Contralesionally beating torsional nystagmus in a unilateral rostral midbrain lesion.

The rostral interstitial nucleus of the medial longitudinal fasciculus (riMLF) and the interstitial nucleus of Cajal (iC) are involved in the generation of vertical and torsional saccades and gaze holding. Midbrain lesions involving either riMLF or iC produce a tonic torsional ocular deviation to the contralesional side. Lesions of the iC are associated with an ipsilesional torsional nystagmus (TN). For the first time, we describe a patient with a unilateral midbrain lesion showing a contralesionally beating torsional nystagmus. This nystagmus was probably caused by a lesion involving the riMLF.