Amniotic band syndrome (ABS) results from rupture of the amniotic sac, leading to fibrous bands that may entangle and constrict fetal structures during intrauterine development(1). Prenatal diagnosis using ultrasound has been reported for over 45 years(2,3), and can be made as early as the first trimester. Recently, we registered a case of ABS by ultrasound beyond the characteristic fetal amputation malformations typically observed in this condition.
A 40-year-old woman at 35 weeks of gestation was referred for magnetic resonance imaging (MRI) of the uterine cavity and myometrial thickness due to a clear separation of the amniotic cavity, with the fetus remaining persistently in a transverse position throughout gestation during ultrasound studies at the referring department. Additionally, the patient had undergone a myomectomy three years prior to pregnancy. MRI was performed using a 1.5T Siemens Aera system (Siemens, Erlangen, Germany).
T2-weighted MRI sequences demonstrated the fetus in a transverse position. The uterine cavity showed a distinct narrow annular constriction in the inferior portion of the uterine body, suggestive of myometrial fibrosis. The fetus remained fixed in position throughout the acquisition of the sequences, with the right arm restricted to the lower uterine segment. Fetal anatomy was otherwise normal, although a hyperintense signal was observed in the subcutaneous tissue of the right arm, which appeared entrapped in the lower uterine cavity compared with the left arm. Absence of arm movement was also noted (Fig. 1. A–C and Video S1).
Fetus at 35 weeks of gestation. (A) T2-weighted magnetic resonance imaging (MRI) sequences demonstrate the uterus with a thick myometrial ring separating it into two segments (arrows). The right arm is entrapped in the lower uterine segment (asterisk), with part of the amnion in constant contact with the right axilla (b – bladder). (B) T2-weighted images demonstrate the difference between the left arm (black arrow) and the right arm (white arrow). The right arm shows a hyperintense signal in the subcutaneous tissue, corresponding to localized skin edema. (C) Three-dimensional reconstruction of MRI images of the fetus. The fetal forearm shows edema (blue) and is restricted to the lower uterine segment. (D) Ultrasound image showing the amniotic membrane (white arrows) originating from the uterine constriction ring (arrowhead), rupturing and infiltrating the fetal skin, with striated hypoechoic fibers. (E) Postnatal image of the neonate at the first week of life, showing the scar resulting from the lysis of the amniotic band
Because of the persistent absence of fetal movement in the right arm during MRI image acquisition, an ultrasound examination was performed using a Voluson E10 system (v. BT19; Madison, Wisconsin, USA). Doppler evaluation revealed normal blood flow in the arm, and the suspected subcutaneous edema was not confirmed. The fetus remained in a transverse presentation, and external maneuvers were performed to assess the integrity of the fetal skin and to exclude an amniotic band. Despite attempts to mobilize the fetus, its position remained unchanged. After intense external maneuvers, an amniotic band was visualized. The hyperechogenicity of the fetal skin was interrupted by the amniotic membrane, which showed hypoechogenic striated bands with shallow penetration into the fetal thorax. The continuity between the amniotic membrane and fetal skin, along with membrane infiltration into the skin, confirmed the diagnosis of ABS (Fig. 1D and Video S2).
The pregnancy progressed until 37 weeks, when the development of preeclampsia and a shoulder presentation necessitated delivery by cesarean section. Following delivery, the amniotic band was carefully separated from the skin over the posterior shoulder and axilla, leaving a small linear scar on the right side of the neonatal dorsum (Fig. 1E). The male neonate weighed 2,300 g, and both arms appeared normal on physical examination with preserved function. The newborn was admitted to the neonatal unit for five days due to jaundice but was discharged home without sequelae.
In 1832, Montgomery, observing children’s malformations, was the first to propose ABS as a cause of limb amputations and severe malformations during intrauterine life(4). Prenatal diagnosis of ABS by ultrasound has been reported for over 40 years and is essential for parental counseling and for assessing the extent of adhesions and related malformations(5). Prenatal identification of ABS can improve outcomes in many cases of fetal limb constriction. Fetuses affected by ABS and at risk of limb amputation during pregnancy have undergone in utero lysis of amniotic bands, achieving favorable prognosis following the procedure(6,7). Prenatal surgical intervention can result in normal functional limbs in 50% of cases(8,9).
For the diagnosis of ABS, some authors consider the presence of a fetal malformation (most commonly sudden fetal limb amputation) in an otherwise normally developing fetus sufficient for diagnosis, while visualization of bands without malformations would exclude it(10). In the present case, these criteria were not applicable: no malformations were present, but an amniotic band infiltrating the fetal skin was visualized. Vigorous external mobilization with simultaneous visualization of the band fixed to fetal tissue was only possible with B-mode ultrasound, which proved fundamental for diagnosis. MRI can serve as an adjunct tool to assess fetal malformations, especially when surgery is considered(3). However, in this case, although MRI showed limb edema, the fixed fetal position only suggested ABS, with definitive diagnosis provided by ultrasound.
In conclusion, we describe the ultrasound characteristics of ABS skin invasion, in a patient with prior uterine surgery. Two-dimensional ultrasound combined with external maneuvers was fundamental for visualizing the amniotic band and its adherence to fetal skin, thereby establishing the definitive diagnosis.