My 15 year old son was suffering from ankle/leg pain off and on for 3 months-with the pain being worse at night.All tests came back negative-including bone scan/CT/Mri.A few weeks ago-he had severe back pain-which prompted an MRI of his back.They found a large what appears to be a neurofibroma on the L-4 L5 vertabrae.It measures 4.3 by 4.0 cm. they said surgery comes with risk of losing that nerve-and if it does not bother him-to have it checked periodically for growth.Is this wise? We are scheduled to have a biopsy done soon.Are most of these benign-or can they become cancerous?? He has not had any pain for a few weeks which i do not understand how or why it stopped??? Also-what should we expect from the biopsy? Is there risk-and how will he feel afterwards? Thank-you for any input you can give us.