The diagnosis is uterus arcuatus, a malformation of the uterus. Normally, the uterus and upper vagina form from fusion of the paired Mullerian ducts. After fusion, the inner fused walls of the ducts degenerate, leaving the uterine cavity and upper vaginal canal.
Malformations can reflect either incomplete fusion, or failure of septal degeneration.
Total failure of fusion results in duplication of the uterus and vagina. Partial fusion may result in a bicornuate uterus with vaginal septum if severe, or in uterus arcuatus, if mild. Failure of fused Mullerian ducts to undergo septal degeneration may give rise to septate uterus, septate vagina, or both. Any of these defects may be associated with infertility or miscarriage.