[Factors influencing the long-term function of the facial nerve following removal of acoustic neurinomas]

Abstract

Thirty-five cases with removal of acoustic neurinomas were reviewed to demonstrate the factors which influenced the postoperative long term function of the facial nerve. All cases were operated on via a suboccipital route. The group consisted of 7 cases with the tumor confined to the internal auditory meatus, 4 cases with a neurinoma of 20 mm or less in diameter, 13 cases with a neurinoma of 30 mm or less, and 11 cases with a neurinoma over 30 mm. The consistency of the tumors was solid in 27 cases, and cystic in 8 cases. Dislocation of the facial nerve was observed during the operation except in 7 intrameatal cases. The dislocation is summarized as follows: dislocated in the cranial direction in 2 cases, ventrocranial in 7, ventral in 5, ventrocaudal in 10, dorsocaudal in one, and caudal in 3 cases. No case showed dislocation of the facial nerve in the dorsocranial or dorsal direction. Careful observation of the facial nerve at the entrance of the internal auditory meatus showed a severe kinking in 2 cases, moderate kinking in 2, but no kinking at all in the remaining 31 cases. The facial nerve was preserved anatomically in all cases. Long term function of the facial nerve can be summarized as excellent in 18 cases, good in 8 cases, and poor in 9 cases. Three cases showed an almost complete paresis of the facial nerve immediately after the operation and recovery was never observed. Neurinoma facial score was defined in 28 cases, except intrameatal cases, according to the degree of preoperative facial nerve function, tumor size, presence of the cystic component within the tumor, direction of the facial nerve dislocation, and the presence of kinking of the facial nerve. The correlation between the long-term facial nerve function and the neurinoma facial score was statistically examined and was found to be significant (Sperman's correlation coefficient by ranks; rs = 0.38596 > 0.375; P = 0.05). In conclusion, neurinoma cases that show the least facial nerve function are: cases in which facial function had deteriorated, cases in which the tumor was large or when the tumor had no cyst, when dislocation of the facial nerve was in the cranial direction, and in cases where there was kinking of the facial nerve at the internal auditory meatus. In such cases, the removal should be carried out intracapsularly so as to preserve facial nerve bundle which may spread and become flattened like a tumor capsule. This might minimize the postoperative deterioration of the facial nerve function.