I'm no doctor. I'm guessing the pain you have is from
the neurofibroma pressing on the sciatic nerve. What
did the lastest MRI show?

This is not the kind of thing Piriformis Syndrome
treatment would work for. The pain will unlikely stop
as long as there is pressure on the nerve. If doctors
won't do surgery & the pain continues, they'll
probably send you to a Pain Clinic where they won't
treat the cause of the pain. (And actually, they will
be ineffective at treating the pain also, unless they
are willing to give you opiods.)

Let us know what the doctor says. Good luck, Mary