Unusual Multifocal Glomeruloid Pattern in a Well-Differentiated Papillary Mesothelioma of the Peritoneum

Abstract

by clefted spaces. The mesothelial origin of the tumor was confirmed by immunoreactivity showing positive immunolabeling for calretinin (1:300; Dako, Carpinteria, California), CK 5/6 (1:30; Bio Sb, Santa Barbara, California), thrombomodulin (1:50; Dako), WT-1 (1:50; Cell Marque, Austin, Texas), and CK7 (1:100; Cell Marque). CK20 (1:50; Cell Marque) was negative (Figure 2). Well-differentiated papillary mesothelioma is an uncommon distinct subtype of mesothelioma that occurs principally in the peritoneum of women in the third and fourth decades. It is often discovered incidentally during abdominal or pelvic surgery, and it is generally regarded as a tumor of low malignant potential. In the English literature, less than 100 cases have been reported affecting both men and women, including cases arising in the pleura and tunica vaginalis. Histologically, WDPM is A46-year-old woman presented to the ABC Medical Center in Mexico City with the clinical picture of acute cholecystitis and underwent cholecystectomy. The patient had no history with regard of asbestos exposure. During surgery, incidental multifocal small firm, white to tan peritoneal nodules were found, ranging from 5 mm to 1 cm, and on frozen section, a diagnosis of papillary epithelial neoplasm consistent with well-differentiated papillary mesothelioma (WDPM) was rendered (Figure 1A). The patient underwent total hysterectomy, along with omentectomy and resection of multiple peritoneal and diaphragmatic implants. The serosal membranes of the uterus and ovary were unremarkable, although a microscopic focus (1 mm) of parenchymal infiltration was found in the left ovary. The histological study disclosed a well-developed tubulopapillary growth pattern with solid areas. The papillae were lined by a single layer of uniform cuboidal to flattened cells with minimal cytological atypia, covering thin fibrovascular cores. Mitosis was absent. The stroma showed focal myxoid change. Focal psammoma bodies were present. Throughout the tumor, constituting approximately 20% of the neoplasm and mainly localized to the periphery of the nodules, the fibrovascular papillae were arranged forming a distinct glomeruloid pattern of growth characterized by round to oval neoplastic mesothelial cell tufts supported by a fibrovascular core (Figures 1B and 1C). The mesothelial cells were sometimes arranged in semicircular concentric rows separated