Chapter 97. Malformations of The Urinary System - Review of Medical Embryology Book

MULTIPLE RENAL VESSELS are common; about 3% of population show variations in the number of renal arteries and their position with respect to the renal veins

Supernumerary arteries (2 or 3) are twice as common as extra veins and usually arise at the level of the kidneys
They are caused by the persistence of embryonic vessels, which normally disappear

Can be caused by no rotation (hilum faces ventrally), overrotation (hilum faces dorsally), or malrotation (hilum faces laterally)
Often associated with ectopic kidneys

SIMPLE RENAL ECTOPIA: one or both kidneys are in an abnormal position. One is usually lower than the other and malrotated. Majority are seen in pelvis or lower abdomen

The pelvic kidney is due to a failure of the kidney to ascen It may fuse to form a round mass or discoid or pancake kidney
These kidneys receive their blood supply from nearby vessels

CROSSED RENAL ECTOPIA: in its ascent, the kidney crosses to the opposite side and may fuse with the other kidney, resulting in one large organ. Note: one ureter descends on the right side, the other on the left (differs from duplication of kidney)
URACHAL MALFORMATIONS: the median umbilical ligament is the adult derivative of the allantois and urachus. The latter lies between the umbilical arteries and connects the umbilicus and bladder in the fetus. The lumen in the lower urachus persists in 50% of people and is continuous with the bladder cavity. Malformations include

Lower urachus may dilate: forms a urachal sinus or diverticulum opening into bladder.
Dilatation of the upper urachus may form a urachal sinus that opens at umbilicus
Urachal fistula: entire urachus remains patent
Urachal cysts: remnants of the allantois may persist

EXSTROPHY OF BLADDER OR ECTOPIA VESICAE: uncommon; chiefly seen in males; seen in about 1/50,000 births as exposure and protrusion of the posterior bladder wall

Associated with epispadias and wide separation of pubic bones, division of penis and clitoris, and wide separation of the labial and scrotal halves
Due to an incomplete midline closure of the lower abdominal wall and anterior wall of urinary bladder as a result of failure of mesenchymal cells to migrate between the surface ectoderm and the urogenital sinus in week 4

No muscle in anterior abdominal wall over bladder, and the epidermis and anterior bladder wall rupture to expose the cavity of the bladder

EXSTROPHY OF THE CLOACA: rare; due to entire infraumbilical body wall rupture and failure of the cloaca to divide into a urogenital sinus and rectum, exposing the posterior wall of the cloaca

In addition, all the viscera (including liver) may be outside the body cavity (eventration of the abdominal viscera)

RECTOURINARY FISTULAS: connecting rectum and lower urinary tract (rectovesical and rectourethral fistulas, etc.) or vagina. Due to an abnormal division of the cloaca into the rectum and urogenital sinus
CONGENITAL HYDRONEPHROSES involve dilatation of the renal pelvis, the calyces, and papillary ducts, resulting in a thinning of the cortex. Anomaly is attributed to a high ureteral obstruction due to a problem of urine elimination. May be result of

Fusion of the pyeloureteral junction (normal in embryo, but should not persist)
Ureteral compression by an aberrant vessel or an abnormal position of ureter
Mucosal narrowing
An anomaly of development of the ureteric bud, resulting in a high insertion of the ureter on the pelvis
In an abnormal persistence of the ureteral membrane, a low ureteral obstruction develops, the ureter is dilated, and a ureterohydronephrosis is created