Ultrasound diagnosis of acrania with major low–lying placenta and polyhydramnios; case report

Abstract

Acrania is a rare foetal anomaly in which the calvaria is absent, and the meninges come into direct contact with the amniotic fluid. Acrania is the most common anomaly in the acrania – exencephaly – anencephaly spectrum, with anincidence of 3.68 to 5.4 per 10,000 live births. We present a case of a primigravida who presented for an ultrasound on account of vaginal bleeding in early cyesis. Transabdominal ultrasound showed a viable foetus at 13 weeks without a calvaria, with the brain in direct contact with amniotic fluid. There was a low-lying placenta extending from the posterior to anterior part of the lower uterine segment, completely covering the internal cervical os (major low–lying placenta), a placental cyst and polyhydramnios (amniotic fluid index, AFI of 17 cm). A diagnosis of acrania with major low–lying placenta and polyhydramnios was made. Detailed ultrasound is required to detect acrania at 13 weeks. The diagnosis of acrania is required to help direct patient counselling and maternal expectation. When acrania and major low–lying placenta occur in the same patient, both diagnoses must be promptly made concurrently, regardless of gestational age and without waiting for placental trophotropism and migration to occur first.

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165
Ultrasound diagnosis of acrania with major low–lying placenta and polyhydramnios;
case report
Jared N. Oblitey1, William K. Antwi1, Benard O. Botwe2 and Mary K. Oblitey2
Ghana Med J 2021; 55(2): 165-168 doi: http://dx.doi.org/10.4314/gmj.v55i2.12
1Department of Radiography, School of Biomedical and Allied Health Sciences, University of Ghana, Korle Bu,
Accra, Ghana.
2Department of Radiology, Korle Bu Teaching Hospital, Accra, Ghana
Corresponding author: Jared N. Oblitey E-mail: Joblitey@ug.edu.gh
Conflict of interest: None declared
SUMMARY
Acrania is a rare foetal anomaly in which the calvaria is absent, and the meninges come into direct contact with the
amniotic fluid. Acrania is the most common anomaly in the acrania – exencephaly – anencephaly spectrum, with an
incidence of 3.68 to 5.4 per 10,000 live births. We present a case of a primigravida who presented for an ultrasound
on account of vaginal bleeding in early cyesis. Transabdominal ultrasound showed a viable foetus at 13 weeks without
a calvaria, with the brain in direct contact with amniotic fluid. There was a low-lying placenta extending from the
posterior to anterior part of the lower uterine segment, completely covering the internal cervical os (major low–lying
placenta), a placental cyst and polyhydramnios (amniotic fluid index, AFI of 17 cm). A diagnosis of acrania with
major low–lying placenta and polyhydramnios was made. Detailed ultrasound is required to detect acrania at 13 weeks.
The diagnosis of acrania is required to help direct patient counselling and maternal expectation. When acrania and
major low–lying placenta occur in the same patient, both diagnoses must be promptly made concurrently, regardless
of gestational age and without waiting for placental trophotropism and migration to occur first.
Keywords: Acrania; exencephaly; anencephaly; major low-lying placenta; placental cyst
Funding: None declared
INTRODUCTION
Acrania is a foetal anomaly in which there is a complete
or partial absence of the calvaria above the orbits and su-
praciliary ridge, allowing the meninges to come into di-
rect contact with amniotic fluid. Acrania is the most com-
mon anomaly in the acrania–exencephaly–anencephaly
spectrum, with an estimated incidence ranging from 3.68
to 5.4 per 10,000 live births.1 When acrania occurs, the
brain is exposed to the amniotic fluid with a risk of me-
chanical and chemical trauma through friction with the
uterine wall, placenta and foetal parts.2 Subsequently, the
brain may suffer progressive degenerations that could ul-
timately lead to partial or total disappearance of the brain
tissues, particularly from the 14th week of gestation.2,3
This presentation seeks to highlight a case of acrania di-
agnosed at 13 weeks to raise the index of suspicion
among obstetricians and radiologists.
CASE REPORT
A primigravida presented at a health facility for a first-
trimester ultrasound examination. She had been experi-
encing bleeding per vaginam with blood clots, and her
obstetricians were concerned she might have been abort-
ing. There was no relevant past obstetric history.
Ultrasound showed a viable foetus at 13 weeks gestation
(Figure 1) with increased amniotic fluid (amniotic fluid
index, AFI of 17cm). The brain appeared well-formed,
but the bony landmarks for the biparietal diameter (BPD)
measurement were difficult to obtain. In addition, the
brain had no bony covering (Figure 2) and appeared to
bulge freely into the amniotic fluid, with dysplastic in-
tracerebral vessels on colour Doppler (Figure 3).
Figure 1 Coronal Ultrasound image showing a foetus at 13 weeks with
no calvaria. White arrowheads show the brain tissue without bony cov-
ering. The amniotic fluid index (AFI) was 17 cm.

