Uterine Isthmocele (Cesarean Scar Defect / Uterine Niche)

An isthmocele is a thin area in the uterine wall where a previous cesarean scar did not heal to full thickness. The medical literature also describes it as a cesarean scar defect or a uterine niche. The missing muscle (myometrium) lies in the front wall of the lower uterus. The defect forms a pouch where menstrual blood collects and drains slowly. This pooling causes the classic sign: brown spotting that persists after the period ends.

Blood retained in the niche creates a setting that is hostile to sperm as they pass through. It may also impair implantation of an embryo. In some women, the remaining muscle wall is too thin. In these women, the defect adds to secondary infertility and a higher risk of early pregnancy loss.¹²

Transvaginal ultrasound (TVUS) and saline infusion sonohysterography (SIS) are the preferred first imaging tests. SIS can measure the size of the defect directly. It also measures the amount of muscle that remains (residual myometrial thickness, or RMT). RMT is the most important measure in the decision to repair. Hysteroscopy gives the surgeon a direct view inside the uterus. It can identify and repair the defect in one procedure.³⁴⁵

The choice of repair depends on the severity of the defect, the RMT, and the woman's fertility goals. Hysteroscopic repair treats the defect from inside the uterus. It suits symptom control when the muscle wall is thick enough. Laparoscopic repair removes (excises) the defect and rebuilds the uterine wall in several layers. It is the preferred approach when the wall is weak or when the woman wants a future pregnancy. Complex defects may require both methods at the same time.¹²