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Birth Defects

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Birth Defects

Birth defects, also called congenital anomalies, are physical abnormalities that occur before a baby is born; they are usually obvious at birth or by 1 year of age.

Birth defects can involve any part of any organ in the body. Some birth defects are more common than others. Birth defects are the leading cause of death in infants in the United States, and some cause the death of the fetus. A birth defect is evident in about 7.5% of all children by age 5 years, although many of these are minor. Major birth defects are evident in about 3 to 4% of newborns. Several birth defects can occur together in the same infant.

Abdominal Wall Defects (Omphalocele and Gastroschisis)

An omphalocele is caused by an opening (defect) in the middle of the abdominal wall at the bellybutton (umbilicus). The skin, muscle, and fibrous tissue are absent. The intestines protrude through the opening and are covered by fine membranes. The umbilical cord is in the center of the defect. Gastroschisis is an abnormal opening of the abdominal wall, usually to the right of the umbilicus, which allows the uncovered intestines to spill out (herniate). Both conditions are diagnosed with prenatal ultrasound.

An omphalocele is commonly associated with other birth defects (such as heart defects) and with specific genetic syndromes. Surgical closure is the treatment of choice. However, the skin of the abdominal wall must often be stretched before surgery so there is enough tissue to cover the opening. Large defects sometimes also require skin flaps.

In gastroschisis, the bowel may be damaged by compression and by exposure to amniotic fluid. Surgical closure is the treatment of choice. Large herniations may require the creation of a "silo," in which the exposed bowel is wrapped in a protective covering and suspended above the baby for several days or weeks. The silo is gradually compressed, forcing the intestines back into the abdomen.

Bone and Muscle Defects

Birth defects can occur in any bone or muscle, although the bones and muscles of the skull, face, spine, hips, legs, and feet are affected most often. Bones and muscles may develop incompletely. Also, structures that normally align together may be separated or misaligned. Usually, bone and muscle defects result in abnormal appearance and function of the affected part of the body. Most of these defects are repaired surgically if symptoms are troublesome. Often, the surgery is complex and involves reconstructing deformed or absent body parts.

The most common defects of the skull and face are cleft lip and cleft palate. Cleft lip is a separation of the upper lip, usually just below the nose. Cleft palate is a split in the roof of the mouth resulting in a passageway into the nose. Cleft lip and cleft palate often occur together.

Cleft lip is disfiguring and prevents the infant from closing his lips around a nipple. A cleft palate interferes with eating and speech. A dental device can temporarily seal the roof of the mouth so the infant can suckle better. Cleft lip and cleft palate can be permanently corrected with surgery. The likelihood of cleft lip and cleft palate can be reduced if a woman takes folic acid before pregnancy and through the 1st trimester of pregnancy.

Another type of facial defect is a small lower jaw (mandible). Pierre Robin syndrome and Treacher Collins syndrome, which are characterized by several defects in the head and face, are among the causes of a small lower jaw. If the lower jaw is too small, the infant may have difficulty eating or breathing. Surgery may correct or diminish the problem.
Cleft Lip and Cleft Palate: Defects of the Face

Limbs or joints can be missing, deformed, or incompletely developed at birth. A child with one limb or joint abnormality is more likely to have another related abnormality. Limbs and joints may form abnormally; for example, bones in the hand and forearm may be missing because of a genetic defect. Normal development of a limb can also become disrupted in the womb; for example, a finger may stop growing because the finger gets constricted by fibers. Another cause for limb and joint abnormalities is mechanical force; for example, pressure may cause the hip to dislocate. Chromosomal abnormalities can cause limb and joint abnormalities. Sometimes the cause is unknown. The drug thalidomide, which was taken by some pregnant women in the late 1950s and early 1960s for morning sickness, caused a variety of limb defects—usually short, poorly functioning appendages developed in place of arms and legs.

Abnormalities of the arms and legs may occur in a horizontal fashion (for example, if the arm is shorter than normal) or in a lengthwise fashion (for example, the arm is abnormal on the thumb side [from the elbow to the thumb] but normal on the little finger side). Children often become very adept at using a malformed limb, and an artificial limb (prosthesis) can often be fitted (usually when the child is able to sit independently) to make the limb easier to use.

Hand defects are common. Sometimes a hand does not form completely; part or all of the hand may be missing. For example, the person may have too few fingers. Sometimes a hand does not develop; for example, the fingers may not separate, producing a weblike hand. Some hand defects involve extra fingers; the little fingers or thumbs are most commonly duplicated. Overgrowth may occur, in which the hands or individual fingers are too large. Surgery is usually carried out to correct the hand defect and provide as much function as possible.

In developmental dysplasia of the hip, formerly called congenital dislocation of the hip, the newborn's hip socket and the thighbone (femoral head), which normally form a joint, become separated, often because the hip has a socket that is not deep enough to hold the head of the femur. Dysplasia of the hip is more common in girls, in newborns born in a breech (buttocks-first) position, and in newborns who have close relatives with the defect. Newborn girls born in breech position should have ultrasounds of their hips. The right and left legs or hips often look different from each other in affected newborns.

The doctor may be able to detect the defect when examining the newborn. In infants younger than 4 months, an ultrasound of the hips can confirm the diagnosis; in infants older than 4 months, an x-ray can be used. The use of triple diapers (an older treatment) is not recommended. The best treatment is early use of the Pavlik harness. The Pavlik harness is a soft brace that holds the infant's knees spread outward and up toward the chest. However, if the defect persists past the age of 6 months, surgery to fix the hip in the normal position is usually needed.

