Transconjunctival approach to the ethmoidal nerve in the cat: a cadaveric study

To describe a new approach to the ethmoidal nerve in cats. Prospective, non-blinded, descriptive, cadaveric study. A total of 13 adult feline cadavers. The course of the ethmoidal nerve through the ethmoidal foramen was initially studied by computed tomography (CT) and dissection in two cat cadavers. The ethmoidal foramen was defined as the target, and an injection technique was proposed using an arc-bent 4.2 mm needle obtained from a 24 gauge venous catheter. A 0.2 mL injection of either methylene blue or radiologic contrast was randomly administered to each peribulbar area of the cat cadaver. Enucleation of the eye that had received methylene blue was performed 5 minutes after injection, followed by a CT scan of the cranium. Primary outcomes measured were staining of at least 6 mm of the ethmoidal nerve and contrast distribution around the ethmoidal foramen. Secondary outcomes assessed potential risks associated with the technique, including presence of contrast within the optic canal, optic nerve staining, ocular globe damage, and evidence of intraconal and intracranial migration. Qualitative data were summarised using frequencies and percentages, and quantitative data as mean ± standard deviation. The technique reached its target in 91% (10/11) of the eyes in both the methylene blue and the contrast groups, with a similar spread pattern observed between them. Optic nerve staining occurred in 55% (6/11) of the methylene blue group, and intraconal migration in 36% (4/11) of the eyes injected with contrast. No intracranial extension or ocular damage were observed. The transconjunctival approach could effectively reach the ethmoidal nerve in cat cadavers.