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Paratesticular extrarenal Wilms' tumor

Wilms’ tumor is a common pediatric malignant tumor, although extrarenal Wilms’ tumor (ERWT) is an extremely rare malignancy. While the histological characteristics are the same as in renal Wilms’ tumor, the tumor arises from outside the kidney. We experienced a case of ERWT that arose in the paratesticular region. A 7-month-old male infant was admitted to the Nagano Children’s Hospital in Nagano, Japan, with a complaint of a right intrascrotal mass. The mass was walnut-sized and had an irregular surface. The right testis was palpated attached to the mass. Ultrasonography of the mass showed an irregular paratesticular solid mass, 2.5 cm in diameter, which had increased blood flow in it (Fig. 1a,b). Systemic examination did not show any other abnormality. Tumor markers (a-fetoprotein, b-subunit of human chorionic gonadotropin and lactate dehydrogenase) were within the normal range. A computed tomography scan of the abdomen showed normal bilateral kidneys. He had a radical orchiectomy with the diagnosis of a paratesticular malignant tumor, and the mass was easily removed. The cut surface of the tumor was milky white, and the mass separated from the testis and the epididymis. The tumor was not adherent to the testis and the epididymis; it also encapsulated a fibrous capsule. Histopathological examination showed the characteristics of Wilms’ tumor exhibiting blastemal, stromal and epithelial elements. Some glomeruloid and tubular structures were scattered in the subcapsular area adjacent to the blastema. The features of anaplasia were not shown. Immunohistochemistry showed epithelial membrane antigen was positive in the tubular structure and Vimentin was positive in the stroma. The boy did not receive any adjuvant therapy, and he was alive and disease free at the end of 36 months of follow up. ERWT accounts for just 3% of Wilms’ tumors. Approximately 100 well-documented cases have been reported. ERWT arises in the retroperitoneal cavity, the uterus, the pelvis, the thorax and the inguinal region, along the line of the spermatic cord. Just three cases of paratesticular ERWT have been reported. The origin of ERWT remains unclear. The genital and urinary structures are in close proximity