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Acrania-exencephaly-anencephaly sequence phenotypic
characterization using two- and three-dimensional
ultrasound between 11 and 13 weeks and 6 days of gestation
Eduardo Félix Martins Santana1,2, Edward Araujo Júnior1,
Gabriele Tonni3, Fabricio Da Silva Costa4,5, Simon Meagher4
1 Department of Obstetrics, Paulista School of Medicine – Federal University of São Paulo
(EPM-UNIFESP), São Paulo-SP, Brazil
2 Department of Perinatology, Albert Einstein Hospital, São Paulo-SP, Brazil
3 Department of Obstetrics & Gynecology, Guastalla Civil Hospital, AUSL Reggio Emilia, Reggio
Emilia, Italy
4 Monash Ultrasound for Women, Melbourne, Victoria, Australia
5 Department of Obstetrics and Gynaecology, Monash University, Melbourne, Australia
Correspondence: Prof. Edward Araujo Júnior, PhD, Rua Belchior de Azevedo,
156, apto. 111 Torre Vitória, São Paulo-SP, Brazil, CEP 05303-000, tel./fax: +55 11 37965944,
e-mail: araujojred@terra.com.br
DOI: 10.15557/JoU.2018.0035
Abstract
The study presents a pictorial essay of acrania-exencephaly-anencephaly sequence using two-
(2D) and three-dimensional (3D) ultrasonography, documenting the different phenotypic char-
acterization 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 se-
quence and/or other neural tube defects, such as meningoencephalocele, may be identified dur-
ing a routine 11–14 week scan. Early first trimester detection of acrania-exencephaly-anenceph-
aly 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, irregu-
lar and overhanging head morphology. Lightening techniques have also been added to 3D ul-
trasound 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-exen-
cephaly-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 malforma-
tion during a scan performed at 11 and 13 weeks and 6 days.
Keywords
acrania-exencephaly-
anencephaly sequence,
central nervous
system scan,
first trimester scan,
two-dimensional
ultrasound,
three-dimensional
ultrasound
Pictorial review
Submitted:
23.03.2018
Accepted:
31.05.2018
Published:
06.09.2018
Cite as: Santana EFM, Araujo Júnior E, Tonni G, Da Silva Costa F, Meagher S:
Acrania-exencephaly-anencephaly sequence phenotypic characterization using two-
and three-dimensional ultrasound between 11 and 13 weeks and 6 days of gestation.
J Ultrason 2018; 18: 240–246.
241
J Ultrason 2018; 18: 240–246
Acrania-exencephaly-anencephaly sequence phenotypic characterization using
two- and three-dimensional ultrasound between 11 and 13 weeks and 6 days of gestation
Introduction
First trimester scan, which is routinely performed between
11 and 13 weeks and 6 days gestation, is a well-established
study for routine aneuploidy screening, but it also facili-
tates anatomical assessment allowing early diagnosis of
structural anomalies(1). ISUOG (International Society of
Ultrasound in Obstetrics and Gynecology) practice guide-
lines for first trimester scan require identification of the
fetal head, appropriate development of cranial bones, and
identification of choroid-plexus and cerebral ventricles(2).
Cranial ossification should be visible from the 11th week
onwards.
Acrania-exencephaly-anencephaly sequence is a rare mal-
formation with an estimated incidence ranging between
3.68 to 5.4 for 10,000 live births(3). A Danish group(3) dem-
onstrated that two-dimensional (2D) ultrasound detec-
tion rate of acrania-exencephaly-anencephaly sequence
improves with training and when performed by a mater-
nal-fetal medicine (MFM) operators, it ranges from 69%
to 86% (mean detection rate of 58.5% during basic scan)
with many undiagnosed cases when gestational age is less
than 11 weeks(3). In contrast, higher detection rates (100%)
were achieved by another research group(4).
The introduction of the transvaginal approach has enabled
detection of acrania-exencephaly-anencephaly sequence at
an early stage of fetal development, with the earliest diag-
nosis at 9 weeks and 3 days and 10 weeks onwards(5–10). In
addition, an increased echogenicity of the amniotic fluid
at 11–14 weeks by 2D ultrasound is a useful sonographic
marker of cases of acrania-anencephaly sequence that may
be seen in 89% of cases(11).
Fig. 1. Acrania detected by 3D ultrasound at 8 weeks and 6 days of
gestation using multiplanar mode (A) and HDlive™ render-
ing mode: note the increased echogenicity of the amniotic
fluid (B)
Fig. 3. 2D transvaginal ultrasound showing “cystic” acrania at 10
weeks and 5 days of gestation
Fig. 2. 2D transabdominal ultrasound performed at 11 weeks and 3
days. A “Mickey-Mouse” bi-lobular face” appearance is cle-
arly evident
Fig. 4. A variant of cystic acrania (A) phenotype with associ-
ated exomphalos (B) detected at 10 weeks and 2 days of
gestation
A B
A B
242
J Ultrason 2018; 18: 240–246
Eduardo Félix Martins Santana, Edward Araujo Júnior, Gabriele Tonni, Fabricio Da Silva Costa, Simon Meagher
The aim of this pictorial essay is to show the different phe-
notypic appearance at 2D- and 3D-ultrasound in fetuses
with acrania-exencephaly-anencephaly sequence diag-
nosed at first trimester scan.
