METHODS OF OPERATING
These operations may be divided into: (1) simple curetting away of a localized lesion of the labyrinthine wall; (2) opening up of the vestibule with removal of the semicircular canals; (3) opening of the cochlea; (4) a combination of these methods—extirpation of the labyrinth.
Curetting away of a localized lesion of the labyrinthine wall. It has been already stated that, provided the labyrinth be not yet destroyed, it is not justifiable to explore it on the mere discovery of an erosion of the semicircular canal. At the same time, if a definite fistula from which granulations protrude is present, a small fragment of bone may be chipped away, the granulations being afterwards removed by the curette. Unless pus is found to exude from the labyrinth, it is not necessary to do anything further at the present moment. If, however, at a later period, symptoms of labyrinthine infection occur, then it is necessary to further explore the semicircular canal and vestibule, the extent of the operation depending on what is discovered at the time of the operation.
Sometimes an examination of the tympanic cavity may be prevented before operation owing to the auditory canal being filled with polypi or granulations. On performing the complete mastoid operation and curetting away these granulations and polypi, a fistula may be found in the promontory, and carious bone may be felt on probing. Not infrequently these cases are tuberculous in origin and are accompanied by facial paralysis. Provided there be no labyrinthine symptoms, it is sufficient to curette out the granulations, but only gently. Violent curetting may break through the barrier between the infected area and the internal meatus and so lead to meningitis. It is wiser to curette too little than too much.
A further condition which may be met with is necrosis of a portion of the promontory, or of the walls of the vestibule, or of the semicircular canals. If the sequestrum be not quite loose at the time of operation, it should be left in situ, provided there be no intracranial symptoms. In fact, there is less danger in leaving the sequestrum than in attempting to remove it. After the operation, the wound cavity is kept open, so that the sequestrum can be removed at a later date after it has separated from the living bone.
Opening the vestibule (with partial or complete removal of the semicircular canals). This may be performed by one of the following methods:—
Above and behind the facial nerve through the semicircular canals. The complete mastoid operation is performed first. The chief difficulty is to expose the field of operation so as to obtain sufficient room for the necessary manipulations. To do this the following steps should be carried out: The tip of the mastoid process and the remains of the posterior wall of the auditory canal are removed to their extreme limit without injury to the underlying facial nerve. The floor of the auditory canal is also chiselled away until the lower level of the tympanic cavity is brought freely into view, the amount of bone removed depending on the anatomical condition found. To expose the anterior portion of the tympanic cavity, the skin incision is extended slightly forwards, but not far enough to wound the temporal artery, the soft tissues being then separated from the bone and the auricle pulled still further forwards and downwards.
Skin meatal flaps are now fashioned—either the Y-shaped flap or Stacke’s flap (see [p. 403])—and are afterwards kept in position by means of sutures. Good illumination is necessary, and for this reason a head-light should be used. One assistant is employed to retract the soft tissues from the wound, another to keep it as dry as possible.
The exposed portion of the external semicircular canal is first identified. If the bone be soft, the arches of the semicircular canal should be defined (Fig. 240). The posterior canal will be discovered by gouging away the bone just posterior to the arch of the external semicircular canal, and the superior, by working inwards and upwards towards the roof of the attic. If the outline of the canals can be made out, the further steps of the operation are rendered very much easier. Unfortunately, the bone is sclerosed in the majority of cases, rendering anatomical exposure of the canals an impossibility.