Typically, X-rays and MRI are used to evaluate a bone sarcoma. The MRI must include the entire bone and adjacent joint. The differential diagnosis is based on the X-ray. MRI can help with the diagnosis but is more important to show the size and extent of the tumor and proximity to the neurovascular structures. Bone scans can be helpful in determining extent in the bone and presence of any skip metastases (metastatic spread in the same bone or across the joint) or distant metastases to other bones. Sometimes, a CT-PET scan may substitute for the CT scans and bone scan. Bone sarcomas are malignant and can spread to the lungs or to other bones. If the bone sarcoma metastasizes to another bone it will usually be shown on a whole body bone scan.