Reversal of cluster headache side following treatment of arteriovenous malformation.

We describe the case of a forty-four year old man who had typical right sided cluster headaches and an arteriovenous malformation supplied mainly by the right anterior cerebral artery. Following endovascular embolisation of this artery the AVM was supplied mainly by the left anterior cerebral artery. Subsequent headaches have always been on the left. Transcranial Doppler studies now suggested an increase of middle cerebral artery flow velocity. We suggest that the change in haemodynamics was responsible for the change in headache side.