lipoma?

I  had a tarsal tunnel release on my left ankle after a 2005 car accident. at the site of incision ( after a sprain on same ankle) a large lump formed . it seems smaller in the morning but swells to golfball size by end of day. painful on ankle and foot (sometimes up leg to knee). MRI reveals lipoma and nerve pressure--it is driving me crazy.  Dr. gave cortisone shots and recommends surgery to remove. will lipoma continue to grow, cause more pain, or destroy compressed nerves if not removed?  could it be something else? Ganglion cyst ruled out prior to this MRI.  It is causing walking problems. any advice or suggestions would be greatly appreciated!   THANK YOU!