Late-onset fistula presenting as buttock abscess in two patients with ileo-anal J-pouches for ulcerative colitis

Two cases are described of patients who presented with a buttock abscess 3 and 5 years after restorative proctocolectomy for ulcerative colitis. In both the abscess was secondary to a fistula, which was shown on further investigation to be a track traversing the greater sciatic notch. Both patients had had an ileo-anal J-pouch after a proctectomy which had included a mesorectal excision. The possibility that these unusual fistulae might be more common following removal of the mesorectum rather than a close rectal dissection is explored.