In recent years, uterine isthmocele has increasingly been included as part of the differential in women with a history of a cesarean section who present with postmenstrual bleeding, pelvic pain, or secondary infertility.
The defect appears as a fluid-filled, pouch-like abnormality in the anterior uterine wall at the site of a prior cesarean section. The best method for diagnosis is usually a saline-infused sonogram. It can be treated in various ways, depending on the patient’s symptoms and desire for future fertility. Although we have treated isthmoceles with hysteroscopic desiccation, or resection, our best success has occurred with laparoscopic resection and reapproximation of normal tissue in a small series of patients.
There is no standard definition of the defect that fully describes its size, depth, and other characteristics. Many words and phrases have been used to describe the defect: It is commonly referred to as an isthmocele, because of its usual location at the uterine isthmus, but others have referred to it as a cesarean scar defect or niche, as the defect may be found at the endocervical canal or in the lower uterine segment. In any case, while diagnoses appear to be increasing, the incidence of the defect is unknown.
More research on risk factors and treatment is needed, but the literature, as well as our own experience, has demonstrated that this treatable defect should be considered in the differential diagnosis for women who have undergone cesarean section and subsequently have abnormal bleeding or staining, pelvic pain, or secondary infertility, especially when fluid is clearly visible in the cesarean section defect.
An isthmocele forms in the first place, it is thought, after an incision scar forms and causes retraction and dilation in the thinner, lower segment of the anterior wall and a thickening in the upper portion. There is a deficient scar, in other words, with disparate wound healing on the sides of the incision site.
The defect and its consequences were described in 1995 by Dr. Hugh Morris, who studied hysterectomy specimens in 51 women with a history of cesarean section (in most cases, more than one). Dr. Morris concluded that scar tissue in these patients contributed to significant pathological changes and anatomical abnormalities that, in turn, gave rise to a variety of clinical symptoms including menorrhagia, dysmenorrhea, dyspareunia, and lower abdominal pain refractory to medical management.
Distortion and widening of the lower uterine segment and “free” red blood cells in endometrial stroma of the scar were the most frequently identified pathological changes, followed by fragmentation and breakdown of the endometrium of the scar, and iatrogenic adenomyosis (Int. J. Gynecol. Pathol.1995;14:16-20).
Several small reports and case series published in the late 1990s offered additional support for a cause-and-effect correlation between cesarean scar defects and abnormal vaginal bleeding. Several years later, the link was strengthened as more investigators reported connections between the defects and various symptoms. These reports were followed by published comparisons of imaging techniques for the diagnosis of isthmoceles.
Diagnosis of the defects can be made with transvaginal ultrasound (TVUS), saline infused sonohysterogram (SIS), hysterosalpingogram, hysteroscopy, and magnetic resonance imaging (MRI). With any modality, imaging is best performed in the early proliferative phase, right after the menstrual cycle has ended.
Comparisons of unenhanced TVUS and SIS – both of which may be easily performed in the office and at a much lower cost than MRI – have shown the latter technique to be superior for evaluating isthmoceles. Distension of the endometrial cavity makes the borders of the defects easier to delineate, which enables detection of more subtle defects and improves our ability to measure the size of defects.
This advantage was described by in 2010 by Dr. O. Vikhareva Osser and colleagues, who performed both TVUS and SIS in 108 women with a history of one or more cesarean sections. They identified more scar defects with SIS than with TVUS (Ultrasound Obstet. Gynecol. 2010;35:75-83).
Another benefit of SIS over TVUS and hysterosalpingogram is that one can measure the thickness of the remaining myometrium overlying the isthmocele, which is especially important knowledge for patients considering another pregnancy. As a result, we have relied on this technique to diagnose every case within our practice. I will perform SIS in a patient who has a history of one or multiple cesarean sections and symptoms of abnormal bleeding, pelvic pain, or secondary infertility as part of the basic work-up.
Similarly, an observational prospective cohort study of 225 women who had undergone a cesarean section 6-12 months prior compared TVUS and gel-infused sonohysterogram (GIS), and found that the prevalence of a niche – defined as an anechoic area at the site of the cesarean scar, with a depth of at least 1 mm on GIS – was 24% with TVUS and 56% with GIS (Ultrasound Obstet. Gynecol. 2011;37:93-9).