4.2\ Scanning of the Fetal Brain at

Thalamus Plane

Fig. 13.16  Section and measurement of biparietal diameter and head circumference at thalamus section. The fetus is in breech presentation. C1, head circumference is

257 mm. A1, biparietal diameter is 71 mm. D1, width of left lateral cerebral ventricle is 4.2 mm. FRONTAL B

frontal bone, S.P. septum pellucidum, THA thalamus, LV left lateral cerebral ventricle, OC occipital bone

OC

LV

T

FRONTAL B S.P.

4.2.1\ Scanning Method

Determine fetal head position according to fetal lie and fetal position at first, and then look for the transverse section across the thalamus in the occipital frontal direction.

4.2.2\ Section Structures

Midline structures including the thalamus, cerebral falx, and septum pellucidum should be shown in this section, as well as bilateral cerebral ventricles, and the white matter and cortex around them. The intact skull ring needs to be shown also, with cerebral falx being in the middle of the

section. The lateral ventricle in the near zone of the image may not be shown very clearly because of reverberation artifacts.

4.2.3\ Measuring Method

Width of posterior horn of lateral ventricle: show the posterior horn of lateral ventricle at thalamus section, and when the posterior horn width at the widest part is measured, the calipers should be placed at the inner edge of both sides of ependyma (Fig. 13.15). Head circumference: circumference­ is measured with the calipers placed along the outer edge of the fetal cranium (Fig. 13.16).

Biparietal diameter: the largest diameter across the midline is measured with the calipers placed at the outer edge of bilateral parietal bones (Fig. 13.16).

4.2.4\ Clinical Significance

(1) The status of cerebral spinal fluid circulation can be learned through measuring the posterior horn width of lateral ventricle, and abnormalities like ventriculomegaly and hydrocephalus can be excluded. (2) There may be measuring errors in biparietal diameter because of molding of fetal head, but it is still used as a correc-

tion index in prenatal serological screening for Down’s syndrome in some laboratories. Head circumference is more objective than biparietal diameter in reflecting the whole outline of the fetal head.

4.2.5\ Normal Reference Values

(1) In normal fetuses, the width of posterior horn of lateral ventricle is smaller than 10 mm. (2) Normal values of biparietal diameter and head circumference change with the growth of gestational weeks.

4.3\ Transverse Scanning of Fetal

Cerebellum

Fig. 13.17  Transverse section of fetal cerebellum in transverse plane of the head, the diameter of the cerebellum, the depth of the cisterna magna, and the thickness of nuchal folder are measured. D1 diameter of the cerebellum, D2 depth of the cisterna magna, D3 thickness of nuchal folder. S.P. septum pellucidum, CP cerebral peduncle, CB cerebellum, PF posterior cranial fossa, NF nuchal folder

S.P.

PF

NF

CB CP

4.3.1\ Scanning Method

Show the transverse plane of fetal head, move the probe downward under the head circumference section, and incline the probe a little to the direction of cranial base, to find out the transverse section across the transverse plane of the cerebellum and septum pellucidum.

4.3.2\ Section Structures

Show the transverse plane of the cerebellum and cisterna magna in the posterior cranial fossa, as

well as the nuchal folder, and the septum pellucidum on the front, with the intact skull ring being shown also.

4.3.3\ Measuring Method

(1) Cerebellum diameter: measure from the outer edge of cerebellar hemisphere of one side to the opposite side. (2) Depth of cisterna magna: measure from trailing edge of cerebellum vermis to inner edge of occipital bone. (3) Nuchal folder thickness: measure from outer edge of occipital

bone to outer edge of neck skin in the cerebellum transverse section, when pregnancy is between 18 weeks and 23 weeks and 6 days.

4.3.4\ Clinical Significance

(1)Cerebellum diameter is an index for estimating the development of the cerebellum and fetus.

(2)Depth of the cisterna magna is helpful in investigating if there is dilatation in the cerebral ventricle system (including cerebral cisterna). And when it is dilated, attentions should be paid to the connection of cerebellum vermis and the

separation of the two cerebellar hemispheres that could be existing, to exclude Dandy-Walker malformations. (3) Nuchal folder thickness is a genetic ultrasound soft marker, reflects the status of fetal lymphatic circulation, and is helpful in detecting fetal hydrops and early heart failure, etc.

4.3.5\ Normal Reference Values

(1) Cerebellum diameter changes with the growth of gestational age. (2) Normal cisterna magna should be smaller than 10 mm. (3) Normal nuchal folder thickness should be smaller than 6 mm.

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4.6\ Sagittal Scanning

of the Fetal Face

Fig. 13.20  Median sagittal section of the fetal face and measurement of the nasal bone length, fetal head, and fetal thorax are also shown. AF amniotic fluid, FB fetal body, NB nasal bone, FH fetal head

NB

FB

YQ. Zhou et al.

AF

FH