What is Amniotic Band Syndrome (ABS)?

In some cases, the strands might be wrapped so tightly that they cause severe deformities to the face, arms, fingers, legs and toes. The most severe cases of ABS can be fatal.

Synonyms of Amniotic Band Syndrome

• ABS
• amnion rupture sequence
• amniotic bands
• amniotic band sequence
• amniotic deformity, adhesions, mutilations (ADAM) complex
• congenital constriction rings
• constriction band syndrome
• limb body wall complex
• Streeter anomaly
• Streeter bands
• Streeter dysplasia

MECHANISMS

Extrinsic Theory
The extrinsic theory for the development of amniotic band syndrome is that strands of tissue separate from the inner layer (amnion) of the amniotic sac. The amniotic sac is the thin membrane that completely surrounds an embryo or developing fetus (amniotic sac). The sac contains a liquid (amniotic fluid), which supports, cushions, and protects a developing fetus. The amniotic sac is composed of two main layers – the outer layer is called the chorion and the inner layer is called the amnion.

According to this theory, amniotic band syndrome occurs when the inner layer (amnion) of the amniotic sac ruptures or tears, exposing the fetus to strands of fibrous tissue that may float freely in the amniotic fluid or remain partially attached to the amniotic sac. These bands of tissue can disrupt the normal development of a fetus. The bands of tissue can wrap around or entangle (constrict) the fingers, toes, arms, legs, and other parts of the developing fetus as when a rubber band had been tightly wrapped around an arm or leg or another body part. The symptoms that occur due to amniotic bands depend on the specific part of the body affected by these strands of tissue and how tightly they have wrapped around a body part. If the amniotic bands are still partially attached to the amniotic sac, they may wrap around a fetal body part and tether (anchor) that body part to the amniotic sac. This can restrict the movement and proper development of the affected fetus.

Intrinsic Theory
The intrinsic theory was proposed because some researchers noted that, while the above theory explains some cases of amniotic band syndrome, it is insufficient to explain all cases. The external theory fails to explain why there is an intact amniotic sac in some infants with amniotic band syndrome; why there are a high number of malformations affecting internal organs in some patients; and why some infants have defects of parts of the body not affected by amniotic (constriction) bands.

The intrinsic theory attributes the development of amniotic band syndrome to impaired blood flow (circulation) to specific parts of the developing fetus (vascular disruption or compromise). The exact, underlying cause(s) of impaired blood flow is unknown. In areas where the blood flow is poor, injury occurs to the blood vessel walls of the fetus. This leads to bleeding (hemorrhaging) and tissue loss in the affected areas, which in turn results in the varied symptoms associated with the disorder. The intrinsic theory attributes the presence of constriction bands as a secondary effect of the impaired blood flow and subsequent damage to the fetus. In a 1987 article in the journal, Teratology, Webster, et al. demonstrated this theory of vascular disruption with an intact amnion in animal models.

ABS causes are unknown. A commonly accepted theory is that the fetus is exposed to bands of tissue when the inner membrane (also known as amnion)—which surrounds and protects the fetus—ruptures and the outer membrane (also known as chorion) does not. Bands from the ruptured amnion move freely within the uterus, entangling the fetus in fibrous tissues.

Damage to the amniotic sac has been implicated as a cause of amniotic band syndrome under the extrinsic theory. The exact reason that the amniotic sac tears or ruptures is not always known and researchers believe that in some cases it may happen as a random occurrence.

In some cases, specific environmental factors have been identified. In some infants, trauma to the abdominal area during pregnancy or blunt trauma to the placenta seemed to have caused the amniotic band syndrome.

A few infants have been affected after the performance of a diagnostic technique chorionic villus sampling (CVS), when performed early during pregnancy. The prenatal test was performed to detect certain problems in a fetus such as chromosomal abnormalities or certain genetic disorders. During the procedure, tissue is removed from the placenta and certain cells called chorionic villi are studied. One estimate of the risk for this occasional risk was 1 in 2,000 CVS procedures.

It has also been reported that intense uterine contractions caused by a drug known as misoprostol (a prostaglandin E1 analogue) has resulted in amniotic band syndrome. Misoprostol is approved by the Food and Drug Administration for the treatment of gastric ulcers. However, the drug has been used to induce abortion. If the pregnancy continues after the use of misoprostol at 6 to 8 weeks of pregnancy, the infant may have the amniotic band syndrome.

The exact cause of impaired fetal blood flow as suggested by the intrinsic theory is unknown. It has been noted, also, that the amniotic band syndrome occurs with greater frequency in first pregnancies, problem pregnancies or premature births. Young women and women of African descent also have higher rates of infants with amniotic band syndrome. Research is ongoing to determine why certain populations have a greater risk of developing the disorder than other populations.

