Q. A 76 year-old man presents with right facial weakness and right side of body weakness (arm worse than leg). His girlfriend accompanies with him. She reports that he does not see doctors and does not take medications. He is a smoker but she is unaware of any other medical comorbidities. Vital signs are normal. On exam, he is unable to speak but can follow simple commands, he has a right facial droop with preserved ability to wrinkle his forehead, preserved visual fields, right upper extremity demonstrates flaccid weakness, right lower extremity has mild weakness. Cardiopulmonary exam is normal. Noncontrast head CT is performed, which is negative for intracranial hemorrhage and is read as normal. Which of the following best explains why the head CT is normal?