Perineural Injection of the Ethmoidal Nerve of Horses

Objective To describe the anatomical location of the ethmoidal nerve in the equine periorbital region and to determine the accuracy of a technique used to deposit local anesthetic solution adjacent to the nerve. Study Design Prospective experimental study. Animals Adult equine cadaver heads (n=6 for preliminary dissection; n=15 [30 nerve sites] for evaluation of injection technique). Methods Preliminary dissections were performed to identify landmarks for injection of local anesthetic adjacent to the ethmoidal nerve. For evaluation of the injection technique a 20 gauge 6 cm spinal needle was inserted into the rostromedial aspect of the supraorbital fossa, where the caudal aspect of the zygomatic process emerges from the frontal bone caudal and medial to the globe. The needle was inserted to its hub at an angle of 110° to the long axis of the head using a protractor, in both a sagittal plane and a transverse plane, and 0.5 mL of new methylene blue dye was injected as a marker. The ethmoidal nerve was identified by dissection immediately after each injection and inspected for proximity of the dye. Results Dye was observed surrounding the nerve in 27 of 30 sites (90%) or lying within 5 mm of the nerve at the other 3 sites. Conclusion The described technique of perineural injection of the ethmoidal nerve proved reliable and simple. Anesthetizing the ethmoidal nerve may be helpful in desensitizing portions of the ipsilateral paranasal sinuses and nasal cavity innervated by the nerve when sinonasal surgery is performed in the standing horse.