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

A new method which facilitates identification of the internal auditory cana l during the middle cranial fossa approach is described. This method uses i llumination of the external auditory meatus as a guide to the internal audi tory canal. When the external auditory meatus is illuminated by a light sou rce system such that used for a flexible fiberscope, areas of the middle ea r 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 b ecause the internal auditory canal is located medial to the attic, and also because such knowledge is helpful in identifying the two conventional land marks of this approach, i.e., the arcuate eminence and the greater superfic ial petrosal nerve, as the locations of these structures are intimately rel ated to the attic. The method described is very simple, timesaving and inex pensive, and is very helpful in detecting the internal auditory canal. Furt her anatomical study is being undertaken to establish a method of pinpointi ng the internal auditory canal, starting from the attic which is readily id entifiable by use of this method. (C) 2000 Tohoku University Medical Press.