A 26-year-old male patient was admitted to our hospital because of an empty scrotum. Empty scrotum was noted when he was an infant. But he did not go to the hospital then, because his family thought the undescended testes could descend. It was only 4 years previously that he was admitted to our hospital for help, and computed tomography (CT) of abdomen showed an undescended testis over the left inguinal region, and the right undescended testis was not found. Surgical intervention was suggested, but the patient hesitated and was discharged without management. Loss of outpatient department follow-up was noted thereafter. This time, he was admitted for management of his condition. After admission, nothing remarkable was noted except for the empty scrotum. Laboratory examination revealed normal results. CT of the abdomen was performed, and showed an undescended testis in the left inguinal region and a mass measuring about 63 × 69 mm in size in the pelvic cavity, with the initial impression of seminoma (Figure 1). Excision of the tumor of the pelvic cavity was done, and the pathologic report confirmed the diagnosis of seminoma. Orchiopexy of the left testis was also carried out. The postoperative course was uneventful, and the patient was discharged in stable condition. Outpatient department follow-up was recommended. Undescended testis is common in infants and children. According to the study by Scorer and Farrington,1 undescended testis occurs in about 30% of premature babies and in only 3.4% of full-term babies. Its occurrence decreases to 0.8% at 1 year old, with no change in its occurrence till puberty.1 This infers that it is not easy for the undescended testis to descend into the scrotum spontaneously after 1 year of age. Undescended testis can cause malignant degeneration and infertility. Besides, malignant change in the undescended testis is about 12–40 times that of the testis in the scrotum.2 Seminoma makes up a larger portion of the germ cell tumors in undescended testes (60%) than in tumors of scrotal testes (40–50%).3 Undescended testes should be placed into the scrotum surgically for the following reasons: assure the greatest possibility of fertility, prevent torsion of the testes, repair an accompanying hernia, achieve cosmetic factor, and permit examination for tumor. About 20% of undescended testis cannot be palpated clinically.4–7 These undescended testes can be located anywhere from the renal hilum to the inguinal region.8 Because of the length of time it takes for complete surgical exploration and because the testis may be missed during surgical exploration, preoperative imaging localization of the undescended testis is essential. Ultrasonography (US) is the initial preoperative imaging localization of the undescended testis in pediatric cryptorchid patients. If the result of US is negative or equivocal, then CT is recommended. In patients with cryptorchidism after puberty, CT is recommended as the initial preoperative imaging localization. If the undescended testis cannot be found in the examination using US and CT, then gonadal venography is recommended. Because of the symmetry of normal structures in the human inguinal canals and pelvic cavity, preoperative imaging localization of undescended testis is achieved by the unexplained soft tissue mass in the inguinal canals and pelvic cavity on US (Figure 2) and CT (Figure 1). Diagnosis of undescended testis is made by demonstration of the pampiniform plexus of gonadal vein in gonadal Accepted: November 26, 2009 *Corresponding author. Department of Radiology, Taipei Veterans General Hospital, 201, Shih-Pai Road, Section 2, Taipei 112, Taiwan. E-mail: wangjh@vghtpe.gov.tw CME Credits