Reversible Cerebral Vasoconstriction Syndrome: an important cause of thunderclap headache.

Reversible cerebral vasoconstriction syndrome (rCVS) is an important cause of acute severe headache that is poorly understood and under-recognised. It typically presents with recurrent thunderclap headaches and is characterised by multifocal, segmental constriction and dilatation of the cerebral arteries, shown by a 'string of beads' appearance, on cerebral angiography. We describe a case of rCVS in a 39-year-old male presenting with post-coital thunderclap headaches following a whiplash-type injury.