In the early stages of the disease, X-rays reveal changes resembling patchy osteoporosis. As the disease progresses, bone deformity occurs with further loss of bone mass, and in the tubular bones (the long bones of the arms and legs), a concentric shrinkage is often seen which has been described as having a "sucked candy" appearance. Once the cortex (the outer shell) of the bone has been disrupted, and vascular channels may invade adjacent soft tissues and joints. Eventually, complete or near-complete resorption of the bone occurs and may extend to adjacent bones, though spontaneous arrest of bone loss has been reported on occasion. Throughout this process, as the bone is destroyed, it is replaced by angiomatous and/or fibrous tissue.