[Relationship between directions of cerebellar retractions and cochlear and vestibular nerve injuries]

It is said that lateral-to-medial retraction of the cerebellar hemisphere is hazardous because, by this retraction, avulsion injury of the cochlear nerve and internal auditory artery may be caused. Caudal-to-rostral retraction of the cerebellar hemisphere is, therefore, recommended in operations in the CP angle such as microvascular decompression procedures. From the results of our present study, however, it can be said caudal-to-rostral retraction can easily cause vestibular nerve damage. However, rostral-to-caudal retraction may damage the cochlear nerve just as lateral-to-medial retraction does. These differences of the eighth nerve injuries according to directions of cerebellar retractions are explicable from the fact that the vestibule and vestibular nerve are located posterior to the cochlea and cochlear nerve. Most of dysequilibrium appearing after manipulations in the CP angle may be due to vestibular nerve damage-avulsion of the vestibular nerve and its accompanying vessels from the vestibular apparatus.