Phenotypic characteristics of absent and hypoplastic nasal bones in fetuses with Down syndrome: description by 3-dimensional ultrasonography and clinical significance.
OBJECTIVE
To determine the frequency and clinical significance of bilateral and unilateral hypoplastic nasal bones for the detection of Down syndrome by 3-dimensional ultrasonography.


METHODS
Thirty-seven volumes of the fetal skull from fetuses with Down syndrome and 37 from fetuses without abnormalities were analyzed by 1 investigator blinded to fetal karyotype. The maximum intensity projection algorithm was used to reconstruct nasal bones. Ossification patterns were identified in anteroposterior and profile views. Sensitivity, false-positive rates (FPRs), and likelihood ratios (LRs) for detection of Down syndrome were calculated.


RESULTS
After exclusions (coronal acquisition [n = 11], hand in front of the face [n = 4], poor imaging [n = 2], incomplete follow-up [n = 2], and anomalies detected after delivery [n = 2]), 53 volumes were analyzed (26 fetuses with Down syndrome and 27 without abnormalities; median gestational age, 21 6/7 weeks [interquartile range, 19 6/7-25 2/7 weeks]). Rendered profile views revealed absent nasal bones in 18.9% (10 of 53) of the fetuses, and, among these, 90% (9 of 10) had Down syndrome (sensitivity, 34.6% [9 of 26]; FPR, 3.7% [1 of 27]; LR, 9.3 [95% confidence interval (CI), 1.3-68.7]). Three ossification patterns were identified in anteroposterior views: (1) normally developed, (2) delayed ossification, and (3) absent nasal bones. Sensitivity, FPR, and LR of absent nasal bones for detecting Down syndrome were 34.6% (9 of 26), 3.7% (1 of 27), and 9.0 (95% CI, 1.3-68.7), respectively. Sensitivity, FPR, and LR of delayed ossification for detecting Down syndrome were 42.3% (11 of 26), 22% (6 of 27), and 1.83 (95% CI, 0.8-4.4).


CONCLUSIONS
Absence of nasal bones is associated with the highest risk of Down syndrome. Delayed ossification is associated with a lower risk of Down syndrome than absent nasal bones. These ossification patterns may be indistinguishable on 2-dimensional ultrasonography.
Gonçalves
Luís F
LF
Department of Obstetrics and Gynecology, Wayne State University, Detroit, MI 48201, USA.
Espinoza
Jimmy
J
Lee
Wesley
W
Schoen
Mary Lou
ML
Devers
Patricia
P
Mazor
Moshe
M
Chaiworapongsa
Tinnakorn
T
DeVore
Greggory R
GR
Romero
Roberto
R
D004314:Down Syndrome / Q000000981:diagnostic imaging*; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional; D009295:Nasal Bone / Q000002:abnormalities* / Q000000981:diagnostic imaging*; D010012:Osteogenesis; D010641:Phenotype; D011247:Pregnancy; D016216:Ultrasonography, Prenatal