Delayed malignant appendiceal fistula with ileal conduit following radical cystectomy: A case report.

Fistula formation after radical cystectomy is rare, often presenting early and involving the small bowel. Herein we describe a case of an appendiceal fistula in a patient who underwent chemoradiotherapy and pelvic exenteration over a decade prior to the presentation of their fistula. Initially suspected to be radiation-induced, final pathology revealed a mucinous neoplasm of the appendix, which had fistulized with the ileal conduit. This case emphasizes the importance of considering alternative causes, such as malignancy, in delayed fistulas, especially in patients with prior radiation. Clinicians should maintain high suspicion for appendiceal neoplasms to guide proper preoperative and intraoperative planning.