Computed Tomography Validation of the Technique of Diagnostic Local Analgesia of the Caudal Part of the Infraorbital Nerve and Caudal Nasal Nerve Used for the Investigation of Idiopathic Headshaking in Horses
Authors: Wilmink S., Warren‐Smith C.M.R., Roberts V.L.H.
Journal: Equine Veterinary Journal
Summary
# Editorial Summary: CT Validation of Infraorbital Nerve Blocks in Equine Headshaking Diagnosis Idiopathic headshaking remains diagnostically challenging, and diagnostic local analgesia targeting the caudal infraorbital and caudal nasal nerves is commonly used to help localise facial pain; however, the anatomical accuracy of this technique had never been formally verified. Wilmink and colleagues used computed tomography to assess where contrast medium was actually deposited during this procedure across 60 injections performed by operators with varying experience levels on 30 cadaver heads. Only 53.3% of injections were accurately placed around the target site, but notably the most experienced operator achieved 80% accuracy compared to just 40% in less-experienced practitioners, a significant difference with clear clinical implications. Because false negatives can arise from misplaced anaesthetic rather than absence of facial pain involvement, clinicians must interpret negative responses cautiously and recognise that procedural experience substantially influences diagnostic reliability. For practitioners routinely using this technique to investigate headshaking cases, the findings underscore the value of acquiring genuine competency through supervised practice rather than assuming the procedure yields definitive answers on limited experience.
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Practical Takeaways
- •A negative result from this diagnostic block does not definitively rule out facial pain as a cause of headshaking—failure to place the anesthetic correctly is a common source of false negatives
- •Clinicians should recognize this procedure requires significant practice to achieve reliable accuracy; seek additional training or refer cases to experienced practitioners if unfamiliar with the technique
- •Building competency with this diagnostic block improves clinical reliability and helps avoid missing cases of neuropathic facial pain that could respond to targeted treatment
Key Findings
- •Contrast material was accurately deposited around the target nerve site in only 53.3% (32/60) of injections across all operators
- •The most experienced operator achieved 80% accuracy (16/20 injections) compared to 40% (16/40) for less experienced performers (P<0.05)
- •Negative responses to diagnostic local analgesia of the caudal infraorbital and caudal nasal nerves may represent false negatives due to incorrect needle placement rather than absence of facial pain