PEComa of the Uterus: A Rare Mesenchymal Tumor Displaying a ≪Snowstorm≫ Pattern at Magnetic Resonance Imaging

Dear Editor in Chief, PEComa is an uncommon mesenchymal tumor with about 100 cases described in the literature up to 2014 [1–3]. If the first mention of this type of lesion dates back to 1943, when Apiz described an « abnormal myoblast », the normal counterpart cell of the lesions has remained unknown up to now [2–4]. The tumors are composed of epithelioid cells or, more seldom, of spindle cells, sometimes mixed in variable proportions and showing numerous analogies with those of the vascular walls, their probable site of origin [2–3]. As soon as 1992, Bonetti et al. suggested the term perivascular epithelioid cell tumor or PEComa to identify these lesions, whose aggressiveness proves variable [3]. The World Health Organization defines PEComa as a mesenchymal tumor composed of perivascular epithelioid cells with specific histologic and immunohistochemical features [3]. This definition applies to a family of neoplasms of variable anatomical topography including angiomyolipomas, clear cell sugar tumors, lymphangioleiomyomatosis and melanocytic tumors of the falciform ligament [1–3]. The histologic and immunohistochemical features of the tumors suggest that they emerge from the vascular parietal structures even if the corresponding normal cell is still not clearly identified (3). Indeed, PEComas consist of variable assemblies of epithelioid cells and, to a lesser extent, of spindle cells expressing a myomelanocytic phenotype, immunoreactive for melanocytic and smooth muscle markers like HMB-45 and smooth muscle actin in particular [1–3]. PEComas occur at any age, with a peak in the 4th decade of life, affecting principally the female gender [1–7]. Case descriptions of this type have been increasing since 2008 and the majority (approximately 65%) involving the retroperitoneum, the kidneys and the genitourinary tract [1–3]. Other locations exist, such as liver, lung, pancreas, small bowel or colon but they are even much rarer [2, 4, 5, 8]. Uterine PEComas are mainly located at the level of the corpus of the organ, the cervix being less often affected. 10% of the cases are associated with Bourneville tuberous sclerosis [1–3]. This association could be due to genetic mutations causing the inactivation of TSC1 or TSC2 genes [3]. The tumor aggressiveness of PEComas remains illdefined and their malignant potential is difficult to assess even histologically [3, 4, 6–8]. Many cases prove benign but the general trend is towards volume increase and malignant transformation [4–8]. In a series of 36 patients with malignant PEComa, 20% had metastases, especially in the lungs or liver, but also in the nodes or in the peritoneum [2]. Moreover, these metastases sometimes develop very late [3]. In 2005, Folpe et al. proposed morphological and histologic criteria to classify gynecological PEComas as benign, intermediate or malignant (Table 1) [2, 3, 7]. Nevertheless, the scarcity of published cases makes these conclusions risky and it is clear that this class of tumors requires much larger studies [3]. The recent increase in cases, linked to the increasing use of cross-sectional imaging and improved histological tumor recognition, certainly contribute in that direction. The symptomatology of PEComas is non-specific, the more as the tumor topography proves variable. Regarding uterine tumors, if the smallest lesions are often discovered incidentally, larger masses may trigger symptoms that range from vaginal bleeding to hemoperitoneum via abdominal discomfort, whose etiology is so vague [1, 3]. PEComas are detected by cross-sectional imaging but only histologic and immunohistochemical analysis enables accurate diagnosis [2, 4, 9]. Ultrasound usually * Department of Radiology, Centre Hospitalier de Luxembourg, rue Barblé, 4, L-1210 Luxembourg, Grand Duchy of Luxembourg verbeeck.nicolas@chl.lu, toukouki.aman@chl.lu † Department of Obstetrics and Gynecology, Centre Hospitalier du Nord, avenue Salentiny, 120, L-9080 Ettelbruck, Grand Duchy of Luxembourg drweis@pt.lu ‡ Department of Obsterics and Gynecology, Centre Hospitalier de Luxembourg, rue Barblé, 4, L-1210 Luxembourg, Grand Duchy of Luxembourg vanwymersch.didier@chl.lu Corresponding author: Dr. N. Verbeeck, M.D. LETTER TO THE EDITOR