Introduction: A tubo-ovarian abscess reflects an inflammatory adhesion of pelvic organs including the fallopian tube and ovary forming a palpable complex, which represents the ultimate process of pelvic inflammatory disease (PID). Fistula formation between the sigmoid colon and other pelvic organs such as the bladder, uterus, and ovary is mainly caused by colorectal cancer or diverticulitis. However, cases in which a tubo-ovarian abscess leads to sigmoidal fistula are extremely rare.
Case Report: Here we present a case of sigmoidal fistula secondary to a tubo-ovarian abscess. A 46-year-old premenopausal woman presented with a two-week history of lower abdominal pain. The patient had received antibiotic therapy with the impression of PID at a local clinic prior to presenting to the emergency room, but her symptoms did not resolve. A pelvic examination showed severe tenderness in both adnexal regions but digital rectal examination findings were negative. Computed tomography (CT) scan showed PID with bilateral tubo-ovarian abscesses and an air-containing abscess in the rectovaginal pouch in which a suspicious fistula within the sigmoid colon was noted. Colonoscopy showed continuous excretion of a pus-like substance at the rectosigmoid colon. During the operation, the tubo-ovarian inflammatory complexes and the abscess cavity in the rectovaginal pouch abutting the sigmoid colon were revealed. Total abdominal hysterectomy, bilateral salpingo-oophorectomy, and resection of the sigmoid colon including the affected segment were performed with primary anastomosis.
Conclusion: This case represents an unusual type of sigmoidal fistula caused by a tubo-ovarian abscess and describes its surgical treatment.

Keywords: Colon, Fistula, Pelvic inflammatory disease, Tubo-ovarian abscess