AJVR • Vol 77 • No. 11 • November 2016 1245 I n horses, each wing of the atlas is perforated by 2 foramina: the caudal one is the transverse foramen and the rostral one is the alar foramen (Figure 1). 1–3 On the dorsal surface of each wing, the alar foramen is connected with the intervertebral foramen by a short groove. Emerging from the transverse foramen of the axis, the vertebral artery enters the transverse foramen of the atlas; after coursing through the atlan- tal fossa and reception of an anastomotic branch from the occipital artery (ramus anastomoticus cum a. oc- cipitali), the vertebral artery runs dorsally through the alar foramen and enters the vertebral canal through the intervertebral foramen. 1,3 The first cervical nerve originates from the spinal cord and emerges from the vertebral canal through the intervertebral foramen. Its dorsal branch (n. suboccipitalis) passes dorso- laterally and supplies branches to the rectus capitis dorsalis, obliquus capitis cranialis, obliquus capitis caudalis, semispinalis capitis, and splenius cervicis muscles; a cutaneous branch innervates the area lo- Feasibility, repeatability, and safety of ultrasound- guided stimulation of the first cervical nerve at the alar foramen in horses Céline Mespoulhès-Rivière DVM, PhD Olivier Brandenberger DVM Fabrice Rossignol DVM Céline Robert DVM, PhD Justin D. Perkins DVM, MS Jean-Paul Marie MD, PhD Norm Ducharme DVM, MSC From the Equine Clinic (Mespoulhès-Rivière, Brandenberger) and the Department of Anatomy (Robert), Université Paris Est, Ecole Nationale Vetérinaire d’Alfort, 94700 Maisons-Alfort, France; the Veterinary Clinic of Grosbois, Domaine de Grosbois, 94470 Boissy-Saint-Léger, France (Brandenberger, Rossignol); the Department of Veter- inary Clinical Sciences, Royal Veterinary College, Hat- feld, Hertfordshire AL9 7TA, England (Perkins); the Department of Otorhinolaryngology, Head & Neck Surgery, Rouen University Hospital, 76031 Rouen and EA 3830 GRHV (Research Group on Ventilatory Handicap), Institute for Research and Innovation in Biomedicine, Normandy University, France (Marie); and the Department of Clinical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853 (Ducharme). Address correspondence to Dr. Mespoulhès-Rivière (celine.mespoulhes@vet-alfort.fr). OBJECTIVE To develop and assess the feasibility, repeatability, and safety of an ultra- sound-guided technique to stimulate the frst cervical nerve (FCN) at the level of the alar foramen of the atlas of horses. ANIMALS 4 equine cadavers and 6 clinically normal Standardbreds. PROCEDURES In each cadaver, the FCN pathway was determined by dissection, and any anastomosis between the frst and second cervical nerves was identifed. Subsequently, each of 6 live horses underwent a bilateral ultrasound-guided stimulation of the FCN at the alar foramen 3 times at 3-week intervals. After each procedure, horses were examined daily for 5 days. RESULTS In each cadaver, the FCN passed through the alar foramen; a communicat- ing branch between the FCN and the accessory nerve and anastomoses between the ventral branches of the FCN and second cervical nerve were identifed. The anastomoses were located in the upper third of the FCN pathway between the wing of the atlas and the nerve’s entry in the omo- hyoideus muscle. Successful ultrasound-guided electrical stimulation was confrmed by twitching of the ipsilateral omohyoideus muscle in all 6 live horses; this fnding was observed bilaterally during each of the 3 experimen- tal sessions. No complications developed at the site of stimulation. CONCLUSIONS AND CLINICAL RELEVANCE Results indicated that ultrasound-guided stimulation of the FCN at the alar foramen appears to be a safe and straightforward procedure in horses. The procedure may have potential for use in horses with naturally occurring recurrent laryngeal neuropathy to assess reinnervation after FCN trans- plantation or nerve-muscle pedicle implantation in the cricoarytenoideus dorsalis muscle. (Am J Vet Res 2016;77:1245–1251) cated medially to the base of the ear. 1,3,4 The ventral branch of the first cervical nerve, which was of in- terest in the study reported here, passes in the short groove between the intervertebral and the alar foram- ina. 4 The nerve then descends through the alar fora- men in the atlantal fossa where it is connected by 1 or more nerve branches to the cranial cervical ganglion of the sympathetic trunk and also to the hypoglos- sal nerve. The connection between the hypoglossal nerve and ventral branches of the first and the second cervical nerves is described as the cervical loop. The ventral branch of the first cervical nerve crosses over the longus capitis and rectus capitis ventralis muscles and lies lateral to the common carotid artery deep to the parotid gland, then divides into 2 branches. 1 The cranial branch enters the omohyoideus muscle. The caudal branch passes ventrally and caudally under that muscle, unites with a branch of the ventral divi- sion of the second cervical nerve, and continues its course on the ventrolateral surface of the trachea to Unauthenticated | Downloaded 09/26/22 05:34 AM UTC