[Idiopathic cranial nerve failure].

Cranial nerve lesions require a thorough diagnostic work-up and known etiologies have to be excluded before the term idiopathic can be considered. The focus of the present review is on idiopathic peripheral facial nerve paralysis (Bell's palsy) for which this terminology has been established. For all other cranial nerve lesions the typical clinical signs, established etiologies and possible diagnostic pitfalls are discussed.