Clinical approach and imaging of cortical vestibular disorders

Abstract

The simple classification of vestibular disorders as “peripheral” or “central” disregards a third category: “higher vestibular dysfunctions”. In analogy to disorders of higher visual functions of the “what” and “where” pathways, a new category, namely disorders of higher vestibular functions, which include cognition and other non-vestibular modalities, has been proposed. The dominance of cortical activations of the vestibular network – seen in fMRI and PET studies - reflects several supratentorial neurological disorders involving higher vestibular function. Since they include impairment of spatial orientation, attention, and balance control, they are not only based on vestibular but on integration of multisensory input (visual, vestibular, somatosensory). Four conditions may serve to further elucidate the characteristics of disorders of cortical vestibular function: spatial hemineglect, room-tilt illusion, pusher syndrome, and also impairment of spatial memory and navigation associated with hippocampal atrophy in peripheral bilateral vestibular loss. Spatial hemineglect is a disorder caused by interrupted attention to visual stimuli within one hemifield contralateral to the acute lesion - mostly of the right temporo-parietal cortex. The rare disorder of paroxysmal transient upside-down vision, called the room-tilt illusion, reflects a cortical dysfunction of visual-vestibular interaction due to lesions within the brainstem or even the peripheral labyrinths. The pusher syndrome is characterized by an apparent tilt of the perceived body position in space which the patient attempts to counteract by actively pushing or tilting the body to the contralesional side; causative lesion sites are in the thalamus and posterior part of the insula.