Measurement of the Biparietal
Diameter(BPD) and Head Circumference(HC)
The BPD is measured at the level of the thalami and cavum septi pellucidi from
the outer edge of the skull table to the inner edge of the opposite skull
This view may be obtained by
rotating the transducer 90 degrees from alignment with the fetal spine.
The contour should be smooth and oval .
There should be no midline shift.
The ventricular atrium should
less than 10 mm in diameter.
The accuracy of the BPD in the
second trimester is +/- 5 to 7 days.
The HC is measured at the same
level as the BPD measuring from outer skull to outer skull.
The lateral ventricles may be
visualized in a plane superior to the axial BPD view.
Measurement of the lateral ventricles
is made at the level of the atria of the occipital horns.
The third ventricle should appear
as a slit-like structure between the thalami.
Agenesis of Corpus
Information and Pathology SlideSOURCE: PathWeb, University
Information and SonogramsSOURCE: TheFetus.net
Aneurysm of the Vein of Galen
Dilation of vein from A-V malformation may compress the aqueduct.
Membrane lined fluid cavity occurring anywhere within the
brain or spinal cord. The cyst may cause obstructive hydrocephaly. Usually
an isolated finding.
Choroid Plexus Cyst
Cleft Lip and/or Palate
and semilobar forms)
Intracranial Mass and Hemorrhage
Microcephaly may be caused by a teratogen, a chromosomal abnormality, or a genetic defect. The diagnosis of microcephaly and its prognostic significance
for intellectual impairment is more likely to be accurate when the head
circumference is 3 SD or more below the mean for dates.
Calculate Head Circumference Percentile
Localized atrophy causing cystic cavities in cerebral
matter from primary maldevelopment (schizencephaly
or secondary to vascular accident (encephaloclastic porencephaly).
sign" SOURCE: CPDX, Indiana
The posterior fossa is imaged by angling the
transducer from the occipitofrontal plane (BPD view) posteriorly. The image
should contain the cisterna magna, the cerebellar hemispheres, the brainstem,
and the cavum.
(fluid filled space posterior to the cerebellum)
The normal size measured from anterior to posterior is less
than 10 mm.
At about 9-12 weeks the rhombic lips, immediately below the
mesencephalon, fuse to form the vermis medially and the globe-like cerebellar
The process continues inferiorly forming the roof of the
Fusion is observed on ultrasound to be complete in all fetuses
by 18 weeks.
The Fourth Ventricle
Anterior to the cerebellum. Usually unable to visualize unless
Dandy-Walker Malformation (DWM)