A new method to identify the internal auditory canal during the middle cranial fossa approach: a preliminary report.

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A new method which facilitates identification of the internal auditory canal during the middle cranial fossa approach is described. This method uses illumination of the external auditory meatus as a guide to the internal auditory canal. When the external auditory meatus is illuminated by a light source system such that used for a flexible fiberscope, areas of the middle ear air cell system are illuminated and observable through the plate of bone constituting the base of the middle cranial fossa. In the case of ordinary pneumatization of the middle ear system, the attic is the site of the most intense illumination. Knowledge of the exact location of the attic obtained by this new method is extremely useful when performing drilling to expose the internal auditory canal in the middle cranial fossa approach. This is because the internal auditory canal is located medial to the attic, and also because such knowledge is helpful in identifying the two conventional landmarks of this approach, i.e., the arcuate eminence and the greater superficial petrosal nerve, as the locations of these structures are intimately related to the attic. The method described is very simple, timesaving and inexpensive, and is very helpful in detecting the internal auditory canal. Further anatomical study is being undertaken to establish a method of pinpointing the internal auditory canal, starting from the attic which is readily identifiable by use of this method.