Are signs of ocular tilt reaction in patients with cerebellar lesions mediated by the dentate nucleus?

A sensitive clinical sign of a vestibular tone imbalance in the roll plane is the ocular tilt reaction (OTR), a combination of skew deviation, ocular torsion and head and perceptual tilts such as tilts of the subjective visual vertical (SVV). Of these OTR components tilts of SVV are the most frequent. While these signs are regularly seen in patients with unilateral brainstem lesions, only a few case studies are available on their occurrence in patients with cerebellar lesions. Thus, the question arises whether cerebellar structures may be involved in contra- and/or ipsiversive tilts of the perceived vertical and other signs of OTR. We used lesion-mapping techniques in a total of 31 patients with acute cerebellar strokes, all showing at least a significant tilt of SVV. Twenty-three patients had a contraversive tilt of the SVV; they were compared with eight patients with ipsiversive tilts. MRI/CT lesion mapping revealed that in patients showing contraversive signs of OTR in general and contraversive SVV tilts in particular the dentate nucleus was the commonly damaged structure. In contrast, in ipsiversive signs of OTR, the dentate nucleus was spared and lesions were located in the biventer lobule, the middle cerebellar peduncle, the tonsil and the inferior semilunar lobule. These data suggest that the dentate nucleus is a critical anatomical structure within the cerebellum, belonging to a network involved in vestibular processing such as the perception of verticality. Therefore, a lesion of the dentate nucleus can lead to tilts of the SVV in the contraversive direction, i.e. a vestibular tone imbalance to the contralateral side, whereas cerebellar lesions excluding the dentate nucleus can induce a tone imbalance to the ipsilesional side.