Diagnostic ultrasound ( PDFDrive )

CHAPTER 45 Neonatal and Infant Brain Imaging 1521
A B C
D
E
FIG. 45.12 Development of Sulci in a Premature Infant Brain. (A) At 24 weeks. No sulci; occipitoparietal issure (arrow) can be seen; corpus
callosum (short arrows) lies above the cavum septi pellucidi and cavum vergae. (B) At 27 weeks. Cingulate sulcus (arrow) is visible. Cavum septi
pellucidi (C), cavum vergae (V), third ventricle (3), and fourth ventricle (4) are shown in this midline sagittal image. (C) At 33 weeks. Cingulate sulcus
(arrow) now has a few branches. (D) At 39 weeks. Cingulate sulcus (medium arrow) has many branches. Cavum vergae (short arrow) is closed;
third ventricle (3) and cerebellar vermis (V) are shown. (E) Cavum veli interpositum (arrow).
he irst sulcus to form is the primitive, almost square, sylvian
issure, best seen on coronal images 31 (see Fig. 45.3C). Later,
ater infolding of the insula (opercularization), the sylvian issure
becomes a narrow, echogenic issure illed with MCA branches. 30,32
Sulcal development, best evaluated on midline sagittal images,
then extends to the calcarine issure as a simple straight line in
the ith gestational month (20 weeks). 33 By 24 to 25 weeks’
gestation, the occipitoparietal issure is present, but no actual
sulci. By 28 weeks, the callosomarginal sulcus over the corpus
callosum and a simple linear cingulate sulcus superior and
parallel to the corpus callosum are seen (see Fig. 45.12B). By 30
weeks, the cingulate sulcus is branched. Between 33 and 40 weeks’
gestation, sulci bend, branch, and anastomose so that a full-term
infant has many peripheral branches over the brain surface (see
Fig. 45.12D).
Although not used routinely, measurement of the subarachnoid
space on a magniied view of the brain can be done from the
triangular sagittal sinus to the surface of the cortex. Armstrong
and colleagues 34 have reported that the subarachnoid space is
normally less than 3.5 mm in 95% of preterm infants before 36
weeks’ gestation. Closer to term, the values tended to be at the
higher end of the range, increasing slightly on a weekly basis,
which suggests that premature infants have reduced brain growth
during extrauterine life.
Cavum Septi Pellucidi and Cavum Vergae
here is one continuous cystic midline structure in the septum
pellucidum during fetal life. he septum contains the cavum
septi pellucidi anterior to the foramen of Monro (see Fig. 45.12)
and the cavum vergae posteriorly. Both parts are normally present
early in gestation, but they close from back to front, starting at
approximately 6 months’ gestation (Fig. 45.13). By full term,
closure has occurred posteriorly in 97% of infants so that there
is only a cavum septi pellucidi at birth. By 3 to 6 months ater
birth, this septum is completely closed in 85% of infants, although
in some the septum remains open into adulthood. 35 In fetal brain
imaging, Callen and colleagues 36 reported that the columns of
the fornix can be mistaken for the cavum septi pellucidi. On
axial views below the frontal horns, the fornix appears as a cystic
structure with a central linear echo. Absence of the corpus callosum
may not be identiied because the fornices are present
and simulate the cavum between the two frontal horns. Careful
evaluation of the inferior position of the fornices below the frontal
horns will avoid this error.
Cavum Veli Interpositi
he cavum of the velum interpositum represents a potential
space above the choroid in the roof of the third ventricle and