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 th e generation of vertical and torsional saccades and gaze holding. Midb rain lesions involving either riMLF or iC produce a tonic torsional oc ular deviation to the contralesional side. Lesions of the iC are assoc iated with an ipsilesional torsional nystagmus (TN). For the first tim e, we describe a patient with a unilateral midbrain lesion showing a c ontralesionally beating torsional nystagmus. This nystagmus was probab ly caused by a lesion involving the riMLF.