Absent nasal bone
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In a fetal sonographic assessment, an absent nasal bone is a feature that can sometimes be used as a surrogate marker for fetal aneuploidy.
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.
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
- 1. Kagan KO, Cicero S, Staboulidou I et-al. Fetal nasal bone in screening for trisomies 21, 18 and 13 and Turner syndrome at 11-13 weeks of gestation. Ultrasound Obstet Gynecol. 2009;33 (3): 259-64. doi:10.1002/uog.6318 - Pubmed citation
- 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;358 (9294): 1665-7. doi:10.1016/S0140-6736(01)06709-5 - Pubmed citation
- 3. Cicero S, Longo D, Rembouskos G et-al. Absent nasal bone at 11-14 weeks of gestation and chromosomal defects. Ultrasound Obstet Gynecol. 2003;22 (1): 31-5. doi:10.1002/uog.170 - Pubmed citation
- 4. Has R, Kalelioglu I, Yuksel A et-al. Fetal nasal bone assessment in first trimester down syndrome screening. Fetal. Diagn. Ther. 2008;24 (1): 61-6. doi:10.1159/000132409 - Pubmed citation
- 5. Sepulveda W, Wong AE, Dezerega V. First-trimester sonographic findings in trisomy 18: a review of 53 cases. Prenat. Diagn. 2010;30 (3): 256-9. doi:10.1002/pd.2462 - Pubmed citation
- 6. Martinez-ten P, Adiego B, Perez-pedregosa J et-al. First-trimester assessment of the nasal bones using the retronasal triangle view: a 3-dimensional sonographic study. J Ultrasound Med. 2010;29 (11): 1555-61. J Ultrasound Med (full text) - Pubmed citation