Cesarean scar niche refers to myometrial defect and tethering of the endometrium in the region of the old cesarean scar. It can have different shapes but are most commonly semicircular or triangular. Blood may persist in the niche after menstruation and may serve as a source of dysfunctional uterine bleeding.

The differential diagnosis for fluid-filled cesarean niche includes nabothian cysts, prominent vessels and small fibroids.