Isolated accessory nerve palsy of unusual cause.

We report the case of a 23 year old male patient who presented for an isolated left accessory nerve palsy which had appeared one year before. Neuroradiological investigations showed that the causative pathology was a giant saccular aneurysm of the intracranial left vertebral artery. Three months after diagnosis, signs of bulbar palsy rapidly developed. An emergency intra-arterial embolization was then attempted, which led to complete recovery except for the accessory nerve palsy which remained unchanged. We conclude that, in cases of apparently isolated accessory nerve palsy, neuroradiological investigations should include the posterior fossa.