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Vestibular disease (Proceedings)

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Nov 01, 2010

     • The vestibular system functions to maintain an animal's balance and orientation with respect to gravity
          o Maintains steady visual image by stabilizing the eyes during head movement
          o Maintains steady body position by stabilizing head positioning in space

     • Clinical anatomy
          o Peripheral components – within inner ear, petrous temporal bone, close to CN VII and sympathetic innervation to the face
               ▪ Membranous labyrinth
                     Utricle, saccule – detect gravity and linear acceleration
                     Semicircular canals – detect head rotation
               ▪ Vestibular portion of CN VIII
          o Central components – at the level of the brain
               ▪ Synapses of CN VIII on vestibular nuclei and neurons at rostral cerebellum
               ▪ Connections of vestibular nuclei to:
                     CN III, IV, VI via medial longitudinal fasciculus
                     Descending pathways to spinal cord
               ▪ Important local anatomy
                     Cerebellar peduncles
                     CN V motor and sensory nuclei
                     CN VII motor nuclei
                     Descending motor and ascending sensory pathways
                     Reticular activating system (RAS)

     • Clinical signs
          o Head tilt – named for the most ventral side
          o Circling, leaning, falling and rolling
          o Ataxia – may be asymmetrical, often in absence of weakness
          o Nystagmus – spontaneous, named for the fast phase
          o Strabismus – generally ventral or ventrolateral
          o "Nausea" – hypersalivation, inappetence, vomiting, seen with acute disease

     • Localization
          o Peripheral vestibular disease classically:
               ▪ Head tilt, circling, leaning, falling, rolling TOWARDS side of lesion
               ▪ Nystagmus conjugate, non positional, horizontal or rotary, fast phase AWAY from lesion
               ▪ Strabismus ipsilateral
               ▪ +/- CN VII deficits
               ▪ +/- Horner's syndrome (NOT expected in central disease)
          o Central vestibular disease classically:
               ▪ Head tilt, circling, falling, rolling TOWARDS side of lesion
               ▪ Nystagmus conjugate or non-conjugate, positional or non-positional, horizontal, rotary or vertical, fast phase AWAY from lesion
               ▪ Strabismus ipsilateral
               ▪ +/- Mentation change
               ▪ +/- Asymmetric conscious proprioceptive deficits, paresis, IPSILATERAL
               ▪ +/- Other CN deficits (CN VII, as well as V, IX, X, XI, XII)
               ▪ +/- Overt cerebellar signs (e.g. hypermetria, intention tremor)