Clubfoot (talipes equinovarus) is a defect in which the foot and ankle are twisted out of shape or position. The usual clubfoot is a down and inward turning of the hind foot and ankle, with twisting inward of the forefoot. Sometimes the foot only appears abnormal because it was held in an unusual position in the uterus (positional clubfoot). In contrast, true clubfoot is a structurally abnormal foot. With true clubfoot, the bones of the leg or foot or the muscles of the calf are often underdeveloped.
Common Types of Clubfoot

Positional clubfoot can be corrected by immobilizing the joints in a cast and by using physical therapy to stretch the foot and ankle. Early treatment with immobilization is beneficial for true clubfoot, but surgery, often complex, is also generally needed.

In metatarsus adductus, the foot appears turned inward. Mobility of the joints of the foot and ankle may be limited. Treatment depends on the severity of the deformity and immobility of the foot. Most mild cases resolve spontaneously. Corrective shoes or splints may be needed in more severe cases. Surgery is required only in exceptional instances.

In arthrogryposis multiplex congenita, many joints become "frozen" and consequently cannot bend. Many children with this defect have weakened muscles. It is likely that decreased movement of the muscles and joints before birth causes the decreased movement of the joints after birth. The cause is unknown. Sometimes the nerves that would normally move the bones in the affected joints are also impaired. Infants with the defect may also have dislocated hips, knees, or elbows. Placing the limbs in a cast and performing physical therapy, in which the stiff joints are carefully manipulated, may improve joint movements. Surgically freeing the bones from attached tissue sometimes results in more normal joint movement.

Brain and Spinal Cord Defects

Of the many possible defects in the brain and spinal cord, those known as neural tube defects develop within the first weeks of pregnancy. Others, such as porencephaly and hydranencephaly, develop later in pregnancy. Many brain and spinal cord defects result in visible abnormalities in the head or back.

Symptoms of brain or spinal cord damage may develop if the defect affects brain or spinal cord tissue. Brain damage can be fatal or result in mild or severe disabilities which may include mental retardation, seizures, and paralysis. Spinal cord damage can result in paralysis, incontinence, and loss of sensation to areas of the body reached by nerves below the level of the defect. Computed tomography (CT) and magnetic resonance imaging (MRI) can reveal brain and spinal cord defects by showing pictures of the internal structures of those organs.

Some defects, such as those that cause visible openings or swellings, can be repaired surgically. Although brain or spinal cord damage from the defect is usually permanent, surgery can help prevent further complications and improve function. Some children have near-normal development as a result of prompt surgical intervention.

The brain and spinal cord develop as a groove that folds over to become a tube (the neural tube). Layers of tissue that come from this tube normally become the brain and spinal cord and their covering tissues, including part of the spine and the meninges. Sometimes the neural tube does not develop normally, which may affect the brain, spinal cord, and meninges. In the most severe form of neural tube defect, the brain tissue may fail to develop (anencephaly); this defect is fatal. Another type of defect results when the neural tube fails to close completely and remains an open channel. In its mildest form, an open channel defect may affect only bone; for example, in spina bifida occulta (which means hidden spine split in two), the bony spine fails to close, but the spinal cord and meninges are unaffected. This common abnormality causes no symptoms. Sometimes, a meningocele develops in which the meninges and other tissue, such as brain tissue (meningoencephalocele) or spinal cord tissue (meningomyelocele), can protrude out of the opening. Sometimes the meninges are not involved when tissue protrudes from the brain (encephalocele) or spinal cord (myelocele). Damage to brain or spinal cord tissue is much more likely when tissue protrudes than when it does not.
Spina Bifida: A Defect of the Spine
In spina bifida, the bones of the spine (vertebrae) do not form normally. Spina bifida can vary in severity. In one form, called occult spinal dysraphism, one or more vertebrae do not form normally, and the spinal cord and the layers of tissues (meninges) surrounding it may also be affected. The only symptom may be a tuft of hair, a dimpling, or a pigmented area on the skin over the defect. In a meningocele, the meninges protrude through the incompletely formed vertebrae, resulting in a fluid-filled bulge under the skin. The most severe type is a meningomyelocele, in which the spinal cord protrudes. The affected area appears raw and red, and the infant is likely to be severely impaired.

In occult spinal dysraphism, newborns are born with visible abnormalities on their lower backs. These include birthmarks, overly pigmented areas (hemangioma and flame nevus), tufts of hair, openings in the skin (dermal sinus), or small lumps (masses). The underlying spinal cord may be connected to the surface, which exposes it to bacteria, greatly increasing the chance for development of meningitis. The nerves of the spinal cord may become damaged as the child grows. Or, the spinal cord may have a fatty tumor (lipoma) on it, which also can lead to nerve damage. Therefore, newborns who have these abnormalities should have the underlying soft tissue and spinal cord evaluated using ultrasound or magnetic resonance imaging (MRI).

Genetic factors can make neural tube defects more likely. The defect often develops before the mother knows she is pregnant. Most symptoms from neural tube defects result from brain or spinal cord damage. Meningoencephaloceles and meningomyeloceles cause severe disability. These include water on the brain (hydrocephalus), learning disabilities, paralysis with bone and joint abnormalities, decreased sensation of the skin, and bowel and urinary problems.

