Diagnostic ultrasound ( PDFDrive )

CHAPTER 31 Chromosomal Abnormalities 1099
the nuchal fold as a highly reproducible measurement. 100 More
recently, some have suggested that because the nuchal fold
measurement its a log gaussian distribution, it should be evaluated
as a continuous variable and interpreted in the context of
gestation-speciic norms, to allow a more reined method of
risk analysis. 101,102 Numerous investigators have conirmed that a
thickened nuchal skin fold is an important marker for detecting
trisomy 21, and ater more than 30 years, it remains one of the
most important second-trimester markers. 103-109
Trisomy 21: Common Second-Trimester
Sonographic Markers
Nuchal fold
Absent or hypoplastic nasal bone
Short femur
Short humerus
Echogenic bowel
Echogenic intracardiac focus
Urinary tract dilation
Mild ventriculomegaly
FIG. 31.8 Nuchal Fold. Axial scan through the fetal head of a secondtrimester
fetus demonstrating a thickened nuchal fold (calipers), measuring
6 mm.
Facial Proile (Nasal Bone)
he appearance of the fetal nasal bone is an important sonographic
marker utilized for identifying fetuses at increased risk for trisomy
21 110 (Fig. 31.9). he fetal nasal bone is evaluated on a midsagittal
view of the fetal proile. he angle of insonation should be 90
degrees to the longitudinal axis of nasal bone although a slightly
oblique angle (45 or 135 degrees) helps to deine the edges of
the nasal bone more sharply. If the nasal bone is viewed “on
end” (0 or 180 degrees), it will appear erroneously as absent. 111
In 239 fetuses referred for amniocentesis because of a risk of
trisomy 21 of 1 in 270 or greater, Bromley et al. 112 reported that
6 in 16 (37%) fetuses with trisomy 21 did not have a detectable
nasal bone. Of the fetuses with a detectable nasal bone, the mean
length was shorter in those with trisomy 21 than in euploid
A
B
C
FIG. 31.9 Second-Trimester Nasal
Bone Assessment. (A) Midsagittal
proile of an 18-week fetus shows a
normal nasal bone (arrow). (B) Midsagittal
proile of a second-trimester
fetus with an absent nasal bone. (C)
Midsagittal proile of a second-trimester
fetus demonstrates a hypoplastic nasal
bone (yellow arrow).