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Figure 2 Ultrasound images showing sagittal and parasagittal images
of the brain demonstrating the absence of the calvaria. See the margins
of the brain (white arrows) without bony margins.
Figure 3 Axial Colour Doppler ultrasound images of the head showing
the absence of the calvaria. Note the dysplastic vessels (white arrows)
within the brain. The arrowheads indicate the margins of the bare brain.
Figure 4 Lower uterine segment ultrasound image showing the urinary
bladder and internal cervical os (C) completely covered by the placenta
from anterior to posterior. White arrowheads indicate placental mar-
gins. Note also the anterior placental cyst. UB refers to the urinary blad-
der.
The placenta completely covered the internal cervical os
(Figure 4 and Figure 5). In addition, there was an ane-
choic cyst with an internal septum at the anterior part of
the placenta, suggesting a placental cyst (Figure 5). A di-
agnosis of acrania with major low–lying placenta, pla-
cental cyst and polyhydramnios was made. The patient
was referred back to an obstetrician for counselling and
continued management. Consent for the case to be pub-
lished (including images, case history and data) was ob-
tained from the patient.
Figure 5 Ultrasound image of the lower uterine segment showing the
placenta completely covering the internal cervical os. Note also the
cystic lesion (white arrow) at the anterior part of the placenta, in keep-
ing with a placental cyst.
DISCUSSION
The acrania – exencephaly – anencephaly spectrum se-
quence is the most severe neural tube defect and results
from a failure to close the rostral end of the neural tube
and abnormal migration of mesenchymal tissue which
normally covers the cerebral hemispheres.4 Embryologi-
cally, this failure of migration occurs at the beginning of
the 4th week, and the major insult is a lack of cranial de-
velopment.
The main mode of diagnosing acrania is by obstetric
ultrasound.5 The calvaria was absent in the foetus in this
case. The International Society of Ultrasound and Gynae-
cology (ISUOG) has issued guidelines emphasizing the
need to recognise the foetal head, cranial bones, choroid-
plexus and cerebral ventricles for all first trimester
scans.6 According to Santana et al. 6, from the 11th week
onwards, cranial ossification ought to be evident. It was,
however, reported in Denmark7 that detection rates for
the acrania- exencephaly – anencephaly were low on
basic scans done before the 11th week, requiring expert
maternal – foetal sonologists for improved detection.7
The key sonographic features of acrania are absent cal-
varia. The damaged brain tissue presents as a 'Mickey
Mouse' sign3 in the early stages and then as echogenic
particles in the amniotic fluid in advanced stages of
the condition.

