A novel approach for regional anaesthesia of the auricular region in horses: an anatomic and imaging study.

OBJECTIVE

To investigate the anatomy of the ear innervation in horses and develop a new approach for the block of the internal and external pinna and acoustic meatus.

STUDY DESIGN

Prospective, descriptive, cadaveric study.

ANIMALS

A total of 25 heads and necks from horse cadavers.

METHODS

Phase I: anatomical dissection and dye deposition on 19 heads. With the head positioned in lateral recumbency, 10 mL methylene blue (1:1 sterile water) for the internal auricular and 2 mL for the great auricular nerve block were injected in 21 ears (seven left, 10 right and two bilaterally). The anatomy of all the ears (bilaterally) and the accuracy of dye deposition (successful nerve staining defined as > 2 cm) was assessed following dissection. Occurrence of intraparotid, intravascular, or intraneural injection was recorded. Phase II: the same technique and volumes were applied, bilaterally, using a lidocaine 2%:iohexol solution mixture (3:1) in six different cadavers. Computed tomography was performed and the needle position and spread of the mixture evaluated and recorded.

RESULTS

Phase I: Inter- and intraindividual differences were found in the anatomy of the great auricular nerve, but not in the internal and lateral auricular nerve branches and the caudal auricular nerve. No auriculotemporal nerve was found. Nerve staining was successful in 95% of the cases for the great auricular nerve, 85% of the cases for the internal auricular nerve, and 100% of the cases for the lateral auricular branch and caudal auricular nerve. Failure was observed in horses with abundant periauricular fat. No intravascular, intraparotid or intraneural injections occurred. Phase II: A 100% success rate was recorded from computed tomography images.

CONCLUSIONS AND CLINICAL RELEVANCE

The described approach seems suitable for blockade of the sensory innervation of the equine ear.