Some recent genetic studies have begun to identify intrinsic, genetic factors that may predispose infants to the development of amniotic band syndrome (genetic predisposition). A genetic predisposition to developing a disorder means that a person carries a gene, or more likely gene(s), for the disorder, but that the disorder is not expressed unless it is triggered or activated under certain circumstances such as particular environmental factors (multifactorial inheritance).

For example, a genetic predisposition to vascular disruption may contribute to the development of amniotic band syndrome in some cases. Two medical journal articles (Hunter, et al. and Carmichael, et al.) have discussed the possibility that genetic factors influence the development of amniotic band syndrome in certain pregnancies.

Although genetic factors are believed to play a role in the development of infants with some cases of amniotic band syndrome, the risk of recurrence in a subsequent child is extremely low. Most cases of amniotic band syndrome occur sporadically. Current, ongoing research into the potential intrinsic factors associated with amniotic band syndrome should reveal more about the complex causes and development of the disorder.

Amniotic band constriction is not an inherited condition. It is rare and no two cases of amniotic band syndrome are exactly alike.

The symptoms and effects of ABS vary depending on where the bands restrict blood flow and how early the bands become entangled around your fetus during development.

Symptoms of amniotic band syndrome might include:

• Cleft lip or palate, if a band wraps around your infant’s face.
• A missing limb or part of a limb (also known as congenital amputation).
• Physical defects of the stomach or chest.
• A permanent mark or indentation on your infant’s finger, arm, leg or toe.

The symptoms associated with amniotic band syndrome vary greatly from one infant to another. Some infants develop only mild deformities; others develop severe and even life-threatening malformations. It seems likely that the features of amniotic band syndrome develop primarily in the first 12 weeks (first trimester) of pregnancy.

Several different patterns have been identified with amniotic band syndrome. The three most common patterns are amniotic band syndrome characterized by one or more limbs being affected; the limb-body-wall complex; and amniotic band syndrome characterized by abnormalities of the head and face (craniofacial abnormalities), defects of the brain and serious malformation of the arms and legs.

Most infants with amniotic band syndrome have some form of deformity of the arms and legs or fingers and toes. One or more limbs may be affected. Upper limbs are affected more often than lower limbs. In some patients, one limb or one hand or foot may be the only symptom of the disorder. The specific physical features can include abnormally short fingers or toes with absence of the end (distal) portion, webbing (fusion) of fingers or toes (syndactyly), constriction rings, and extra strands of tissue adhering to the fingers. The constriction rings that encircle a limb or digit can alter blood flow.

Another pattern associated with amniotic band syndrome is referred to as the limb-body wall complex, a lethal condition. Affected infants usually have protrusion of a portion of the brain and its surrounding membranes (meninges) through the skull defect (encephalocele), facial clefts, protrusion of the viscera (the soft internal organs of the body including those found in the abdominal or chest cavities) through a fissure in the abdominal wall (abdominoschisis) or the chest wall (thoracoschisis), and a variety of defects affecting the arms and legs.

A third pattern associated with amniotic band syndrome involves craniofacial abnormalities such as incomplete closure of the roof of the mouth (cleft palate), facial clefts, small, underdeveloped eyes (microphthalmia), narrowing of the nasal passages (choanal atresia), and malformations affecting the size and shape of the skull. In some infants, the head is adherent to the placenta.

ABS can be diagnosed during a prenatal ultrasound because the abnormalities it causes are sometimes visible in the womb. If amniotic bands develop later in pregnancy, the condition might not be diagnosed until birth. Most cases of amniotic band syndrome are diagnosed after performing a physical examination once your infant is born.

If your child has amniotic band syndrome, here’s what you can expect during treatment at Gillette Children’s Specialty Healthcare:

• During a prenatal consultation orthopedic specialists share information about current treatment options, provide appropriate counseling and help plan a course of treatment.
• Your child might need surgery to release the constricting bands—the type of surgery depends on the location of the bands, number of bands and how deeply they constrict your infant’s tissues. Surgery might happen immediately after birth, or it might not happen until your child is older.
• If amniotic band syndrome affects your child’s face—such as with cleft lip—specialists in craniofacial and plastic surgery might need to perform reconstructive surgery to repair the cleft.
• Physical therapy or occupational therapy can help your infant increase strength and improve function.
• If your child loses an entire limb because of amniotic band syndrome, they might need a prosthesis. Most children can begin using one at 12 to 18 months, or around the time your child begins to stand and walk.
• Sometimes amniotic band syndrome causes mild abnormalities that don’t require treatment.

At Gillette, your family can feel at home with facilities and technology designed specifically to help your child achieve the highest possible levels of independence, comfort, and happiness.

An integrated team will help you navigate the services you need and often, your family will see a team of specialists during a single visit to one location. For amniotic band syndrome treatment, your family might work with experts in:

• Assistive technology.
• Casting.
• Child life.
• Craniofacial and plastic surgery.
• Dentistry and orthodontics.
• Occupational therapy.
• Orthopedics.
• Physical therapy.
• Rehabilitation medicine.
• Rehabilitation therapies.