Need help with abscess found on MRI

they said they found a .9 centimeter abscess and will treat with antibiotics and possible surgery. Dr. also said antibiotics don't heal the abscess just prevent it from spreading.

A couple of things:

a) in the past, doctors treated my abscesses with antibiotics and no surgery
b) if the above is true, how come those previous abscesses didn't show up on the MRI?

Your doctor should not prescribe you antibiotics unless the abscesses are skin-related (boils, HS) and you're on immunosuppressive meds. Antibiotics do not work for abscesses and they should be surgically drained, even when smaller as they could cause systemic symptoms like fever and muscle pain. You should not rely on MRI's for such serious things, I had an abscess not showing up on MRI either.

Same, I've had 2 previous perianal abscesses and they had to be surgically drained both times - antibiotics alone don't work because they can't reach the abscess. My GI drs also usually prescribe the same antibiotics because Crohn's patients tolerate a few better than all the others. The last time they also thought they saw a fistula on the CT scan but it turned out it wasn't there so maybe they read the test results wrong? Regardless, in my experience an untreated abscess can trigger a Crohn's flare for me so if you aren't getting sick then maybe antibiotics alone are working for your situation but across the board abscesses generally need to be drained then a course of antibiotics. If that is the case for you then at least know you it often alleviates the pain and the surgery isn't bad. Good luck!