The retronasal triangle (RT) is an ultrasound view of the fetal face taken in the coronal plane, showing three echogenic (bright) structures: the two frontal processes of the maxilla and the nasal bone, forming a triangular shape behind the nose. It is assessed during first-trimester (11–14 week) or early second-trimester scans.

Absence or abnormality of the retronasal triangle is associated with cleft lip/palate and has also been studied as a soft marker for chromosomal abnormalities, since nasal bone and midface development can be affected in conditions like Trisomy 21.

It’s assessed as part of a detailed NT/anomaly scan performed by a trained sonologist – not a routine finding on a basic dating scan.

An absent retronasal triangle typically prompts closer evaluation of the fetal palate and face, and may be factored into overall chromosomal risk alongside other markers.

Limitations:

*Requires a specific imaging plane and operator expertise which not all centers assesses routinely.
*Isolated absence, especially with an otherwise normal detailed scan, has a lower predictive value than when combined with other findings.