Posterior canal-type ocular tilt reaction caused by unilateral rostral midbrain hemorrhage

A 56-year-old man receiving treatment for hypertension experienced sudden-onset dizziness and was admitted to our hospital. Computed tomography of the brain revealed a small high-density lesion in the right rostral midbrain. Subsequent magnetic resonance imaging revealed a small hemorrhagic lesion in the same position. The patient complained of double vision affecting the right side when viewing a horizontal linear target. Vergence was intact, but vertical gaze was severely restricted downward and moderately restricted upward. Vestibulo-ocular reflex maneuvers did not alleviate the patient's vertical gaze palsy. By 40 days after the incident, his motility had recovered and he could begin to tilt his head to the left. Consecutive Hess tests demonstrated a skew deviation of right hypertropia, which continued for over two years. Funduscopic examination revealed left extorsion but no right intorsion. A diagnosis of posterior canal-type ocular tilt reaction (OTR) was made from these signs. The patient's course indicated that periaqueductal syndrome dominated in the acute stage whilst unilateral symptoms became more apparent in the chronic stage. The rostral interstitial nucleus of the medial longitudinal fasciculus and the posterior commissure were estimated to contain the main causative lesion for the acute symptoms, whereas the interstitial nucleus of Cajal (INC) was implicated in the chronic stage. Posterior canal-type OTR caused by unilateral INC lesion has been reported only rarely.