Amniotic band syndrome is a rare occurrence in fetal development, leading to structural malformations and intrauterine amputation.
Amniotic banding occurs during fetal development, when the amniotic sac ruptures and its fibrous bands of tissue surround and constrict the limbs and other areas of fetal growth. Depending on where the constriction occurs, the baby may present with a permanent band or indentation around an arm, leg or digit; an abnormal gap in the face (cleft) or an abdominal or chest wall defect, or severe underdevelopment or complete amputation of the limbs, primarily the arms.
Also called Constriction Band Syndrome and Streeter dysplasia, amniotic band syndrome (ABS) is a sporadic but complex disorder with an incidence of one per live 10,000 to 15,000 births. Hippocrates suggested as early as 300 B.C. that extrinsic pressures from a ruptured amniotic membrane led to the formation of fetal bands or digital amputations, resulting in ABS.
In 1930, George Streeter hypothesized that a germ plasm defect might cause ABS. According to this theory, the defect causes the soft tissue to slough. External healing of the slough leads to the constricting rings and resulting localized developmental defects. At that time, his theory was well accepted because of the presence of associated distal anomalies. Cases of ABS in which the amnion is intact support this theory, as do the frequently associated (37% of cases) renal abnormalities and occasional cardiac abnormalities. Streeter aggressively defended his theory, and many surgeons still describe ABS as Streeter dysplasia.
However, in 1965, Richard Torpin proposed that intrauterine trauma led to the premature rupture of the amniotic membrane, echoing the idea originally put forth by Hippocrates. The encircling strands then cause extrinsic compression on the body or limb, leading to formation of bands, vascular occlusion, and, sometimes, amputations. Currently, this is the most widely supported hypothesis. There seems to be no inherent or genetic component to the condition. Both genders are affected equally.
Range of effects
The defect could be merely cosmetic, depending on the severity of the constriction. Deeper bands may cause lymphatic obstruction leading to edema and vascular compromise, conditions that require immediate release. Abnormalities may occur distal to the constriction, such as anterolateral bowing, hemihypertrophy, pseudarthrosis, leg-length discrepancy, and teratologic clubfeet. These conditions may lead to limited function and movement.
Early in gestation, spontaneous abortions may result from the encircling bands. If the constriction occurs after development is almost complete, fissures, acrosyndactylization, or intrauterine amputation occur typically on the extremities.
ABS affects the hands in almost 90% of cases. The distal portion of the extremities is most often involved, especially in the longer central fingers of the hand. The thumb and small finger are rarely involved, presumably because of their shorter lengths. In the feet, constricting bands most commonly involve the big toe (hallux).
Lymphatic and vascular compromise may result from severe band compression. Immediate surgical release is required if at birth the child presents with a swollen, engorged digit or limb.
More often, the constricted digit or limb has been amputated in utero. Acrosyndactyly occurs after digital separation is complete, but the fingers get twisted by bands and eventually join together.
Clubfoot occurs in up to 25% of cases of amniotic banding. In half of occurrences of clubfoot, a tight band wraps around the peroneal nerve, which causes muscle imbalance and clubfoot.
Constriction bands across the face and head may result in facial clefts. Cleft lip and palate require reconstruction when the child is approximately 3 to 6 months of age.
Interventions and treatment
There are no laboratory tests that detect the presence of ABS. And because ABS is an intrauterine phenomenon, there is medical treatment for the condition. Serial ultrasounds may reveal the gross lack of formation, such as anencephaly or intrauterine amputations, but are not always definitive. Magnetic resonance imaging may be used preoperatively on limbs with deep bands to evaluate neurovascular status.
Magnetic resonance angiography of affected limbs may show vessel deficiencies and variable anatomy that might affect surgical outcome.
Indications for intervention depend on the medical stability of the child and on the neurovascular status of the limb.
Bands that only cosmetically affect the superficial skin generally do not require any intervention.
Only the tight constriction bands, resulting in gross lymphedema, vascular compromise, or both necessitate immediate surgical release.
Surgery also is indicated for patients with syndactyly or acrosyndactyly that compromises hand function. Thumb amputation (which is rare), club feet, cleft lip, and cleft palate require reconstruction, but these procedures can be performed electively at a later time.
Intrauterine amputations do not require intervention unless they involve the thumb at the metacarpophalangeal joint. In these cases, on-top plasty or toe-to-thumb transfer may improve function.
Follow-up and prognosis
All patients with ABS should be monitored regularly until skeletal maturity is reached, because of the potential for recurrence of the rings and for secondary contractures that may develop.
The prognosis is good for limbs affected by isolated superficial extremity bands. Aside from cosmetic irregularities, no functional defects are usually present. Deeper bands may be associated with progressive problems leading to lymphatic and neurovascular compromise that requires operative intervention.
For patients with acrosyndactyly, hand function is limited secondary to stiffness of the joints, but reconstruction can result in good prehension and grasp. Children whose limbs have been amputated in utero usually adapt well to their physical limitations, and aside from fitting with a prosthesis, little often needs to be done. In children with a transverse deficiency proximal to the ankle joint, a prosthesis is required for full function.
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Carey Cowles is an editor for O&P Business News.