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

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.