Many neural tube defects can be detected before birth. A high level of alpha-fetoprotein in the woman's blood or amniotic fluid may indicate a neural tube defect in the fetus. Ultrasound performed late in pregnancy may show the defect or characteristic abnormalities. Folic acid taken before a woman gets pregnant and through the first three months of pregnancy can decrease the risk of neural tube defects by as much as 50%. For this reason, women of child-bearing age are encouraged to take folic acid if they think that they may become pregnant. Neural tube defects are usually closed surgically.

Hydrocephalus is an accumulation of extra fluid in the normal open spaces within the brain (ventricles), usually causing an enlarged head and developmental problems.
The fluid surrounding the brain (cerebro-spinal fluid) is produced in spaces within the brain called ventricles. The fluid must drain to a different area, where it is absorbed into the blood. When the fluid cannot drain, hydrocephalus (water on the brain) develops. Hydrocephalus often increases the pressure in the ventricles, which compresses the brain. Many conditions, such as a birth defect, bleeding within the brain (often associated with prematurity), or brain tumors, can block drainage and cause hydrocephalus.

An abnormally large head may be a symptom of untreated hydrocephalus. The infant usually does not develop normally. Computed tomography (CT), ultrasonography, or magnetic resonance imaging (MRI) of the head reveals the diagnosis as well as the degree of brain compression.
The goal of treatment is to keep pressure normal within the brain. A permanent alternate drainage path (shunt) for cerebrospinal fluid decreases the pressure and volume of the fluid inside the brain. A doctor places the shunt in the ventricles in the brain and runs it under the skin from the head to another site, usually the abdomen (ventriculoperitoneal shunt). The shunt contains a valve that allows fluid to leave the brain if the pressure becomes too high. Although a few children can eventually do without the shunt as they get older, shunts are rarely removed. On occasion, a surgical hole placed between the third and fourth ventricles (ventriculostomy) may treat the hydrocephalus.

If needed, pressure within the brain can often be temporarily reduced with repeated spinal taps (lumbar punctures) until a shunt is placed.
Some children with hydrocephalus develop normal intelligence. Others, especially those who develop hydrocephalus early in the pregnancy, are mentally retarded or have learning disabilities.

Digestive Tract Defects
A birth defect can occur anywhere along the length of the digestive tract—in the esophagus, stomach, small intestine, large intestine, rectum, or anus. In many cases, an organ is not fully developed or is abnormally positioned, which often causes narrowing or blockage (obstruction). The internal or external muscles surrounding the abdominal cavity may weaken or develop holes. The nerves to the intestines may also fail to develop (Hirschsprung's disease, or congenital megacolon).
Blockages (obstructions) that develop in the intestines, rectum, or anus can cause rhythmic, crampy abdominal pain, abdominal swelling, and vomiting.
Most digestive tract defects require surgery. Generally, obstructions are surgically opened. Weakenings or holes in the muscles surrounding the abdominal cavity are sewn shut.

In esophageal atresia, the esophagus narrows or comes to a blind end. Most newborns with esophageal atresia also have an abnormal connection between the esophagus and the trachea (tracheoesophageal fistula).
Normally, the esophagus, a long tubelike organ, connects the mouth to the stomach. In esophageal atresia, food is delayed or prevented from going from the esophagus to the stomach. A tracheoesophageal fistula is dangerous because it allows swallowed food and saliva to travel through the fistula to the lungs, leading to coughing, choking, difficulty breathing, and possibly pneumonia. Food or fluid in the lungs may impair oxygenation of blood, leading to a bluish discoloration of the skin (cyanosis). Characteristically, a newborn with esophageal atresia coughs and drools after attempting to swallow. Many children with esophageal atresia and tracheoesophageal fistula have other abnormalities, such as heart defects.
Atresia and Fistula: Defects in the Esophagus
In esophageal atresia, the esophagus narrows or comes to a blind end. It does not connect with the stomach as it normally does. A tracheoesophageal fistula is an abnormal connection between the esophagus and the trachea (which leads to the lungs).

To detect a blockage, x-rays are taken as a tube is passed down the esophagus.
The first steps in treatment are withholding oral feedings and placing a tube in the upper esophagus to continuously suction out saliva before it can reach the lungs. The infant is fed intravenously. Surgery needs to be performed soon to establish a normal connection between the esophagus and stomach and to close the connection between the esophagus and the trachea.

Anal atresia is narrowing or obstruction of the anus.
Most infants with anal atresia develop some type of abnormal connection (fistula) between the anus and either the urethra, the area between the urethra and anus (the perineum), the vagina, or the bladder.
Infants with anal atresia fail to defecate normally after birth. Eventually, intestinal obstruction develops. However, doctors often detect the abnormality by looking at the anus when they first examine the baby after birth, before symptoms develop.

Using x-rays, a radiologist can see the path of a fistula. Anal atresia usually requires immediate surgery to open a passage for feces and to close the fistula. Sometimes, a temporary colostomy (making a hole in the abdomen and connecting it to the colon to allow stool to flow into a plastic bag on the abdominal wall) may be necessary.

Intestinal malrotation (abnormal rotation of the intestines) is a potentially life-threatening defect in which the intestines develop incompletely or abnormally.
Malrotation can cause the intestines to later twist (volvulus), cutting off their blood supply. Infants with intestinal malrotation can suddenly develop symptoms of vomiting, diarrhea, and abdominal swelling; these symptoms can also come and go. If the blood supply to the middle of the intestine is completely cut off (midgut volvulus), sudden, severe pain and vomiting develop. Bile, a substance formed in the liver, may be vomited and appear yellow, green, or rust-colored. Eventually, the abdomen swells. X-rays may help the doctor determine the diagnosis.However, the volvulus can be seen only on x-rays taken after placing barium, a substance visible on the x-ray, in the rectum (barium enema).
Treatment, including intravenous fluids and usually emergency surgery, must begin within hours. If not treated rapidly, the defect can result in loss of intestinal tissue or death.

