The amniotic band syndrome (ABS) is a group of sporadic congenital anomalies that involve the limbs, craniofacial regions, and trunk, ranging from constrictive bands, pseudosyndactyly to amputation, as well as multiple craniofacial, visceral, and body wall defects (Torpin, 1965; Jones et al., 1974; Higginbottom and Jones, 1979; Seeds et al., 1982; Ray et al., 1988; Lockwood et al., 1989; Seidman et al., 1989; Kulkarni and Gopal, 1990). The term amniotic band syndrome encompasses many congenital anomalies, including amniotic band disruption complex (Higginbottom and Jones, 1979), amniochorionic mesoblastic fibrous strings (Torpin, 1965), aberrant tissue bands (Jones et al., 1974), amniotic deformity, adhesion and mutilation (ADAM) complex (Keller et al., 1978; Orioli et al., 2003), amniotic adhesion malformation syndrome (Herva and Karkinen-Jaaskelainen, 1984), and the limb and/or body wall defect (Bamforth, 1992).

Several theories have been advanced to explain the occurrence of these anomalies but two are most commonly held. In 1930, Streeter proposed that a disruption in embryogenesis at the time of formation of the germ disk and the amniotic cavity initiated a chain of events leading to the multiple defects. He suggested that amniotic bands were the result, not the cause, of the pathologic process. In 1992, Bamforth reviewed this theory in a series of 54 cases of ABS and concluded that it may be caused by a localized disturbance in establishment of basic embryonic organization. The most widely accepted theory was proposed by Torpin in 1965. He examined the placenta and fetal membranes in a number of affected individuals and concluded that the disorder was caused by primary rupture of the amnion early in gestation (Keller et al., 1978; Higginbottom and Jones, 1979; Seeds et al., 1982; Herva and Karkinen-Jaaskelainen, 1984).

More recently, Moerman et al. (1992) proposed that the ABS is a collection of three distinct entities that can reconcile both Streeter’s and Torpin’s hypotheses. They suggested that ABS consists of three distinct lesions: (1) constrictive tissue bands; (2) amniotic adhesions; and (3) the more complex pattern of anomalies designated the limb-body wall complex (LBWC) (see Chapter 60). In this report of the fetopathologic evaluation of 18 cases of ABS, 4 had clearly constrictive bands, which formed as a result of the amnion rupture sequence. The bands that resulted from amnion rupture encircled the limbs, resulting in annular constrictions, secondary syndactyly, and intrauterine amputations. In addition, constriction of the umbilical cord is a recognized cause of fetal death (Hong and Simon, 1963; Torpin, 1965). These authors distinguish cases caused by constrictive bands from those caused by broad amniotic adhesions. Moerman et al. (1992) suggested that adhesive amniotic bands were morphologically and pathogenetically different from constrictive bands. Adhesive amniotic bands are usually associated with severe defects such as encephalocele and facial clefts. This group demonstrated pathologically that cranioplacental adhesions are broad adhesions, with the fetal skin fused to the amnion at the margins of the cranial defect. They speculated that the amnion covering the placenta or membranes seals the cranial defect separating the protruding brain from the chorion. Van Allen et al. (1987) proposed that the amnion becomes adherent to the embryo in areas of ischemic necrosis following vascular disruption. In short, the amniotic adhesions are secondary to fetal defects.

Moerman et al. (1992) considered the LBWC to be due to both band-related and non–band–related defects. The band-related defects include limb defects such as clubfoot. Non-band-related defects occur as a result of vascular disruptions or from compression (Miller et al., 1981). The thoracoabdominoschisis of LBWC is characterized by an anterolateral body wall defect with evisceration of abdominal and/or thoracic organs. The eviscerated organs are in an extra-amniotic sac bounded by the chorionic plate, a persistent extraembryonic coelom. The amnion is continuous with the skin. The umbilical cord is extremely short, with umbilical vessels running in the amniotic sac, often with an absent umbilical artery. The severe scoliosis is a postural deformity caused by abnormal fixation of the fetus to the placenta. They also cite the high incidence of internal structural defects such as cardiac anomalies, unilateral absence of a kidney, or intestinal atresia, which do not fit with simple amnion rupture.

The fetal malformations that can occur as a result of ABS can be categorized into neural tubelike defects, craniofacial anomalies, limb anomalies, and constrictive bands (Seeds et al., 1982; Lubinsky et al., 1983; Ho and Liu, 1987; Seidman et al., 1989). The neural tubelike defects include cases of anencephaly and encephalocele, which may be asymmetric or multiple. The craniofacial anomalies include facial clefts, nasal deformity, asymmetric microphthalmia, and abnormal cranial calcification. Limb anomalies may be multiple and asymmetric, including limb or digital amputation, pseudosyndactyly, abnormal dermatoglyphics, and some cases of clubbed feet. Abdominal wall and thoracic wall defects can occur, and some cases are mistaken for gastroschisis or omphalocele with rupture.

The most puzzling component of the ABS is its association with visceral anomalies, including bladder exstrophy, vertebral hypoplasia, and other renal, gonadal, cardiac, and pulmonary defects (Bamforth, 1992). Constrictive bands involving the extremities are the most common defect associated with the ABS (Huang et al., 1995).

The variation in manifestations of the ABS are thought to be due to differences in timing of amniotic rupture and the degree to which the fetus becomes entangled by strands of amnion (Higginbottom and Jones, 1979; Seeds et al., 1982). The effects the amniotic bands have on the developing fetus have been classified into malformation, disruption, and deformation (Higginbottom and Jones, 1979). Amniotic bands that interrupt the normal sequence of embryologic development lead to malformations such as cleft lip and palate, and abdominal wall defects. In contrast, bands may tear normally developed structures, leading to disruption such as central nervous system or calvarial defects, acrosyndactyly, amputations, and nonanatomical facial clefts (Lockwood et al., 1989). The effects of fetal compression and tethering may lead to deformations such as clubbing of the feet and angulation of the spine.

