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As the story goes with medical terminology, lesions are a simple word with lots of moving parts. In general, a lesion is an area of damage on tissue caused by injury or disease. There are many types of lesions and they can range in size and severity. With MS, lesions appear on the brain and (sometimes) spinal cord—it’s these areas of damaged tissue that result in the signals from your brain not being properly delivered to the rest of your body.