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Amniotic Band Syndrome
Amniotic band syndrome (ABS) is an uncommon,
congenital fetal abnormality with multiple disfiguring and disabling
manifestations. A wide spectrum of clinical deformities are encountered
and range from simple ring constrictions to major head, face and
internal organ defects. Lower extremity limb malformations are
extremely common and consist of asymmetric digital ring constrictions,
distal atrophy, congenital intrauterine amputations, and clubfoot.
Although debated, early amnion rupture with subsequent entanglement of
fetal parts (mostly limbs and appendages) by amniotic strands is the
primary theory of pathogenesis. Amniotic band
syndrome is associated with an excessive number of synonyms and
acronyms such as congenital constriction band syndrome, Streeter's
dysplasia, Simonart's bands, amniotic band disruption complex,
congenital annular defects, congenital ring constrictions, ADAM
(Amniotic Deformity, Adhesion, Mutilations) complex, TEARS (The Early
Amnion Rupture Spectrum) of defects, and fetal disruption complex. The
overabundance of synonyms/acronyms used to describe the congenital
malformations in ABS attest partly to the confusion surrounding its
etiology. Current literature supports the theory
that early amniotic rupture leads to the formation of fibrous strands
that entangle limbs and appendages. This sequence affects the
development of the embryo and leads to the findings seen in ABS.
Therefore, nearly all cases reach their final form before birth with
tissue damage healing before birth. The nature and severity of
deformities that result appears to be related to the timing and
initiating event of amniotic rupture. Clinical Findings Amniotic
band syndrome is a complex collection of asymmetric congenital
anomalies, in which no two cases are exactly alike. However, several
characteristic features are relatively consistent findings. Distal ring
constrictions and intrauterine amputations, are the most common
findings of ABS and are typically seen in the distal aspect of
extremities. Multiple extremity involvement is usually expressed with
an average of three extremity parts affected. Incidence Amniotic
band syndrome is not a rare anomaly as first described more than a
century and a half ago and appears to be rising. Once believed to have
an incidence of 1:100,000, recent literature supports the incidence
today as 1:1200 to 1:1500 births. No distinct sex predilection has been
determined. Nearly sixty percent of the cases documented have some sort
of abnormal gestation history. Prenatal risk factors associated with
amniotic band syndrome include prematurity (<37 weeks), low birth
weight (<2500 g), maternal illness (during pregnancy), maternal drug
exposure and maternal hemorrhage/trauma. Attempted abortion in the
first trimester is also a highly associated finding. Family
history seldom reveals any direct inheritance pattern, since the
syndrome occurs in no particular association with know genetic or
chromosomal disorders. Karotypes are virtually always normal, and the
syndrome is almost always sporadic in nature. Infants of young, black
women who have been pregnant more than once (<20 years, more than
one pregnancy) show the highest prevalence. incidences of malformations
seen in the hand are two times as common as accompanied foot
deformities. Pathogenesis Many
theories concerning the pathogenesis of ABS have been proposed and
debated. Furthermore, no single pathogenic conclusion has been
determined to reconcile the diverse findings seen in ABS. However, much
of the controversy still centers around a fundamental question: Is ABS
a primary event of an intrinsic (endogenous) fetal anomaly or a
condition extrinsic (exogenous) to the fetus that is secondarily
involved? Although a number of experimental
models have been developed to reproduce its occurrence, no unified
theory exists. It is easy to believe the amniotic band theory proposed
when the majority of pregnancies (60%) demonstrate an abnormal
pregnancy history. However, this does not explain the remaining 40%
occurrence of ABS in mothers with no abnormal prenatal history. One may
never reconcile the differences in findings seen in ABS into a single
pathogenic scheme. Perhaps, ABS is composed of a combination of causes
as stated above. Characteristic Features Amniotic
band syndrome is a poorly defined clinical entity, owing partly to its
debated causes and large number of different names. However, it is
routinely characterized by distinct fetal malformations, which should
make its diagnosis unmistakable. The most
common triad of clinical manifestations include congenital distal ring
constrictions, intrauterine amputations, and acrosyndactyly. These
anomalies appear most frequently in the distal aspect of extremities
without other organ involvement. It has been found that ABS is the most
common cause of a terminal congenital malformation of a limb. Additional
abnormalities encountered routinely with ABS include webbing of the
fingers or toes, progressive lymphedema (swelling), clubfoot, stunted
growth of the small bones in the fingers and toes and limb length
discrepancy. Less common findings include: pseudarthrosis, metatarsus
adductus, peripheral nerve palsy, dystrophic nails, postnatal gangrene,
cleft lip and palate, skin-tube pedicles, dislocated hip visceral body
wall malformations and eccentric craniofacial synostosis defects. Owing
to the fact that no two cases are exactly alike, only some of these
above-mentioned defects are present in each individual case. Other
congenital brain abnormalities, cardiac malformations, short statue,
spina bifida, and added miscellaneous conditions reported in the
literature probably represent coincidental findings. Fetal death
associated with amniotic band strangulation of the umbilical cord has
also been reported. Amniotic bands are more likely to
constrict, entangle or amputate fingers or toes that protrude the
furthest. In the hand, digital amputations most commonly involve the
index, middle, and ring fingers, whereas in the foot, amputations of
the big toe are most often noted. Congenital band indentations are
usually at multiple levels with or without distal lymphedema
(swelling). However, these fibrous band indentations are noted
encircling the fingers or toes of the newborn child most frequently.
