Amniotic band syndrome (ABS) refers to a condition in which bands extend from (and originating from) the inner lining of the amnion. The amnion is the sac that surrounds the baby in the womb. As the baby develops in the womb, its extremities may become entangled in the amniotic band resulting in constriction or even amputation. When this happens the baby is said to have amniotic band syndrome. Amniotic bands are thought to happen sporadically or in association with trauma to the abdomen. It can be a complication after an amniocentesis and/or it can indicate early rupture of the amniotic sac.
It is potentially associated with a variety of different birth defects. It is important to note that two cases of amniotic band syndrome are not exactly alike and associated symptoms are highly variable. The severity of this syndrome can range from a single, isolated finding to multiple, disfiguring complications. Most often legs and arms are affected but in some cases head and face as well as various internal organs have been affected.
The symptoms of amniotic band syndrome depend on the severity and location of the constrictions. The mildest constrictions affect only the superficial skin and may not require treatment. Deeper constrictions may block lymphatic vessels, impair blood flow, and require immediate surgical care. When the bands affect the limbs, the lower part of the limbs are most often involved, especially the middle, long, and index fingers of the hand. When the feet are involved, the bands most commonly affect the big toe.
Pressure from the bands may result in additional abnormalities, such as underdevelopment of a limb, bone abnormalities, amputations, leg-length discrepancy, and club feet. Constriction bands across the head and face may lead to facial clefts. Severe clefts affecting vital organs are often life-threatening.
- Amniotic constriction ring
- Finger syndactyly
- Split hand
The exact cause of amniotic band syndrome is unknown and controversial. Two main theories have been proposed to explain the development of the disorder. One theory attributes the disorder to causes that arise internally within the fetus (intrinsic theory); the other theory attributes the disorder to causes acting upon the fetus externally (extrinsic theory). It is likely that both internal and external factors can cause amniotic band syndrome, and that the cause of the disorder in one infant may be different from the cause in another infant.
Amniotic band syndrome is often difficult to detect before birth as the individual strands are small and hard to see on ultrasound. Often the bands are detected indirectly because of the constrictions and swelling upon limbs, digits, etc. Misdiagnosis is also common so if there are any signs on amniotic bands further detailed ultrasound tests should be done to assess the severity.
The earliest reported detection of an amniotic band is at 12 weeks gestation, by vaginal ultrasound. On ultrasound the bands appear as thin, mobile lines, which may be seen attached to or around the baby.
Because the prognosis of people with amniotic band syndrome can vary from patient to patient, the best person to provide your family with information regarding your child's prognosis, is the health care providers involved in their care. In general, the outlook for infants with a single band involving the superficial skin of the wrist and/or hand is good. While the family and child will need to adjust to the cosmetic difference, the functional use of the hand is normal. Deeper bands can be associated with complications (i.e., blockage of lymph and blood vessels) that can worsen over time and may require surgery. Some people with amniotic band syndrome are born with acrosyndactyly, a fusion of the fingers that may limit the hand function and cause stiffness of the joints. In many cases a good ability to hold and grasp may be obtained with reconstructive procedures.
Mild cases may not require treatment, however all bands need monitoring as growth occurs to watch for progressive constriction and swelling. Other constrictions may require surgical management; surgical options will vary depending on the abnormality. People with amniotic band syndrome who have amputations may benefit from the use of prosthetics.
Treatment usually occurs after birth and where plastic and reconstructive surgery is considered to treat the resulting deformity. Plastic surgery ranges from simple to complex depending on the extent of the deformity. Physical and occupational therapy may be needed long term. In rare cases, if diagnosed in utero, fetal surgery may be considered to save a limb which is in danger of amputation or other deformity. This typically would not be attempted if neither vital organs nor the umbilical cord are affected. This operation has been able to be successfully performed on foetuses as young as 22 weeks.