German sherherd health concern peri fistula's?

You need to discuss the potential treatments with a vet that knows about this condition. It is a fistula, and opening or tract from inside the dog to the outside that isn't a natural opening -- they can be caused by a number of things but the ones I recall were most likely from impacted/infected glands that caused a fistular formation. From what I understand sometimes surgical intervention can help with closure of the fistula - I think this is dependent upon where the fistula opens to though and that is where having an experienced vet to discuss this with is going to be helpful. I don't know why the discussion of hypoallergenic diets along with peri fistulas but eukanuba isn't at all hypoallergenic and actually the eukanuba brand foods I don't like at all.