Malignant Mesothelioma Diagnosed From a Spermatic Cord Lesion After Inconclusive Thoracoscopy: A Case With Concomitant Pleural and Peritoneal Involvement.

Malignant mesothelioma typically arises in the pleura or peritoneum; however, involvement of the spermatic cord is extremely rare. Here, we report a case in which a definitive diagnosis was achieved through evaluation of a spermatic cord lesion after an inconclusive thoracoscopic biopsy. A 69-year-old man presented with dyspnea and right inguinal swelling. Imaging revealed a right pleural effusion, peritoneal nodules, and increased fluorodeoxyglucose uptake in the diaphragm and bilateral inguinal canals. Thoracoscopy under local anesthesia revealed a diaphragmatic mass; however, the biopsy specimen was insufficient for a definitive diagnosis. Subsequent right orchiectomy and laparoscopic examination revealed disseminated peritoneal nodules and a spermatic cord tumor. Histopathological examination of spermatic cord specimens showed invasive epithelioid malignant mesothelioma. This case highlights the limitations of small thoracoscopic biopsy specimens and underscores the importance of selecting the appropriate biopsy sites and techniques when mesothelioma is suspected.