Amniotic band syndrome

The amniotic band syndrome (ABS) comprises of a wide spectrum of abnormalities which results from entrapment of various fetal parts from a disrupted amnion. Due to the randomness of entrapment, each affected individual has the potential to form a very unique deficit. 

Epidemiology

The phenomenon is estimated to occur in ~ 1 : 1200 - 1300 live births ^1,8.

Pathology

The exact pathogenesis is not well known although several theories have been proposed. 

Exogenous theory

An early disruption of the amnion allows the embryo or fetus to enter the chorionic
cavity and contact the chorionic side of the amnion leading to fibrous bands, which entrap the fetal body components

Endogenous theory 

Occurs as a result of vascular compromise with mesoblastic strings not being a causal agent ⁴

Associations

The vast majority of cases have a sporadic occurrence ^8. It rare situations it may be be associated with 

• Ehlers-Danlos syndrome 
• epidermolysis bullosa

Radiographic features

There is a massive spectrum of  of abnormalities depending on what part gets entrapped and at what point in time of gestation. Features are often asymmterical. Observable features according to position include

Head / face entrapment

• acrania
• anencephaly
• facial clefts 

Truncal entrapment

• abdominal wall defects
• rib clefting
• congenital scoliosis

Extremity entrapment

Limb defects tend to be the commonest ⁷

• variable levels of limb amputation
• variable levels of limb constriction + / - atrophy
• lymphoedema distal to the level of the band constriction
• pseudosyndactylity
• phocomelia ²

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

Treatment and prognosis

The prognosis is extremely variable dependent on the part that gets entrapped. This can range from normal life expectancy at one extreme in the case of a minor distal limb entrapment to in-utero death if there is anencephaly from head entrapment. There is no recognised recurrence risk for future pregnancies.

Differential diagnosis

The differential is extremely variable dependent on the type of deficit and is best left for individual features

See also

• limb body wall complex