A 28-year-old male presents to the emergency department 4 hours after a fall from a 15-foot scaffold. He was initially unconscious for 20 minutes, then regained consciousness and appeared well for 2 hours. He now complains of severe headache and is becoming increasingly drowsy. On examination, his right pupil is dilated and sluggish. CT head shows a lens-shaped hyperdensity over the right temporal region with midline shift. Which of the following is the most appropriate next step in management?