Materials and methods
Voluson E8/E10 (GE Medical Systems, Milwaukee, WI) ul-
trasound systems equipped with real-time high frequency
4–8.5 MHz transabdominal/transvaginal 2D and 3D/4D
volumetric probes (RIC 5–9W and RAB 4–8L) were used.
For the purpose of standardization, ultrasound was per-
formed according to the ISUOG guidelines for first trimes-
ter scan. In some cases, acrania was detected at an early
stage (8 weeks); in these instances, transvaginal approach
was employed. Two and three-dimensional volume data-
sets were digitally acquired during fetal rest period and
analyzed in the ultrasound system during the examination.
The embryos and fetuses were insonated preferentially in
the coronal and sagittal plane with a sweep time of 8–15 s
for volume acquisition. Multiplanar mode with surface
Fig. 5. Fore shortened phenotype of acrania diagnosed at 11 weeks
and 1 day of gestation by 3D ultrasound with HDlive™ ren-
dering mode
Fig. 6. Elongated phenotype of acrania by 2D ultrasound at 11
weeks and 1 day of gestation
Fig. 8. Discordant amniotic fluid echotexture in the setting of
monochorionic diamniotic twin pregnancy may be the
first sign of acrania-exencephaly-anencephaly sequence
Fig. 7. 3D ultrasound in multiplanar mode in sagittal (A, detail) and sagittal and coronal planes (B): the “overhanging” phenotype is well
depicted
BA
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J Ultrason 2018; 18: 240–246
Acrania-exencephaly-anencephaly sequence phenotypic characterization using
two- and three-dimensional ultrasound between 11 and 13 weeks and 6 days of gestation
rendering was used as standard 3D ultrasound visualiza-
tion. Lightening technique (HDlive™) was also applied
to enhance image rendering. Written informed consent
signed by each participant was obtained during exams at
the Monash Ultrasound for Women, Clayton, Victoria, Aus-
tralia.
Results
Two-dimensional ultrasound was routinely used for nor-
mal and pathological cases. In the latter ones, 3D ultra-
sound was applied as a complementary diagnostic tool.
An ultrasound perspective of different phenotypic appear-
ance of acrania-exencephaly-anencephaly sequences is de-
scribed (acrania with increased amniotic fluid echogenici-
ty; “Mickey-Mouse” bi-lobular face, cystic, elongated, and
irregular head shape) and shown in Fig. 1, Fig. 2, Fig. 3,
Fig. 4, Fig. 5, Fig. 6, Fig. 7.
Notwithstanding, discordant amniotic fluid echotexture
in the setting of twin pregnancies may be the first sign of
acrania-exencephaly-anencephaly sequence (Fig. 8, Fig. 9).
Furthermore, a very rare malformation was observed at
13 weeks and 6 days, when acrania-exencephaly was seen
in both monochorionic/monoamniotic (MCMA) twins. In
this case, TRAP (twin reversed arterial perfusion) sequence
was the underlying cause of acrania and acardia in the co-
twin (Fig. 10). Finally, acrania-exencephaly-anencephaly
sequence may be present in only one fetus of dichorionic
twin pregnancies (Fig. 11).
Exencephaly can be greatly visualized by using 3D ultra-
sound especially at an early stage of embryonic develop-
ment (8 weeks and 2 days) or to document associated
facial dysmorphism such as low set ears at later stage
(Fig. 12). This defect can be clearly displayed at necrop-
sy (Fig. 13).
Although it may be challenging, precise antenatal differ-
entiation between acrania-exencephaly-anencephaly se-
quence and other types of NTDs such as meningo-enceph-
alocele is fundamental for appropriate genetic counseling
and pregnancy management (Fig. 14). The additional use
of 3D ultrasound enables patients to better understand
brain malformations, which is of value in certain situations
when a patient is doubtful about the diagnosis, particularly
if folate prophylaxis was implemented.
