Malleus and Incus: Correlates of Size

Abstract

Wide ranges of dimensions of the malleus and incus have been reported for various human populations. Unaddressed are concordance of malleus and incus sizes, bilateral symmetry, whether ossicle size correlates with otitis media, and whether second-branchial arch derivatives have more variability than first-arch derivatives. We sought to quantitatively describe the malleus and incus in a population not heretofore reported, with the following hypotheses in mind: 1) an ear's malleus and incus sizes are concordant; 2) a cranium's malleus and incus sizes have bilateral symmetry; 3) the sizes of the malleus and incus are unrelated to the mastoid-size indicator of childhood otitis media; and 4) second-branchial arch derivatives have more variability than do first-arch derivatives. We performed a postmortem material analysis of 41 adult crania without clinical otitis. The sizes of clinically normal mallei (eg, 21.2 to 30.7 mg) and incudes (eg, 24.4 to 37.4 mg) were varied. Concordance of malleus mass and incus mass was found. However, no relation of malleus and incus sizes with mastoid size was found. The variability of first-arch derivatives was similar to that of second-arch derivatives. Clinically normal mallei and incudes had masses and dimensions that varied even more than previously reported. Nevertheless, bilateral symmetry was exhibited, as was concordance of masses.