Paratesticular malignant mesotheliomas are exceedingly rare and make up less than 1% of all mesotheliomas. They arise from the tunica vaginalis which is formed by the evagination of the abdominal peritoneum into the scrotum. The age range is between 40 and 80 years (mean around 60 years). Most of the patients present with a hydrocele. Some have history of asbestos exposure. Morphologically, the majority of the tumors are purely epithelioid type (almost 80% of cases), showing an admixture of papillary, tubular, and solid patterns. The remaining 20% of cases show mixed epithelioid/sarcomatoid pattern. This image shows tubular structures infiltrating a densely sclerotic stroma. For a more detailed discussion of mesotheliomas, check out peritoneal mesotheliomas
Reference:Winstanley AM et al. The Immunohistochemical Profile of Malignant Mesotheliomas of the Tunica Vaginalis: A Study of 20 Cases. Am J Surg Pathol 2006;30:1-6.