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.
Microscopically, the damaged white matter shows axonal swellings. These can occur anywhere but are particularly common in the parasagittal parts of the brain, the corpus callosum, fornix, internal capsule, and the brain stem. Axonal swellings can be detected with H&E and silver stains 15 hours after the injury.