Not Just a Cyst: A Draining Gluteal Lesion Revealing a Rectocutaneous Fistula in Ulcerative Colitis

We report a 48-year-old man with poorly controlled ulcerative colitis (UC) who presented with severe rectal pain, hematochezia, and a chronically draining lesion on the left buttock. Initial cross-sectional imaging revealed active colitis, and targeted ultrasound of the left buttock suggested a benign epidermal inclusion cyst. Colonoscopy demonstrated continuous Mayo 3 proctosigmoiditis with a normal proximal colon and terminal ileum. While he clinically improved with intravenous corticosteroids, the gluteal lesion persisted. Before discharge, pelvic magnetic resonance imaging unexpectedly revealed a rectocutaneous fistula extending from the distal rectum into the left gluteal soft tissues. This case illustrates that, although rare, rectocutaneous fistulas can complicate UC. Clinicians should include fistulizing disease in the differential diagnosis of any chronically draining perianal or gluteal lesion in UC, and consider early pelvic magnetic resonance imaging when symptoms are discordant with endoscopic findings or fail to resolve with standard therapy.