In biliary atresia, the bile ducts are destroyed – either partially or completely – so bile cannot reach the intestine.
Bile, a fluid secreted by the liver, carries away the liver's waste products and helps digest fats in the small intestine. Bile ducts within the liver collect the bile and carry it to the intestine. In biliary atresia, bile eventually accumulates in the liver and then escapes into the blood, causing a yellowish discoloration of the skin (jaundice). Progressive, irreversible scarring of the liver, called biliary cirrhosis, starts by the age of 2 months if the defect is not treated.

In infants with biliary atresia, the urine becomes dark, the stools become pale, and the skin becomes increasingly jaundiced. These symptoms and an enlarged, firm liver are usually first noticed about 2 weeks after birth. By the time infants are 2 to 3 months old, they may have stunted growth, be itchy and irritable, and have large veins visible on their abdomen, as well as a large spleen.

To prevent biliary cirrhosis, the diagnosis of biliary atresia must be made before the age of 2 months. To make the diagnosis, a doctor performs a series of blood tests. Ultrasound may be helpful. If the defect is still suspected after these tests, surgery (which consists of examination of the liver and bile ducts and a liver biopsy) is performed to diagnose the defect.

Surgery is needed to create a path for bile to drain from the liver. Constructing replacement bile ducts that flow into the intestine is best, and this kind of operation is possible in 40 to 50% of infants. Most of the infants with replacement bile ducts can lead normal lives. Infants who cannot have replacement bile ducts constructed usually require liver transplantation by age 2 years.

A diaphragmatic hernia is a hole or weakening in the diaphragm that allows some of the abdominal organs to protrude into the chest.
Diaphragmatic hernias occur on the left side of the body 90% of the time. The stomach, loops of intestine, and even the liver and spleen can protrude through the hernia. If the hernia is large, the lung on the affected side is usually incompletely developed. Many children with diaphragmatic hernias also have heart defects.

Diaphragmatic Hernia

 After delivery, as the newborn cries and breathes, the loops of intestine quickly fill with air. This rapidly enlarging structure pushes against the heart, compressing the other lung and causing severe difficulty breathing, often right after birth. A chest x-ray usually shows the defect. The defect can also be detected before birth using ultrasound. Diagnosis before birth allows the doctor to prepare for treatment of the defect. Surgery is required to repair the diaphragm. Measures to deliver oxygen, such as a breathing tube and ventilator, may be needed.

In Hirschsprung's disease (congenital megacolon), a section of the large intestine is missing the nerve network that controls the intestine's rhythmic contractions. Symptoms of intestinal obstruction occur.
The large intestine depends on a network of nerves within its walls to synchronize rhythmic contractions and move digested material toward the anus, where the material is expelled as feces. In Hirschsprung's disease, the affected section of intestine cannot contract normally.

At the time of birth, newborns should pass a dark green fecal material (meconium). Delayed passage of meconium raises the suspicion of Hirschsprung's disease. Later in infancy, children with Hirschsprung's disease can have symptoms that suggest intestinal obstruction—bile-stained vomit, a swollen abdomen, and refusal to eat. If only a small section of the intestine is affected, a child may have milder symptoms and may not be diagnosed until later in childhood. These children may have ribbonlike stools and a swollen abdomen; they often fail to gain weight. In rare cases, constipation is the only symptom.

Hirschsprung's disease can also lead to life-threatening toxic enterocolitis, which produces sudden fever, a swollen abdomen, and explosive and, at times, bloody diarrhea.
Rectal biopsy and measurement of the pressure inside the rectum (manometry) are the only tests that can reliably be used to diagnose Hirschsprung's disease. A barium enema may also be performed. During a barium enema, the doctor instills barium and air into the child's rectum and then takes x-rays.
Severe Hirschsprung's disease must be treated quickly to prevent toxic enterocolitis. Hirschsprung's disease is usually treated with surgery to remove the abnormal section of intestine and to connect the normal intestine to the rectum and anus. In some cases, for example, if the child is quite ill, the surgeon connects the lower end of the normal part of the intestine to an opening made in the abdominal wall (colostomy). Stool can thus pass through the opening into a collection bag, restoring normal movement of food through the intestines. The abnormal section of intestine is left disconnected from the rest of the intestine. When the child is older and healthier, the colostomy is closed, the abnormal section of intestine is removed, and the normal part of the intestine is reconnected to the rectum and anus in a so-called pull-through procedure.

Genital Defects

Defects of the external genital organs (penis, testes, or clitoris) usually result from abnormal levels of sex hormones in the fetus before birth. Congenital adrenal hyperplasia (a metabolic disorder) and chromosomal abnormalities commonly cause genital defects.
A child may be born with genitals that are not clearly male or female (ambiguous genitals, or intersex state). Most children with ambiguous genitals are pseudohermaphrodites—that is, they have ambiguous external genital organs but either ovaries or testes (not both). Pseudohermaphrodites are genetically male or female.

