Absent nasal bone

Last revised by Jeremy Jones on 20 Sep 2021

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

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Cases and figures

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