Diagnostic ultrasound ( PDFDrive )

1150 PART IV Obstetric and Fetal Sonography
A B C
D
E
F
FIG. 33.19 Midface Hypoplasia. A 21-week fetal sonogram (A-D) and magnetic resonance images (E and F) show bilateral cleft lip
and midline incisor. The lat proile of the fetus can be well appreciated on the three-dimensional views (C and D). Proptosis is evident in (D) and
(E).
Absent Nasal Bone
Hypoplastic or absent nasal bone is seen with increased incidence
in fetuses with trisomy 21 and can be evaluated sonographically
in the irst trimester as part of early risk assessment. he fetal
nasal bone is best evaluated in a midsagittal plane at sonography
(Fig. 33.20). Some have found that combining data regarding
the presence or absence of the fetal nasal bone with NT measurements
improves the accuracy of detection of trisomy 21 at
irst-trimester screening. 50 Cicero’s initial study on evaluation of
the nasal bone in irst-trimester examinations found that 73%
of fetuses with trisomy 21 had an absent nasal bone. 50 Other
studies have reported absent nasal bone in 50% to 67% of fetuses
with trisomy 21. 51,52 he absence of a nasal bone at secondtrimester
sonography, or abnormally short nasal bone measurements
in combination with other markers of aneuploidy, increases
detection of aneuploidy. 53,54
It is important to note, however, that accurate sonographic
evaluation of the fetal nasal bone can be technically challenging.
here are speciic guidelines for nasal bone imaging. 55 Studies
have shown that even experienced sonographers need to perform
at least 80 supervised examinations that conform to speciied
FIG. 33.20 Absent Nasal Bone. Proile of third-trimester fetus with
trisomy 13 and absent nasal bone.