Purpose or Case Report: Ulnar hemimelia is a rare congenital disorder characterized by absence of the ulna with an estimated incidence of 1/100,000-150,000 live births. The etiology of this disease remains uncertain, however it is thought that the deformity develops between the 4th and 7th week of gestation. The disease can be either partial or complete, and can be found in isolation or in association with other skeletal dysplasias such as Gorlin-Goltz Syndrome, Cornelia de Lange syndrome, Klippel-Feil syndrome, finger anomalies including syndactyly and oligodactyly. The purpose of this educational review is to describe the characteristic imaging findings of ulnar hemimelia with attention paid to clinically important associated features; review the differential diagnosis for ulnar anomalies; and discuss the range of congenital anomalies that can be associated with this condition. We will also perform a brief review of the literature concerning this rare entity, present two cases of complete ulnar hemimelia with oligodactyly from our institution, and review the various treatment options.
Methods & Materials: This is an educational review which will focus on describing the characteristic imaging findings of ulnar hemimelia; reviewing the differential diagnosis for ulnar anomalies; and discussing the range of congenital anomalies that can be associated with this condition. This discussion will be based on two cases of complete ulnar hemimelia with oligodactyly from our institution. All imaging was reviewed by consensus by two fellowship-trained pediatric radiologists.

Results: Two cases of complete ulnar hemimelia in newborn males are presented. Ulnar hemimelia involves the left arm for both cases; although in cases where only one arm is involved, the right arm is typically more commonly affected. One case demonstrated normal right limb and the other demonstrated additional right limb anomalies. Both patients presented at birth with obvious limb deformities.
Conclusions: Ulnar Hemimelia is a rare disorder with only a few case reports in the literature. Recognition and appreciation of this rare pediatric entity by the radiologist is central for appropriate diagnosis, and will aid in directing a specific search for known associated musculoskeletal syndromes. Current preferred treatment approach consists of physical therapy and surgery to aid in functionality of the affected arm.