primary PEComa have been reported to be nonspecific . In this patient’s case, we considered omental liposarcoma, PEComa, teratoma, and accessory spleen as the preoperative diagnosis, considering the MRI findings and partial calcification in CT. Omental tumors have been reported to cause torsion [9–11]. Indeed, in our patient’s case, the possibility of twisting was considered because the preoperative diagnosis of omental PEComa was difficult and because the approx. 5-cm tumor was located at the tip of the greater omentum, which also presents a risk of torsion of the omentum. The surgery was thus carried out concurrently with the patient’s diagnosis and treatment.
Omental PEComas are very rare. To the best of our knowledge, only two prior cases of omental PEComa or perivascular epithelioid cell tumor have been reported. Our literature search using PubMed with “omental PEComa” or “omental perivascular epithelioid cell tumor” as keywords revealed that only one case of omental PEComa was reported between 1950 and 2018; the case was an omental angiomyolipoma reported by Takamura et al. . That case was quite different from our patient’s because multiple angiomyolipomas coexisted in the liver. In addition, the case previously received right nephrectomy and enucleation of the left kidney for angiomyolipomas of both kidneys 11 years ago. Another case could not be retrieved by PubMed search with the above keywords, but the case was included in the 26 perivascular epithelioid cell neoplasm cases reported by Folpe et al. . However, details are unknown. Our case is the first single PEComa of the greater omentum.
Laparoscopic surgery is less invasive compared with open surgery [13–16]. In addition, umbilical single-incision laparoscopic surgery (SILS) is cosmetically superior to open surgery . As a malignant PEComa that caused intraperitoneal seeding has been reported in the past, it is necessary to firmly search the abdominal cavity during surgery . For these reasons, in a mobile omental tumor, it is a good indication of SILS. In our case, SILS was chosen because the patient emphasized the cosmetic result of the wound. This is the first report of omental PEComa excised by SILS which is cosmetic and enables simultaneous observation in the abdominal cavity and tumor resection.
Classification of PEComas proposed by Folpe et al
Uncertain malignant potential
No worrisome features
Nuclear pleomorphism/multinucleated giant cells only
Two or more worrisome features
Size < 5 cm
Size > 5 cm
Size > 5 cm only
Non-high nuclear grade and cellularity
High nuclear grade and cellularity
Mitotic rate ≦ 1/50HPF
Mitotic rate ≧ 1/50HPF
No vascular invasion
We presented the case of a primary greater omental PEComa with uncertain malignant potential in a 49-year-old woman. Although omentum PEComas are very rare, omental tumors following a malignant course must be treated correctly and should be considered a differential diagnosis.
We are grateful to the patient for allowing us to use her medical records in our case report.
Availability of data and materials
Data are available on request due to privacy.
KO was involved with the concept and design of this manuscript. KO, YO, TY, MT, TA, RS, TH, TT, KN, and KM contributed as a gastrointestinal surgeon in operative performance and perioperative treatment. TI and FK had contributed as tumor pathologist. YH supervised the report. All authors read and approved the final manuscript.
Ethics approval and consent to participate
It is approved by the ethics committee of Teikyo University (approval date, 23 August 2016, registration number; 16-032).
Consent for publication
Written consent was obtained from the patient for publication of this case report and any accompanying images. A copy of the written consent is available for review by the Editor-in-Chief of this journal.
The authors declare that they have no competing interests.
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