What is Amniotic band Syndrome?
Amniotic band syndrome is a condition that results from presence of intrauterine constriction bands and their effects on fetal development causing birth defects that range from a single, isolated finding to multiple, disfiguring complications. The arms and legs are most often affected. The head and face and, in some cases, various internal organs can also be affected.
The severity of the defect varies from merely cosmetic band to limb or life threatening conditions.
The estimated frequency of amniotic band syndrome is 1 per 3000 pregnancies.
Amniotic band syndrome is also known by many other names. These are
- Amnion rupture sequence
- amniotic bands
- amniotic band sequence
- amniotic deformity, adhesions, mutilations (ADAM) complex
- congenital constriction rings
- constriction band syndrome
- limb body wall complex
- Streeter anomaly
- Streeter bands
- Streeter dysplasia
Causes of Amniotic Band Syndrome
The causes and underlying mechanisms of amniotic band syndrome are complex and controversial.
The two main theories are known as the extrinsic theory which holds factors outside the fetus responsible and intrinsic which states that found within the fetus are responsible.
There is no single causative agent or gene identified yet but following factors are thought to increase the risk.
- Blunt trauma to the placenta
- Chorionic villus sampling [ risk was 1 in 2,000 CVS procedures.]
- Intense uterine contractions caused by a drug known as misoprostol (a prostaglandin E1 analogue)
- Genetic factors
The amniotic sac is the thin membrane that completely surrounds an embryo or developing fetus. It contains a liquid called amniotic fluid which supports and protects a developing fetus. The amniotic sac is composed of two main layers – the outer layer is called the chorion and the inner layer is called the amnion.
The inner layer (amnion) of the amniotic sac ruptures or tears. This exposes the fetus to strands of fibrous tissue that may float freely in the amniotic fluid or remain partially attached to the amniotic sac.
These bands can wrap around and constrict the fingers, toes, arms, legs and other parts of the developing fetus. A band that is partially attached to the amniotic sac, may tether the body part to the amniotic sac causing restriction of movement and proper development of fetus.
But external theory does not explain the presence of intact amniotic sac in some infants with amniotic band syndrome and presence of defects in the internal organs in some cases.
intrinsic theory attributes the presence of constriction bands as a secondary effect of the impaired blood flow and subsequent damage to the fetus.
Defects Found in Amniotic Band Syndrome
Extremities are most commonly affected by amniotic band syndrome especially the distal part. Amputation, constriction bands and acrosyndactyly are common problems
Hand is involved in almost 90% of cases with middle, long, and index fingers showing common involvement [longer digits are more involved]. Thumb or small finger are rarely involved.
Greater toe is most commonly involved in foot.
The presentation varies from small indentations at the base of the phalanx, usually distal to the metacarpophalangeal joints in mild constriction. Greater constriction can lead to scar tissue formation.
Sever compression can lead to , lymphatic and vascular compromise and child is born with a swollen engorged part distal to constriction. If the constriction is in the limb, the limb gets engorged. Severe cases require immediate surgical release.
In utero amputation also occurs
Acrosyndactyly occurs after digital separation is complete, but the fingers fuse again due to pressure from band.
If the residual sinus tracts are usually present in the remnant web, it is called fenestrated syndactyly.
Patterson’s classification of deformity in extremity in amniotic band syndrome
- Type I – Simple ring constriction.
- Type II – Ring constriction accompanied by fusion of the distal bony parts, with or without lymphedema.
- Type III – Ring constrictions accompanied by fusion of soft tissue parts.
- Type IV – Intrauterine amputations.
Apart from limb involvement following findings could be associated, depending on the part involved
- Cleft lip or palate
- Renal abnormalities
- Cardiac defects
- Anterolateral bowing of the tibia
- Tibial pseudarthrosis
- Leg-length discrepancy
- Clubfoot [ up to 25%]
- Craniofacial abnormalities.
Presentation of Amniotic band Syndrome
No two cases of amniotic band syndrome have similar presentation as the presentation depends on the sites of defect.
However, three patterns have been identified with amniotic band syndrome.
This is most common type of presentation. One or more limbs may be affected. Upper limbs are affected more often than lower limbs.
In some cases, one limb or one hand or foot may be the only presenting symptoms
Specific symptoms are
- Abnormally short toes or fingers
- Absence of the distal part of one or more fingers and toes
- Webbed digits – Fusion of fingers or toes (syndactyly)
- Strands of tissue hanging from to the ends of the digit
Sometimes the infants have the constriction band that encircle the area but not constricting enough to damage the limb or digit and despite their look part of the limb or digit retains its normal size and function
Limb Body Wall Complex
Defects of the abdominal wall that occur in association with defects of the arms and legs and other abnormalities.
- Enencephalocele leading to protrusion of brain and other neural tissue
- Facial clefts
- Protrusion of the viscera through a fissure
- in the abdominal wall (abdominoschisis)
- the chest wall (thoracoschisis)
- Varied defects of the arms and legs.
- Additional abnormalities
A third pattern associated with amniotic band syndrome involves craniofacial abnormalities
- Cleft palate
- Cleft lip
- underdeveloped eyes (microphthalmia)
- Narrowing of the nasal passages (choanal atresia),
- malformations affecting the size and shape of the skull.
- Neural tube defects
- Terminal transverse limb deficiencies – Missing portion or whole limb
No laboratory tests exist to detect its presence of amniotic band syndrome.
Serial ultrasounds can show the gross lack of formation in the fetus.
Prenatal diagnosis of atypical facial clefting should alert physicians to the possibility of amniotic band syndrome and other anomalies.
MRI can be used for preoperative evaluation to evaluate the neurovascular status that could affect the surgical outcome.
Treatment of Amniotic Band Syndrome
No medical treatment exists for the condition. Avoiding drugs that cause spontaneous rupture of membranes, such as cocaine and mifepristone, may help decrease the potential risk.
Rarely, fetoscopic surgery on the fetus may be performed to cut amniotic bands that are tightly constricting and may cause loss of a limb or digit.
Treatment after Birth
The treatment of infants and children with amniotic band syndrome is symptomatic and supportive.
In cases with tight bands on the digits or extremities with vascular compromise urgent surgical treatment may be necessary. Band is excised with 1-2 mm of normal skin to avoid recurrence. The entire band requires excision.
Correction or repair associated malformations is done as necessitated by type of defect.
- Syndactyly requires surgical release
- Cleft lip and palate require surgical repair and reconstruction
- Absent, short or afunctional thumb requires toe to thumb transfer or on-top plasty
- Club foot requires surgical correction due to its rigid nature.
Physical and occupational therapy may also be necessary.
Complications of Amniotic Band Syndrome
Severe lymphatic or venous congestion at the time of birth may lead to necrosis and gangrene if not urgently treated.
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