Morphologic Variations of Clinically Normal Mallei and Incudes

Abstract

Objectives: Various features and shapes of malleus and incus are reported. Partially or unaddressed are their bilateral symmetry, correlation with otitis media, and concordance of features and shapes. Such information may contribute to the understanding of malleus and incus ontogeny and the installation and function of implantable middle ear devices. We sought to address the following hypotheses: (1) a cranium’s malleus and incus have bilateral symmetry, with respect to their features and shapes; (2) features and shapes of malleus and incus are unrelated to the mastoid size indicator of childhood otitis media; and (3) an ear’s malleus and incus have concordant features and shapes (ie, the presence or absence of a feature or shape of a malleus or incus is associated with the presence or absence of another feature or shape in that ear’s malleus or incus). Methods: Postmortem material-analysis prevalence study of 41 adult crania without clinical otitis media. Mastoid sizes were assessed radiographically. Results: Most mallei had lateral processes and inflected manubrium tips. Most incudes had concave superior borders of their short processes, non-notched inferior borders of their short processes, and anteriorly curved anterior edges of their long processes. Only 1 feature, absence of the lateral process of the malleus, was suggested to have a relationship to small mastoid size. Concordance was not found for any shape or feature of the malleus or incus. Conclusion: Clinically normal mallei and incudes have feature and shape variations that are mostly bilaterally symmetric.