Acrania-exencephaly-anencephaly sequence phenotypic characterization using two- and three-dimensional ultrasound between 11 and 13 weeks and 6 days of gestation

Abstract

The study presents a pictorial essay of acrania-exencephaly-anencephaly sequence using two-(2D) and three-dimensional (3D) ultrasonography, documenting the different phenotypic characterization of this rare disease. Normal and abnormal fetuses were evaluated during the first trimester scan. The International Society of Ultrasound in Obstetrics and Gynecology practice guidelines were adopted to standardize first trimester anatomical ultrasound screening. The guidelines outline the importance of systematic fetal head and brain examination including the formation of cranial bones, choroid-plexus and ventricles. Acrania-exencephaly-anencephaly sequence and/or other neural tube defects, such as meningoencephalocele, may be identified during a routine 11–14 week scan. Early first trimester detection of acrania-exencephaly-anencephaly sequence with the characterization of different related phenotypes, 2D and 3D ultrasound imaging as well as differential diagnosis are also presented in this pictorial essay. The main diagnostic ultrasound features of the disease may be characterized by findings of acrania with increased amniotic fluid echogenicity; “Mickey-Mouse” bi-lobular face, cystic, elongated, irregular and overhanging head morphology. Lightening techniques have also been added to 3D ultrasound to enhance anatomical details. Moreover, discordant amniotic fluid echotexture in the setting of twin pregnancies may be the first sign of acrania-exencephaly-anencephaly sequence. Extracranial malformations, aneuploidy and genetic syndromes associated with acrania-exencephaly-anencephaly sequence are also reported and described. First trimester neuroscan by an expert sonographer with appropriate training together with the application of standardized protocol are essential for a high detection rate of this rare type of neural tube defect malformation during a scan performed at 11 and 13 weeks and 6 days.

An Unusual First‐Trimester Ultrasound Presentation of the Acrania‐Anencephaly Sequence

“…A number of different types of the acrania-anencephaly sequence have been previously described in the literature. 7,9,10 However, none of these descriptions matched the US and clinical characteristics observed in our cases. Indeed, our 3 cases presented a constriction ring around the external base of the developing fetal skull, with a detailed assessment of this area revealing that the amniotic membrane was wrapped around the head in at least 2 of them.…”

“…A number of different types of the acrania‐anencephaly sequence have been previously described in the literature . However, none of these descriptions matched the US and clinical characteristics observed in our cases.…”

“…5,6 Recent efforts to classify the different types of acrania-anencephaly sequence when presenting in the first trimester have been reported. 9 These include the exposed cerebral hemispheres taking on a bilobular shape (the "Mickey Mouse" sign), 9,10 as well as cystic, foreshortened, elongated, and overriding types of acrania. 9 The aim of this report is to describe another subtype that we have termed the "Turkish turban" type.…”

“…9 These include the exposed cerebral hemispheres taking on a bilobular shape (the "Mickey Mouse" sign), 9,10 as well as cystic, foreshortened, elongated, and overriding types of acrania. 9 The aim of this report is to describe another subtype that we have termed the "Turkish turban" type. We also provide US evidence that this presentation is probably secondary to early-stage amniotic band syndrome, which suggests that this specific type of NTD is the result of a disruptive insult.…”

“…An associated but indirect sign of acrania‐anencephaly is the presence of echogenic amniotic fluid, resulting from bleeding and disaggregation of dysplastic brain tissue . Recent efforts to classify the different types of acrania‐anencephaly sequence when presenting in the first trimester have been reported . These include the exposed cerebral hemispheres taking on a bilobular shape (the “Mickey Mouse” sign), as well as cystic, foreshortened, elongated, and overriding types of acrania .…”