Diagnostic evaluation of a child with ambiguous genitals includes physical examination and blood tests to analyze the chromosomes (the XY chromosome pattern is male and the XX chromosome pattern is female) and hormone levels (pituitary hormones and male sex hormones, or androgens, such as testosterone). X-rays and ultrasound of the pelvis may help identify internal sex organs. Treatment with testosterone may help enlarge the penis so that assignment to a male sex is more realistic.
Most experts believe that the child's sex must be assigned quickly. Otherwise, bonding by the parents to the child may become more difficult, and the child may develop a gender identity disorder. The decision to assign gender to a baby with ambiguous genitals depends on several factors. They include how much testosterone the fetus was exposed to; what the potential for sexual function is (as determined for example, by how much erectile tissue the baby has); and the potential for reproduction. Environmental and psychologic factors, such as parents' perception of gender, also affect the decision. Surgery to correct the ambiguous genitals can be performed later, especially if the defect is complex. The underlying problem causing pseudohermaphroditism may also need treatment.

Male and female sex organs develop from similar tissue in the embryo. When acted on by high levels of testosterone before birth (as in a normal male fetus), the genitals become the penis, scrotum, and penile urethra. Low or absent testosterone levels lead to the development of a clitoris, labia majora, and separate vaginal and urethral canals. Intermediate levels of testosterone cause ambiguous genitals: Genetic males have a small penis and testicles that remain in the abdomen instead of descending into the scrotum (undescended testicles, also known as cryptorchidism), and genetic females have an enlarged clitoris with fused labia. The appearance of the genitals in both sexes is very similar.
Pseudohermaphroditism in the male (better termed undervirilized 46,XY intersex), results in a genetic male who has female-appearing external genitals but has undescended testicles. Pseudohermaphroditism may be caused by a prenatal deficiency of male sex hormones (androgens), an inability of the body's tissues to respond to androgens, exposure to female sex hormones (estrogens), or a chromosomal abnormality.

After they develop, the testes produce most of the male body's androgens. Absent or underdeveloped testes cause androgen deficiency.
Androgen deficiency during childhood causes incomplete sexual development. An affected boy retains a high-pitched voice and has poor muscle development for his age. The penis, testes, and scrotum are underdeveloped. Pubic and underarm hair is sparse, and the arms and legs are abnormally long.
Androgen deficiency can be treated with testosterone. The testosterone is usually given by injection or through a skin patch. Injection and skin application cause fewer side effects than taking testosterone by mouth. Testosterone stimulates growth, sexual development, and fertility.

Female pseudohermaphroditism (also called virilization or overvirilized 46,XX intersex) is caused by exposure to high levels of male hormones. The most common cause is enlarged adrenal glands (congenital adrenal hyperplasia) that overproduce male hormones because an enzyme is missing. The male hormones cannot be converted to female hormones as occurs in normal females. Sometimes, male hormones enter the placenta from the mother's blood; for example, the mother may have been given drugs such as progesterone to prevent a miscarriage, (some progesterone is changed into the male hormone testosterone by the fetus) or the mother may have had a hormone-producing tumor, although this is much less common.

A female pseudohermaphrodite has female internal organs but has an enlarged clitoris that resembles a small penis.
If the child is assigned to the female gender, surgery is performed to create female-appearing genitals. This surgery can include reduction of the clitoris, formation or repair of a vagina (vaginoplasty), and repair of the urethra.
Congenital adrenal hyperplasia can be life-threatening because it can cause serious abnormalities of electrolytes (sodium and potassium) in the blood. These are diagnosed with blood tests and treated with corticosteroids.

Heart Defects
One of 120 babies is born with a heart defect. Some are severe, but many are not. Defects may involve abnormal formation of the heart's walls or valves or of the blood vessels that enter or leave the heart.
Blood flow is different in the fetus than in children and adults. In children and adults, all blood returning to the heart (venous blood) goes through the right atrium and then through the right ventricle to the pulmonary artery, and from there it enters the lungs. In the lungs, the blood picks up oxygen from the air sacs (alveoli) and also releases carbon dioxide.  The blood then returns from the lungs to the left atrium and left ventricle and from there it is pumped out of the heart to the body (arterial blood) through a large artery called the aorta. However, because there is no air to breathe before birth, a fetus uses oxygen obtained from the mother's blood through the placenta. Because the fetus does not breathe, only a small amount of blood needs to go through the lungs, so the path by which blood circulates through the heart and lungs is different in the fetus.

Before birth, much of the venous blood coming to the right side of the heart bypasses the lungs and mixes in two different places with blood that has already traveled to the lungs. Such mixing occurs through the foramen ovale, a hole between the right and left atria. Mixing also occurs through the ductus arteriosus, a blood vessel connecting the pulmonary artery and the aorta. In the fetus, because blood arriving at the heart has already received oxygen from the placenta. Both venous blood and arterial blood contain oxygen, so mixing arterial blood and venous blood does not affect how much oxygen gets pumped to the body. After birth, however, such mixing would severely limit the amount of oxygen in the blood, so the foramen ovale and ductus arteriosus normally close within days to a couple of weeks after birth.
Normal Circulation in a Fetus
Blood flow through the heart in a fetus differs from that in children and adults. In children and adults, blood picks up oxygen in the lungs. But in a fetus, the blood that enters the heart already contains oxygen, supplied from the mother by the placenta. Only a small amount of blood goes through the lungs (which do not contain air). The rest of the blood bypasses the lungs through two structures: the foramen ovale, a hole between the right and left atria, and the ductus arteriosus, a blood vessel that connects the pulmonary artery and the aorta. Normally, these two structures close soon after birth.

