Katie, There are not always people on here who have had a fistula, so sorry nobody has replied to your particular question.
I believe you are seeing your doctor on the 6th, if I remember rightly, so you should get an answer then. I do know that they do an MRI to see where the fistula is located, its tract if I remember. It is a very good idea and a thorough surgeon would recommend this as a better view of the fistula's direction is found in this way. Fistulas usually follow on from an infection. I did mention on one of your posts as to whether you were taking antibiotics for this, but you did did not reply to the question.
I wish you all the very best with your doctor's appointment. Make sure that he/she answers all your questions; always a good thing to write them down or to have someone go with you.

P.S. We are
all volunteers on here!