ultrasound diagnosis of fatal anomalies

HOLOPROSENCEPHALY
References
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Holoprosencephaly
Definition: Holoprosencephaly is characterized
by an abnormal separation of the cerebral hemispheres
due to absent or incomplete cleavage of
the brain hemispheres. This results in fusion of
lateral and third ventricles. Depending on the
degree of severity, alobar, semilobar and lobar
forms are identified (see below).
Incidence: One in 5000–10 000 births, but one in
250 embryos.
Sex ratio: M : F = 1 : 3 (alobar); M : F = 1 : 1
(lobar).
Clinical history/genetics: In multifactorial inheritance,
the rate of recurrence is 6%. Autosomaldominant
and autosomal-recessive forms of inheritance
have also been reported. Various syndromes
have been described in addition to chromosomal
abnormalities—for example, structural
anomalies such as 7 q and 2 q deletion.
Teratogens: Alcohol, phenytoin, excessive vitamin
A, diabetes mellitus, congenital infections,
exposure to radiation.
Embryology: Separation of the hemispheres in
the early embryonic stage is absent.
Associated malformations: Heart anomalies (especially
double-outlet ventricle), omphalocele,
Dandy–Walker syndrome, maldevelopment of
the extremities, microcephaly and macrocephaly,
and singular umbilical artery are often
associated.
Associated syndromes: Shprintzen syndrome;
ectrodactyly–ectodermal dysplasia–clefting
(EEC) syndrome; chromosomal abnormality in
up to 70%: trisomy 13, trisomy 18, triploidy, and
various structural aberrations such as 7q deletion.
Ultrasound findings: Early diagnosis is possible
even before 12 weeks (single ventricular cavity
and facial anomalies). In the alobar and semilobar
forms, fusion of the thalami, absence of the
third ventricle, and a single horseshoe-shaped
intracranial ventricle are observed.
The common ventricle flows into a dorsal sac.
The corpus callosum, falx cerebri and interhemispheric
fissure are absent. Facial malformations
are always present—such as hypotelorism,
cyclopia, median facial clefts, and a flat nose
with only one nasal opening. In the lobar form,
the ventricle is fused with the falx in the frontal
region, and the posterior horns of the lateral
ventricle are separated. Hydranencephaly resembles
alobar holoprosencephaly, except for
the presence of the third ventricle and unfused
thalami.
Clinical management: Karyotyping, exclusion of
diabetes mellitus. If the mother continues the
pregnancy, she should be informed about the
poor prognosis so that she can decide about any
interventions that may be necessary during
labor. Vaginal delivery may be impossible due to
the large fetal head. In such cases, cephalocentesis
is indicated. In late pregnancy, development
of hydramnios may cause premature labor
and birth.
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