Cesarean delivery is one of the most common surgical procedures in women, with rates of 30% or more in the United States.1 As a result, the rate is rising for cesarean scar defect—the presence of a “niche” at the site of cesarean delivery scar—with the reported prevalence between 24% and 70% in a random population of women with at least one cesarean delivery.2 Other terms for cesarean scar defect include a niche, isthmocele, uteroperitoneal fistula, and diverticulum.1–9
Formation of cesarean scar defect
Cesarean scar defect forms after cesarean delivery, at the site of hysterotomy, on the anterior wall of the uterine isthmus (FIGURE 1). While this is the typical location, the defect has also been found at the endocervical canal and mid-uterine body. Improper healing of the cesarean incision leads to thinning of the anterior uterine wall, which creates an indentation and fluid-filled pouch at the cesarean scar site. The exact reason why a niche develops has not yet been determined; however, there are several hypotheses, broken down by pregnancy-related and patient-related factors. Surgical techniques that may increase the chance of niche development include low (cervical) hysterotomy, single-layer uterine wall closure, use of locking sutures, closure of hysterotomy with endometrial-sparing technique, and multiple cesarean deliveries.3,4 Patients with medical conditions that may impact wound healing (such as diabetes and smoking) may be at increased risk for niche formation.
Viewed hysteroscopically, the defect appears as a concave shape in the anterior uterine wall; to the inexperienced eye, it may resemble a second cavity (FIGURE 2).
Pelvic pain and other serious consequences
The presence of fibrotic tissue in the niche acts like a valve, leading to the accumulation of blood in this reservoir-like area. A niche thus can cause delayed menstruation through the cervix, resulting in abnormal bleeding, pelvic pain, vaginal discharge, dysmenorrhea, dyspareunia, and infertility. Accumulated blood in this area can ultimately degrade cervical mucus and sperm quality, as well as inhibit sperm transport, a proposed mechanism of infertility.5,6 Women with a niche who conceive are at potential risk for cesarean scar ectopic pregnancy, with the embryo implanting in the pouch and subsequently growing and developing improperly.
Read about evaluation and treatment.
