SUSTAINED UTERINE CONTRACTIONS - A CAUSE OF HYPOINTENSE MYOMETRIAL BULGING

Fifteen pregnant women were studied with magnetic resonance (MR) imagi ng. In 14 women, the myometrium exhibited distinct hypointense bulging on T2-weighted images that distorted the gestational sac and decidua but not the outer uterine coutour. In 12 women, an obvious discrepancy was observed between the inner myometrial configuration on T1-weighte d images and that on intermediate and T2-weighted images. In three wom en who underwent serial T2-weighted studies separated by about 30 minu tes during one MR examination, hypointense myometrial bulging was obse rved at a different site on each study. In two women who underwent fol low-up MR study within a week after dilation and curettage, the previo usly distinct hypointense bulging completely disappeared. These findin gs confirm the transient and mobile nature of this myometrial bulging. This phenomenon can be attributed to sustained uterine contractions, which partially force the blood out of the uterus. The decrease in blo od volume results in a decrease in water content, which accounts for t he decrease in myometrial signal intensity on T2-weighted images.