4 yr old son has recently developed small bump on right wrist , pinky side, outside. Very active, could have mildly sprained it (often get complaints of this or that hurting but never wanting ice for it, for example), and just appeared this evening. No pain, lump moves somewhat freely, is hard and seemingly perfectly round. He has no problems moving his wrist or holding on to anything. Could this be something other than a ganglia cyst?