Amniotic Band Syndrome
What is amniotic band syndrome?
Amniotic band syndrome can occur when the inner layer of the placenta, called the amnion, is damaged during pregnancy. If this happens, thin strands of tissue (amniotic bands) form inside the amnion. These fiber-like bands tangle around the developing fetus, restricting blood flow, thus affecting the growth of certain body parts. This can cause congenital deformities of limbs. In some cases, strands can tangle so tightly around the limbs of a fetus that they amputate them. Amniotic band syndrome is usually diagnosed at birth, but can sometimes be detected in the womb by ultrasound.
A fetus develops in the cavity of the uterus, which is lined by a thin membrane called the amnion. Under rare circumstances a sheet (amniotic sheet) or band (amniotic band) made out of this membrane can run through the uterine cavity. When this occurs parts of the fetal body can become entangled in an amniotic band. Of all the fetal body parts, the limbs are at greatest risk to get tangled in an amniotic band. If the entanglement becomes tight enough to constrict blood flow in the limb, the development of the limb may become affected. When an amniotic band causes such damage to part of the fetal body, it is called amniotic band syndrome. Overall, amniotic bands have been reported in up to 1 in 1200 live births. However, a much smaller proportion of these babies develop amniotic band syndrome.
When an extremity is tangled in an amniotic band, the tissue on the far end of the band (distal end) is at risk for several problems. When the extremity is constricted there can be swelling of the distal tissues, developmental abnormality with physical deformity or even complete amputation. The type of abnormality depends on two events:
The stage of pregnancy when the constriction occurs
Whether or not blood flow to the distal part of the limb is cut off
Under rare circumstances an amniotic band can also affect development of other parts of the body. For example, a band that passes over the face has been associated with cleft lip and even clef palate. In cases where the amniotic band encircles the umbilical cord of the fetus, obstruction of blood supply can lead to fetal death. These last two complications are relatively rare.
Amniotic Band Syndrome Diagnosis
It is typically very difficult to detect amniotic band syndrome before birth, but the condition can sometimes be detected via ultrasound. Many times amniotic band syndrome is diagnosed after delivery during a physical examination of the newborn.
The Johns Hopkins Center for Fetal Therapy
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Amniotic Band Syndrome Treatment
The treatment options for amniotic band syndrome include in utero fetal surgery and postnatal repair of the resulting abnormalities.
Fetal surgery: The goal of fetal surgery is to release the constriction caused by the amniotic band before it can cause further damage. This is done by operative fetoscopy, which allows the direct visualization of the amniotic band and its release using various surgical techniques. The success of fetal surgery depends on the degree of damage that has been caused by the amniotic band. If the distal part of the extremity is swollen, releasing the band allows the swelling to resolve and normal development to continue. If the constriction has been more severe, release of the band can stop further damage and prevent amputation of the affected extremity.
Treatment after birth consists of plastic and reconstructive surgery, followed by physical and occupational therapy as required by the type of deformity. Prosthetics may also be recommended for children suffering from loss of limbs or limb functionality. Advances in 3-D printing have led to the creation of more functional prostheses for these patients.
The decision about which treatment option is the most appropriate depends on a detailed assessment involving high-resolution 2-D and 3-D ultrasound, examination of the blood supply of the affected limb and sometimes, additional magnetic resonance imaging (MRI).