Diagnostic ultrasound ( PDFDrive )

CHAPTER 34 The Fetal Brain 1169
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m
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B
C
c
D
E
FIG. 34.2 Standard and Additional Planes for Viewing Cerebral Structures. (A) Thalamic view at 20 menstrual weeks. This transverse
view at the level of the diamond-shaped thalamus-hypothalamus complex (t) contains the slitlike midline third ventricle. The echogenic triangular
area behind the thalamus and between the occipital lobes is the ambient cistern (arrow), which contains cerebrospinal luid (CSF) but is rendered
echogenic because of strands of meninges supporting the brain structures. The insula is a short, brightly echogenic line (thick arrow) containing
the pulsating middle cerebral artery branches. It is surrounded by normal white matter that is very hypoechoic and should not be mistaken for luid.
The echogenic band between thalamus and insula is the basal ganglia. Anteriorly are the tips of the anterior frontal horns of the lateral ventricles
(v), and between them is the boxlike cavum septi pellucidi (c). (B) Ventricular view at 18 weeks. The atrium of the occipital horn is illed with
echogenic choroid, and the ventricle measurement is indicated (arrowheads). Note that the choroid ills more than 60% of atrium width. The measurement
between the medial ventricle wall and the choroid is less than 3 mm. The tips of the anterior frontal horns are visible (arrows). c, Cavum
septi pellucidi. (C) Cerebellar view at 18 menstrual weeks is obtained by rotating the transducer from the thalamic view so that the cerebellar
hemispheres (arrows) in the posterior fossa come into view, connected in the midline by the slightly more echogenic and narrower vermis. The
cisterna magna (m) is visible between the cerebellum and the occipital bone. Also visible in this view are the thalamus, third ventricle, anterior
horns, and cavum septi pellucidi. (D) Coronal view at 19 weeks through the coronal suture shows anterior frontal horns (black arrows) and
large nerve trunks; the fornices (white arrows) are clearly visible below the cavum septi pellucidi (c). (E) Midsagittal view through metopic suture
at 19 weeks shows normal corpus callosum (arrows) containing the cavum septi pellucidi in its arc below the corpus callosum. The echogenic
cerebellar vermis is visible posteriorly. (F) Sagittal color Doppler image shows the pericallosal artery. Coronal and median views such as (E)
and (F) are invaluable when there are concerns regarding midline structures.
F
cisterna magna, cavum septi pellucidi (CSP), and frequently
the anterior horns of the lateral ventricles. Up to about 24 weeks,
the transverse cerebellar diameter corresponds to gestational
weeks. he cisterna magna is the cerebrospinal luid (CSF) space
behind the cerebellum and is measured between the cerebellar
vermis and inner occipital bone on an axial plane that includes
the anterior end of the CSP and the midplane of the cerebellum.
It is normally 2 to 10 mm 5,44 (see Fig. 34.2C). Cisterna magna
obliteration suggests Chiari II malformation and spina biida.
Excessive enlargement may be seen with mega–cisterna magna,
Blake pouch cyst, vermian dysplasia, Dandy-Walker syndrome,
and arachnoid cysts. 45-47
Additional sonographic views and projections using the
windows provided by the fontanelles and sutures can help to
clarify brain anatomy and development. he median (midsagittal)
view through the metopic suture–anterior fontanelle–sagittal
suture shows midline structures such as the corpus callosum
and occasionally the cerebellar vermis and brainstem 5 (see Fig.
34.2E-F). he posterolateral mastoid fontanelles can provide
access to the cerebellum and occipital lobes and ventricles.
he sulci and gyri undergo predictable development patterns
that can be assessed as early as 18 weeks. Special views to evaluate
development of sulci and insula can be helpful in detecting
abnormal development such as lissencephaly 48-50 (Fig. 34.4).
Multiplanar three-dimensional (3-D) imaging can be used
to reconstruct axial and median views to assess the brain in any
orientation. Midsagittal reconstructions are especially helpful
in evaluating abnormalities of the corpus callosum and cerebellum.
40,51-53 Head shape and ossiication should be noted with all
these views (see Chapter 33). Although ultrasound is the mainstay