Malignant mesothelioma of the tunica vaginalis testis initially misdiagnosed as a benign testicular hydrocele: a case report.

OBJECTIVE: To improve the clinical understanding, diagnostic accuracy, and therapeutic management of mesothelioma of the tunica vaginalis testis. METHODS: We present a case of mesothelioma of the tunica vaginalis in a patient recently admitted to our institution. The clinical characteristics, histopathological features, and therapeutic modalities used are described. FAPI PET/CT was applied as an adjunctive diagnostic tool for preoperative surgical planning. A narrative review of the relevant literature was conducted to discuss current diagnostic approaches, treatment options, and prognostic outcomes. RESULTS: Postoperative histopathological examination revealed an epithelioid mesothelioma of the left testis. The tumor infiltrated the visceral tunica vaginalis and extended outward into the subcutaneous fibrous connective tissue of the scrotum. The infiltration also extended through the parietal tunica vaginalis to the tunica albuginea and involved the smooth muscle of the spermatic cord and the pampiniform venous plexus, with formation of a tunica vaginalis cyst. The adjacent testicular parenchyma and epididymis were not involved, and the spermatic cord surgical margin was free of malignancy. CONCLUSION: Mesothelioma of the tunica vaginalis is a rare malignancy with distinctive histopathological features. Because its clinical presentation resembles that of hydrocele, it is readily misdiagnosed. This case underscores the need to maintain a high index of suspicion when evaluating patients who present with hydrocele. The absence of recurrence at the limited 2-month follow-up does not permit any conclusion regarding disease control, cure, or recurrence, and prolonged surveillance is required. The efficacy and necessity of postoperative adjuvant treatment-including chemotherapy, radiotherapy, and targeted therapy-warrant further validation in prospective studies.