"I've looked at Scott's brain images," the ER doctor said. "There are several small areas of stroke in many parts of his brain." Our son, an eighth-grade honor student, had awakened that February morning unable to walk or lift his left arm. "OK," I said. What else was there to say? A stroke? He's thirteen. How could he have a stroke? I tried to think past the word "stroke" to useful questions. How many are several? How small is small? What parts of...