Absence of fetal nasal bone/ hypoplastic nasal bone

  • Presence of nasal bone can be observed on ultrasound as early as 11-12 weeks of gestation. It is visualized in the mid-sagittal section of the fetal face as an hyperechogenic line parallel to the nasal skin;
  • The presence of the well-ossified nasal bone is a reassuring feature as it is associated with a drop in risk of fetal chromosomal anomalies;
  • Absence of (or hypoplastic) nasal bone is found in 0.5-1% of normal fetuses;
  • It is found more commonly among fetuses with chromosomal anomalies:
  1. (i) Downs syndrome: 70%
  2. (ii) Edwards syndrome: 55%
  3. (iii) Patau syndrome: 40%
  4. (iv) Turners syndrome: 9%
  • With the absence of nasal bone, it is important to have an early fetal morphology scan to look for any additional ultrasound markers for chromosomal abnormalities;
  • Isolated absence of nasal bone is associated with a much lower percentage of chromosomal anomalies (0-4.5%) compared with those with the presence of other ultrasound markers/ abnormalities (75-88%);
  • With the absence of nasal bone and the presence of other ultrasound markers/ abnormalities, invasive prenatal diagnosis such as chorionic villous sampling or amniocentesis is advised;
This article is contributed by Dr. T.N. Danny Leung
updated on 25.09.2020