Histopathologic Characteristics of Internal Auditory Canal Diverticula

Abstract

Hypothesis: We hypothesize that internal auditory canal (IAC) diverticula occur independent of otosclerosis as demonstrated by temporal bone histopathology. Background: Diverticula at the anterior-inferior aspect of the internal auditory canal have been described histologically in the setting of cavitary otosclerosis. Recent radiographic studies show the prevalence of IAC diverticula that is higher than what can be accounted for by cavitary otosclerosis alone. Methods: We examined hematoxylin and eosin temporal bone histopathology slides with otosclerosis involving the internal auditory canal. We also examined bones from normal hearing subjects with normal histologic findings. Temporal bones were included if donors were >18 years of age at time of death and adequate horizontal cuts were available to evaluate the area of interest. Results: IAC diverticula were found in 33 of 47 (70%) temporal bones with IAC otosclerosis and in 5 of 20 (25%) normal temporal bones. The difference in mean pure tone averages (PTA) in the normal temporal bones with (PTA 7.3 +/− 7) and without (PTA 8 +/− 2) diverticula was not statistically significant (p = 0.86) Conclusion: Internal auditory canal diverticula which have been previously demonstrated to occur in the setting of cavitary otosclerosis can also occur independent from otosclerosis. Subjects with diverticula but without other temporal bone pathology have normal hearing thresholds.

Internal Auditory Canal Diverticula in Children: A Congenital Variant

“…Hearing results were not significantly different between the two sides. These findings are in accord with prior studies, which have found that IAC diverticula are unrelated to hearing loss 9–11 …”

“…In a large imaging series, this site was shown to be the most common location of cavitary otosclerosis 13 . Notably, IAC diverticula have also been shown to exist independently from otosclerosis in adults, supporting our theory that higher prevalence in adults is a result of the inclusion of both congenital and acquired diverticula 10 …”

“…In patients with radiographic findings of IAC diverticula, the prevalence of otosclerosis is 16% to 34% 1,9 This co‐occurrence is likely due to the propensity of the anteroinferior IAC (where IAC diverticula are located) to develop otosclerosis. Foci of otosclerosis have been demonstrated at this site on histologic sections in the absence of diverticula 10 . In a large imaging series, this site was shown to be the most common location of cavitary otosclerosis 13 .…”

“…An internal auditory canal (IAC) diverticulum is a nonvascular outpouching from the normal linear contour of the anterior inferior aspect of the IAC 1–11 ; Figures 1 and 2. Large radiographic studies have found the prevalence of IAC diverticula to be around 5% in the adult population 1,9 .…”

“…Nearly half of patients with osteogenesis imperfecta also have evidence of IAC diverticula 15 . IAC diverticula have been shown to occur in the absence of histopathology 10 and are unrelated to hearing loss 9–11 …”