Primary Malignant Mesothelioma of the Tunica Vaginalis Presenting as a Benign Scrotal Mass: A Case Report.

Primary malignant mesothelioma of the tunica vaginalis is an exceptionally uncommon neoplasm, comprising a very small fraction of all mesothelioma cases. Due to its nonspecific clinical presentation, it is frequently misdiagnosed as benign scrotal conditions, such as a hydrocele. In our case, a 77-year-old male presented with a gradually enlarging swelling in the left hemiscrotum. Scrotal Doppler ultrasonography (USG) and magnetic resonance imaging (MRI) revealed a hydrocele with polypoid masses and nodular soft tissue components of the tunica vaginalis. Tumor markers were normal. Surgical exploration revealed multiple solid masses on the testis and spermatic cord. Histopathologic examination confirmed malignant mesothelioma of epithelioid type, supported by immunohistochemical reactivity for calretinin, cytokeratin 7 (CK7), cytokeratin 5/6 (CK5/6), pan-cytokeratin (PanCK), Wilms tumor 1 (WT1), and loss of BRCA1-associated protein-1 (BAP1). Following the diagnosis of primary tunica vaginalis mesothelioma, the patient underwent radical inguinal orchiectomy and hemiscrotectomy. Adjuvant chemotherapy with pemetrexed and cisplatin was administered. No recurrence was detected after seven cycles, and the patient remains disease-free. This case highlights the diagnostic challenges of tunica vaginalis mesothelioma because of its infrequency and clinical similarity with benign processes. Diagnosis needs to be based on multimodal imaging, histopathology, and immunohistochemistry. Early and total surgical intervention followed by adjuvant therapy may hold the key to successful treatment.