Complete (radical) nephrectomy is surgery to remove all of a kidney. Kidney-sparing surgery (partial nephrectomy) removes part of a kidney.
White matter signal changes on the MRI essentially means that on the MRI, the white matter showed some scattered bright spots. White matter in the brain refers to the fiber tracts that carry information to and fro from the brain. My first question when somebody asks me what next and what does this mean is to ask them why was the MRI done in the first place.
The researchers also examined the brain's white matter - the wiring that transmits messages round the brain. They found that people over 70 who were more physically active had fewer 'damaged' areas - visible as abnormal areas on scanning - in the white matter than those who did little exercise.