Abnormally formed hearts alter the normal blood flow to the lungs and body. Either the flow of blood gets re-routed (shunted) or a defective heart valve or a blood vessel blocks the flow of blood.
Shunting can cause oxygen-poor blood to mix with oxygen-rich blood that is pumped to the body tissues (right-to-left shunt). The more oxygen-poor blood (which is blue) that flows to the body, the bluer the body appears, particularly the skin and lips. Many heart defects are characterized by a bluish discoloration of the skin (called cyanosis); cyanosis indicates that not enough oxygen-rich blood is reaching the tissues where it is needed.

Shunting can also mix oxygen-rich blood, which is pumped under high pressures, with oxygen-poor blood being pumped through the pulmonary artery to the lungs (left-to-right shunt). Shunting makes the circulation inefficient and increases the pressure in the pulmonary artery. The high pressure damages the pulmonary artery and lungs. The shunt also eventually leads to an insufficient amount of blood being pumped to the body (heart failure).

In heart failure, blood also backs up, often in the lungs. Heart failure can also develop when the heart pumps too weakly (for example, when a baby is born with a weak heart muscle) or when blood is blocked from flowing to the baby's body.

Blockages may develop in the valves of the heart or in the blood vessels leading away from the heart. Blood may be impeded from flowing to the lungs because of narrowing of the pulmonary valve (pulmonary valve stenosis) or narrowing within the pulmonary artery itself (pulmonary artery stenosis). Blood may be impeded from flowing through the aorta to the body because of narrowing of the aortic valve (aortic valve stenosis) or blockage within the aorta itself (coarctation of the aorta).

Symptoms and Diagnosis
Often, heart defects produce few or no symptoms and are not detectable even during a physical examination of the child. Some mild defects produce symptoms only later in life. However, many heart defects do result in symptoms during childhood. Because oxygen-rich blood is necessary for normal growth, development, and activity, infants and children with heart defects may fail to grow or gain weight normally. They may not be able to exercise fully. In more severe cases, cyanosis may develop, and breathing or eating may be difficult. Abnormal blood flow through the heart usually produces an abnormal sound (murmur) that can be heard using a stethoscope; however, the vast majority of heart murmurs that occur during childhood are not caused by heart defects and are not indicative of any problems. Heart failure makes the heart beat rapidly and often causes fluid to collect in the lungs or liver. Some congenital heart defects (such as a hole in the atrium [patent foramen ovale]) increase the risk that a blood clot will form and block an artery in the brain, leading to a stroke.

Many heart defects can be diagnosed before birth by using ultrasound. After birth, heart defects are suspected when symptoms develop or when particular heart murmurs are heard.
Diagnosing heart defects in children involves the same techniques used for diagnosing heart problems in adults. A doctor may be able to diagnose the defect after asking the family specific questions and performing a physical examination, electrocardiography (ECG), and a chest x-ray. Ultrasound (echocardiography) is used to diagnose almost all of the specific defects. Cardiac catheterization often can show small abnormalities that are not detected with echocardiography or can further illuminate the details of the abnormality.

Many significant heart defects are effectively repaired with open-heart surgery. When to perform the operation depends on the specific defect, its symptoms, and severity. For example, it may be better to postpone surgery until the child is a little older. However, severe symptoms resulting from a heart defect are most effectively relieved with immediate surgery.

A narrowing can sometimes be relieved by passing a thin tube (catheter) through a blood vessel in the arm or leg into the narrowed area. A balloon attached to the catheter is inflated and widens the narrowing, usually in a valve (a procedure called balloon valvuloplasty) or blood vessel (a procedure called balloon angioplasty. These balloon procedures spare the child from general anesthesia and open-heart surgery. However, balloon procedures are not usually as effective as surgery.

If the aorta or pulmonary artery is severely blocked, a temporary shunt can sometimes be created to keep an adequate amount of blood flowing. A shunt can be created with a catheter balloon (for example, between the right and left atria—balloon septostomy). Or drugs such as prostaglandin can be given to keep the ductus arteriosus open, shunting blood between the aorta and pulmonary artery. In rare cases, when no other treatment helps, a heart transplant is performed, but the lack of donor hearts limits the availability of this procedure.

Most children who have significant heart defects are at increased risk for developing life-threatening bacterial infections of the heart and its valves (endocarditis). They need to take antibiotics before certain treatments and procedures.

In patent ductus arteriosus, the blood vessel connecting the pulmonary artery and the aorta (ductus arteriosus) fails to close as it usually does within the first 2 weeks after birth.
In patent ductus arteriosus, a left-to-right shunt of blood from the aorta back into the pulmonary artery causes extra blood flow into the lungs, and high blood pressure in the lungs may damage the lung tissue. Premature newborns are especially susceptible to patent ductus arteriosus and lung damage.

Patent Ductus Arteriosus: Failure to Close
The ductus arteriosus is a blood vessel that connects the pulmonary artery and the aorta. In the fetus, it enables blood to bypass the lungs. The fetus does not breathe air, and thus blood does not need to pass through the lungs to be oxygenated. After birth, blood does need to be oxygenated in the lungs, and normally, the ductus arteriosus closes quickly, usually within days up to 2 weeks. In patent ductus arteriosus, this connection does not close, allowing some oxygenated blood, intended for the body, to return to the lungs. As a result, the blood vessels in the lungs may be overloaded and the body may not receive enough oxygenated blood.

Most often, the defect causes no symptoms. When symptoms do occur, they are usually difficulty breathing or cyanosis, which may be present at birth or not for several weeks after birth. When the infant has no symptoms, doctors most often suspect the defect when they hear a heart murmur.
Indomethacin, a drug that inhibits the production of chemicals called prostaglandins, closes the defect in 80% of infants. Indomethacinis most effective if given within the first 10 days after birth and is more effective in premature newborns than in full-term newborns. If the defect does not close after several doses of indomethacin, it is closed surgically.

