The auditory and vestibular systems share the same end organ and cranial nerve, yet vestibular signs and symptoms are common with stroke, whereas hearing disturbances are much less frequent. Several reasons would appear to account for this striking dissimilarity. One is that the auditory pathway is less ubiquitous than the vestibular pathways (Nieuwenhuys et al., 1988). The likelihood that a stroke involves the auditory pathway is, therefore, less on this basis alone. A second difference, to our knowledge not previously reported, is that the auditory pathway is often spared by the most common strokes. This is because major parts of the auditory pathways, such as the cochlear nucleus, the inferior colliculus and the medial geniculate body have multiple sources of blood supply (Duvernoy, 1978). A third well-recognized factor is the redundancy of the central auditory system and its strong bilateral representation above the level of the cochlear nuclei (Webster, 1992). Consequently, rostral to the cochlear nuclei, gross deficits in hearing, such as measured by standard pure-tone audiometry and speech discrimination only occur if lesions are bilateral. Furthermore, widespread bilateral lesions of the auditory system typically render the patient unable to respond or are incompatible with life. In contrast, language disorders are more frequent because language is usually unilaterally represented in the cortex. Certainly, cerebral stroke often includes the auditory system, resulting in various types of auditory disorders, but most hemispheral lesions produce subtle hearing dysfunctions that can only be detected with sophisticated psychoacoustical and electrophysiological testing.

The purpose of this chapter is to provide an overview of the auditory system and its blood supply and to review how auditory processing can be affected by stroke.