Isolated bilateral abducens nerve palsies caused by the rupture of a vertebral artery aneurysm.

We report two cases with isolated bilateral abducens nerve palsies due to the rupture of a vertebral aneurysm. Surgery revealed that the aneurysm did not directly compress the abducens nerve. Within a year after the subarachnoid hemorrhage, the patients gained full recovery from the bilateral abducens nerve palsies. In view of the clinical and operative findings, it may be regarded as a compression and/or stretching of the bilateral abducens nerves by a thick clot in the prepontine cistern, and not as a manifestation of the raised intracranial pressure. The mechanisms of the isolated abducens nerve palsy are discussed.