*Sainte-Clotilde, Reunion Island; **Department of Obstetrics, Felix Guyon Hospital, Saint-Denis, Reunion Island
Posting Dates: September 1 - September 14, 2021
This is an incidental finding at 22 weeks gestation in a woman with no medical or family history. Her obstetric course thus far was unremarkable,
Our ultrasound examination showed the following findings:
-Image 1: Normal crown-rump length and nuchal translucency at 12 weeks gestation.
-Images 2,3,4: Ultrasound at 22 weeks gestation showing left foot edema with narrowing and stricture of the soft tissue due to an amniotic band (marked as ??? on image 2).
-Images 5,6,7 and video 1: Ultrasound at 23 weeks gestation showing similar finding to images 2,3,4.
-Images 8,9: Ultrasound at 23 weeks gestation showing an amniotic band near the external right ear causing a stricture on 3D image.
-Video 2: Ultrasound at 23 weeks gestation showing the umbilical cord whirling around the left leg.
Our prenatal diagnosis was therefore: Amniotic band sequence
We considered fetal surgery to release the amniotic bands and alleviate the strictured tissues, however at 24 weeks gestation there was fetal demise. External examination of the fetus confirmed the left foot edema and stricture of the left leg soft tissue. Additionally, there was amputation of several fingers of the right hand that was missed on prenatal ultrasound (see images below):
Amniotic band sequence refers to a broad group of highly variable congenital defects involving anomalies of multiple fetal structures that occur in association with amniotic bands . First described in 1832 by Montgomery , different terms have been used to describe this pathology, including amniotic band sequence, amniotic band syndrome, amniotic band disruption complex, amniotic adhesion malformation syndrome, limb and/or body wall defect, ADAM (amniotic deformity, adhesion, mutilation) sequence, and Streeter dysplasia. Bodamer considers amniotic band sequence the most appropriate term, since the pattern of congenital anomalies is due to a single insult caused by one or more amniotic bands that results from different etiologies .
Due to the difficulty in diagnosing this pathology with certainty, the reported incidence varies widely, ranging from 1 in 1200 to 1 in 15000 live births [1, 3]. Some studies have related it to maternal factors such as hyperthermia, cigarette smoking during early pregnancy, residence at high altitude, and genetic factors, but the data is inconclusive .
Two main theories have been suggested for the pathogenesis of amniotic band sequence. The most widely accepted is the “extrinsic theory,” proposed by Torpin in 1965 . This theory suggests that the birth defects are caused by the action of fibrous amniotic bands produced after rupture of the amnion. With loss of amniotic fluid, there is extrusion of all or parts of the fetus into the chorionic cavity. The cause of the amnion rupture is unknown in most cases, although maternal disorders such as epidermolysis bullosa  and connective tissue disorders , or an invasive procedure such as failed curettage, amniocentesis, fetoscopy or septostomy , have occasionally been reported. The “intrinsic theory” proposed by Streeter in 1930 maintains that vascular endothelial injury is the underlying pathogenesis of the anomalies and the fibrous constriction bands . This theory explains defects that cannot be easily explained by the existence of amniotic bands, such as craniofacial defects, body wall abnormalities, and internal organ malformations. Finally, a small subset of cases that cannot be explained by amniotic bands or a primary vascular insult may be due to single gene mutations .
In utero, normal fetal structures become entangled in amniotic bands, leading to three types of defects: (1) deformation: altered shape or position of a body part due to aberrant mechanical force(s) that distorts an otherwise normal structure; (2) disruption: a non-progressive, congenital morphologic anomaly due to the breakdown of a body structure that had a normal developmental potential; and (3) malformation: a non-progressive, congenital morphologic anomaly of a single organ or body part due to an alteration of the primary developmental program .
Display of isolated or multiple defects with no specific pattern should lead to suspicion of amniotic band sequence. The demonstration after 16 weeks of gestation of bands in amniotic fluid that appear as thin echogenic strands attached to the defect and to the uterine wall supports the presumptive diagnosis. However, this finding is only seen in a minority of cases and is not necessary to establish the diagnosis . The visualization of fetal movement restriction and the absence of fetal displacement with changes in the maternal position can aid in the diagnosis. Three-dimensional sonography and fetal magnetic resonance imaging can visualize amniotic bands and their secondary manifestations, and could be complementary to two-dimensional ultrasound [13, 14].
Sonographic findings include constrictive rings, limb defects, craniofacial abnormalities, neural defects, and body wall defects [15-17]. The most frequent findings are those caused by constriction rings in the extremities (present in at least 80% of cases), which can cause pseudosyndactyly (fusion of distal digits), edema of the distal extremity, and amputation of limbs or digits . In addition, there may be craniofacial abnormalities such as encephaloceles, facial clefts, atypical cleft lip/cleft palate, asymmetric microphthalmia, severe nasal deformity, and exencephaly/anencephaly, as well as chest wall and abdominal wall defects not located in the midline.
The fibrous bands of amnion may extend deep inside the fetal tissue compromising the vascular supply, lymphatic system, bone, and nerves. Color/pulsed Doppler should be used to assess extremity perfusion. In normal conditions, flow should be symmetrical and reproducible on either side of the constrictive ring. Hüsler et al  proposed a prenatal staging system of amniotic band sequence involving the extremities, which may be useful in selecting candidates for fetal surgery. They distinguish five stages with progressive involvement:
1. Amniotic bands without signs of constriction
2. Constriction without vascular compromise:
a. Without or only mild lymphedema
b. With severe lymphedema
3. Severe constriction with progressive arterial compromise:
a. Abnormal distal Doppler studies when compared to the contralateral extremity
b. No vascular flow to the extremity
4. Bowing or fracture of long bones at the constriction site
5. Intrauterine amputation
The differential diagnosis is dependent on the specific defects noted on ultrasound. If the bands are identified, they should be distinguished from other conditions that can produce intrauterine linear echogenicities in the gravid uterus such as uterine synechiae with amniotic sheets, uterine duplication anomalies, chorioamniotic nonfusion or separation, and circumvallate placenta . Synechiae are intrauterine adhesions that develop from the endometrial lining after an insult such as dilation and curettage or prior caesarean delivery. Amniotic sheets form when an existing synechia contact the expanding fetal membranes, creating a linear four-layered structure. Septate uterus has a sagittally-oriented septum arising symmetrically from the midline fundus. Unlike amniotic bands, synechiae and thin septa may have blood flow detected with Doppler, do not restrict fetal movements, and are not associated with fetal abnormalities. In circumvallate placenta, a linear echogenicity extends from one placental margin to the other, and is oriented parallel to the placenta. In the most severe cases, the differential diagnosis must be made with body stalk anomaly (fetal abdominal wall adherent to placenta, short umbilical cord, scoliosis) and with specific craniofacial or abdominal wall defects.
The prognosis depends on the severity of the anomalies, and varies from a single mild abnormality with an excellent prognosis to multiple severe anomalies incompatible with life. Fetal decapitation by amniotic bands has been described . Amniotic band sequence has been associated with an increased risk for miscarriage, preterm birth, and stillbirth, which may be related to cord strangulation [1, 21].
In fetuses with simple constriction rings compatible with life, fetoscopic release of the bands to restore blood flow to the affected limb can be performed [18, 22, 23]. Before the procedure, it is important to verify normal Doppler flow proximal to the constriction band and abnormal, but present flow distal to the band . Postnatal treatment includes surgical intervention to enhance function or for cosmetic purposes, and physiotherapy and prosthesis in individuals with limb defects.
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