Development of the ureterovesical junction in human fetus: in consideration of the vesicoureteral reflux.

The ureterovesical junctions in human fetuses from 11 to 27 weeks of age were studied histologically. Anatomical relationships and origins of the periureteral sheaths, intravesical ureteral muscles, and trigonal muscles were shown. The superficial periureteral sheath arising from the vesical wall was not the source of the trigonal muscles; the deep periureteral sheath arising from the intravesical ureteral wall formed the deep trigonal muscles. The muscles of the intravesical ureter were differentiated longitudinally and formed the superficial trigonal muscles. The development of the two trigonal muscles--superficial and deep--depends on the development of the deep periureteral sheath and the intravesical ureteral muscles. From the finding that both trigonal muscles are present in fetuses compared with both periureteral sheaths or intravesical ureteral muscles in the latest stage, the ability to maintain the valve mechanism in the ureterovesical junction in the human fetus is based on the periureteral sheaths and intravesical ureter--not on the trigone.