Ten months after the cesarean section. (a) Transvaginal ultrasonography shows a normal-sized uterus, but a clot-like mass with a low-to-iso-echoic inhomogeneous content, measuring 20 × 15 mm, is shown at a location corresponding to the site of a uterine incision in the vesicouterine pouch. (b) Saline infusion sonohysterography was performed using a physiological saline solution. During the saline infusion the uterine lumen did not expand and a fistula, measuring 4 mm in diameter, was observed (+- - -+). The images show that the physiological saline solution flowed out and spread from the uterine cavity into the peritoneal cavity through the vesicouterine pouch. In addition, the findings show that when the infusion continued, the saline solution accumulated in the Pouch of Douglas (arrow).