Topology of brainstem lesions associated with subjective visual vertical tilt

We aimed to determine the topology of anatomical pathways for verticality perception in the brainstem.

We measured the subjective visual vertical (SVV) in 82 patients with acute unilateral infarction of the brainstem alone. The topology of the brainstem lesions responsible for pathologic SVV tilt were determined using MRI-based voxel-wise lesion-behavior mapping, from which probabilistic lesion maps were constructed.

Fifty percent of patients (41/82) with acute unilateral brainstem infarcts had abnormal SVV tilt, of which 76% (31/41) had ipsiversive tilt and 24% (10/41) had contraversive tilt. Patients with contraversive SVV tilt exhibited overlapping lesions of the rostral medial vestibular nucleus, medial longitudinal fasciculus, rostral interstitial medial longitudinal fasciculus, and interstitial nucleus of Cajal. In contrast, patients with ipsiversive SVV tilt and oculomotor disturbances exhibited lesions of the medial and inferior vestibular nuclei in the caudal medulla, while those with isolated vertical perceptual changes had injury to the medial side of the medial lemniscus.

Our findings provide evidence of a pathway transmitting ipsiversive otolithic signals that bypass the oculomotor system at the medial side of the medial lemniscus, called the ipsilateral vestibulothalamic tract.