Facial nerve abnormalities after acoustic tumor removal. Morphological and clinical study of seven patients with postoperative facial paralysis.

Operative specimens of the tympanic segment of the facial nerve obtained from seven patients during hypoglossal-facial anastomosis surgery were studied under light and electron microscopy. All patients previously underwent acoustic tumor removal during which the facial nerve was left anatomically intact but attenuated; immediate postoperative facial paralysis was present and persisted. In all specimens, the fascicular area of the nerve had two differing zones: a smaller one with normal-looking populations of myelinated nerve fibers, and a large one with severe reduction of myelinated nerve fibers and an increase of the deposition of endoneurial collagen. The changes indicate that in all cases, the motor fibers have undergone degeneration with subsequent regeneration. However, regeneration has remained incomplete with total lack of normal-sized (7 to 10 micrometers) motor fibers. Incomplete regeneration explains the lack of functional improvement. The structural features of the distal stump of the facial nerve with numerous Schwann's cell tubes were evaluated to provide favorable preconditions for reinnervation through anastomosis. Clinical follow-up of all patients showed varying degrees of functional restoration indicating regeneration.