Ethmoid adenocarcinoma: Severe neurological complications after combined laser ablation and intralesional formalin injection

An 11‐year‐old Warmblood gelding with chronic bilateral epistaxis was diagnosed with an adenocarcinoma of the right ethmoid, based on transendoscopic biopsy. On computed tomography images, the cribriform plate was considered intact and the tumour was minimally invasive in surrounding tissue. The palliative treatment included a combination of surgical exploration and laser ablation. Following recurrence of the clinical signs one month later, intralesional formalin injection was performed. In the immediate post injection period, the horse developed severe neurological signs. Because of the overall poor prognosis, the horse was subjected to euthanasia. On post mortem examination, changes were seen in the frontal lobe consistent with diffusion of formalin through the cribriform plate. Care is needed when treating horses with intralesional formalin because macroscopic appearance of the cribriform plate may not relate to its functionality.