Absent nasal bone
In a fetal sonographic assessment, an absent nasal bone is a feature that can sometimes be used as a surrogate marker for fetal aneuploidy.
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Radiographic assessment
Antenatal ultrasound
It is assessed on a midline sagittal view. In this section, the nasal bone is often seen as a bright echogenic line. It is best visualized at around 11th to 14th weeks of gestation (1st trimester). A magnified image may assist in visualization.
When the mid-sagittal view is difficult to assess, some authors suggest a coronal view of the fetal face to look for paired echogenic structures located at the upper tip of the retronasal triangle 6.
Significance
When the nasal bone is absent at 11 to 12 weeks, while the other ultrasound markers and serum biochemistry are normal; a follow-up scan after a week is suggested.
The incidence of an absent nasal bone is related to nuchal translucency (NT), crown-rump length (CRL), and ethnic origin, as well as aneuploidy. It is more common with increased NT, smaller CRL measurements, and in fetuses of Afro-Caribbean parents.
The reported prevalence range of an absent nasal bone on ultrasound for euploid as well as the following aneuploidy states are
- euploid: nasal bone absent in 0.5-3% 1
- trisomy 21: nasal bone absent in 60-73% 1-3
- trisomy 18: nasal bone absent in 53-57% 1,3
- trisomy 13: nasal bone absent in 32-45% 1,3
- Turner syndrome: nasal bone absent in 9% 3
See also
Related Radiopaedia articles
Ultrasound - obstetric
- ultrasound (introduction)
- obstetric ultrasound
- first trimester and early pregnancy
- ectopic pregnancy
- multiple gestations
- subchorionic hematoma
- failed early pregnancy
-
second trimester
- fetal biometry
- fetal morphology assessment
- fetal echocardiography views
- non-visualization of the fetal stomach
-
soft markers
- nuchal fold thickness
- ventriculomegaly
- absent nasal bone
- choroid plexus cysts
- enlarged cisterna magna
- shortened fetal long bones
- echogenic intracardiac focus (EIF)
- echogenic fetal bowel
- aberrant right subclavian artery
- fetal pyelectasis / fetal renal pelvic dilatation
- single umbilical artery
- sandal gap toes
- amnioreduction
- Doppler ultrasound
- nuchal translucency
- 11-13 weeks antenatal scan
- chorionic villus sampling (CVS) and amniocentesis
- placenta
- other