INTRODUCTION
The amniotic sac is a pair of membranes that surrounds the placenta, umbilical cord and amniotic fluid during pregnancy, performing the task of protecting the fetus against infections or injury.
Amniotic fluid is a watery substance within the amniotic sac that surrounds the fetus and protects it. It acts as a shock absorber and also contains hormones, nutrients, antibodies and other fluids. It is important for fetal development.
Amniotic band syndrome is a rare congenital anomaly with an estimated incidence ranging between 1 in 1000 to 1 in 15,000 live births and 1 in 70 stillbirths. Males and females are known to be equally affected. Most cases are sporadic though, in some familial association is found. Amniotic Band Syndrome or ABS, has many synonyms like amnion rupture sequence, ADAM complex (amniotic deformities/adhesions/mutilations), amniotic band disruption complex, congenital constricting bands, terminal transverse defects, and Streeter anomaly.
DEFINITION
ABS refers to a condition in which loose fibrous bands of tissue develop from the inner lining of amnion. These bands may tangle around various parts of the fetus’s body and affect their development by constricting them. Even amputations may result in some cases.
No clear causes of ABS have been defined but it is said that a partial rupture of the amnion may form fibrous bands that float in amniotic fluid and entangle the fetus. Procedures like Chorionic villus sampling or amniocentesis can damage the amnion, though it is rare. Some experts believe that if the amnion is intact, the cause could be a problem in blood flow of the fetus or an abnormal gene.
SIGNS AND SYMPTOMS
The following 4 major defects are common during presentation:
- Limb defects
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Constrictive rings
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Craniofacial defects
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Neural defects
Other common findings include:
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Limb or digital amputation, with lower limbs being more affected than upper
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Swelling of part distal to the constriction
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Contractures or fractures of digits
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Pseudosyndactyly
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Facial clefts, cleft lip/palate
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Encephalocele
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Scoliosis
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Chest and abdominal abnormalities
DIAGNOSIS AND EVALUATION
ABS can be difficult to detect before birth but signs can be noticed on ultrasound scan and MRI.
On ultrasound, thin membrane-like strands attached to fetal bodies can be seen. There could also be constriction rings associated with distal lymphedema.
TREATMENT AND MANAGEMENT
Treatment of ABS usually occurs after birth by plastic and reconstructive surgery to correct the resulting deformity depending on its extent. In rare cases, if the diagnosis has been made in utero, fetal surgery can be considered to save a limb, though it is not usually attempted if a vital organ or umbilical cord aren’t affected.
ABS is an accidental event. The chances of recurrence in another pregnancy are very slim because it is neither genetic nor hereditary. There are no known preventive measures for amnion tearing.
PROGNOSIS
The prognosis of a child with ABS depends on the body part involved and the severity of bands. In severe cases, amputations can occur and if the bands become wrapped around the head or umbilical cord, it could be life threatening.
Since ABS is difficult to diagnose, a pregnant woman with history of chorionic villus sampling, amniocentesis and decreased fetal heart rate must be monitored for ABS.