ultrasound diagnosis of fatal anomalies

THE CENTRAL NERVOUS SYSTEM AND THE EYE
References
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with Walker–Warburg syndrome. Gen Diagn Pathol
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congenital inherited cataracts. Ultrasound Obstet
Gynecol 1997; 9: 62–3.
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Microcephaly
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Definition: Microcephaly is defined as severely
reduced head circumference (lower limit 2or
3 SD) in otherwise normal body measurements,
resulting in thoracocephalic disproportion.
The small head circumference is caused
mostly due to insufficient development of the
brain tissue, leading to reduction in brain
volume. A premature synostosis of fetal skull is a
rare cause of microcephaly.
Incidence: One in 6000–10 000 births.
Sex ratio: M:F=1:1.
Clinical history/genetics: It may be inherited as
an autosomal-recessive or dominant trait. Over
300 syndromes have been described in which
microcephaly is an accompanying feature.
Teratogens: Congenital infections, radiation,
various drugs, and alcohol have been implicated
as causal factors. In addition, maternal phenylketonuria
may also cause fetal microcephaly.
Embryology: Microcephaly results from underdevelopment
of the brain tissue. The first prenatal
manifestation of this may be late in the
third trimester, or even after birth.
Associated malformations: Meningoceles and
porencephalic cysts are associated with microcephaly.
Others include holoprosencephaly, intracranial
calcifications, ventricular distension,
lissencephaly.
Depending on the presence of other syndromes,
heart and other anomalies are evident.
Associated syndromes: Cornelia de Lange syndrome,
Seckel syndrome, Smith–Lemli–Opitz
syndrome, Meckel–Gruber syndrome, Miller–
Diecker syndrome, Neu–Laxova syndrome,
Shprintzen syndrome, Walker–Warburg syndrome,
Fancini anemia, Freeman syndrome,
multiple pterygium syndrome, Roberts syndrome,
Wolf–Hirschhorn syndrome (4 p deletion),
cri-du-chat syndrome (5 p deletion), Jacobsen
syndrome (11 q deletion), trisomy 9
mosaic, trisomy 13, arthrogryposis.
Ultrasound findings: The head circumference is
small, whereas the facial structures are normal.
In order to minimize false-positive findings, microcephaly
should only be diagnosed when the
head circumference measures less than three
standard deviations below average. Measurement
of the frontal lobes may help in diagnosis.
Microcephaly cannot always be diagnosed with
certainty before 23 weeks. Repeated controls
maybe helpful. False-positive findings are seen
in up to 70% of cases; this means that in these
cases, there is no evidence of microcephaly postnatally.
Caution: Small head may be a familial condition
and may not be a pathological finding.
Clinical management: Detailed clinical and
family history and exclusion of phenylketonuria
is important. TORCH serology, further sonographic
screening including fetal echocardiography,
karyotyping, possibly magnetic resonance
imaging.
Procedure after birth: Magnetic resonance imaging
may detect associated neural malformations.
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