Cytology of benign multicystic peritoneal mesothelioma in peritoneal washings

To describe the cytological aspect of peritoneal washings in benign multicystic peritoneal mesothelioma (BMPM). Three peritoneal washing specimens stained by standard cytological and histological procedures and analysed by light microscopy. The specimens showed an abundance of monomorphous mesothelial cells devoid of atypia or mitoses. The mesothelial cells were calretinin positive. They also showed numerous squamous metaplastic cells arranged in flat sheets or isolated cells. The background contained some inflammatory cells. The combination of cytology of the peritoneal washing, histology (cell block and surgical specimen) and clinical history allow differentiation of BMPM from other cystic lesions (cystic lymphangioma and malignant mesothelioma).