Otoscopic, cytological, and microbiological examination of the equine external ear canal

Abstract

Otoscopic examination and cytology of the equine ear would be beneficial in diseases such as head trauma, headshaking, otitis externa secondary to otitis media, vestibular disease, aural neoplasia and aural pruritus secondary to parasites. In practice, otic examinations of horses are rarely done due to the perceived difficulty in visualizing the equine external ear canal and tympanic membrane, as well as the need for chemical restraint. In this study, the proximal external ear canal was examined in live horses using a handheld otoscope and in cadaver heads using video otoscopy. Visualization of the proximal ear canal of the sedated horse could be done with a handheld otoscope, but more sedation or general anaesthesia and a video otoscope would be required to adequately visualize the tympanic membrane in the live horse. The proximal ear canals of 18 horses were examined cytologically and cultured aerobically. In three horses, both ears were sampled. No cells or organisms were seen on cytological examination of 11/21 ears. Nine of the 21 ears were sterile when cultured. Ten of the 21 ears had mixed growth with low numbers of organisms (Corynebacterium sp. being most common). Two of the 21 ears had heavy growth of a single organism (Corynebacterium sp. and Staphylococcus intermedius, respectively). Equine cadaver heads were examined in cross-section by computed tomography (CT) imaging and histopathology in order to further understand the anatomy of the equine external ear canal. Equine practitioners should be aware that otic examination is possible and may provide important diagnostic information.

Anatomical Study on the Middle Ear of Donkey (Equus acinus)

“…In contrast with the description of Pracy et al (1998)& Gurr et al (2009 in pig and in sheep they noted the absence of mastoid antrumand only mentioned that the hypotympanicum open in spongy like air cells and cited that the mastoid process wasn't pneumatized. In this respect, Gandhi (1975) in horse denied the air cells in the floor of the middle ear and Sargent et al (2006) reported the relatively smallest size bulla tympanicain horse.…”

Resection of a ceruminous adenocarcinoma in a horse by a modified vertical ear canal ablation

“…), with the osseous component being 2.52–2.65 cm (Sargent et al . ) and there appears to be little difference in size between breeds. Therefore, almost half of the vertical canal was resected in this case, which may be the limit for the procedure to be successful.…”

“…The histological pattern of the mass was similar to an apocrine sweat gland neoplasm but its location in the ear canal identified it as ceruminous in origin (Sargent et al . ; Blanke et al . ).…”

Preliminary investigation into the effects of earplugs on sound transmission in the equine ear

“…The positioning of the microphone was selected in order to minimise variations in microphone position. The osseous section of the external ear canal is a narrow tube with an approximate diameter of 9mm and length of 25mm (Sargent et al 2006). The microphone was selected based on the dimensions of this part of the ear so as to ensure a snug fit.…”

“…The volume settings of the speakers and media player were identical for each cadaver. A microphone 9 , was positioned in the narrow portion of the external ear canal, at the junction between the cartilaginous and osseous regions, (Sargent et al 2006) and connected to a recording device 10 . The positioning of the microphone was selected in order to minimise variations in microphone position.…”