Multiple cranial nerve deficits secondary to a mass lesion of the skull base in a Swiss shepherd dog (Canis lupus familiaris)

A 10‐year‐old, 27 kg, spayed, female Swiss shepherd dog was referred for neurological examination because of a 4‐week history of left eye mydriasis and keratoconjunctivitis sicca, bilateral crusted nasal passages, and progressive left‐sided masticatory muscle atrophy. The neurological examination showed unilateral multiple cranial nerve deficits. Magnetic resonance imaging findings included a mass lesion affecting the sphenoid bones. The intracranial component appeared as an extra‐axial mass primarily affecting the left middle cranial fossa, including the sella turcica, while the extracranial portion caused bilateral obstruction of the nasal passages. This case report highlights the importance of inclusion of skull base mass lesions in the differential diagnosis for multiple cranial nerve deficits in dogs.