A Retroperitoneal Inflammatory Myofibroblastic Tumor Mimicking a Germ Cell Tumor of the Undescended Testis: A Case Report and Literature Review

We report here a case of an inflammatory myofibroblastic tumor in the retroperitoneum, which mimicked a germ cell tumor of the undescended testis. A 75-year-old healthy man presented with a palpable abdominal mass. On the computed tomography image, there was large, well-defined soft tissue mass in the left side of the retroperitoneum, and there was no visible left testis or seminal vesicle. After contrast enhancement, the mass appeared to be relatively homogeneous, considering its large size. With ultrasonography, it appeared as a well-defined, hypoechoic mass with intratumoral vascularity. This solid mass was surgically diagnosed as an inflammatory myofibroblastic tumor.