MUSCULAR DEVELOPMENT OF URETER AND BLADDER WITH PARTICULAR EMPHASIS ON THE CONSTRUCTION OF URETEROVESICAL JUNCTION

Abstract

The structure of the ureter and ureterovesical junction was investigated serially in 17 fetuses (from 3 to 21 fetal weeks) and in 2 neonates with particular emphasis on their muscular development in reference to renal excretion of urine and development of bladder wall. Urine is believed to be formed at around 8th week since the pelvis starts to expand and the ureter communicates with the bladder at this stage in the presence of developing renal units. Bladder wall is formed by the vesical detrusor muscle which is recognized at around 7th week from the apical dome, continues the differentiation caudally, and to complete the development by the 17th week. Contribution of vesical detrusor to the ureterovesical junction as superficial periureteral sheath was documented at the 12th week. Around the same period muscles of the pelvis and the ureteral wall start to differentiate from the cephalad to caudad direction coursing spirally. In the most caudal end of the ureter, however, the muscular development of the intravesical ureter and the contributing unit from the trigone as a deep periureteral sheath is delayed and the formation of distinct muscle bundles becomes recognizable later some time between 14 to 16th week. Generally there seems to be a parallelism between the development of trigonal muscle and intravesical ureteral muscle, although at times the latter appeared to be preceding the former. Discussion was made on the inference of these orderly development of the bladder, ureter and ureterovesical junction to the disease entities such as congenital vesical diverticulum, primary VUR, ureterocele, ureteral ectopia and megaloureter.