My 14-year-old Son Has A Lump At The L-5/S1 Region,

My 14-year-old son has a lump at the L-5/S1 region, 2 inches to the right of the spine. He had a tethered cord surgery 17 months ago, and he has a connective tissue disorder, called Ehlers-Danlos Syndrome. His GP doesn't feel that this isfluid-filled like a cyst, nor is it a lipoma, in his opinon. He said it may be a lump of connective tissue, attached to the bone, because while it moved a bit, it is not as mobile as a lipoma would be. He said it will probably be okay unless it grows larger or creates significant pain. So far, it is not painful. We discovered it several months ago, when rubbing in compounded pain cream to his muscles, but we have no idea how long it has been there. The doctor could not tell us what this was for sure. What does it sound like to you? And, I feel that it should be imaged so we know what we're dealing with. Does anyone have any insight?