Isolated sixth nerve palsy from hemorrhage of a pontine cavernous malformation.

A 32-year-old woman who developed binocular horizontal diplopia was found to have an isolated fascicular sixth nerve palsy secondary to hemorrhage of a cavernous malformation within the left pontine tegmentum. There was sparing of the paramedian pontine reticular formation and absence of a horizontal gaze palsy. The natural history of cavernous malformations and a mechanism by which hemorrhage of these vascular lesions may produce minimal neurologic signs, including isolated ocular motor cranial nerve palsies, is discussed. Magnetic resonance imaging (MRI) that includes susceptibility-weighted sequences leads to their accurate diagnosis.