Neuroradiological Endovascular Intervention for Diplopia in a Case of Aneurysmal Aberrant Regeneration of the Third Nerve

Aberrant regeneration of the third nerve occurs as a result of synkinetic ‘miswiring’ of the third nerve following its injury, such as in third cranial nerve palsy due to tumor, trauma, or aneurysm. The case presented is an elderly woman with new vertical diplopia, which led to a diagnosis of a third cranial nerve palsy, thought to be caused by a 5 mm blister aneurysm of the posterior communicating artery. However, neuro-ophthalmological evaluation diagnosed aberrant regeneration of the third nerve, with the cause of her new vertical diplopia being an ipsilateral fourth nerve palsy. The patient underwent endovascular treatment of her aneurysm using stent-assisted coiling. This procedure was complicated by an episode of air embolism, from which the patient made a good recovery. This patient’s presentation demonstrates that the cause of any diplopia must be established, and presents a novel, semi-schematic illustration of aberrant regeneration of the third nerve that should aid clinicians in its recognition.