Horseshoe kidney

The kidneys filter waste materials and excess fluid from the blood and also produce hormones that are important for blood formation, blood pressure, and bone formation. Entering the kidneys through the renal artery, blood is processed in tiny tubes called nephrons and returned to circulation through the renal veins. The waste substances that are filtered out are turned into urine, which collects in the central part of the kidney (called the renal pelvis) and passes through the ureters to the bladder. When a half pint or more of urine has collected in the bladder, it is emptied from the body through the urethra.

The kidneys and ureters begin to form when an embryo is about four or five weeks old and are complete, in a rudimentary form, by the eighth week. However, they still need to travel to their correct place in the lower back, an activity that occurs throughout the rest of the prenatal period. Urine is produced and excreted before birth, forming part of the amniotic fluid, but it is the mother's placenta that filters out most of the waste products produced by the fetus. Upon birth, the baby's kidneys, which weigh about half an ounce each, have to take over this function on their own.

Most infants urinate for the first time within 24 hours of birth and between 8 and 20 times or more a day after that. Infants' urine generally ranges from clear to pale yellow in color, although foods, vitamins, and even urate (one of the salts contained in the urine) may cause it to change color. The urine of infants under the age of two has practically no odor but then becomes stronger due to higher concentrations of ammonia (especially when it is allowed to collect in a diaper for a while). Children cannot control urination until the sphincter muscles and the nerves at the base of the bladder are sufficiently developed, which does not occur until at least the age of two. Most children learn to control their bladders during the daytime by the age of three. However, enuresis (bedwetting) may occur in a healthy child (especially one who is a sound sleeper) until the age of four or five.

Congenital abnormalities

A number of congenital kidney abnormalities may occur in children, often originating during that part of the prenatal period when the kidneys are moving into their permanent position. Often these defects do not cause symptoms and require no medical attention. Some children are born with only one kidney (renal agenesis), a condition that poses no health threat as long as the remaining kidney stays healthy. An ectopic kidney--one that is in the wrong place--generally functions normally, although it may cause a malformation of the ureter, obstructing the flow of urine. A horseshoe kidney, one of the more common abnormalities, consists of two kidneys that are joined to each other, forming a U-shaped structure that lies lower than the normal position. The joint kidney may or may not act as a single organ. A malrotated kidney is one that faces the wrong direction but still functions properly. Kidneys may also be underdeveloped (hypoplastic) or develop abnormally (dysplastic), conditions that are not necessarily debilitating if they affect only one kidney. With two hypoplastic kidneys, however, renal failure eventually occurs.

Other abnormalities include supernumerary kidneys (two normal kidneys with an extra renal pelvis); multicystic kidney (one kidney filled with cysts, which doesn't function normally and may become cancerous); polycystic kidney (numerous cysts in both kidneys, which become enlarged and fail to function normally); double ureters (two ureters--instead of the normal one--draining one or both kidneys); and ureteropelvic junction obstruction, or UPJ (a narrowing of the place where the renal pelvis and ureter join, blocking the flow of urine to the bladder and usually requiring surgery).

Kidney disorders

Nephrotic syndrome is a disorder that affects the ability of the glomeruli (the kidney's filtering units) to retain protein in the blood. Protein is excreted through the urine, creating a protein deficiency that leads to fluid retention. Symptoms are swelling around the eyes and in the feet and other parts of the body, as well as weight gain from the excess fluid and a dramatic decline in urine output. While this condition often follows an infection or other illness elsewhere in the body, its exact cause is not known. It is treated with steroids, which reduce the amount of protein in the urine (the dosage of these drugs is reduced as soon as possible to avoid potential side effects). Although nephrotic syndrome tends to recur after the initial episode, it disappears by the late teens or before and causes no lasting damage in over three-fourths of the children affected by it.

Nephritis is the general name for inflammation of the kidneys, of which there are several different types. Although they can potentially lead to kidney failure, they are all treatable. Glomerulonephritis, or inflammation of the glomeruli, occurs in both acute and chronic forms. The acute form generally occurs after a bacterial infection, such as streptococcus, when antibodies accumulate in the glomeruli and damage them. Symptoms include blood in the urine, swelling from fluid retention, high blood pressure, headaches, and blurred vision. Although glomerulonephritis usually resolves on its own, it is necessary to monitor the child for high blood pressure, fluid retention, and other potentially dangerous symptoms. Sometimes this monitoring is done in the hospital, where a special high-protein, low-salt diet may also be administered. In addition, kidney failure may occur, requiring temporary dialysis.

In pyelonephritis, unlike glomerulonephritis, the kidneys are directly infected by bacteria that enter from the lower urinary tract. In addition to infections, a variety of disorders can cause nephritis, including lupus and other diseases that weaken the immune system, and reactions to medication. Alport's syndrome, a progressive condition that often leads to kidney failure, is a hereditary disease that results in chronic nephritis due to a genetic defect in the glomeruli. It is often associated with nerve deafness and, in some cases, with eye problems as well.

Other portions of the urinary tract besides the kidneys may become inflamed. Cystitis is a bladder inflammation produced by infection or by other causes, including drugs and radiation. Symptoms include frequent urination, a burning sensation when urinating, and pain in the lower abdomen. When caused by infection, cystitis is treated with antibiotics . Urethritis is an inflammation of the urethra, with symptoms similar to those of cystitis.

