Anatomical and computed tomographic study of equine cervical spinal nerves and intervertebral foramina

BACKGROUND: Osseous enlargement of the cervical articular process joints due to osteoarthropathy or developmental hypertrophy can narrow the intervertebral foramen (IF), resulting in compression and neuritis of the exiting spinal nerves. Associated clinical signs may include neck pain, forelimb lameness or muscle atrophy. Computed tomography (CT) is the gold standard for IF evaluation; however, to date, visualisation of the equine spinal nerves based on CT imaging is insufficient. OBJECTIVES: To improve the diagnostic accuracy of foraminal stenosis and cervical spinal nerve (CSN) compression based on CT, this study aims to describe the anatomical size and position of the CSN at the level of the IF. STUDY DESIGN: Cadaveric study. METHODS: Anatomical dissection was performed to expose the dorsal and ventral rami of CSN3-CSN8 in 10 cervical specimens (n = 88 IF and CSN). Barium sulfate was applied to the nerves, and CT imaging was performed. The cross-sectional area (CSA) of the IF and CSN, the CSN shape and position within the foramen were quantified. RESULTS: Both IF and CSN CSA significantly increased caudally, with the largest values identified at C7-Th1. The ratio of the spinal nerves CSA to IF CSA was significantly higher caudally, suggesting a greater risk of compression in this region. The CSN position within the IF varied between vertebral levels and was positioned in the mid-caudal third of the IF between C3 and C6 and more cranial in the IFs between C6 and Th1. MAIN LIMITATIONS: Ex vivo character of the study and the relatively small sample size. CONCLUSIONS: These findings demonstrate significant anatomical variation in the size, shape and position of the CSN inside the IF depending on the vertebral level. Detailed knowledge of these patterns enables increased diagnostic precision and the development of targeted therapeutic interventions in equine CSN compression.