Teaching Video NeuroImage: Unilateral Gaze Palsy With Nystagmus and Facial Weakness

A 27-year-old man presented with 6 months of binocular horizontal diplopia worsening over 2 weeks. Examination (Video 1) showed near complete inability to look to the left with left-beating nystagmus. He was orthotropic on alignment testing in primary gaze. There was mild left facial weakness with nasolabial fold flattening. MRI revealed left pontine cavernoma with small area of acute hemorrhage (Figure). Horizontal gaze palsy with ipsilateral facial weakness localizes to the sixth nerve nucleus and encircling facial nerve fascicles1; esotropia is minimal unlike fascicular sixth nerve palsy. Involvement of the horizontal gaze integrator/nucleus prepositus hypoglossi accounts for horizontal nystagmus.