Uterine dehiscence

Cesarean sections (C-sections) are performed in the United States at the rate of 20% to 50% of deliveries depending on clinical environment and demographics. The C-section scar is readily visible sonographically in the nonpregnant uterus as a focal narrowing of the anterior lower uterine segment, which becomes more pronounced with increasing number of prior sections. There is often a small myometrial discontinuity within the scar, seen as a triangular fluid collection or “niche,” likely representing menstrual blood that pools within the defect. Many patients who have had C-sections complain of intermittent intermenstrual or prolonged menstrual bleeding. Uppal and colleagues reported that among 71 patients with a history of C-section, 29 (40%) had a sonographically visible fluid-filled defect in the hysterotomy incision, and the presence of such a defect was significantly associated with prolonged periods or intermenstrual spotting. The incidence of abnormal bleeding was more frequent in patients with larger defects, and the size of the defect or niche was directly related to the number of prior C-sections. Wang and colleagues studied 207 patients with C-section scars and also found that those who had multiple C-sections had larger myometrial defects (width and depth) compared with those with only one prior C-section. Patients with retroflexed uteri also had wider defects than those whose uterus was anteflexed.

The C-section scar defect is a wedge-shaped cystic or hypoechoic area in the anterior lower uterine segment myometrium, directly above the level of the cervix.