Anatomical studies of canine vascular and ligamentous ear structures with revelance to acute-onset deafness

Hearing loss in dogs and cats following dental or ear procedures performed under anesthesia has recently been reported. The most likely causes for this acute-onset deafness were considered to be mechanical or vascular. Jaw manipulation as a possible cause of acute-onset deafness in the dog was investigated in the current study. Structures adjacent to the temporomandibular joint were of interest because changes in jaw orientation could disrupt vessels and nerves in this area. Current descriptions of the anatomy of the vasculature supplying the canine ear are either incomplete or inconsistent. Another considered cause was a jaw-ear connection via a ligamentous remnant of Meckel’s cartilage. A ligament from the jaw to the ear, while recognized in humans, has not been described in the dog. The goal of this research was to provide more accurate anatomical descriptions of relevant canine juxta-articular structures to support future physiological studies. The occurrence of hearing loss in dogs and cats following procedures performed under anesthesia was documented. Occurrence was low, with only 62 identified cases between 2002 and 2009, but the true occurrence may be greater. No relationship was observed between hearing impairment following these procedures and breed, gender, size of dogs, or anesthetic drug used; however, older animals may be more vulnerable. New anatomical variations of three arteries are described in this study. (1) The rostral tympanic artery is a branch of the mandibular ramus and is accommodated by a small foramen located within a depression medial to the temporomandibular joint. (2) A rostral auditory tube branch of the caudal deep temporal artery was identified. (3) The origin of the caudal auricular artery occurred opposite the lingual artery in 25% of dissected specimens, contrary to published descriptions. The rostral tympanic artery and the rostral auditory tube branch may be susceptible to damage during jaw manipulation due to their locations. Variability of the caudal auricular artery can create problems during surgical procedures. The tympanomandibular ligament, a remnant of Meckel’s cartilage and equivalent to the human sphenomandibular ligament, was established as a jaw-ear connection in the dog. Tension on this ligament did not produce malleus movement