A 32-year-old man is brought to the emergency department with a 2-week history of progressive headache, vomiting, and blurred vision. On examination, blood pressure is 160/95 mmHg, and he is drowsy. Fundoscopy reveals bilateral optic disc swelling with obscured margins, retinal folds (Paton's lines), and cotton-wool spots. Visual acuity is 6/6 in both eyes. Pupils are reactive and symmetric with no RAPD. CT head shows enlarged lateral ventricles. What is the most likely diagnosis?