FCEM2-1235
A 55-year-old man with a history of hypertension presented to the emergency department with a sudden onset severe occipital headache accompanied by vomiting and neck stiffness. There is no reported history of head injury. Upon clinical examination, his temperature is recorded as 37ºC, respiratory rate at 18 per minute, pulse at 88 beats per minute, and blood pressure at 160/100. It is observed that his right eye is laterally and inferiorly deviated, with a dilated pupil and drooping of the right upper eyelid.
Which of the following would be the most appropriate initial investigation?