Below and anterior to the facial nerve through the promontory. The preliminary steps of the operation having been performed and the field of operation freely exposed, the stapes, if still present, is extracted by means of a small hook passed between its crura. The bridge of bone between the fenestra ovalis and fenestra rotunda is then cut through by light taps on a very fine gouge. The bone is removed by attacking the lower limit of the fenestra ovalis, and working downwards until the fenestra rotunda is reached. With a fine curette or scoop the loosened fragments of bone are removed. Care must be taken not to work above the region of the fenestra ovalis or the facial nerve will probably be injured. After a sufficient opening has been made, a bent probe can be passed through the opening in the promontory in an upward and backward direction behind the facial nerve into the inferior and anterior portion of the vestibule (Fig. 241).
Removal of the cochlea. If necessary, the first turn of the cochlea can now be removed by gouging away the promontory from behind forwards. If the anterior wall of the external auditory canal interferes with this being done, it may be partially removed by means of the gouge and mallet. After the first half-turn of the cochlea has been opened, its contents may be curetted out, care, however, being taken to avoid the carotid canal, which lies in close relationship with its anterior inferior portion. If the bone be carious only gentle curetting is necessary. If, however, this be not the case, simple curetting may not be sufficient, and the gouge and mallet may have to be used. To destroy the cochlear nerve, the whole of the cochlea should be removed. This is sometimes a difficult matter to determine. If the operation be done for the relief of tinnitus, then, after as much as possible of the cochlea has been removed, the interior may be swabbed out with strong carbolic acid solution, which should set up sufficient inflammatory reaction to destroy the nerve-terminals.
Fig. 242. Extirpation of the Labyrinth. The vestibule is freely opened and the greater portion of the semicircular canals and cochlea is removed.
Extirpation of the labyrinth. This consists in the removal of the semicircular canals, and opening of the vestibule and cochlea, the steps of which have already been described in the above operations.
Before the operation is completed, the inner wall of the vestibule and the cochlea should be carefully examined for fistulæ, and in order to see if any pus enters these cavities from within. If this be the case it means that, in addition to labyrinthine suppuration, there is presumably an extra-dural abscess of the posterior intracranial fossa, drainage of which is essential in order to obtain a recovery.
After the operation has been completed, the cavity should be filled with hydrogen peroxide, then gently syringed out with weak biniodide solution, and finally dried and lightly packed with sterilized gauze.
Even although the operation may have been performed in a non-suppurative case, it is wiser to leave the posterior wound open for the first few days in order to permit of free drainage.
After-treatment. If the suppuration has been limited to the internal ear, a successful result may be expected if the symptoms subside rapidly as a result of the operation. If there be complete destruction of the labyrinth before operation its performance should give rise to no symptoms of shock nor further disturbance of equilibrium.
In the majority of cases, however, owing to the nerve-terminals being still in a state of activity, the irritation set up as a result of the operation may cause increased attacks of nystagmus, vertigo, and vomiting. The vomiting is the first symptom to disappear, and then the nystagmus; but complete recovery of equilibrium may not occur for a considerable period, during which time the patient, though otherwise well, may still have a slightly staggering gait.