CHAPTER 12: MISCELLANEOUS ABNORMALITIES

12.1 AMNIOTIC BAND SYNDROME

EPIDEMIOLOGY/GENETICS

Definition Amniotic band syndrome (ABS) is a rare spectrum of congenital anomalies caused by entanglement of fetal parts, or disruption of anatomic structures, by fibrous amniotic bands.

Epidemiology The exact incidence of ABS is uncertain but may be as high as 1 in 15,000 live births.

Embryology There are two theories proposed for ABS: (1) The bands are due to early amniotic rupture, leaving fibrous bands floating in the amniotic fluid to become entangled with the fetus; or (2) the bands are secondary to membrane malformations caused by ischemia. There are others who postulate that ABS is part of the limb–body wall spectrum. The timing of the insult determines the effect of the amniotic band on fetal development. An amniotic band can be: (1) disruptive, resulting in finger, toe, or extremity amputation; (2) an early insult may give rise to a malformation (i.e., an encephalocele); and (3) if a band constricts movement, a deformation (scoliosis) may result.

Inheritance Pattern ABS appears to be sporadic. ABS has been associated with maternal Ehlers-Danlos syndrome and epidermolysis bullosa.

Teratogens None are known.

Prognosis The prognosis depends on the resulting anomalies. Cranial and chest anomalies are more likely to be fatal, while limb involvement may have a better prognosis.

SONOGRAPHY

FINDINGS

• Atypical anomalies or an unusual constellation of abnormalities are frequently the presenting findings for ABS. Some anomalies that have been associated with ABS are as follows:

  • Isolated limb amputations or missing hands, feet, or digits in 80% of cases

  • Midline cleft lip, or transverse facial clefts

  • Asymmetric craniofacial defects

  • Acrania or encephalocele

  • Body wall defects (i.e., ectopia cordis, gastroschisis, omphalocele, and limb–body wall)

KEY FINDINGS/PITFALLS

• If an isolated abnormality, or group of anomalies, seems asymmetric or atypical, ABS should be considered.

• The amniotic fluid volume may be decreased.

• ABS has been detected as early as the first trimester.

• ABS can be definitively identified when the following occur:

  • Bands can be visualized within the amniotic fluid and appear as single or multiple thin membranes that attach to, or limit the motion of, specific fetal parts.

    • They can be difficult to identify; only the sequelae of the amniotic bands may be apparent.

    • Extremity constriction can be the first sign and usually presents with edema of the distal extremity. This is frequently followed by limb amputation.

• Look for

  • Amnion in continuity with the fetal parts

  • Extremity edema/localized swelling with reduced distal vascular flow detected with Doppler

  • Fetal scoliosis

  • Echogenic debris within the amniotic fluid

DIFFERENTIAL DIAGNOSIS

• Anomalies that can be isolated, can be related to aneuploidy or a syndrome, or can be ABS-related defects, including

  • Body stalk anomaly

  • Cephalocele

  • Acrania

  • Cleft lip

  • Omphalocele

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