Vestibular System Disorders

The vestibular system provides vital sensory information for the control of balance and posture. Vestibular end organs on each side sense linear and angular acceleration in three-dimensional space: the saccule and the utricle (linear motion), and the anterior, posterior and lateral semicircular canals (angular motion) and transduce this information to electrochemical signals. The central nervous system integrates this information from the vestibular system with visual and proprioceptive information to a best possible estimate of the actual movement of the head and body to stabilise gaze during head motion by means of the vestibulo-ocular reflex (VOR) and to control balance by modulation of muscle tone through the vestibulocollic and vestibulospinal reflexes. Disorders of the vestibular system, either peripheral or central, often give rise to the sensory illusion of rotation, vertigo, disequilibrium or imbalance, common symptoms in clinical practice. Key Concepts: The role of the vestibular sensory organs is to transduce the forces associated with head acceleration and gravity into a biological signal. The control centres in the brain use this signal to develop a subjective awareness of head position and head movement in relation to the environment and to produce motor reflexes for equilibrium. The two main motor reflexes are the vestibule-spinal reflex (responsible for the stability of the body) and the vestibule-ocular reflex (responsible for stabilising gaze in space). Pathological dysfunction in the sensory organs or in the central pathways of the motor reflexes lead to the sensation of vertigo. History together with a careful clinical neuro-otological examination are the keys for most vestibular disorders and much more important than recordings of eye movements or brain imaging techniques. Benign positional vertigo is the single most common cause of vertigo that can easily be diagnosed clinically and effectively treated by specific deliberation manoeuvres. Vestibular migraine, a since recently much underestimated disorder, should be suspected when frequent attacks of fully reversible vertigo occur with or without headaches and can be treated successfully with classical migraine medication both for the acute attack as well as prophylactic treatment. Keywords: vestibular system; vertigo; dizziness; postural control; vestibulo-ocular reflex; vestibule-spinal reflex