The amount of bone removed should be such that at the end of the operation the auditory canal is only separated from the main cavity of the mastoid antrum by a slight eminence, the remainder of the posterior wall, which is continuous with that of the external semicircular canal.
Occasionally the facial canal and the stylo-mastoid canal are abnormally superficial. Provided the bone be removed in the manner just described, the facial nerve should not be injured, even though it may be exposed inadvertently. A warning of this occurrence is given by bleeding from the vessels within the canal (see [p. 374]).
If the malleus and incus be still in situ, they can now be seen and can usually be removed by the curette. No force must be used. Removal of the incus is a matter of no difficulty. In the case of the malleus there may be some resistance owing to the attachment of the tendon of the tensor tympani muscle. If so, the malleus should be grasped by a fine pair of forceps and the tendon severed by means of Schwartze’s tenotomy knife.
The overhanging edge of the outer wall of the attic can now be felt by means of the seeker. It is best removed by gentle taps of the chisel or small gouge. Especial care must be taken not to drive the gouge too far inwards. If this be done inadvertently, the transverse portion of the facial nerve passing along the inner wall of the tympanic cavity may be injured. As a safeguard some surgeons use an attic punch-forceps or a burr, others a Stacke’s protector which should be inserted into the attic before chiselling away its outer wall.
Fig. 224. Pfau’s Curette for the Eustachian Tube.
After the outer attic wall has been removed, the roof of the auditory canal and the attic should be continuous. This is verified by inserting the seeker, with its point turned upwards, within the attic, and then withdrawing it; no ridge of bone should now prevent its withdrawal.
Fig. 225. The ‘Radical’ Mastoid Operation completed. A, Attic and antrum; B, External semicircular canal; C, Promontory and inner wall of tympanic cavity; D, Remains of posterior wall of auditory canal; E, Facial nerve canal; F, Floor of auditory canal.
Granulations or the epithelial lining of cholesteatomata should be removed from the recesses of the tympanic cavity with a small curette. Care must be taken not to injure the surface of the promontory, or the region of the fenestra ovalis and fenestra rotunda. It is especially important to curette away the mucous membrane from the orifice of the Eustachian tube in order that scar tissue may obliterate its lumen and so prevent reinfection of the middle ear from the naso-pharynx. For this purpose a narrow curette is necessary (Fig. 224).