Spatial occupancy of vessels and facial nerve in the facial canal.

The vascularity and spatial relationships of the content of the labyrinthine portion of the facial canal were studied by measuring the diameters of arteries, the areas of the arteries, veins, facial nerve, and canal; and by expressing these areas as percentage of the areas of the facial canal facial nerve. These results were compared for each of these segments of the facial canal. Using temporal bone sections which contained transverse or oblique sections of the three representative (labyrinthine, tympanic , and mastoid) portions of the facial canal, the size of the largest artery, and the area of the sectioned vessels, facial nerve, and facial canal were measured. Relative values of measured areas were calculated as an index of spatial occupancy of vessels and facial nerve in the canal. By comparing these results in three portions, we could demonstrate that, in the labyrinthine portion, the internal diameter of the main artery was less than four tenths of the diameter of the arteries in the other portions, and that the ratio of spatial occupancy of the vessels to the canal and to the nerve in the labyrinthine portion was extremely small compared with that in the other two portions. We also found that the labyrinthine and tympanic portions of the canal have less extra space for the nerve than does the mastoid portion. Considering both the vascularity of the three portions of the facial canal, and the spatial relationships of elements in the canal in each of the three segments of the canal, we feel that the facial nerve in the labyrinthine portion of the facial canal is indeed anatomically the most vulnerable portion of the nerve in its course through the temporal bone.