Learning Objectives: To shed some light on the erosive processes that affect the incus in respect to the cholesteatoma localization.

Background: The degree of invasiveness of a cholesteatoma is usually based on some clinical features, such as its extension, relapsing tendency and erosive capacity. For this latter, the ossicular chain, and mostly incus, is usually involved, leading the surgeon to its accurate cleansing or removal.

Material and Methods: For this study, incus specimens were collected during tympanomastoid surgery from adult patients with cholesteatomatous otitis media. The samples were processed for scanning electron microscopy and the investigation aimed to consider at first the whole bone, then to give a detailed mapping of the eroded parts of the incus adjacent to the cholesteatoma tissue. The different degrees of erosion (in terms of presence/absence of erosion, lacunae and their diameter and depth) and the presence/absence of biofilm were considered. Erosion degree was recorded with 0 if absent, and with 1–2–3 if mild, moderate or severe, respectively. Five consecutive fields at 100X magnification, aligned in 3 raws, the first one proximal and the last one distal to the surgical erosive point were analized. A total of 60 fields for each raw were observed.

Results: Erosion lacunae were clustered on the surface of the eroded areas, their diameter being 75 ± 15μm. Although a proximal to distal gradient exists, looking to the distribution of the eroded areas, grade 3 erosion was not only limited to the area proximal to the ossicle erosive edge (first raw) but also in raw 2 and sometimes scattered up to raw 3. Grade 3 erosion was observed around nutrient foramina of the bone (65%).

Discussion: Our observations confirm the hypothesis that the erosion degree is higher near the resection edge, but also prove that erosion areas of degree 3 can also be observed in regions far from the erosive point.