Table 1 Differential diagnoses for sudden onset headache [2, 4]

• Subarachnoid hemorrhage (aneurysmal, arteriovenous malformation, traumatic, perimesencephalic, unknown etiology)

• Meningitis/encephalitis

• Temporal arteritis/complicated migraine

• Cluster headache

• Reversible cerebral vasoconstriction syndrome

• Acute narrow-angle closure glaucoma

• Hypertensive emergencies

• Acute strokes: hemorrhagic or ischemic

• Carbon monoxide poisoning

• Idiopathic intracranial hypertension (pseudotumor cerebri)

• Spontaneous intracranial hypotension

• Cerebral venous and dural sinus thrombosis

• Mass lesions

• Cervico-cranial artery dissections

• Pituitary apoplexy