It should now be easier to determine the need to enter the mastoid. The intact-wall (IBM) mastoidect-omy begins with drilling the wall of the posterior ear canal from canal toward mastoid. Drilling the other way, mastoid to canal, results in a smaller, not larger, middle ear space and locates the bridge more anteriorly than is desirable for good reconstruction. Putting the bridge as far posterior as possible in an enlarged middle ear with a smaller mastoid is best (Fig. 10-6A).
In the IBM, air cells of the facial or suprapyramidal recess are usually not drilled open, which helps to avoid postoperative retraction pockets. The incus buttress is left intact, overlying and posterior to the
tympanic annulus, and this bony circumferential platform then allows reconstruction of the ossicular chain and eardrum with minimal development of posterosuperior retraction (Fig. 10-6B). When all diseased tissue has apparently been eradicated, the undersurface of the bridge is carefully examined with a rigid otic endoscope (30 and 70 degrees) to evaluate for total removal of cholesteatoma or other diseased tissue.
The mastoid cavity is reduced in size by lowering its walls with a cutting drill as much as possible. To remove all angulations and achieve a smooth outer cortex, air cells of the mastoid tip and outer mastoid cortex are completely saucerized and lowered to allow for collapse of posterior skin tissue into the mastoid and to achieve a much smaller mastoid long-term. Mastoid cortical bone superior to the level of the dura of the middle fossa is drilled completely to obliterate this area. Drilling is continued posteriorly to the lateral sinus and inferiorly through the mastoid tip. This may seem to develop a larger mastoid cavity, but the opposite occurs once the postauricular wound heals and collapses inward.
The undersurface of the bridge is cleaned of all residual diseased mucosa or cholesteatoma using / % -inch umbilical tape passed from the middle ear into the mastoid and moved very gently back and forth to remove all diseased tissue without fracturing the bridge; then full removal is checked using an endoscope. A free graft of temporalis muscle and periosteum is used to obliterate the defect from the posterior atticotomy, obliterate the mastoid, and separate the mastoid air-cell system from the middle ear space, thus "exteriorizing" the mastoid so that it is no longer dependent on the eustachian tube for drainage. This helps keep the middle ear space well pneumatized and free of discharge from the mas-toid.
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