BACKGROUND: Appendico-colic fistula is a rare condition characterized by an abnormal communication between the appendix and colon, most commonly involving the sigmoid colon (ie, appendico-sigmoid fistula) because of their close anatomical proximity. It is usually associated with chronic or recurrent appendicitis, diverticular disease, inflammatory bowel disease, or malignancy. Preoperative diagnosis is challenging due to nonspecific clinical and radiologic findings.

CASE REPORT: A 46-year-old woman presented with a 3-month history of lower abdominal pain, which had worsened over the preceding 15 days and was associated with vomiting. Initial contrast-enhanced computed tomography (CECT) suggested sigmoid diverticular perforation with a localized collection. Because of discordant radiologic findings, repeat CECT with rectal contrast was performed, revealing inflammatory changes involving the appendix and sigmoid colon, along with rectal contrast entering the appendiceal lumen; these observations were suggestive of an appendico-sigmoid fistula. Exploratory laparotomy demonstrated a fistulous communication between the tip of the appendix and the sigmoid colon with surrounding inflammatory adhesions. The patient underwent sigmoid colectomy with appendectomy, colorectal anastomosis, and diverting loop ileostomy. Histopathology demonstrated inflammatory changes without evidence of diverticula or malignancy. The postoperative course was uneventful, and ileostomy reversal was performed after 2 months.

CONCLUSIONS: Appendico-colic fistula is a rare complication of chronic or recurrent appendicitis that can mimic sigmoid diverticular perforation. Careful interpretation of imaging, particularly CECT with rectal contrast, is important for diagnosis. Surgical management should be individualized according to the underlying etiology and intraoperative findings.

Keywords: appendicitis, Case Reports, complications, Fistula, Gastroenterology, Sigmoid Colon