If an mri shows a 1 cm iliac bone lesion that radiologist speculates could be hemangioma, what, if anything, should be done to further define the lesion or follow up? what else could the lesion be?

See an orthopedist: There are several types of lesions that can be included in the differential diagnosis, but generally if the radiologist thinks it is a hemangioma they are correct. Defining this further will depend upon its clinical relevance, risks and cost of procedures (more imaging v. Surgery). Lnfections and lymphangiomatoses may be included in the differential diagnosis.

Use a second modality: I would probably evaluate with a second modality such as plain film and possibly ct to confirm the trabecular pattern of the lesion as typical of a hemangioma.