Urinary Tract Defects
Birth defects are more common in the kidney and urinary system than in any other system of the body. Defects can develop in the kidneys, the tubes that transport urine from the kidneys to the bladder (ureters), the bladder, or the tube that expels urine from the bladder (urethra). Any birth defect that blocks or slows the flow of urine can cause urine to stagnate, which can result in infections or formation of kidney stones. Blockage also causes urine pressure to increase, which damages the kidneys and ureters over time.
Symptoms
Many urinary tract defects cause no symptoms. Some, such as kidney defects, may cause blood in the urine after minor injuries. Infections due to defects can develop anywhere in the urinary system and cause symptoms. Kidney damage results from blockage, but it usually causes symptoms only when very little kidney function remains. Then, kidney failure develops. Kidney stones may develop and cause severe, crampy pain in the side between the ribs and the hip (flank) or groin, or blood in the urine.
Diagnosis and Treatment
The techniques used to diagnose abnormalities of the urinary tract include physical examination, ultrasound, computed tomography (CT), nuclear scans, intravenous urography, and rarely, cystoscopy (see Section 11, Chapter 142). Defects that cause symptoms or those that lead to increased pressure on the kidneys usually need to be surgically corrected.
Kidney and Ureter Defects
A number of defects may result in abnormal formation of the kidneys. The kidneys may be in the wrong place (ectopia), in the wrong position (malrotation), joined together (horseshoe kidney), or missing (kidney agenesis). In Potter's syndrome, which causes death, both kidneys are missing. Kidney tissue may also develop abnormally. For example, a kidney may contain many cysts (fluid-filled sacs), as in polycystic kidney disease (see Section 11, Chapter 146). If an abnormality blocks an infant's urine flow, the affected kidney may swell so that it becomes visible and can be felt by a doctor.
Many birth defects involving the kidney do not cause symptoms and are never detected. Some defects may interfere with the function of the kidneys, leading to kidney failure, which can require dialysis or kidney transplantation.
Abnormalities of the tubes that connect the kidneys to the bladder (ureters) include formation of extra ureters, misplaced ureters, and narrowed or widened ureters. A narrowed ureter prevents urine from passing normally from the kidney to the bladder.
Bladder and Urethra Defects
The bladder may not close completely, so that it opens out onto the surface of the abdomen (exstrophy). The wall of the bladder may develop outpouchings (diverticula) where urine can stagnate, sometimes causing urinary tract infections. The bladder outlet (the passageway from the bladder to the urethra) may be narrowed, causing the bladder to empty incompletely. In this case, the urine stream is weak.
The urethra may be abnormal or missing altogether. In posterior urethral valves, abnormal tissue blocks (usually partially) the flow of urine from the bladder. Affected infants have a weak urinary stream and urinary tract infections; they may fail to gain weight normally or may have anemia. Less severe defects may not cause symptoms until childhood. In this case, the symptoms that develop are also milder. Surgery to open the blockage must be performed in infants.
In boys, the opening of the urethra may be in the wrong place, such as on the underside of the penis (hypospadias). In boys with hypospadias, the penis may bend downward (chordee). Both hypospadias and chordee can be repaired surgically. The urethra in the penis may lie open as a channel rather than closed as a tube (epispadias). In both boys and girls, a narrowed urethra may obstruct the flow of urine.
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