2. Cases of complete facial paralysis with complete deafness.
The greater number of middle fossa fractures involve the middle and external ears, as is evidenced, amongst other symptoms, by hæmorrhage from the ear. Some degree of facial paralysis is frequently existent, not always evident at first sight, but requiring careful examination and comparison between the two sides of the face. The fracture involves both roof and floor of the external ear and passes inwards towards the junction of anterior and inner walls of the middle ear, the membrana tympani undergoing a variable degree of destruction whilst the ossicles may also be injured. Thence, the fracture passes inwards towards the petro-sphenoidal suture in such a manner that the geniculate ganglion of the facial nerve is exposed and laid bare on the anterior aspect of the posterior portion of the skull.
The facial nerve, therefore, escapes direct injury except in so far that the ganglion may be compressed by blood-clot or fragments of bone. Partial loss of function results. In most cases the blood is absorbed and a complete recovery may be anticipated. The degree of deafness is directly proportionate to the damage incurred by the membrana tympani and ossicles.
[Illustration: FIG. 39. TO SHOW THE RELATION OF A TYPICAL BASIC FRACTURE TO THE MIDDLE EAR AND ITS ADJUNCTS. A, Malleus; B, Middle ear and aditus; C, Geniculate ganglion (facial nerve); D, Groove for great superficial petrosal nerve; E, Canal for tensor tympani muscle; F, Processus cochleariformis; G, Eustachian tube; H, External auditory meatus; I, Membrana tympani; J, Mastoid cells.]
In the second group of cases a different picture is obtained. Usually the result of blows applied to the occipital region, the fracture traverses the thin cerebellar fossa towards the outer angle of the jugular foramen, thence cutting across the petrous bone, external to the internal auditory meatus, and terminating, usually by comminution, in the tegmen tympani. It is in the transpetrous part of the fracture that the damage is done, for, not only is the facial nerve cut across in the region of the ganglion, but the auditory apparatus is also severed into two parts. The exact line of the fracture is shown in Figs. 40 and 41.