Thunderclap headache: diagnostic considerations and neuroimaging features.

Thunderclap headache (TCH) is an acute and severe headache that has maximum intensity at onset; TCH can be primary or secondary. Primary TCH is diagnosed when no underlying cause is discovered; however, imaging is crucial in distinguishing secondary causes, which are wide-ranging. The radiologist should be aware of the list of potential diagnoses. Subarachnoid haemorrhage (SAH) is the most common cause of secondary TCH. Aneurysmal SAH accounts for the majority of cases, although other causes should also be considered and these include perimesencephalic haemorrhage, arteriovenous malformations, and dural arteriovenous fistula as well as reversible cerebral vasoconstriction syndrome. Conditions that may present with TCH, with or without SAH include cervical artery dissection and cerebral venous sinus thrombosis. Ischaemic stroke, pituitary apoplexy, and posterior reversible leucoencephalopathy are other potential causes, whereas non-vascular causes include colloid cysts of the third ventricle and spontaneous intracranial hypotension. Imaging features are reviewed with reference to clues gleaned from initial imaging using computed tomography, as well as characteristics that should be sought using magnetic resonance imaging or angiographic imaging.