This 13 y/o male was referred to MRI for further evaluation a focal swelling in the upper arm and an abnormal x-ray exam of the humerus. Selected T1 and T2 weighted images shown above demonstrate a broad based exophytic lesion of bone. The marrow space of the bone and the lesion are contiguous. There are areas of T2 brightening at the periphery of the lesion, but without frank invasion of the surrounding tissues. The lesion is consistent with an osteochondroma.