A kidney tumor known as Wilms' tumor (also called nephroblastoma) is one of the most common forms of childhood cancer . It occurs most frequently in children under the age of five (especially under the age of two), but it is also found in adolescents. A hereditary component has been found for this disease, which is also associated with congenital urinary tract and genital deformities, such as undescended testicles. The first sign of the tumor is often a lump in the abdomen or side; symptoms may include blood in the urine, abdominal pain, swelling, loss of appetite, weight loss, and fever. With surgery and chemotherapy, the two-year survival rate for Wilms' tumor is 80% (up dramatically from 33% in the 1960s).

The tumor may spread to other organs, including the lungs and liver, necessitating the removal of additional tissue besides the affected kidney. However, even if the tumor has spread, children usually recover rapidly from surgery for this disease. Since the cancer may recur, children who have had Wilms' tumor need to be monitored carefully following treatment and recovery. Mesoblastic nephroma is another kidney tumor found in children (usually very young infants) and requires removal of the kidney to ensure long-term survival.

Kidney stones, which are most often found in adults, can also occur in children. These usually pebble-sized pieces of crystallized mineral (including phosphates, calcium, urates, or other substances) are often passed out of the body through the urinary tract but sometimes obstruct the flow of urine, damage the kidney, or lodge in the ureters, causing severe pain. They can also trigger infections. Treatment to dissolve the stone depends on its composition, which can be analyzed from a urine sample in which fine grains of the stone are contained. Sometimes surgery is indicated. Another option is removal of the stone with special calipers. Once the nature of the stone is determined, dietary modifications may be recommended to prevent a recurrence.

Kidney failure

Kidney failure--when the kidneys are no longer able to adequately eliminate waste materials from the blood--does not generally happen until the kidneys lose 70% or more of their function, since they normally have considerably more capacity than is needed. In acute kidney (or renal) failure, the kidneys stop functioning suddenly. It usually has a cause other than kidney disease, such as blood loss, dehydration, a drug reaction, or a variety of other serious conditions. Symptoms include decrease in urination, swelling, drowsiness, and irregular heartbeat. Chronic kidney failure, which can be caused by a variety of kidney disorders, occurs gradually. Many types of kidney disease have few symptoms in their early stages, allowing significant deterioration to take place before kidney failure becomes apparent. Often, fatigue is the first symptom of chronic kidney failure, followed by loss of appetite, low urine output, and thirst. Other symptoms include pallor, headaches, nausea, cramps, facial puffiness, and dry or itchy skin. Kidney failure also slows growth and can even stop it altogether. The first measures in treating kidney failure include dietary changes, oral nutritional supplements, and medications that lower the levels of phosphate absorbed into the blood from the intestine. Blood pressure must also be controlled. In most cases, the condition progresses to end-stage renal disease (deterioration to 5-10% of normal capacity), and dialysis or transplantation often becomes necessary.

There are several types of dialysis. Hemodialysis is a means of filtering the blood through a machine--often called an artificial kidney--that performs the functions of a normally working kidney. Blood is pumped from the body into an artificial membrane that performs a filtering operation similar to that of the kidney's own glomeruli while a special dialysis solution, called dialysate, helps regulate the blood's chemical content and remove waste and excess fluids. The patient, who often has a shunt surgically implanted in an arm or leg artery to simplify the connection process, undergoes dialysis sessions two or three times a week in the hospital, at a special dialysis center, or at home with proper medical supervision. Each session lasts about four hours.

Instead of using an external machine, peritoneal dialysis uses the small blood vessels in the membranes of the patient's own peritoneal cavity as a filtering agent for the blood. A catheter is inserted into the abdomen, and a fluid similar to that used for hemolytic dialysis is infused through it, providing the body with needed electrolytes and carrying waste materials with it when it drains. Peritoneal dialysis may be administered several different ways. The intermittent form, which is repeated every hour for 24 to 48 hours, is generally used for acute renal failure that is not expected to require long-term treatment. Continuous ambulatory peritoneal dialysis (CAPD) is performed four or five times a day, and the dialysis fluid is left inside the patient between sessions, for periods of four to six hours. Continuous cycling peritoneal dialysis is performed at night while the child sleeps. During this period, the peritoneal cavity is filled and flushed several times.

A child with end-stage renal failure is also a candidate for a kidney transplant, one of the most successful and frequently performed transplant operations. Although the body has a natural tendency to reject all foreign matter, it is less likely to reject the transplanted kidney if the tissue of the donor closely matches that of the recipient. The most compatible donor organs are those from siblings and parents, in that order. If a kidney from a relative isn't available, transplant centers throughout the country are contacted for a compatible kidney from an accident victim or other recently deceased donor. The operation, which is not a complicated one, takes about four hours, followed by up to six weeks in the hospital. The medication cyclosporine, which suppresses the body's immune system, is commonly taken by transplant recipients, with the dose lowered sharply after the first year following surgery, since an immune system suppressant also impairs the body's ability to fight infections.

The first two years are the most crucial period for acceptance or rejection of the new kidney. A kidney donated by a sibling has a two-year success rate of 90-95%; a kidney transplant from a nonrelative has a success rate between 65 and 80%.

Gale Encyclopedia of Childhood & Adolescence. Gale Research, 1998.