The brain is like an apple:
The outside red part of the apple is the brain's gray matter. It consists of the "heads" of the neurons. Damage there means death of the neuron as a whole.
The inner white part of the apple is the brain's white matter. It consists of the neuron's axons, along with their insulation (myelin) and some other kinds of cells. Damage there does not directly kill the nuron.
Of course, not all lesions are real damage. They don't really matter, anyway.
Shortest joke: "We may not be able to cure MS but we can manage its symptoms."