Atrial and ventricular septal defects are holes in the walls (septa) that separate the heart into the left and right sides.
Atrial septal defects are located between the heart's upper chambers (atria), which receive blood. Ventricular septal defects are located between the lower chambers (ventricles), which pump blood. These holes typically cause left-to-right shunting of blood. Many atrial septal defects close by themselves, especially in the first year of life; many ventricular septal defects close within the first 2 years.

Infants and most older children with atrial septal defects have no symptoms. However, children who have no symptoms but who do have a small shunt require annual echocardiography. In more severe cases, children may develop heart murmurs and fatigue and may have difficulty breathing. Rarely, the first sign of an atrial septal defect is a stroke. The symptoms caused by atrial septal defects increase as the child ages. For example, heart failure may develop during middle age.
Septal Defect: A Hole in the Heart's Wall
A septal defect is a hole in the wall (septum) that separates the heart into the left and right sides. Atrial septal defects are located between the heart's upper chambers (atria). Ventricular septal defects are located between the lower chambers (ventricles). In both types, some oxygenated blood, intended for the body, is shortcircuited. It is returned to the lungs rather than pumped to the rest of the body.

Ventricular septal defects can vary from small holes, which may cause a heart murmur but no symptoms and usually close by themselves, to larger holes that cause symptoms in infants. Significant ventricular septal defects usually cause more severe symptoms than atrial septal defects, because there is more shunting of blood. Recurrent lung infections and heart failure may develop. Because of the way lungs develop, shunting increases during the first 6 weeks after birth. Usually the murmur becomes louder, and symptoms, typically rapid breathing, sweating, and difficulty feeding, worsen. Echocardiography usually confirms the diagnosis. Mild symptoms of a ventricular septal defect may be treated with diuretics (such as furosemide) or drugs that decrease resistance to the flow of blood to the body (such as captopril). If atrial and ventricular septal defects are large, do not close spontaneously during the first few years of life, or cause symptoms, they are usually closed surgically.

In tetralogy of Fallot, four specific heart defects occur together.
The defects are a large ventricular septal defect, displacement of the aorta that allows oxygen-poor blood to flow directly from the right ventricle to the aorta (causing a right-to-left shunt), a narrowing of the outflow passage from the right side of the heart, and a thickening of the wall of the right ventricle.
Tetralogy of Fallot: Four Defects

In infants with tetralogy of Fallot, the narrowed passage from the right ventricle restricts blood flow to the lungs. The restricted blood flow causes the oxygen-poor blood in the right ventricle to pass through the septal defect to the left ventricle and into the aorta (right-to-left shunt). The most important symptom is cyanosis, which can be mild or severe. Some infants have life-threatening attacks (hypercyanosis or "tet" spells), in which cyanosis suddenly worsens in response to activity, such as crying or having a bowel movement. The infant becomes very short of breath and may lose consciousness. Infants with tetralogy of Fallot usually have a heart murmur. Echocardiography confirms the diagnosis.

When an infant has a hypercyanotic spell, oxygen, morphine, and beta-blockers  may provide quick relief. The infant may breathe more easily when the knees are close to the chest (knee-chest position). Giving intravenous fluids or a drug such as phenylephrine, both of which increase resistance to the flow of blood to the body, may be helpful. A doctor may give the infant propranolol to prevent future spells until corrective surgery can be performed. In infants who have tetralogy with complete blockage of outflow from the right side of the heart (pulmonary atresia) and who depend on an open ductus arteriosus for survival, giving a prostaglandin such as alprostadil to maintain an open ductus arteriosus can be lifesaving.

Infants with tetralogy of Fallot eventually need surgery. If symptoms are frequent or severe, surgery is performed in early infancy, but can be delayed until later in infancy if the child has few symptoms. To keep blood flowing to the lungs until corrective surgery can be performed, some doctors use less invasive procedures such as balloon valvulotomy, in which a long catheter with a balloon on its tip is passed through a vein into the heart. The balloon is inflated in the valve, widening the opening. During corrective surgery, the ventricular septal defect is closed, the narrowed passageway from the right ventricle and the narrowed pulmonary valve are widened, and any abnormal connections between the aorta and pulmonary artery are closed.

Transposition of the great arteries is a reversal of the normal connections of the aorta and the pulmonary artery with the heart.
Oxygen-poor blood returning from the body flows from the right atrium to the right ventricle as usual, but then flows to the aorta and the body, bypassing the lungs. Oxygenated blood travels back and forth between the heart and lungs (from the lungs to the pulmonary vein, then left atrium and ventricle, then the pulmonary artery) but is not transported to the body. The body cannot survive without oxygen. However, infants with this defect may survive briefly after birth because the foramen ovale (a hole between the right and left atria) and the ductus arteriosus (a blood vessel connecting the pulmonary artery with the aorta are still open at birth. These openings allow oxygen-rich blood to mix with oxygen-poor blood, sometimes supplying enough oxygen to the body to keep the infant alive. Transposition of the great arteries is often accompanied by a ventricular septal defect.

