It could be fissures...fistulas don't really coincide with UC, but they do with crohn's. I just got my summer 2008 journal from the CCFC of which my own GI answers questions in the "Dear Doctor" section (he's one of the top lead researchers for IBD in Canada, Dr. Remo Panaccione)
One of the questions asked was from a UCer that complained of having a fistula (she's 70 yrs old) in his answer to her he states that fistulas are related to crohn's disease, not UC and that every attempt should be made for a correct DX and to review all the previous investigations and perform new investigations (tests) to ensure that it is not crohn's disease...he also does mention that some people can actually have both CD and UC and that a UCer that has their colon removed can infact develop crohn's disease if they happen to have both forms of IBD and were not aware...it's not very common but it is possible.
Fissures can happen with UC or crohn's.
:)