Paratesticular papillary mesothelioma: a case with borderline features.

Most often, mesotheliomas involve the serosal (serous) membranes of the pleura and peritoneum. Sometimes, mesothelial proliferations are identified in other locations. On very rare occasions, a mesothelioma is found within the tunica vaginalis of the paratesticular region. We report a case of papillary mesothelioma of the tunica vaginalis in a 52-year-old man. Although this lesion had papillary structures lined by a single layer of mesothelial cells with predominantly bland nuclear and cytologic features, there was evidence of a minimal presence of mesothelial cells in the underlying stroma. This combination of benign and semimalignant characteristics can make the diagnosis of such a lesion problematic. We think that a diagnosis of "borderline papillary mesothelioma" can be considered for similar mesothelial proliferations to allow for a possible increase in diagnostic accuracy and provide an enhanced informational platform from which patients and clinicians can benefit.