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These echogenic particles lead to an increased amniotic
fluid texture, a feature reported by both Cafici5 and
Santana6 as a likely very first indication of the spectrum.
It has thus been suggested that this feature could be a
potential marker for first-trimester acrania. However,
such echogenic particles were not noted in this current
case, likely because much brain destruction had not yet
occurred at the time of examination.
It has also been suggested that the acrania – exencephaly
– anencephaly spectrum is actually the same disorder but
presents as acrania in the first trimester and later as anen-
cephaly after the brain destruction has occurred.5 For in-
stance, during one longitudinal study in the same cohort
of patients8, it was noted that exencephaly was the pre-
dominant finding in the first trimester. In contrast, in the
second trimester, the classic appearance of anencephaly
was seen more often. In fact, in one particular foetus, the
transition from exencephaly to anencephaly was docu-
mented by serial ultrasound exams.8
Many types of the acrania–anencephaly spectrum have
been described. One retrospective study of 88 cases of
the spectrum concluded that there are six subtypes;
described as overhanging, elongated, bilobular, cystic,
foreshortened, and irregular, with the first three
accounting for 75% of all cases.9 In his pictorial essay,
Santana et al1 showed images of acrania with cysts in the
brain, describing them as cystic acrania. Sepulveda et al10
also recently described a previously unknown first-
trimester presentation of the sequence in three foetuses.
There was a constriction ring noted around the external
skull base with an enlarged globular head. It was,
therefore, suggested that this subtype of the sequence
may be due to segmental amniotic rupture with the
remnants entrapping the foetal head. All three cases were
either aborted therapeutically or suffered intrauterine
demise.
The current case was associated with polyhydramnios
(AFI of 17cm; reference range at 15 weeks – 8.7 -13.7
cm, 5th -95th percentile)11, a feature also reported by
Santana.1 In Cameroun, Koaum12 described a case of
anencephaly complicated by acute polyhydramnios and
underscored the need to actively screen for anomalies in
all cases of polyhydramnios.
This current case showed acrania with major low–lying
placenta diagnosed at 13 weeks and a cystic area within
the placenta. Oppenheimer13 also showed images of a
patient with placenta percreta, placenta praevia and
anencephaly. However, whether a relationship exists
between the acrania–exencephaly–anencephaly spectrum
and low–lying placenta is not clear.
Oppenheimer13 further asserted that because of normal
trophotropism and first-trimester migration of the pla-
centa, a diagnosis of placenta praevia should not be made
until after 15 weeks gestation. However, there may be
spontaneous abortion or elective termination in cases of
acrania shortly after diagnosis and before placental mi-
gration has occurred. Therefore, the early diagnosis of
placenta praevia becomes critical to help craft a delivery
plan that prevents maternal haemorrhage.14 In our opin-
ion, therefore, whenever acrania and major low–lying
placenta occur in the same patient, the diagnosis of major
placenta praevia must be made promptly, regardless of
gestational age and without waiting for placental migra-
tion or trophotropism (which may not be allowed to occur
in such a patient). We further assert that such a clear
diagnosis of Major placenta praevia (even when made in
the early second trimester) helps quickly classify the
patient as high risk and appropriate interventions
instituted. The differential diagnoses of acrania include
osteogenesis imperfecta and hypophosphatasia. In both
cases, however, bones are present around the brain but
are poorly mineralized. The presence of other bones with
fractures may also help distinguish acrania from osteo-
genesis imperfecta.15
Management of acrania is generally by elective termina-
tion. However, in all cases, early in - utero diagnosis
helps manage maternal expectations and directs appropri-
ate counselling. In most cases, the prognosis is lethal,
with 65% dying in –utero and 35% dying during delivery.
Short term survival (minutes to days) has also been re-
ported as well as a 2 – 5% recurrence risk in future preg-
nancies.16
CONCLUSION
Detailed ultrasound is required to detect acrania at 13
weeks gestation. The diagnosis of acrania is required to
help direct patient counselling and maternal expectation.
When acrania and major low–lying placenta occur in the
same patient, both diagnoses must be made promptly and
concurrently regardless of gestational age and without
waiting for placental trophotropism and placental migra-
tion to occur first.
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