Amniotic band syndrome (ABS) comprises of a wide spectrum of abnormalities, all of which result from entrapment of various fetal body parts in a disrupted amnion. Due to the randomness of entrapment, each affected individual has the potential to form a unique deficit.
The phenomenon is estimated to occur in ~1:1200-1300 live births 1,8.
The exact pathogenesis is not well known, although several etiologies have been proposed.
Proposed by Torpin in 1965 10, it is still the most widely accepted theory.
A disruption in the amnion allows the embryo or fetus to enter the chorionic cavity, where body parts become entangled in fibrous mesodermic strands emanating from the chorionic side of the amnion. If occurring early in gestation, this can potentially cause multiple malformations.
Proposes that a vascular insult during early embryogenesis is responsible for amniotic band syndrome 4.
The vast majority of cases have a sporadic occurrence 8. In rare situations, it may be associated with:
There is a massive spectrum of abnormalities, depending on which part becomes entrapped and at what stage of gestation. Features are often asymmetrical. Observable features according to location include:
Limb defects tend to be the commonest 7:
- variable levels of limb amputation
- variable levels of limb constriction, with possible distal atrophy
- lymphedema distal to the level of the band constriction
- phocomelia 2
In addition to these defects, actual background amniotic bands may also be detected on antenatal ultrasound.
Treatment and prognosis
The prognosis is extremely variable, depending on the part that becomes entrapped. This can range from normal life expectancy at one extreme in the case of a minor distal limb entrapment to in-utero demise in the case of anencephaly from head entrapment. There is no recognised risk of recurrence for future pregnancies.
The differential is extremely variable, depending on the type of deficit.
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- 8. Entezami M, Albig M, Knoll U et-al. Ultrasound Diagnosis of Fetal Anomalies. Thieme. (2003) ISBN:1588902129. Read it at Google Books - Find it at Amazon
- 9. Merz E, Bahlmann F. Ultrasound in obstetrics and gynecology. Thieme Medical Publishers. (2005) ISBN:1588901475. Read it at Google Books - Find it at Amazon
- 10. Torpin R. Amniochorionic mesoblastic fibrous strings and amniotic bands: Associated constricting fetal malformations or fetal death. American journal of obstetrics and gynecology. 91: 65-75. Pubmed