Pathological features of the facial nerve in patients with facial palsy of varying aetiology. Light and electron microscopic study.

Facial nerve specimens obtained during reinnervation surgery from 31 patients with facial palsy of varying aetiology were studied. In patients who had a facial palsy after attenuation during acoustic schwannoma removal the facial nerve had normal populations of myelinated nerve fibres in the sensory zone but their numbers and sizes were severely reduced and fibrosis was increased in the motor zone. The latter also had large numbers of endoneurial tubes with thin unmyelinated axons. When the facial nerve had been severed in tumour removal, it had practically no remaining nerve fibres. In three out of four patients with middle ear cholesteatoma, the distal facial nerve stump showed severe fibrosis. In patients with iatrogenic trauma and skull fracture, the distal stump usually showed few myelinated nerve fibres, endoneurial tubes with thin unmyelinated fibres and increased fibrosis. The pathological changes observed indicate that in all cases the motor fibres distal to the lesion have undergone Wallerian degeneration and demyelination and in most a subsequent partial regeneration. However, the regeneration remained incomplete. The distal stump of the facial nerve with numerous endoneurial tubes in most cases of the material presented appear to provide favourable structural preconditions for reinnervation surgery.