Diagnostic ultrasound ( PDFDrive )

CHAPTER
34
The Fetal Brain
Ants Toi and Deborah Levine
SUMMARY OF KEY POINTS
• Protocol-based ultrasound carefully performed
by a knowledgeable and experienced examiner
following established guidelines is very sensitive in
evaluating the central nervous system
(CNS).
• Ventriculomegaly can be due to many underlying
conditions, including obstruction, destruction, and
dysmorphism, or a combination.
• In cases of brain abnormalities in which additional
morphologic or functional information is needed beyond
that available with ultrasound, magnetic resonance imaging
can be helpful.
• Best results in assessment of complex CNS abnormalities
are obtained when there is a multidisciplinary consultation
and collaboration among specialists in imaging, genetics,
and prenatal and postnatal care.
CHAPTER OUTLINE
DEVELOPMENTAL ANATOMY
Embryology
Sonographic Anatomy
Variants (Usually Normal)
Choroid Plexus Cysts
Blake Pouch Cyst
Cavum Veli Interpositi
VENTRICULOMEGALY AND
HYDROCEPHALUS
Pathogenesis of Ventriculomegaly
Ultrasound Evaluation of
Ventriculomegaly
SPECIFIC ABNORMALITIES
ERRORS OF DORSAL INDUCTION
Anencephaly and Exencephaly
Cephalocele and Encephalocele
Ciliopathies
Joubert Syndrome
Meckel-Gruber Syndrome
Amniotic Band Sequence/Limb–Body
Wall Complex
Cranial Changes in Spina Biida
ERRORS OF VENTRAL INDUCTION
Holoprosencephaly
Posterior Fossa and Cerebellum
Dandy-Walker Malformation
Vermis Hypoplasia or Dysplasia
Mega–Cisterna Magna
Rhombencephalosynapsis
Other Posterior Fossa Abnormalities
Arachnoid Cysts
Malformations of Cortical Development
Microcephaly
Macrocephaly and Megalencephaly
Hemimegalencephaly
Lissencephaly
Focal Cortical Changes
Other Malformations of Cortical
Development
Tuberous Sclerosis
Agenesis and Dysgenesis of Corpus
Callosum
Absence of Septi Pellucidi and
Septo-Optic Dysplasia
INTRACRANIAL CALCIFICATIONS
INFECTIONS
VASCULAR MALFORMATIONS
Thrombosis of Dural Sinuses
Hemorrhagic Lesions
Hydranencephaly
TUMORS
CONCLUSION
Acknowledgments
Anomalies of the central nervous system (CNS) are the most
common cause of referral for prenatal diagnosis and result
in great anxiety for parents. CNS anomalies occur with a frequency
of about 1.4 to 1.6 per 1000 live births but are seen in about 3%
to 6% of stillbirths. 1 he increased use of maternal serum alphafetoprotein
(MS-AFP) screening and irst-trimester nuchal
translucency (NT) screening has resulted in increased numbers
of pregnancies being referred for evaluation of the CNS and
suspected anomalies. Fortunately, protocol-based ultrasound
carefully performed by a knowledgeable and experienced examiner
following established guidelines is very sensitive in evaluating
the CNS. 2-6 Routine scanning is currently recommended at 18
to 20 weeks of gestation. Although many cerebral anomalies are
detectable in the irst trimester and early second trimester, others
develop or become apparent only later in pregnancy. 7-11
Magnetic resonance imaging (MRI) has become an important
supplement ater initial ultrasound evaluation. Multiparametric
MRI using special sequences allows evaluation of areas that are
diicult to assess with ultrasound, can be used to evaluate tissue
properties beyond morphology, and provides new insights into
ischemia, tumor characteristics, bleeding, brain metabolism, and
neural tracts, which can allow unprecedented clariication of
suspected disorders. 12-15 Debate continues regarding the role of
ultrasound versus MRI in evaluating the fetal CNS. 16,17 We believe
that ultrasound will continue to be the initial screening modality
and that MRI will increasingly be used to clarify indings. he
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