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FEATURES JULY/AUGUST 2018 37 Head Tilt in Dogs: A Clinical Approach NEUROLOGY Michelle Carnes, MS, DVM, DACVIM (Neurology) Specialists in Companion Animal Neurology, Clearwater and Naples, FL Head tilt in dogs ( FIGURE 1 ) is a clinical presentation that most veterinarians encounter frequently in practice. When a patient presents for evaluation of a head tilt, it can sometimes be challenging to know the best course of diagnostics to recommend and whether or what primary treatment is warranted. Differentiation of the varied clinical presentations of vestibular disease and how they relate to the generation of a list of differential diagnoses can be extremely helpful in providing appropriate primary care and being able to better predict possible outcomes. The primary reason for a dog to exhibit a head tilt is dysfunction of the vestibular system. The vestibular apparatus is responsible for an animal's maintenance of balance and the spatial orientation of the eyes, head, trunk and limbs relative to gravity. From a clinical perspective, it is divided into two components: peripheral, which involves the vestibulocochlear nerve (cranial nerve VIII) and its receptor in the inner ear; and central, which involves the brainstem and sometimes the cerebellum. BASIC REVIEW OF NEUROANATOMY The receptor organ of the vestibular system is located within the petrous temporal bone in the inner ear and consists of the saccule, utricule and crista ampularis within the semicircular canal ( FIGURE 2 ). Through movement of the hair cells bathed in endolymph, the position and movement of the animal as it relates to gravity is detected and then transmitted by cranial nerve VIII (vestibulocochlear nerve) to the vestibular nuclei in the brainstem.1 The vestibular nuclei function to provide output to many other areas of the brain which result in:2 ■ Movement and position of the eyes via the medial longitudinal fasciculus and synapse on cranial nerves III, IV and VI. ■ Provision of extensor tone to the muscles to support the body against gravity via the vestibulospinal tract. ■ Conscious perception of position via the thalamus to the somatosensory cortex of the forebrain. FIGURE 1. Evaluating a Head Tilt Differentiating the varied clinical presentations of vestibular disease can help in providing appropriate primary care.

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