Accidental PEComa: Case Report of a Rare Entity

A previously healthy girl was referred to the paediatric gastroenterology consultation at the age of four due to recurrent umbilical pain. During workup, an abdominal ultrasound (US) revealed two gallstones with 4 mm of diameter without dilation of the biliary tract. She remained in follow-up, asymptomatic, no physical findings and stable US. At the age of ten, a supra-umbilical mass was detected on US, and MRI revealed an umbilical intra-peritoneal tumor (45x40x45mm) with well-defined limits, heterogeneous, predominantly solid, highly vascularized, and compressing inferior vena cava without local invasion. Surgical mass resection was performed, and histology revealed morphological and immunohistochemical aspects of a PEComa of the abdominal wall. Given the size of the lesion (> 5 cm) and admitting uncertain malignant potential, she was referred to the pediatric oncology center and submitted to margin enlargement. Three years later, she remains asymptomatic without clinical or imagiological evidence of relapse.

Perivascular epithelioid cell tumor (PEComa) is a rare mesenchymal tumor with myomelanocytic differentiation. It mainly occurs in middle aged females and can be found at any location, being kidney the most common. The differential diagnosis of PEComas is fairly broad but the immunohistochemical coexpression of melanocytic (HMB45) and smooth muscle (actin and desmin) biomarkers make the diagnosis. They may behave indolently but entail variable malignant potential. When there isn’t evidence of metastasis, surgical resection is the recommended approach. The benefits of chemotherapy or radiation haven’t been established thus far but some clinical reports show good results with mTOR inhibitors.

With this case we intend to recall the importance of considering this rare etiology in the evaluation of a mesenchymal tumor and enhance the importance of immunohistochemical biomarkers for the definitive diagnosis. The correct histological classification is essential to assess the potential of malignancy and thus assure the most appropriate therapeutic approach.