Vestibular syndromes in the roll plane: topographic diagnosis from brainstem to cortex.

Central vestibular syndromes may be classified according to the three major planes of action of the vestibuloocular reflex, secondary to a lesional tone imbalance in either the horizontal yaw plane or the vertical pitch or roll plane. The clinical signs, both perceptual and motor, of a vestibular tone imbalance in the roll plane are ocular tilt reaction (OTR), ocular torsion, skew deviation and tilts of the perceived visual vertical (SVV). Either complete OTR or skew torsion without head tilt indicates a unilateral peripheral deficit of otolith input or a unilateral lesion of graviceptive brainstem pathways from the vestibular nuclei (crossing midline at the pontine level) to the interstitial nucleus of Cajal (INC) in the rostral midbrain. SVV tilts are the most sensitive sign of a vestibular tone imbalance in roll and occur with peripheral or central vestibular lesions from the labyrinth to the vestibular cortex. All tilt effects, perceptual, ocular motor and postural, are ipsiversive (ipsilateral eye undermost) with unilateral peripheral or pontomedullary lesions below the crossing of the graviceptive pathways. All tilt effects are contraversive (contralateral eye undermost) with unilateral pontomesencephalic brainstem lesions and indicate involvement of the medial longitudinal fasciculus or the rostral midbrain (INC). Unilateral lesions of vestibular structures rostral to the INC typically manifest with deviations of perceived vertical without concurrent eye-head tilt. OTR in unilateral paramedian thalamic infarctions indicates simultaneous ischemia of the paramedian rostral midbrain including the INC. Unilateral lesions of the posterolateral thalamus can cause thalamic astasia and moderate ipsiversive or contraversive SVV tilts, thereby indicating involvement of the vestibular thalamic subnuclei. Unilateral lesions of the parietoinsular vestibular cortex cause moderate, mostly contraversive SVV tilts. An SVV tilt found with monocular but not with binocular viewing is typical for a trochlear or oculomotor palsy rather than a supranuclear graviceptive brainstem lesion.