My 9 Year Old Grandson Was Diagnosed With A Aneurysmal

My 9 year old grandson was diagnosed with a aneurysmal tumor. He has had a x-ray and CT Scan with contrast. He has also had a CBC and everything looked good. Radiologist and Oncologist says things look ok, but the radiologist saw some "Mass" "Soft Tissue" growing around the tumor and wants to do an MRI with and without contrast. I'm so worried and want to know what this could be. Would they already know with x-ray and CT scan if he has cancer? I cannot eat or function because of worry and thought maybe you could ease my mind. Thank you!