NORMAL / ABSENT / SHORT NASAL BONE 

 

 

 

  • An increase in the length of the nasal bone throughout pregnancy parallels growth of other fetal parameters especially femur length.
  • Measure the hyperechoic synostosis that joins the left and right nasal bones.
    Nasal bone measured on a strict mid sagittal view of the face, as the inner edge of the nasal bone is shorter than the outer edge due to the trapezoidal shape of the nasal bone. (a measurement more laterally would overestimate the size and overlook hypoplasia) (1).

 

 

 

ABSENCE OF NASAL BONE IN

FETUSES WITH TRISOMY 21 (2) 

 

 

A recent study was undertaken by researchers at King’s College Hospital Medical School to investigate absence of the nasal bone in fetuses with trisomy 21.

Over a ten-month period beginning January 2001, 701 fetuses were examined at a routine ultrasound prior to chorionic villus sampling at 11–14 weeks of gestation.

·        The crown rump length ranged from 45–84 mm, which is in keeping with that suggested for nuchal translucency screening.

·         A fetal profile that enabled establishment of the presence of absence of the nasal bone was obtained in all cases. The optimal plane for nasal bone imaging was a mid-sagittal section with the sound beam perpendicular to the nasal bone. The authors warned that care should be taken not to confuse the echogenic skin surface of the nose with the nasal bone.

·        This study has shown that, at 11 – 14 weeks of gestation:

o       The nasal bone is visible by ultrasonography in 99.5% of chromosomally normal fetuses.

o       The nasal bone was absent in 73% of trisomy 21 fetuses (and in 0.5% of chromosomally normal fetuses), which could be due to hypoplasia or deferred ossification.

o       The likelihood ratio for trisomy 21 was 146 (95% CI 50,434) for absent nasal bone and 0.27 (95% CI 0.18, 0.4) for present nasal bone.

o       This study suggests that sensitivity would be increased from 75% to 85% and that the false positive rate would decrease from 5% to 1% when the fetal profile was included with maternal age and NT measurement.

o        They interpreted that ‘in screening for trisomy 21, examination of the fetal nasal bone could result in major reduction in the need for invasive testing and a substantial increase in sensitivity’.

 

 

  • Small or hypoplastic nose is found in many syndromes including Trisomy 21 and 18, Apert’s Syndrome, de Lange syndrome and fetal toxins.

 

 

 

 

 

 

 

 

 

 

 

 

 

Absent nasal bone –

11 wks of gestation

 

 

 

 

Absent nasal bone

 

 

 

 

Absent nasal bone at 32 wks

 

 

 

 

Depressed nasal bridge on 3D view (same case as above image)

 

 

 

 

 

 

 

 

Hypoplastic nasal bone

 

·        Absent nasal bone and Fragile X Syndrome.

·        Nasal bone may be absent in trisomy 18.

 

 

 

 

 

 

 

Trisomy 18 – Absent nasal bone

 

 

REFERENCES

 

  1. Guis F, Ville Y, Doumerc S et al: Ultrasound evaluation of the length of the fetal nasal bones throughout gestation. Ultrasound Obstet. Gynecol. 1995, 5: 304-307.
  2. Cicero  S, Curcio P, Papageorghiou A et. al.  Absence of nasal bone in fetuses with trisomy 21 at 11–14 weeks of gestation: an observational study. Lancet 2001(November); 358:1665–67