• hydronephrosis;
  • leiomyoma;
  • type 1 multiple endocrine neoplasia;
  • ureter

A rare case of leiomyoma of the ureter in a patient with type 1 multiple endocrine neoplasia (MEN) is reported. The case is of a Japanese man in his forties who had a past history of parathyroid gland hyperplasia, pancreatic islet cell tumors, and bilateral adrenocortical nodular hyperplasia. The leiomyoma, measuring 15 × 13 × 12 mm, was located in the right upper ureter, obstructing the lumen and causing hydronephrosis. Three small leiomyomas were also detected in the lower portion. Furthermore, histological examination revealed three tiny leiomyomatous nodules embedded in the muscular layer. It has been reported that type 1 MEN is often complicated by multiple leiomyoma in many organs, including the esophagus, stomach, lung, uterus, and skin. However, it is believed that this is the first report of leiomyomatosis of the ureter occurring in a patient with type 1 MEN. It should be recognized that multiple ureteral leiomyomas may develop in patients of type 1 MEN and can potentially result in hydronephrosis. The multiple development of leiomyoma suggests a causal relationship to MEN1 gene alteration.