This is a rare anomaly distinct from anencephaly. There is partial
or complete absence of the cranial vault. Brain tissue is always
present but it may be abnormal. Thus the presence of brain tissue
on sonography helps to differentiate from anencephaly.
Acrania is a serious malformation that occurs because of abnormal
migration of mesenchymal tissue, which normally covers the cerebral
hemispheres. This faulty migration results in the faulty formation
of the cranial bones, muscles, and dura mater (7).
The diagnosis of acrania can be established sonographically even
in the first trimester if a large mass of disorganized brain tissue
covered only by a thin membrane is detected (6). 3-D US may contribute
to early detection of fetal acrania (1).
Typically, there is progression in utero from a relatively normal-appearing
brain to an amorphous brain mass to no recognizable brain tissue,
which is the usual US appearance of anencephaly in the second
and third trimesters. In the first trimester, the brain of affected
fetuses may appear relatively normal or may demonstrate varying
degrees of distortion and disruption (exencephaly). However, the
important US feature is an absent cranium, which allows diagnosis
from 11 weeks onward (3, 5). At 11-14 weeks gestation, no vault
ossification is visible. The absence of cranial ossification may
be noted, and the head may appear abnormal. Brain tissue may appear
to be unorganized and have irregular echogenicities. A high percentage
(90%) of fetuses with acrania had echogenic amniotic fluid (4).
The abnormal brain tissue of acrania is destroyed by amniotic
fluid exposure and atrophy and becomes the rudimentary brain found
* Large cephaloceles : in cephaloceles, the cranial vault can
always be detected and a part of the brain is intracranial.
* Anencephaly : cerebral tissue is completely absent.
* osteogenesis imperfecta and hypophosphatasia (6)
Acrania is a lethal malformation. death of the neonate is unavoidable.
Antenatal identification allows the clinician to make appropriate
and timely management decisions.
* 1: Liu IF, Chang CH, Yu CH, Cheng YC, Chang FM. Prenatal diagnosis
of fetal acrania using three-dimensional ultrasound. Ultrasound
Med Biol. 2005 Feb;31(2):175-8.
* 2: Fong KW, Toi A, Hornberger LK, Keating SJ, Johnson JA. Detection
of fetal structural abnormalities with US during early pregnancy.
Radiographics. 2004 Jan-Feb;24(1):157-74.
* 3: Cincore V, Ninios AP, Pavlik J, Hsu CD. Prenatal diagnosis
of acrania associated with amniotic band syndrome. Obstet Gynecol.
2003 Nov;102(5 Pt 2):1176-8.
* 4: Cafici D, Sepulveda W. First-trimester echogenic amniotic
fluid in the acrania-anencephaly sequence. J Ultrasound Med. 2003
Oct;22(10):1075-9; quiz 1080-1.
* 5: Chatzipapas IK, Whitlow BJ, Economides DL. The 'Mickey Mouse'
sign and the diagnosis of anencephaly in early pregnancy. Ultrasound
Obstet Gynecol. 1999 Mar;13(3):196-9.
* 6: Weissman A, Diukman R, Auslender R. Fetal acrania: five new
cases and review of the literature. J Clin Ultrasound. 1997 Nov-Dec;25(9):511-4.
* 7: Bar-Hava I, Bronshtein M, Ornoy A, Ben-Rafael Z. [First trimester
sonographic diagnosis of acrania] Harefuah. 1993 Jun 1;124(11):685-7,