The timing of amnion rupture has been suggested to occur between 28 days after conception to 18 weeks of gestation. If amnion rupture occurs prior to 45 days of gestation, the results are likely to be devastating, including severe skull defects and major visceral defects (Huang et al., 1995). Rupture occurring after 45 days of gestation is likely to result in more limited defects.

The cause of amnion rupture and band formation is not well understood, but it has been observed following amniocentesis (Rehder, 1978). Late gestation bands, even in the absence of an amniocentesis, can also occur. Lage et al. (1988) reported ABS presenting at birth with multiple abnormalities of the extremities despite a normal sonographic appearance at 21 weeks of gestation. There have also been cases of ABS associated with underlying disease. Young et al. (1985) reported two cases in fetuses with Ehlers–Danlos syndrome type IV and one with osteogenesis imperfecta. They speculated that the premature amnion rupture may have been due to reduced or abnormal collagen in the amnion. There have been rare familial cases of ABS, and some teratogens, such as lysergic acid diethylamide and methadone, have been reported in association with the syndrome (Chemke et al., 1973; Lubinsky et al., 1983; Daly et al., 1996). Other significant exposures include misoprostol and maternal fever (Orioli et al., 2003; Ribeiro et al., 2004).

Chorioamniotic separation, occurring spontaneously or as a consequence of invasive procedures, is a potential cause of the ABS. The incidence of chorioamniotic separation diagnosed by ultrasound is reported to range from 1 in 187 to 1 in 4333 births (Kaufman et al., 1985; Borlum, 1989). The natural history of chorioamniotic separation occurring in normal pregnancies was initially thought to be benign. However, Graf et al. (1997) reported a case of chorioamniotic separation that resulted in the formation of amniotic bands involving the umbilical cord, resulting in fetal death. The incidence of chorioamniotic separation may be even higher in cases of fetal surgery. In the same report, Graf and colleagues described 5 cases of chorioamniotic separation occurring in a series of 40 patients undergoing open fetal surgery. Three of the five fetuses had amniotic bands involving the umbilical cord, leading to fetal death in one. This report speculated that because the amnion is adherent and fixed to the umbilical cord, once formed amniotic bands may retract to the cord, causing strangulation. Heifetz (1984), in a review of ABS, reported that as many as 10% of cases had umbilical cord strangulation.

ABS is often misdiagnosed, especially in cases of early amniotic band rupture. Infants affected by early amniotic rupture present with anencephaly, encephalocele, abdominal or thoracic wall defects, and severe limb abnormalities. The severity of the anomalies obscures the cause, especially if the amniotic bands are not evident at birth. It has been estimated that a correct neonatal diagnosis of ABS is made in only 24% to 50% of patients without specialized genetic consultation (Seeds et al., 1982).

Because of difficulties in accurately diagnosing ABS, the estimates of its incidence vary widely. The reported incidence ranges from 1 in 1200 to 1 in 15,000 livebirths (Chemke et al., 1973; Seeds et al., 1982; Ho and Liu, 1987; Ray et al., 1988). More recent estimates place the incidence of ABS at 1 in 1200 because of the more frequent recognition of an amniogenic cause for congenital anomalies (Ossipoff and Hall, 1977; Seeds et al., 1982; Moerman et al., 1992). In a retrospective analysis of 3173 autopsies performed during a 14-year period, Czichos et al. (2005) found 744 cases of malformations of which 14 had anomalies thought to be a consequence of amnion rupture. This series yielding an incidence of 1:226 among fetuses and newborns undergoing autopsy suggested that it may be a more common cause of anomalies than generally appreciated.

Hands are more frequently affected than feet, with the largest fingers (third, fourth, and second) more commonly afflicted (Ribeiro et al., 2004).

ABS is associated with numerous antenatal sonographic features, as there are numerous forms of the syndrome and these features may occur as isolated problems or in combination. The earliest that amniotic bands have been seen is at 12 weeks of gestation, by endovaginal probe. The bands can be extremely difficult to detect sonographically and ABS is more often diagnosed by the effect that they have on fetal anatomy (Figure 100-1). The effect of amniotic bands on the extremities may be manifested by absent digits or portions of limbs, or a swollen distal arm or leg resulting from constrictive amniotic bands (Paladini et al., 2004) (Figure 100-2). ABS may affect the face with cleft lip or palate, asymmetric microphthalmia, or severe nasal deformity. Encephalocele may be a manifestation of ABS, especially when eccentrically placed (Figure 100-3). Abdominal wall defects can be the result of ABS, typically with large defects with free-floating intestine herniated outside the abdomen. The characteristic appearance of an aberrant sheet or band of amnion attached to the fetus with resultant deformity and restriction of motion allows a diagnosis of ABS to be made (Figure 100-3). However, prenatal diagnosis is the exception rather than the rule.

The findings in ABS may be limited to isolated defects, including isolated facial cleft, digital amputation, or mild elephantiasis of an extremitybeyond a constrictive band (Sentilhes et al., 2004; Dyson et al., 2000). These isolated features may be difficult to diagnose sonographically because the detailed fetal visualization required is beyond the scope of routine obstetrical ultrasound examinations. At the worst end of the spectrum, the fetus may be so severely deformed by the amniotic bands that the spine is contracted and organs are formed in perplexing and bizarre proportions. The head may be completely misshapen or absent. The bands responsible for these deformities are rarely seen and a presumptive diagnosis of ABS is made based on the commonly associated deformities.