Introduction
Amniotic band sequence results from in utero entrapment of fetal parts by fibrous bands, which leads to a collection of malformations that can affect multiple organ systems.
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There is typically an asymmetric distribution of these defects; the most common manifestations involve limb deformities.4
The cause of amniotic band sequence is unclear and has been ascribed to both intrinsic and extrinsic factors.1
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The intrinsic model suggests that formation of amniotic bands and resultant anomalies are due to disruption of the developing embryonic disk; the extrinsic model, which is accepted more widely, suggests a sequence mechanism of disruption of the amnion that leads to the entanglement of fetal structures by mesodermic bands.2
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In most cases, the cause is unknown, and there are no commonly accepted risk factors. The severity of amniotic band sequence varies from relatively minor to being lethal to the fetus. The incidence varies from 1 in 1200 to 1 in 15,000 live births.6
Definition
Amniotic band sequence is a collection of fetal malformations that are associated with fibrous bands that entangle or entrap various fetal parts in utero.
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Ultrasound Findings
A constellation of multiple fetal abnormalities, particularly asymmetric limb and digital amputations and constrictions, should make one suspect amniotic band sequence. Defects can be isolated or multiple and usually do not follow a specific pattern.
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The following ultrasound findings are characteristic of amniotic band sequence:- •Bands in amniotic fluid appear as thin echogenic strands attached to the defect and usually connect to the uterine wall. It is important to note that visualization of bands is not required to suggest the diagnosis.1,4Random anomalies that do not follow a pattern should lead to suspicion for amniotic band sequence (Figure 1).
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Figure 1Amniotic bands attached to fetal torsoShow full captionSMFM Fetal Anomalies Consult Series #2. Am J Obstet Gynecol 2019. - •Constriction ring defects of the extremities typically are present.1,7,8These usually involve fingers or toes with or without edema of a distal extremity.4These constriction rings can lead to amputation of limbs or digits and the appearance of syndactyly on ultrasound imaging (pseudosyndactyly) [Figure 2].
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Figure 2Amniotic band that involves the upper extremitiesShow full captionSMFM Fetal Anomalies Consult Series #2. Am J Obstet Gynecol 2019. - •Craniofacial deformities can include single orbital involvement, severe clefts that do not conform to a pattern of developmental clefts, severe nasal deformity, or asymmetric encephaloceles.1,4,9,10
- •Chest wall and abdominal wall defects can occur but are less common. Examples include ectopia cordis, gastroschisis-like bowel herniation, omphalocele-like liver herniation, and bladder exstrophy.
If an unusual distribution of defects raises suspicion for amniotic band sequence, one should look carefully for bands and scan in various maternal positions to see if the fetus stays in a fixed position or if bands restrict certain movements. Occasionally, fetal movement can help reveal amniotic bands.
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Associated Abnormalities
It is important to evaluate all organ systems because there can be limb, craniofacial, or body wall abnormalities as described earlier. Diagnostic accuracy relies on the ability to connect all sonographically visualized abnormalities to a direct disruption from the amniotic bands.
Differential Diagnosis
The differential diagnosis depends on the type of anomalies and the type of amniotic disruption that is seen. The differential includes the following conditions
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:- •Body stalk anomaly: Fetal abdominal wall adherent to placenta, short umbilical cord, no cranial or limb defects, no evidence of fibrous bands
- •Specific craniofacial defects or abdominal wall defects: Typically isolated and can cause specific functional abnormalities that are associated with embryologic development
- •Amniotic sheets: Amnion wrapped around synechiae and a structurally normal, mobile fetus; importantly, amniotic band sequence should not be diagnosed in the absence of fetal abnormalities.
- •Chorion-amnion separation: No entrapment of fetal parts, no associated bands
Genetic Evaluation
Genetic evaluation in the setting of amniotic band sequence is not typically recommended. These cases are generally sporadic with no family history and no increased risk or incidence based on race or sex.
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Although a few familial cases have been reported, almost all cases are sporadic with no identified underlying genetic cause. If the diagnosis of amniotic band sequence is uncertain, chromosomal microarray analysis may be considered.Pregnancy and Delivery Management
A detailed ultrasound examination is recommended to identify the extent of the abnormalities. Pregnancy termination is an option that should be discussed with all patients in whom a fetal anomaly is detected. Fetoscopic in utero lysis of bands is an investigational approach that has been reported to have favorable outcomes for extremities at risk because of constriction bands, although this procedure is associated with an increased risk of premature rupture of membranes and preterm birth.
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Assessment of arterial and venous flow across constriction bands in the extremities detected with Doppler imaging has been reported to be possible13
and potentially useful, although experience and data are limited. Antenatal surveillance is appropriate in some cases, including if fetal growth restriction is present. Mode of delivery should be based on the usual obstetric indications, and site of delivery should be based on the severity and type of anomalies.Prognosis
The prognosis is widely variable and depends on the severity and extent of the findings.
Summary
Amniotic band syndrome can vary in severity, depending on the organ systems that are affected; findings are typically asymmetric in distribution. The limbs are affected most commonly, and investigational fetal interventions have been reported. Patients can be reassured that recurrence is rare.
References
- Amniotic band syndrome.Am J Obstet Gynecol. 1982; 144: 243-248
- Amniochorionic mesoblastic fibrous strings and amnionic bands: associated constricting fetal malformations or fetal death.Am J Obstet Gynecol. 1965; 91: 65-75
- The amniotic band disruption complex: timing of amniotic rupture and variable spectra of consequent defects.J Pediatr. 1979; 95: 544-549
- Diagnostic imaging: obstetrics.3rd ed. Elsevier, Philadelphia2016
- Prenatal diagnosis of amniotic band syndrome: risk factors and ultrasonic signs.J Matern Fetal Neonatal Med. 2015; 28: 281-283
- Epidemiology of the early amnion rupture spectrum of defects.Am J Dis Child. 1988; 142: 541-544
- Congenital transverse defects of limbs and digits (‘intrauterine amputation’).Arch Dis Child. 1962; 37: 263-276
- A pattern of craniofacial and limb defects secondary to aberrant tissue bands.J Pediatr. 1974; 84: 90-95
- 3D/4D sonographic evaluation of amniotic band syndrome in early pregnancy: a supplement to 2D ultrasound.J Obstet Gynaecol Res. 2011; 37: 656-660
- 3D and 4D sonographic imaging of amniotic band syndrome in early pregnancy.J Clin Ultrasound. 2008; 36: 573-575
- “ADAM complex” (amniotic deformity, adhesions, mutilations): a pattern of craniofacial and limb defects.Am J Med Genet. 1978; 2: 81-98
- Etiologic factors in the amniotic band syndrome: a study of 24 patients.Birth Defects Orig Artic Ser. 1977; 13: 117-132
- Fetoscopic approach to amniotic band syndrome.J Pediatr Surg. 2014; 49: 359-362
- Fetoscopic release of umbilical cord amniotic band in a human fetus.Ultrasound Obstet Gynecol. 2009; 33: 232-234
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© 2019 Published by Elsevier Inc.
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