Radial ray defects (RRDs) encompass partial or complete absence of the radius and/or radial ray structures. The radial ray gives rise to the first carpal and metacarpal bones, and the phalanges of the thumbs.
The use of 3-D ultrasound facilitates the diagnosis of RRD, even at early gestation, by providing a better surface appearance, panoramic views, and spatial orientation.
The incidence is approximately 1:30,000 live birth. Most defects are bilateral and sporadic, while bilateral defects are more likely a part of a multiple malformation syndromes. Isolated RRD comprises 8%–30% of the cases, and the majority of the cases are associated with other anomalies, such as trisomy 13, 18, and 22q 11.2, and anomalies, such as VACTERL associations, Holt-Oram, Fanconi anemia, and thrombocytopenia with absent radius (TAR). Detailed ultrasonography, including 2-D or 3-D imaging, offers an opportunity to better appreciate subtle anomalies.
Cytogenic studies using cord blood helps.