True uterine diverticulum. A partial müllerian duct duplication?

True uterine diverticulum is an exceedingly rare entity. We report only the second case, to our knowledge, of a nulliparous uterus containing a diverticulum communicating with the endometrial cavity. True uterine diverticula probably arise from a localized duplication of the distal Müllerian duct on one side. They may be confused pathologically with uterine sacculations of pregnancy, but tend to have thicker walls. Associated conditions include "ectopic" pregnancy in the diverticulum, dysmenorrhea, and abnormal uterine bleeding.