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

A 56-year-old man to whom antihypertensive drugs had been administered suddenly felt dizziness and was admitted to our hospital. Magnet resonance imaging showed a small hemorrhagic lesion in the right rostral midbrain. Ocular vergence was intact but vertical gaze was restricted severely downward and moderately upward. The vertical gaze palsy did not change after oculocephalic reflex maneuvers. Forty days after the incident, motility recovered and the patient began to tilt his head to the left. Hess tests started to show skew deviation of right hypertropia, which continued for over 2 years. Funduscopic examination showed left extorsion without right intorsion. From these signs we diagnosed him as having posterior canal type ocular tilt reaction (OTR). The patient course indicated that periaqueductal syndrome was dominant in the acute stage with unilateral symptoms becoming more apparent in the chronic stage. The rostral interstitial nucleus of the medial longitudinal fasciculus (riMLF) and posterior commissure were estimated to be the main causative lesion for symptoms in the acute stage and the interstitial nucleus of Cajal (INC) for the chronic stage. Posterior canal type OTR caused by a unilateral INC lesion has only rarely been reported before.