Case Report
Diffuse intra-abdominal clear cell myomelanocytic tumor: report of an unusual presentation of “PEComatosis” simulating peritoneal mesothelioma

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Abstract

We report a case of diffuse myomelanocytic tumor of the peritoneum that simulates, clinically and instrumentally, a malignant mesothelioma. The patient was a 70-year-old woman with a history of ancient hysterectomy for fibroids, who presented with abdominal discomfort. Exploratory laparotomy revealed diffuse encasing of the peritonealized organs by a thin, fleshy, gray-white tissue rind. Scattered tumor masses were present as well. A dominant lesion measuring 6 cm in larger size was resected from the pelvis. Histological examination revealed a tumor composed of epithelioid and spindle cells, exhibiting either a clear or slightly eosinophilic cytoplasm and a mild to moderate nuclear pleomorphism. Focal areas of necrosis could be documented. Immunohistochemically, tumor cells were positive for HMB45, melan-A, and smooth muscle actin, but negative for other antibodies, including epithelial markers, desmin, and S100 protein. We believe that this case represents an example of myomelanocytic tumor of uncertain biologic potential, a member of the recently devised perivascular epithelioid cell tumors (PEComa), with an unusual presentation simulating a diffuse mesothelial neoplasm. The origin of this particular lesion is briefly discussed in light of the recent literature published on the subject.

Introduction

After their initial description in the early 1990s [1], [2], tumors of perivascular epithelioid cells (PEComas) have now emerged as a group of typical microscopic entities sharing a spindled/epithelioid morphology and showing a consistent immunoreactivity to actins and the so-called melanoma antigens [3], including the pulmonary “sugar” tumor and lymphangiomyomatosis and, in the abdominal cavity, the renal angiomyolipoma and the clear cell myomelanocytic tumor (CCMMT) of the falciform ligament/ligamentum teres [4]. The latter usually arises within the female genital tract, occurs in young females, and pursues a benign course. Nevertheless, cases exhibiting a significant deviant clinical presentation as well as phenotypic features have been reported, including extra-pelvic, extra-abdominal location, and tumors occurring in aged or in male patients [3], [4], [5], [6], [7], [8]. However, to the best of our knowledge, CCMMT has not presented with diffuse peritoneal involvement that simulates, clinically and macroscopically, a diffuse peritoneal neoplasm.

We report a case of CCMMT presenting with exclusive peritoneal involvement, raising clinically the suspicion of a diffuse mesothelial tumor.

Section snippets

Case report

A 70-year-old patient was admitted to the hospital because of pain and abdominal distension. About 27 years previously, she had undergone total hysterectomy with bilateral oophorectomy for “uterine leiomyomata.” Glass slides pertaining to the uterine specimen were no longer accessible. Computed tomographic scans revealed confluent nodules in the pelvis, omentum, and visceral peritoneum (Fig. 1). A dominant mass measuring 6 cm was documented between the lower rectum and urinary bladder. The

Discussion

Diffuse neoplastic involvement of the peritoneal surface is usually secondary to metastatic spreading from primary tumors in the ovary or in the gastrointestinal tract. Primary serosal tumors, such as mesothelioma or psammocarcinoma, are less common, although they account for a sizable proportion of cases [10], [11], [12], [13]. Soft tissue analogues may sometimes present with a preponderant peritoneal involvement [14], [15]. PEComas arising within the female pelvis feature a spindle and

Acknowledgments

The authors are indebted to Dr Elvio G. Silva for having kindly revised the original manuscript and providing his accountable suggestions.

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