We present a case of amniotic band sequence.

Our ultrasound images demonstrated abnormal outlines of the fetal head, with destruction of the parietal bone leading to an irregular cranial contour, asymmetry of the brain, enlargement of the lateral ventricle, and deviation of the falx. The maxillary and mandibular alveolar ridges showed deep, irregular clefts. The nasal cavity and external nasal structures were severely disrupted. Destruction of the midface resulted in extreme hypertelorism and exophthalmos. Even the morphology of the globes appeared abnormal. A branching linear structure, consistent with an amniotic band, was seen attached to the face. When examining the four limbs, the upper limbs were attached to amniotic bands, with distal edema beyond the level of constriction, possibly associated with syndactyly. These findings led us to diagnose amniotic band sequence.

The patient had previously been informed at another center about a suspicion of trisomy 18 and underwent chorionic villus sampling (CVS), which showed a normal array CGH result. Importantly, in that center, the fetus had only been scanned transabdominally and not transvaginally. After counselling, the patient elected to terminate the pregnancy. 

Discussion – When anatomy makes no sense

Amniotic band sequence is a disruptive process resulting from rupture of the amnion, leading to fibrous strands that can entrap or constrict fetal structures [1] and occurs with a prevalence of 0.89 in 10,000 births [2]. The spectrum of anomalies is wide, ranging from isolated ring constrictions and syndactyly to severe craniofacial and limb-body wall defects. Patients affected with more severe anomalies are thought to have developed amniotic rupture earlier in gestation [3]. Genetic analysis is typically normal, underscoring the non-genetic, disruptive nature of the condition.

Limb anomalies including constrictions, amputations and deformations are the more common manifestation of amniotic band sequence. However, facial clefts and cranial defects such as anencephaly, cephalocele, and acrania can occur when bands adhere to the cephalic pole of the fetus.  In a study reviewing a South American hospital-based birth registry, nearly 300 cases of amniotic band sequence were identified, of which 15% of neonates presented with neural or cranial defects and 12% with a facial cleft [2]. In this study, approximately 25% of fetuses with amniotic band sequence were stillborn or died in the neonatal period [2].

In the absence of directly visualized amniotic bands, the diagnosis of amniotic band sequence can be challenging [4]. Bands are delicate structures, sometimes invisible on ultrasound, especially when aligned longitudinally to the ultrasound beam. Direct visualization of bands is helpful but not always possible. In case series reviewing prenatally diagnosed amniotic band sequence, 33-92% of fetuses have visualized amniotic bands on ultrasound [5-7]. Transvaginal ultrasound can facilitate visualization of amniotic bands in the first trimester [8]. A key diagnostic clue for the diagnosis of amniotic band sequence is the presence of abnormalities that cross normal embryologic and anatomic boundaries and cannot be explained by a known genetic syndrome or developmental sequence [4].

In our case, the defects crossed normal anatomic boundaries, were not compatible with known embryogenetic mechanisms, and did not match any recognized syndromes or malformation patterns. Differential diagnosis includes genetic syndromes with craniofacial clefts, limb defects, and holoprosencephaly spectrum anomalies. Our case was initially thought to be caused by Trisomy 18, though genetic analysis was found to be normal. The pattern of irregular, asymmetric, and “disruptive” defects favors amniotic band sequence.

References

[1] Torpin R. Amniochorionic mesoblastic fibrous strings and amnionic bands: associated constricting fetal malformations or fetal death. Am J Obstet Gynecol. 1965 Jan 1:91:65-75.
[2] Orioli IM, Ribeiro MG, Castilla EE. Clinical and Epidemiological Studies of Amniotic Deformity, Adhesion, and Mutilation (ADAM) Sequence in a South American (ECLAMC) Population. Am J Med Genet A. 2003 Apr 15;118A(2):135-45.
[3] Higginbottom MC, Jones KL, Hall BD, et al. The amniotic band disruption complex: timing of amniotic rupture and variable spectra of consequent defects. J Pediatr. 1979 Oct;95(4):544-9.
[4] Ferreira CR, Lima CFP, Melo AMAGP. Preventing misdiagnosis in amniotic band sequence: a case report. Autopsy Case Rep [Internet]. 2013;3(1): 15-22.
[5] Neuman J, Calvo-Garcia MA, Kline-Fath BM, et al. Prenatal imaging of amniotic band sequence: utility and role of fetal MRI as an adjunct to prenatal US. Pediatr Radiol. 2012 May;42(5):544-51.
[6] Barros M, Gorgal G, Machado AP, et al. Revisiting amniotic band sequence: a wide spectrum of manifestations. Fetal Diagn Ther. 2014;35(1):51-6.
[7] Barzilay E, Harel Y, Haas J, et al. Prenatal diagnosis of amniotic band syndrome - risk factors and ultrasonic signs. J Matern Fetal Neonatal Med. 2015 Feb;28(3):281-3.
[8] Hata T, Tanaka H, Noguchi J. 3D/4D sonographic evaluation of amniotic band syndrome in early pregnancy: a supplement to 2D ultrasound. J Obstet Gynaecol Res. 2011 Jun;37(6):656-60.