Abnormal blood supply to the kidneys
25% of adult kidneys have accessory renal arteries arising from aorta, superior or inferior to the main renal artery. Sometime an accessory artery to the inferior pole of the kidney is present. Such an artery may pass anterior to the ureter and obstruct it causing hydronephrosis, which is distension of the renal pelvis and calices with urine (figure 8).
Congenital abnormalities of the kidneys and ureter
Ectopic kidneys means that the one or both kidneys failed to ascend. Most ectopic kidneys are located in the pelvis; however, other positions could be present. Crossed kidneys could be present when one kidney crosses to the other side resulting in crossed renal ectopia.
In some cases, kidneys fused while developing in the pelvis region. When one kidney ascends, it pulls the other one with it resulting in a condition called unilateral fused kidneys. Horseshoe kidney happens in 1per 500 people where the inferior pole of the kidneys fuse together to give the characteristic shape of a horse shoe. Such kidney gets trapped by the inferior mesenteric artery while ascending.
Absence of one kidney is called unilateral renal agenesis. If both kidneys are absent then the condition is called bilateral renal agenesis. It is caused by the failure of the metanephric diverticulum to penetrate the metanephrogenic blastema and thus no nephrons formation is induced by the collecting duct.
When the metanephric diverticulum divide, it causes an abnormal duplications of the ureter and the renal pelvis. Incomplete division result in a divided kidney with bifid ureter, whereas complete division result in a double kidney with bifid ureter or separate ureters (figure 9).
In some cases, kidneys fused while developing in the pelvis region. When one kidney ascends, it pulls the other one with it resulting in a condition called unilateral fused kidneys. Horseshoe kidney happens in 1per 500 people where the inferior pole of the kidneys fuse together to give the characteristic shape of a horse shoe. Such kidney gets trapped by the inferior mesenteric artery while ascending.
Absence of one kidney is called unilateral renal agenesis. If both kidneys are absent then the condition is called bilateral renal agenesis. It is caused by the failure of the metanephric diverticulum to penetrate the metanephrogenic blastema and thus no nephrons formation is induced by the collecting duct.
When the metanephric diverticulum divide, it causes an abnormal duplications of the ureter and the renal pelvis. Incomplete division result in a divided kidney with bifid ureter, whereas complete division result in a double kidney with bifid ureter or separate ureters (figure 9).
Figure 9: Various anomilies of the kidneys and the ureters. A, unilateral renal agenesis; B, right pelvic kidney and left divided kidney; C, right kidney malrotation and left bifid ureter and double kidneys; D, crossed fused renal ectopia; E, pelvic fused kidneys; F, supernumerary kidney. (Moore and Persaud, 2008)
Congenital abnormalities to the urinary bladder
When the remnant of the urachus persists, it forms an urachal fistula which allows urine to escape through the umbilicus. If only a local area of the urachus persist and the due to the secretory activity of its lining, an urachal cyst could be formed. Urachal sinus is a dilation in the urachus that could open into the bladder or the umbilicus (figure 10).
Another rare yet sever anomaly that occurs in almost 2/100,000 births is exstrophy of the bladder. The mucosal surface of the posterior wall of the bladder is exposed and protruded. Epispadias is when the open urinary track extends to the dorsum of the penis, through the bladder and to the umbilicus. It is believed that the condition occurs as a result of the mesenchymal cells failure to migrate between the endoderm and ectoderm of the abdominal wall, and thus the lateral body wall folds fails to close in the midline of the pelvic region. A more sever case is the exstrophy of the cloaca, which result in defects in urinary system, external genitalia, and the hindgut. |