What is Amniotic Band Syndrome?
Amniotic Band Syndrome (also known as Streeter Dysplasia, Constriction Band Syndrome and ABS) is a complex collection of fetal congenital malformations, affecting primarily the limbs. Amniotic Band Syndrome can also affect the craniofacial area and internal organs.
Amniotic Band Syndrome is characterized by constricting rings, , and (often) amputations of the extremities of newborns.
Depending upon the severity of the constriction, a defect caused by amniotic band syndrome can be as minimal as a superficial cosmetic band. Deeper constrictions may lead to lymphatic obstruction, leading to edema and vascular compromise, which requires release. Pressure from the bands can possibly cause abnormalities below the constricted band, which may lead to limited functioning and trouble with movement.
Amniotic Band Syndrome was once estimated to occur in one in every 3,000 pregnancies in the US (taking into account the potential for miscarriage that extreme banding can cause). More common statistics suggest that only one infant per 10,000-15,000 may be affected by Amniotic Band Syndrome.
ABS is caused by the development of small break-away strands of the amniotic sac that entangle parts of the fetus.
What Causes Amniotic Band Syndrome?
Researchers remain baffled by the cause of Amniotic Band Syndrome, chalking it up to either internal or external factors, but cannot reach a conclusion.;
What is known is that infants born with Amniotic Band Syndrome do not have any familial recurrences, which indicates that there is no genetic component to ABS.
ABS often occurs at random. As such, there are no preventative measures that may be taken to prevent the development of Amniotic Band Syndrome. The only exception is a family history of Ehlers-Danlos Syndrome, in which tissues break down more easily.
Types of Constrictions Associated With Amniotic Band Syndrome:
Depending upon the severity of the constriction, the defect caused by amniotic band syndrome could be minimal. The deeper amniotic bands may cause lymphatic system obstruction which can lead to swelling and vascular compromise that require immediate treatment.
If the amniotic band crosses the body, it may compress the chest of the fetus, causing the heart to develop outside the chest wall (extrathoracic heart) or a crack in the chest wall (thoracoschisis).
Amniotic bands that cross the abdomen can cause gastroschisis, a type of intestinal hernia.
Pressure from the amniotic band may potentially cause abnormalities in the legs, feet, arms or hands. These distal abnormalities may impact function and/or mobility, and include:
- leg-length discrepancy
- resistant teratologic clubfeet: a deformity of the foot, ankle and toes
- hemihypertrophy: one side of the body or one body part is larger than the other
- pseudarthrosis: formation of a false joint in a weight-bearing long bone
How Do Amniotic Bands Form?
A developing embryo exists within two cavities: the chorion and the amnion. As the embryo develops, the amnion presses against the extracoelomic space (the membrane between the chorion and amnion), eventually obliterating it sometime during the twelfth week of gestation.
If the extracoelomic space isn't obliterated completely, it can cause the amnion to be more fragile and more susceptible to traumatic or spontaneous rupture. If it ruptures, low amniotic fluid may occur.
The fetus's ability to move is restricted until the chorion adjusts, which may contribute to the severity of clubfoot deformities associated with amniotic band syndrome. This decrease in uterine space also allows floating amniotic bands to wrap around a developing body part.
If this occurs in early gestation, a miscarriage may occur. If the constriction from the amniotic band occurs once a fetus is nearly formed, fissures, intrauterine amputation, and acrosyndactylization (fused or webbed fingers) may result.
If the fetus swallows an amniotic band while still partially attached to the placenta, this tether may result in facial clefts and palate deformities.
How Does Amniotic Band Syndrome Present?
Most children born with amniotic band syndrome are typically full term (or a few weeks preterm) after an uncomplicated pregnancy. It should be worth noting that it is rare - but not unheard of - for an ultrasound to detect the presence of amniotic band syndrome, which means that the new parents may be emotionally shocked by the discovery that their new baby has Amniotic Band Syndrome.
On the extremities, the part farthest away from the body is most frequently involved, especially the central digits of the hands, which are affected in 90% of children born with amniotic band syndrome. Likewise, the longer digits of the feet are more commonly affected than the shorter toes. Generally, the affected digit has been amputated while the fetus was in the womb.
Amniotic band syndrome, because the location of the formation of the amniotic band is variable, presents differently for each infant.
The most common symptoms associated with ABS are:
- Amputation - the loss of one or more limbs
- Constriction bands - strands of amniotic fluid surrounding a child in the womb.
- Acrosyndactyly - fused, or webbed, fingers or toes.
Other findings associated with amniotic band syndrome may include:
- Cleft Lip/Cleft Palate
- Renal (kidney) abnormalities
- Cardiac defects
- Hemihypertrophy - a side of the body, or body part, that is larger than the other
- Bowing of the tibia - the large bone between the knee and ankle
- Leg-length discrepancies.
Classification of Extremity Deformities:
ABS extremity deformities are classified into Patterson's 4 Types:
Type One Amniotic Band Constriction - this type of ABS involves a simple ring constriction.
Type Two Amniotic Band Constriction - this type of ABS includes one or more ring constrictions as well as the fusion of distal bony parts (with or without lymphedema)
Type Three Amniotic Band Constriction - this type of ABS includes one or more ring constrictions plus fusion of soft tissue parts
Type Four Amniotic Band Constriction - this type of ABS presents with intrauterine amputations.
What Other Congenital Deformations Occur with Amniotic Band Syndrome?
Amniotic Band Syndrome is associated with other congenital deformations approximately fifty percent of the time. Specifically cleft lip, cleft palate, and clubfoot are associated with ABS, with hand and finger anomalies occurring approximately 80% of the time. It is not uncommon for the fingers, toes, and limbs to become tangled and damaged or amputated, which occurs approximately 80% of the time.
Further, it is believed that approximately 178 of every 10,000 miscarriages are caused by ABS.
How Is Amniotic Band Syndrome Diagnosed?
ABS can be extremely difficult to diagnose prior to birth. In very rare instances can an amniotic band be seen via routine ultrasound. In fact, most babies born with Amniotic Band Syndrome have had relatively easy pregnancies and are born at full-term.
The amniotic strands are very thin and hard to see on an ultrasound. Prenatal diagnosis generally occurs when a part of the fetus becomes inflamed and swollen. MRI and other imaging can be used to confirm diagnosis and assess the damage.
How Is Amniotic Band Syndrome Treated?
Treatment varies depending on the severity of the damage. Surgery is often utilized (after birth) to repair damage. In some cases, in-utero surgery may be an option to save a limb or prevent deformity.
Rehabilitative or occupational therapy may be required after birth, or for the long-term.
Additional Amniotic Band Syndrome Resources:
The Fetal Treatment Center provides a description of ABS, treatment options, and other information.
Birth Defect Research for Children is non-profit organization that provides parents and expectant parents with information about birth defects and support services for their children. BDRC has a parent-matching program that links families who have children with similar birth defects.
Fetal Hope Foundation - provides support, information, funds research, increases awareness and is an outlet for leading medical information pertaining to fetal syndromes. Many different syndromes are showcased on the site.