Paratesticular malignant mesothelioma is a rare and potentially aggressive malignancy, accounting for approxi- mately 0.3-1.4 percent of all malignant mesotheliomas. The tumor presents as a painless scrotal mass associated with recurrent hydrocele. We report an incidental case of paratesticular malignant mesothelioma in a 73-year- old man that was found during an operation to remove a progressively enlarging, symptomatic hydrocele. During the procedure the surgeon noted multiple, irregular, extratesticular masses, and subsequently submitted a sam- ple for frozen section analysis. Frozen section assessment revealed a papillary-appearing, malignant tumor and the surgeon proceeded with a radical orchiectomy. Examination of the orchiectomy specimen revealed multiple, yellow-white, papillary, exophytic excrescences that tracked along the hydrocele and coursed up the tunica vagi- nalis of the spermatic cord. Microscopically, the tumor was composed of papillary fronds and nests of malignant cells with enlarged, hyperchromatic, pleomorphic nuclei. Pankeratin and calretinin immunohistochemical stains strongly highlighted the tumor cells, supporting the diagnosis of malignant mesothelioma. Suspicion of malignant mesothelioma as a differential diagnosis in the setting of enlarging hydrocele is imperative, as the care of the patient is dramatically altered to address the aggressive nature of the disease and the unfavorable outcome.
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