Amniotic band syndrome

Last revised by Joshua Yap on 8 May 2023

Amniotic band syndrome (ABS) comprises 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 vast majority of cases have a sporadic occurrence 8. In rare situations, it may  be associated with:

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.

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 7,11:

In addition to these defects, actual background amniotic bands may also be detected on antenatal ultrasound.

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 as a surgical repair, to in-utero demise in the case of anencephaly from head entrapment 11. There is no recognized risk of recurrence for future pregnancies.

The differential is extremely variable, depending on the type of deficit.

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