Malignant mesotheliomas of the tunica vaginalis testis

: Malignant mesothelioma of the tunica vaginalis is rare, and is usually not diagnosed until surgery is undertaken. We report here a case in a 62-year-old man with malignant mesothelioma tunica vaginalis testis. He was referred to our hospital with a painless swelling of the left scrotal contents. There is a thickening of mesothelia of the tunica vaginalis with left sided hydrocele by ultrasonography and computed tomography scan. The tumor was resected under the diagnosis of testicular malignant tumor. However, the pathologist reported malignant mesothelioma and positive margin. He received external beam radiation therapy at a total dose of 44 Gy. Disease progression was not apparent 2 years after treatment. To our knowledge, 26 cases of malignant mesothelioma in the perineum or intrascrotum have been reported in Japan and this case is thought to be the 27th case in Japan.