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Headshaking in horses is commonly a clinical sign of a facial dysaesthesia (abnormal sensation), suspected to be due to a neuropathy of the maxillary branch of the trigeminal nerve (Newton and others 2000, Roberts 2011, Roberts and others 2013, Pickles and others 2014). A diagnosis of facial dysaesthesia can be made by observing a marked decrease in headshaking in response to local anaesthesia of the innervating sensory nerves (Roberts and others 2013, Pickles and others 2014).
Where no cause of this facial dysaesthesia can be identified on endoscopy, imaging of the head, ophthalmological and dental examination the dysaesthesia is likely to be neuropathic (Newton and others 2000, Roberts and others 2013).
The maxillary nerve exits the brain via the round foramen, runs cranially and enters the maxillary foramen into the infraorbital canal to become the infraorbital nerve. The infraorbital nerve innervates the upper check teeth and the skin of the muzzle. The caudal nasal nerve (CNN) branches off the maxillary nerve just proximal to the maxillary foramen and enters the caudal nasal foramen before running towards the dorsal meatus of the nasal cavity to innervate the nasal mucosa (Dyce and others 2002). In previous articles, the CNN has been called the ‘posterior ethmoidal nerve’ (Newton and others 2000, Roberts and others 2013), but due to possible confusion with the ethmoidal nerve which branches of the ophthalmic nerve rather than the maxillary nerve, we will refrain from using this term.
Local anaesthesia of the infraorbital nerve as it leaves the infraorbital canal resulted in a decrease in headshaking in 3/19 (16 per cent) horses only (Mair 1999). However, local anaesthesia applied around the maxillary nerve at the location of the maxillary foramen resulted in a marked decrease in headshaking in 11 of 17 …