Bands are of variable width and depth, ranging from shallow
indentations of the skin and subcutaneous tissue to deep grooves
extending down to deep fascia or bone. Proximal bands occur more
commonly in the lower extremity and have been associated with neural
compression. Osseous abnormalities occurring at or below band
indentation such a bony fusion, angular deformities, and discontinuity
have infrequently been reported. If ring constriction is
severe, the veins, arteries, lymphatics, and nerves may be comprised.
However, vascular insufficiency is seldom symptomatic. Neurological
impairment is usually attributed to axontmesis or neurotmesis. This may
be caused by direct pressure from the constriction band or attributable
in compartment syndrome distal to the band in infants with rapidly
progressive swelling. Distal digits are typically malformed,
owing to phalageal hypoplasia or terminal amputation. Acrosyndactyly
(fenestrated syndactyly) is frequently associated with distal
amputation. This type of syndactyly involves the binding of adjacent
digits in a ﾓlassoedﾔ appearance. If acrosyndactyly is present, it
invariably is associated with a proximal interdigital sinus or cleft
that communicates from dorsal to plantar. The cutaneious syndactyly
seen usually does not involve underlying bony fusion. A strong
relationship between ABS and clubfoot exists. A 31.5% incidence of
associated clubfoot deformity and ABS can be correlated with 20%
occurring bilaterally. In the majority of cases, the clubfoot deformity
present is inordinately rigid and unresponsive to conservative
modalities. Limb length discrepancy has also been noted in legs
encircled by amniotic bands with an average functional deficit of
greater than 2.5 cm. This often results in biomechanical abnormalities
and altered gait patterns. Diagnosis Ultrasonographic
analysis allows for the detection of ABS prenatally by visualization of
amniotic sheets or bands attached to the fetus. In the first trimester,
it is extremely difficult to detect ABS, especially if the bands are
limited to the extremities. However, in the second and third trimester
of pregnancy, it is relatively easy to detect the major anomalies of
ABS by its characteristic features and restrictions of motion. When
characteristic asymmetric fetal anomalies are observed
ultrasonographically, regardless of the presence or absence of fibrous
membranes, ABS should be considered. Although visualization of
amniotic bands on ultrasonography is helpful in confirming ABS, it is
not in itself a diagnostic feature of the ABS. Recently, amniotic
sheets or bands have been described as aberrant sheets of tissue, often
amnion and chorion, having a free edge within the amniotic fluid. The
free edge does not attach to the fetus and have been labeled ﾓinnocent
amniotic sheetﾔ. These sheets do not restrict fetal motion nor cause
any fetal abnormalities. Additionally, elevated maternal serum
alpha-fetoprotein (MASFP) has been associated with ABS. However,
elevated MSAFP is not diagnostic for ABS, since it is also elevated in
neural tube defects, placental chorioangioma, and congenital nephrosis.
MSAFP is now a standard screening test recommended for all pregnancies,
though rarely elevated. Treatment Several
treatment options are available for the lower extremity manifestations
of ABS. Shallow grooves or bands require no operative treatment, unless
they interfere with circulation or lymphatic drainage. Deep
constriction bands often present with swelling distal to the band,
extreme pain, and diminished circulation and must be surgically
released immediately to prevent risk of gangrene or auto-amputation.
Surgical excision of the fibrous band and any necrotic tissue with
circumferential Z-plasty or W-plasty are the procedures most commonly
employed. Removal of the constriction band may be accomplished in a one
or two stage release, usually beginning at three months of age. Early
surgical intervention is necessary to prevent progressive lymphedema.
Patients treated late in the course of the syndrome often heal very
slowly with secondary eczematous skin changes to distal parts. When
deemed necessary, subcutaneous fat and fascial flaps are advanced into
the defect to prevent reoccurrence of the deformity. If edema persists
after correction of the band, excision of the edematous area
(debulking) may be necessary, with direct closure or conversion of the
overlying skin to thick, free partial thickness skin grafts. Gross
motor and sensory deficits distal to the bands resulting in neuropathy
with secondary ulceration and osteomyelitis (bone infection) are best
treated with amputation and fitting of a prosthesis. It is fairly
uncommon that the underlying bones to be affected, however, if they are
then cresentic osteotomies may be indicated. Desyndactylizations
may also need to be performed in conjunction with skin grafting of
hypoplastic bones. Due to the high incidence of associated rigid
clubfoot deformity, aggressive surgical correction is often required.
Limb length discrepancies greater than 6 cm may require leg-lengthening
procedures. Overall, the goal of pedal care is to create a
functional foot and to minimize additional problems as the child grows.
Parental counseling is recommended to convey there is no known
associated risk for subsequent pregnancies. Conclusion Amniotic
band syndrome is an uncommon fetal malformation with increasing
prevalence. It is a constellation of congenital anomalies that lacks a
precise definition and satisfactory pathogenic explanation. Multiple
asymmetrical limb, craniofacial, visceral, and body wall defects are
commonplace. Although a myriad of fetal deformities can ensue,
manifestations in the foot such as distal ring constrictions,
intrauterine pedal amputations, acrosyndactyly, and clubfoot are
encountered routinely. With the aid of ultrasonography, a prenatal
diagnosis of ABS can be made by serial observations demonstrating
restriction of fetal movement. Appropriate surgical intervention can
eliminate potential limp threatening constrictions and provide a
remarkably improved quality of life for these patients.
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