Transposition of the great arteries usually results in severe cyanosis and difficulty breathing, beginning at birth. A doctor performs a physical examination, x-ray, electrocardiography, and echocardiography to confirm the diagnosis. Usually, surgery is performed within the first few days of life. Surgery consists of attaching the aorta and pulmonary artery to the appropriate ventricles and reimplanting the heart's coronary arteries in the aorta after the aorta is repositioned. Giving alprostadil or performing a balloon septostomy can shunt the blood, which can keep the infant alive until surgery can be performed.

Aortic valve stenosis is a narrowing of the valve that opens to allow blood to flow from the left ventricle into the aorta and then to the body.
To propel blood through the narrowed aortic valve, the left ventricle must pump under very high pressures. Sometimes, not enough blood is pumped to supply the body with oxygenated blood.
Most children with aortic valve stenosis do not develop symptoms other than a heart murmur. In some older children, the defect causes fatigue, chest pain, shortness of breath, or fainting. In adolescents, severe aortic valve stenosis may lead to sudden death, presumably because of an erratic heart rhythm caused by poor blood flow through the coronary arteries to the heart. A few infants who have aortic valve stenosis develop irritability, an unnatural lack of color to the skin (pallor), low blood pressure, sweating, rapid heartbeat, and severe shortness of breath.

A doctor suspects aortic valve stenosis after detecting a particular murmur or if the child develops symptoms. Cardiac catheterization is often used to determine the severity of the narrowing.
For older children with severe narrowing or symptoms, the aortic valve must be replaced or widened. Usually the valve is opened surgically (using a procedure called balloon valvulotomy) or replaced with an artificial one. Children with an artificial valve must take an anticoagulant drug, such as warfarin, to prevent blood clots from forming. Infants with heart failure must have emergency treatment, usually including drugs and emergency surgery or balloon valvoplasty.

Pulmonary valve stenosis is a narrowing of the pulmonary valve, which opens to allow blood to flow from the right ventricle to the lungs.
In most children with pulmonary valve stenosis, the valve is mildly to moderately narrowed, making the right ventricle pump harder and at a higher pressure to propel blood through the valve. Severe narrowing increases pressure in the right ventricle and prevents almost any blood from reaching the lungs. When pressure in the right ventricle becomes extremely high, oxygen-poor blood is forced through abnormal paths (usually a hole in the atrial wall [atrial septal defect]) instead of the pulmonary artery, causing right-to-left shunting.

Most children with pulmonary valve stenosis have no symptoms other than a heart murmur. However, severe cyanosis or heart failure is possible. Moderate symptoms, such as difficulty breathing with exertion and fatigue, may develop as the child gets older. Echocardiography is done to confirm the diagnosis. Occasionally, cardiac catheterization is needed to assess the severity of the narrowing.
If the valve is moderately narrowed, it may be opened with balloon valvuloplasty. If the valve is not well formed, it can be surgically reconstructed.

Severe disease that causes cyanosis in newborns is treated by giving a prostaglandin, which opens the ductus arteriosus, until a surgeon can create another way to open or bypass the pulmonary valve. For some of these newborns, more surgery is needed when they are older.

Coarctation of the aorta is a narrowing of the aorta, usually just before the point where the ductus arteriosus joins the aorta.
Coarctation reduces blood flow to the lower half of the body; therefore, the blood pressure is lower than normal in the legs and tends to be higher than normal in the arms. Coarctation is a serious but treatable cause of high blood pressure. A heart murmur is sometimes present. Without treatment, coarctation eventually strains and enlarges the heart, causing heart failure; it also causes high blood pressure. Coarctation makes the child susceptible to rupture of the aorta, bacterial endocarditis, and bleeding in the brain. Children with coarctation often have other heart defects, such as aortic valve stenosis or an atrial or ventricular septal defect.

For most infants, mild or moderate coarctation does not cause symptoms. Rarely, children with coarctation have headaches or nosebleeds because of high blood pressure in the arms, or leg pains during exercise because of insufficient blood and oxygen to the legs.
With a severe coarctation in infancy, blood can flow only to the lower portion of the aorta (at a point past its narrowing) through the open connection between the aorta and the pulmonary artery, the ductus arteriosus. Symptoms usually do not occur until the ductus closes, usually when the newborn is a few days to about 2 weeks old. After the closure, the blood supplied through the ductus disappears, sometimes causing sudden loss of almost the entire blood supply to the lower body. Sudden, catastrophic heart failure and low blood pressure can result.

Coarctation is usually suspected only when a doctor notices a heart murmur or differences in pulses or blood pressures between the arms and legs when performing a physical examination. X-rays, electrocardiography, and echocardiography are usually used to confirm the diagnosis.
Coarctation that does not cause severe symptoms should be surgically repaired in early childhood, usually when the child is about 3 to 5 years old. Infants with severe symptoms from coarctation require emergency treatment, including giving a prostaglandin to reopen the ductus arteriosus, other drugs to strengthen the heart's pumping, and emergency surgery to widen the narrowing. Some infants who undergo emergency surgery need more surgery when they are older. Sometimes, instead of surgery, doctors use balloon angioplasty and stents to relieve coarctation.

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 results in an increase in urine pressure, which causes urine to flow backward from the bladder into the kidneys (reflux) and damages the kidneys and ureters over time. The combination of reflux and frequent infections is especially damaging to the kidneys.

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, cramping 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, ultrasonography, computed tomography (CT), nuclear scans, intravenous urography, and rarely, cystoscopy. Defects that cause symptoms or those that lead to increased pressure on the kidneys usually need to be surgically corrected.

A number of defects may result in abnormal 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. 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 kidneys 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.

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 are prone to urinary tract infections and possibly a widespread infection in the bloodstream (sepsis); 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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