Fig. 9. 3D ultrasound volume contrast imaging (VCI) enhancement in sagittal (A) and coronal (B) plane in monochorionic-monoamniotic
(MCMA) twin pregnancy: note the increased echogenicity of the amniotic fluid
Fig. 10. 2D transvaginal ultrasound: TRAP (twin reversed arterial perfusion) sequence in a co-twin is documented in a monochorionic/
monoamniotic (MCMA) twin pregnancy (A). 3D ultrasound in HDlive™ rendering mode (B)
BA
A B
244
J Ultrason 2018; 18: 240–246
Eduardo Félix Martins Santana, Edward Araujo Júnior, Gabriele Tonni, Fabricio Da Silva Costa, Simon Meagher
Another differential diagnosis which may be considered is
craniopagus parasiticus (Fig. 15), an extremely rare form
of conjoined twins which occurs in approximately 5 per 10
million births and presents with a parasitic head attached
to the normal head in the developed twin.
Discussion
First trimester scan is a well-established examination dur-
ing routine obstetric practice. The examination has the po-
tential to identify embryo-fetal defects in pregnant women
who are at increased risk of congenital anomalies.
The use of a standardized protocol in the ultrasonograph-
ic assessment of the embryo-fetal anatomy is fundamental
for the early prenatal diagnosis of fetal abnormalities. If
the ultrasound examination is performed by a maternal-
fetal medicine operator using high frequency real-time
2D/3D ultrasound equipment, the sensitivity of the de-
tection of major congenital anomalies overall can be as-
sessed to be around 60% in high-risk pregnancy popula-
tions, while a detection rate of nearly 100% can be re-
ported for acrania(1).
Combining abdominal and transvaginal ultrasonography
can be extremely helpful in improving the diagnostic ac-
curacy. In the case of a retroverted uterus, elevated body
mass index, and myomata, the transvaginal approach is
beneficial in most cases. Limitation in the movements of
the transvaginal probe and patient’s acceptance are condi-
tions which may limit the value of transvaginal ultrasonog-
raphy(12,13).
Acrania represents the first stage of this maldevelopment
sequence that takes place 18–20 days post-fertilization(14)
and the progression from exencephaly to anencephaly was
first described by Wilkings et al.(15). When acrania is seen at
an early stage, disorganized brain tissue (vasculo-membra-
nous area) is detectable above the orbits, a process called
exencephaly(16). Anencephaly evolves as a result of failed
closure of the midbrain and forebrain, but with normal
fusion at the level of the hindbrain and the cervical cord
region(17). It has been demonstrated that about 12–25% of
these cases have other associated structural anomalies,
with 1–5% being aneuploidy(3,18,19).
Tonni et al. (20) reported early 3D ultrasound diagnosis of
acrania/exencephaly sequence in a fetus with a diagnosis
of tetraploidy by coelocentesis. These authors concluded
that 3D ultrasound using the transvaginal approach aided
early prenatal diagnosis of acrania/exencephaly sequence
and was useful in excluding different disorders, such inien-
cephaly and/or alobar holoprosencephaly(20). Three-dimen-
Fig. 11. Dichorionic diamniotic (DCDA) twin pregnancies showing
one fetus with acrania-exencephaly-anencephaly sequence
(A, B)
Fig. 12. Exencephaly can be visualized by using 3D ultrasound in the rendering mode, especially at an early stage of embryonic devel-
opment (A, 8 weeks and 2 days of gestation) or to demonstrate associated facial dysmorphism, such as low set ears at a later
stage (B, 13 weeks of gestation)
BA
A B
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J Ultrason 2018; 18: 240–246
Acrania-exencephaly-anencephaly sequence phenotypic characterization using
two- and three-dimensional ultrasound between 11 and 13 weeks and 6 days of gestation
sional ultrasound, especially during the first trimester
scan and the use of the transvaginal approach to display
the coronal or sagittal planes may be particularly useful
in this regard. It is known for instance that the coronal
plane may be difficult to achieve using conventional 2D
ultrasound(21–24).
A training program for the detection and definition of the
diverse types of NTDs as well as precise knowledge of em-
bryologic development according to the Carnegie Classifi-
cation(25) are important in understanding the pathogenesis
and achieving accurate diagnoses in clinical practice(26,27).
The diagnosis of the acrania-exencephaly-anencephaly se-
quence is particularly difficult at lower gestational ages,
and many cases still remain undetected at this stage of
pregnancy(4,28).
Conflict of interest
Authors do not report any financial or personal connections
with other persons or organizations, which might negatively
affect the contents of this publication and/or claim author-
ship rights to this publication.
Fig. 13. Exencephaly: note the developing brain located completely
outside the fetal skull
Fig. 14. Encephalocele (arrow) is another type of neural tube defect
(NTD) that may be differentiated from acrania-exencepha-
ly-anencephaly sequence
Fig. 15. Case of acrania in craniopaghus parasiticus conjoined twins: 2D ultrasound (A) and 3D ultrasound (B) with HDlive™ rendering mode
are reported at 9 weeks and 3 days of gestation
A B
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Eduardo Félix Martins Santana, Edward Araujo Júnior, Gabriele Tonni, Fabricio Da Silva Costa, Simon Meagher
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