Invasive squamous cell carcinoma causes trigeminal nerve dysfunction in a horse

A 12-year-old Irish Sports Horse gelding was presented for investigation of a 4-month history of recurrent right sided corneal ulceration and sudden onset dysphagia and inappetence. Cranial nerve examination revealed dysfunction of the right oculomotor nerve and trigeminal nerve. Computed tomography of the skull demonstrated a mass in the region of the orbital fissure, in close association with the oculomotor and trigeminal nerves. Following the assessment, the gelding was euthanised and post-mortem examination was performed. Histopathology of the mass confirmed that the tumour was a squamous cell carcinoma. This case report highlights the benefits of detailed clinical examination to localise a neurological lesion, and the need for histology to confirm the diagnosis.