Recurrent thunderclap headache after endovascular embolization of pial AV malformation by onyx material.

Thunderclap headache is a sudden severe headache with onset to peak within one minute. Multiple excruciating, short-lived thunderclap headaches over a few days to weeks are highly suggestive of reversible cerebral vasoconstriction syndrome (RCVS). RCVS can be primary or secondary to several factors, but it is rarely described after neuro-endovascular procedures using onyx material. A 10-year-old child presented with RCVS heralded by recurrent thunderclap headache following endovascular embolization of pial arteriovenous malformation with onyx material (contains organic solvent dimethyl sulfoxide). Dimethyl sulfoxide is an angiotoxic material that can cause dysregulation of cerebral vascular tone triggering reversible cerebral vasoconstriction syndrome. Recurrent thunderclap headache after embolization procedures using onyx material should prompt for the diagnosis of reversible cerebral vasoconstriction syndrome.