Clinician to Clinician: A case of amniotic band sequence

June 1, 2005

Amniotic band disruption sequence is a rare disorder in which bands of string-like mesoderm originating from the chorionic side of the amnion are inserted into the fetus's body. The results of this sporadic, congenital nongenetic anomaly vary in severity from an abnormality in a single digit to major craniofacial or visceral defects.

We present the case of a nonviable 31-week fetus diagnosed on early obstetric ultrasound with amniotic band disruption sequence that was born with cleft lip and palate; no nose; encephalocele and exteriorization of the brain, thoracic, and abdominal organs; and placental adhesion to the brain and caudal appendage (pseudotail).

Discussion Amniotic band disruption sequence encompasses a broad spectrum of sporadic congenital nongenetic anomalies, which can vary in severity from a simple digit abnormality to major craniofacial or visceral defects. It is a rare disorder characterized by bands of string-like mesoderm originating from the chorionic side of the amnion, which insert on the fetal body. The underlying defect is theorized to be a rupture of the amnion before the amnion and chorion fuse. The fetus may herniate through the rupture and become entwined in the resulting strands of amnion.1 As the fetus grows, the anatomy is distorted by the fibrous bands, resulting in vascular disruption with constriction of blood flow and alteration in normal development.

Amniotic band sequence occurs in about 7.8/10,000 live births. The prevalence rate in spontaneous abortions is estimated to be 10 times as high,2 but there is no difference in fetal gender. Because this is a sporadic abnormality, subsequent pregnancies are not associated with increased recurrence.

Prenatal diagnosis is usually made with U/S examination and may be possible as early as 12 weeks' gestation.3 Multiple anomalies are common in a fetus with amniotic band sequence. The most common defects include lower extremity limb malformations, such as distal ring constrictions, congenital fetal intrauterine amputation, and clubfoot.4 Other associated abnormalities include multiple craniofacial defects like facial clefts, abdominal wall defects, scoliosis, and encephaloceles. Identification of more than two of these anomalies is suggestive of amniotic band sequence. Visualization of amniotic bands with restriction of fetal movement is virtually diagnostic.5 In milder forms, U/S detection may be difficult and the diagnosis may be made after birth.

Our case illustrates an example of caudal appendage (pseudotail, since no spine structure was visible on U/S).

The prognosis for amniotic band sequence depends on the type and number of malformations the fetus has. Milder abnormalities may be detected only after birth and may not affect the long-term prognosis. Fetuses that have multiple abnormalities may not survive. A clinically related lethal abnormality is the limb-body wall complex, which consists of failure of closure of the ventral wall, marked scoliosis, and evisceration of the abdominal contents.6

REFERENCES1. Walter JH Jr, Goss LR, Lazzara AT. Amniotic band syndrome. J Foot Ankle Surg. 1998;37:325-333.