If a lump above the elbow shows by an ultrasound that it is not a cyst then what is it? what will an mri be able to show?

If it is not: a cyst, then it is a solid mass. There are a variety of possibilities for a solid mass. MRI may be able to narrow down the possibilities, or make a specific diagnosis. For example, if the mass demonstrates fat signal characteristics, it is probably a benign lipoma. Ultrasound cannot provide this kind of soft tissue specificity. MRI also provides superior anatomic delineation.