Spontaneous peritoneal malignant mesothelioma in a geriatric japanese macaque (Macaca fuscata)

Reactive mesothelial hyperplasia mimicking mesothelioma in an African green monkey (Chlorocebus aethiops)

A spontaneous reactive mesothelial hyperplasia occurred in a female, 15.7-year-old African green monkey (grivet; Chlorocebus aethiops). At necropsy, massive effusions were found in the abdomen, the thorax, and the pericardium. Additionally, multiple small, beige-gray nodules were detected on the serosal surfaces of the abdominal organs. Histopathologically, the mesothelial cells resembled the epithelioid subtype of a mesothelioma, but no infiltrative or invasive growth could be demonstrated. The mesothelial cells on the thoracis, liver, and intestinal serosa were accompanied by chronic serositis. Mesothelial cells expressed cytokeratin, vimentin, calretinin, desmin, Wilms Tumor 1 (WT-1) protein, and epithelial membrane antigen (EMA). Cells were negative for carcinoembryonic antigen (CEA), cluster of differentiation 15 (CD15), and podoplanin. Ultrastructurally, cells revealed a moderate amount of microvilli of medium length, perinuclear tonofilament bundles, and long desmosomes. In fluorescence in situ hybridization (FISH) for the detection of characteristic gene loss (p16; CDKN2A), NF2, and MTAP, no deletions were detected. No asbestos fibers and no presence of Simian virus 40 antigen (SV40) could be demonstrated.

A Case of Peritoneal Sarcomatoid Mesothelioma with Absence of Occupationl Exposure to Asbestos

Sarcomatoid mesothelioma is not very common, mesothelioma is directly attributable to occupational asbestos exposure, with 90% of cases showing a history of exposure. A 66-year-old male was admitted with an abdominal pain that persisted for 3 weeks. He had no abdominal mass. Computed tomography showed soft tissue thickening in perihepatic space and nodularities in omentum and peritoneum with ascites. There was no absolute diagnosis evidence in ascites analysis. Although the pathology of ascites was free for malignancy, the patient underwent omentum biopsy for definitive diagnosis. In laproscopic exploration, there was omental cake, peritoneal nodular seeding. It was suspected cancer carcinomatosis. Immunohistochemical findings suggested that it was sarcomatoid masothelioma. This is the rare case of a peritoneal sarcomatoid mesothelioma, without any exposure to asbestos.

Vasoformative disorder, resembling littoral cell angioma, of the spleen in a geriatric Japanese macaque (Macaca fuscata)

A 30-year-old female Japanese macaque showed marked splenomegaly. The enlarged spleen consisted of neoplastic proliferation of anastomosing vascular channels resembling morphologic structures of red pulp sinuses; occasionally, papillary fronds were seen in dilated channels. Immunohistochemically, the lining cells reacted to both endothelial cell (von Willebrand factor) and macrophage (macrophage scavenger receptor class A) markers, indicating features of littoral cells of the spleen. Based on the pathologic characteristics, particularly the presence of neoplastic cells with macrophage/histiocyte-like attributes, this tumor was regarded as littoral cell angioma; this is a rare benign splenic vascular tumor.

Malignant mesothelioma

Malignant mesothelioma is a fatal asbestos-associated malignancy originating from the lining cells (mesothelium) of the pleural and peritoneal cavities, as well as the pericardium and the tunica vaginalis. The exact prevalence is unknown but it is estimated that mesotheliomas represent less than 1% of all cancers. Its incidence is increasing, with an expected peak in the next 10–20 years. Pleural malignant mesothelioma is the most common form of mesothelioma. Typical presenting features are those of chest pain and dyspnoea. Breathlessness due to a pleural effusion without chest pain is reported in about 30% of patients. A chest wall mass, weight loss, sweating, abdominal pain and ascites (due to peritoneal involvement) are less common presentations. Mesothelioma is directly attributable to occupational asbestos exposure with a history of exposure in over 90% of cases. There is also evidence that mesothelioma may result from both para-occupational exposure and non-occupational "environmental" exposure. Idiopathic or spontaneous mesothelioma can also occur in the absence of any exposure to asbestos, with a spontaneous rate in humans of around one per million. A combination of accurate exposure history, along with examination radiology and pathology are essential to make the diagnosis. Distinguishing malignant from benign pleural disease can be challenging. The most helpful CT findings suggesting malignant pleural disease are 1) a circumferential pleural rind, 2) nodular pleural thickening, 3) pleural thickening of > 1 cm and 4) mediastinal pleural involvement. Involvement of a multidisciplinary team is recommended to ensure prompt and appropriate management, using a framework of radiotherapy, chemotherapy, surgery and symptom palliation with end of life care. Compensation issues must also be considered. Life expectancy in malignant mesothelioma is poor, with a median survival of about one year following diagnosis.