Transvaginal ultrasound diagnosis of colouterine fistula secondary to sigmoid colon cancer: A case report.

Colouterine fistula is an exceptionally rare pelvic fistula, typically arising from diverticulitis, malignancy, or trauma.‌ The thick uterine myometrium serves as a natural barrier, rendering direct intestinal invasion of the uterine wall unlikely and thus complicating preoperative diagnosis. ‌Dynamic real-time imaging plays a pivotal role in evaluating such lesions. This case report describes a 74-year-old woman patient who presented with a 1-month history of vaginal flatus and fecaloid discharge. The symptoms were caused by a colouterine fistula secondary to a sigmoid colon malignancy. Gynecological examination confirmed the presence of vaginal flatus and fecal-like discharge. Transvaginal ultrasound revealed a 3 mm wide discontinuity in the left myometrial wall of the uterus, communicating with the sigmoid colon. Dynamic observation demonstrated intestinal gas entering the uterine cavity through the fistula, accompanied by a mobile air-fluid interface and color Doppler twinkling artifact. CT and MRI further confirmed sigmoid colon tumor invasion of the uterine wall with fistula formation. ‌Intraoperatively, the diagnosis was confirmed as sigmoid colon cancer secondary to colouterine fistula.‌ Owing to extensive tumor invasion, only a double-barrel transverse colostomy was performed. The patient experienced an uncomplicated postoperative recovery. ‌This case underscores the value of transvaginal ultrasound in early diagnosis, as it enables noninvasive, dynamic visualization of fistula morphology and gas-liquid flow, serving as a critical adjunct to CT/MRI.