Rudimentary horn pregnancy: first-trimester prerupture sonographic diagnosis and confirmation by magnetic resonance imaging.

OBJECTIVE: Two cases of rudimentary horn pregnancy diagnosed in the first trimester by sonography and confirmed by magnetic resonance imaging (MRI) are reported. We suggest criteria for early, prerupture sonographic diagnosis of this rare condition. METHODS: We report a case in which pregnancy in a rudimentary horn was suspected on routine sonographic examination. In the second case, sonographic examination at 11 weeks' gestation revealed a right unicornuate uterus and a noncommunicating left rudimentary horn containing a gestational sac. In both cases, MRI clearly confirmed the sonographic diagnosis, showing an empty cavity of the uterine body and a pregnant uterine horn without an endometrial communication to the uterine body. RESULTS: Both patients underwent surgery, and the pregnant rudimentary horns were resected with no complications. CONCLUSIONS: We suggest the following criteria for sonographic diagnosis of rudimentary horn pregnancy: (1) a pseudopattern of a asymmetrical bicornuate uterus, (2) absent visual continuity tissue surrounding the gestational sac and the uterine cervix, and (3) the presence of myometrial tissue surrounding the gestational sac. Typical hypervascularization of placenta accreta may support the diagnosis. Additionally, MRI can be used to confirm the diagnosis before an invasive procedure is undertaken.