title: Tympanum-canal angles anteriorly, anteroinferiorly, and inferiorly: a postmortem study of 41 adult crania.
abstract: The angles formed by the tympanic membrane and the external ear canal anteriorly, anteroinferiorly, and inferiorly can pose surgical challenges, and the spaces they form can harbor iatrogenic cholesteatoma. The range of values previously reported for these angles--27 degrees to 60 degrees--seems not to have been determined in a clinically applicable manner. To clinically describe the tympanum-canal angles, assess bilateral symmetry, assess the angles relative to mastoid pneumatization, and assess the relationship of the angles to manubrium orientation in the skull, the author conducted a postmortem anatomic study of 41 bequeathed adult crania without clinical otitis media. As viewed through the external ear canal, the tympanum-canal angles were measured in 10 degrees increments anteriorly, anteroinferiorly, and inferiorly relative to the line of the manubrium. Mastoid sizes were determined radiographically. In the right ear, the tympanum-canal angles ranged from 40 degrees to 60 degrees anteriorly (median: 55 degrees), from 50 degrees to 70 degrees anteroinferiorly (median: 60 degrees), and from 70 degrees to 80 degrees inferiorly (median: 75 degrees). Bilateral symmetry was found (each rs > or = 0.69, p < 0.001). Although the angles did not correlate with either mastoid pneumatization or manubrium orientation relative to the Frankfort plane, nonvisualization of the annulus anteriorly was significantly more common in specimens with well-pneumatized mastoids (p < 0.05). The author concludes that the tympanum-canal angles anteriorly, anteroinferiorly, and inferiorly have comparatively narrow ranges, exhibit bilateral symmetry, and are unrelated to both mastoid size and manubrium orientation in the skull.
authors.affiliation: Department of Otolaryngology-Head and Neck Surgery, Emory University School of Medicine, Atlanta, GA 30322, USA. ntodd@emory.edu
authors.forename: N Wendell
authors.initials: NW
authors.lastname: Todd
mesh_terms: D000328:Adult; D004424:Ear Canal / Q000033:anatomy & histology*; D004431:Ear, External / Q000033:anatomy & histology; D005260:Female; D006801:Humans; D008297:Male; D008416:Mastoid / Q000033:anatomy & histology*; D011180:Postmortem Changes; D012016:Reference Values; D018709:Statistics, Nonparametric; D014432:Tympanic Membrane / Q000033:anatomy & histology*