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In chronic otitis media, cholesteatoma formation classically starts in the space just medially to the pars flaccida portion of the tympanic membrane and the scutum (a sharp bony spur formed by the lateral wall of the tympanic cavity and the superior wall of the external auditory canal, usually the first bony structure to erode as a result of a cholesteatoma). This space is referred to as Prussak’s space. It continues posteriorly to become the epitympanum. So, to access this space posteriorly, it is necessary to unroof the epitympanum. This is done by removing air cells in the root of the zygoma between the middle fossa dura and the thinned posterior canal wall until the head of the malleus and the incudomalleolar joint are identified (Figs. 2.9 and 2.10). The floor of the dissection is the tympanic portion of the facial nerve and the superior semicircular canal. If necessary, the dissection can be carried anteriorly through the zygomatic root to the glenoid fossa. In the anterior epitympanum, after removal of the head of the malleus and the body of the incus, a bony spicule (the cog) descending from the tegmen can sometimes be identified (Fig. 8.1). This spicule separates the epitympanum in anterior and posterior compartments. If present, this landmark can be identified on pre-operative CT scans and needs to be removed in order to fully remove disease in the anterior epitympanum.