Fluid On Pelvis?

I have crohns disease for 6 years. The past year it has been very bad. Had to be admitted into hospital for 3 days last week to see diff docs and get a cat scan done asap, tho the cat scan showed fluid on my pelvis, which I never heard of before.

What is this? They nearly didnt let me go home the weekend because of this. I see my crohns doc on wednesday but ive no idea what this is and cant find anything online. They did mention an op to drain the fluid so would this be just a couple of hours in hosp or longer? They seem to think that my intestines that are inflammed are pushin on themselves which is creating the fluid

ive had aches and pains in my pelvis and legs but I just thoguht it was period pains or my crohns or something...

Thanks!!!