Anatomy and anaesthesia of the equine external ear canal.

The research article is about identifying accurate landmarks for blocking the internal auricular nerve to achieve efficient anaesthesia of a horse’s external ear canal.

Anatomical Dissection and Sampling

• In this study, the researchers conducted a detailed anatomical dissection of the equine external ear canal and its nerve supply using fifteen horse cadaver heads.
• To further understand the anatomic structure, tissue samples from dissected nerves were extracted from two of the cadaver heads. These samples were prepared and analyzed under microscopes.

Ultrasonographic Evaluation and Simulations

• Before dissection, the researchers made ultrasonographic evaluations of the area of interest. They aimed to use ultrasound images to identify the internal auricular nerve’s entrance point which is formed by the styloid process of the auricular cartilage.
• The authors also simulated local anaesthetic injections using methylene blue injections on ten cadaver heads to verify the success rate of their identified landmarks.

Microdissection and Evaluation of Tympanic Membranes

• The research team obtained and examined the tympanic membranes from three cadaver heads through a specialized method known as microdissection.
• The histological composition of the equine tympanic membrane was also described and illustrated in the study, providing further insights into the anatomy of the equine external ear canal.

Results and Landmarks Establishment

• As a result of the ultrasound imaging, the styloid process was recognized as a thin hyperechoic line 2.17-2.97 cm deep, based on measurements from the skin surface.
• With the findings, the researchers were able to establish reliable landmarks for performing a complete and successful anaesthesia of the external ear canal.
• All ten simulated anaesthesia procedures using methylene blue injections were successful, further validating the identified landmarks.