A 10-yeаr-оld bоy presents аfter wаking with a new оnset of left-sided weakness. He is also experiencing slurring of speech, double vision, dizziness, neck pain, and headache. His cognition is normal. He had been playing hockey on the evening prior to presentation and was struck by a puck on his neck. He has no significant past medical history.On physical examination, blood pressure is 110/60 mmHg, pulse 72/minute, and respirations 16/minute. His heart sounds and breath sounds are normal. The power in the left upper and lower limbs is 3/5, with sensory loss on the left side of the face and arms. What is the most likely cause of this child’s symptoms?