Article
Split facial nerve course in acoustic neuromas
Gedoppelter Verlauf des N. Facialis bei Akustikusneurinomen
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Authors
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C. Strauss
- Department of Neurosurgery, University of Erlangen-Nuremberg, Erlangen
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J. Prell
- Department of Neurosurgery, University of Erlangen-Nuremberg, Erlangen
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B. Bischoff
- Department of Neurosurgery, University of Erlangen-Nuremberg, Erlangen
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J. Romstöck
- Department of Neurosurgery, University of Erlangen-Nuremberg, Erlangen
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R. Fahlbusch
- Department of Neurosurgery, University of Erlangen-Nuremberg, Erlangen
| Published: | May 4, 2005 |
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Outline
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Objective
The facial nerve in acoustic neuromas is located on the ventral tumor surface in more than 90% of the cases. Other courses are extremely rare. A split nerve course with two distinct bundles has not been described so far.
Methods
Between 1996 and 2004 15 cases (six male and nine female patients) out of a series of 212 operated acoustic neuromas, had been observed with a distinct splitting of the facial nerve. The average tumor size in contrast enhanced axial T 1-weighted MRT images measured 26 mm with an average of 3 mm extension into the auditory canal. The fundus of the canal was free of tumor in all cases. All patients were operated upon using a suboccipito-lateral approach. Patients underwent extensive neurophysiological monitoring using 3 EMG-channels for facial nerve monitoring and conventional BAEP for cochlear nerve monitoring. Patients were reevaluated 1 year following surgery including MRT.
Results
In all 15 patients a distinct splitting of the facial nerve could be demonstrated. The major portion of the nerve showed a typical ventral course of the nerve, the smaller portion in all cases ran parallel to the brainstem up to the level of the trigeminal root exit zone and crossed to the internal auditory canal dorsally to the course of the trigeminal nerve in the cranial tumor capsule. Splitting occurred at the root exit zone and the two portions rejoined at the level of the auditory canal. The smaller portion selectively carried fibers to the orbicularis oris muscle, whereas the major portion supplied all three branches of the facial nerve.
Conclusions
In up to one third of acoustic neuromas with little or no extension into the internal auditory canal an aberrant course of the facial nerve with a distinct splitting of the nerve can be expected. Long-term facial nerve results are excellent (HB 1 and 2: 9 cases, HB 3: 3 cases) with sophisticated electrophysiological monitoring. Multiple channel recordings in contrast to the conventional two channel set up help to differentiate and identify aberrant facial nerve fibers, which otherwise can be mistaken for the motor portion of the trigeminal nerve.
