Intra-abdominal seminoma in polyorchidism with ipsilateral vanishing testis syndrome: A rare case report.

Polyorchidism is a rare anomaly, often associated with cryptorchidism and risk of malignancy. Vanishing testis syndrome results from antenatal torsion with resorption. A 38-year-old male with prior orchiectomy for atrophic testis presented with abdominal pain. Imaging revealed a 12 cm pelvic mass. Resection confirmed pure seminoma with epididymis and rete testis but no viable parenchyma. Review of prior histology showed features of testicular regression. This case demonstrates malignant transformation in a supernumerary intra-abdominal testis with ipsilateral regression, highlighting the importance of histological review and long-term vigilance.