Ultrasound-guided injection of the maxillary nerve in the horse.

ABSTRACT

REASONS FOR PERFORMING STUDY Infiltration of the equine maxillary nerve with local anaesthetic can be useful for both diagnostic and surgical procedures. The deep location and proximity of the nerve to surrounding vascular and orbital structures make an accurate, complication-free injection a challenge using traditional techniques reliant upon surface anatomical landmarks. OBJECTIVES: To develop an ultrasound-guided injection technique of the maxillary nerve in equine cadavers and to evaluate its efficacy and potential for complications in vivo. STUDY DESIGN: Descriptive cadaver anatomical and clinical study. METHODS: The relevant anatomy of the pterygopalatine fossa was reviewed in 6 cadaver heads from mature horses of a range of ages, breeds and genders. In an additional 13 cadaver heads, ultrasound-guided injection of 0.2 ml New Methylene Blue dye was performed on both left and right maxillary nerves (n = 26 attempts) in the pterygopalatine fossa. An independent observer dissected the area and recorded the number of times that dye successfully contacted the nerve, along with inadvertent penetration of other structures. The procedure was then performed on 8 clinical cases undergoing a variety of standing surgical procedures on the head. RESULTS: Dye was successfully deposited in contact with the nerve during all attempts on cadaver heads, with no penetration of the orbital cone, deep facial vein and maxillary artery or associated branches. In a single cadaver, a unilateral gas artefact in the masseter muscle prohibited an injection attempt. Analgesia of the maxillary nerve was achieved in <15 min in all clinical cases, with complete loss of ipsilateral cutaneous sensation over the rostral face. No gross or ultrasonographic abnormalities were detected following the procedure. CONCLUSIONS: Using ultrasonographic landmarks of the pterygopalatine fossa, local anaesthetic can be deposited around the maxillary nerve without the inadvertent penetration of adjacent vital structures. POTENTIAL RELEVANCE The technique allows for vascular structures to be visualised and avoided, which is currently not possible using traditional blind approaches.