Isolated Internal Auditory Canal Diverticula: A Normal Anatomic Variant Not Associated with Sensorineural Hearing Loss

Abstract

BACKGROUND AND PURPOSE: Bony internal auditory canal diverticula are relatively common, occurring in approximately 5% of temporal bone CTs. Internal auditory canal diverticula have historically been considered incidental; however, a recent publication reported that internal auditory canal diverticula are associated with sensorineural hearing loss. The objective of this study was to further characterize this potential association in a large cohort of patients. MATERIALS AND METHODS: A total of 1759 patients undergoing high-resolution temporal bone CT were collected during a 6-year interval, and audiometric data were obtained from those with internal auditory canal diverticula. To assess any association of isolated internal auditory canal diverticula with sensorineural hearing loss, we excluded from further analysis patients with concomitant otosclerosis and bilateral diverticula and those without audiometric data, leaving 22 index cases. Audiometric data for the ear with a diverticulum was compared with that in the contralateral ear, to serve as an internal control. RESULTS: Of 1759 patients, 82 (4.7%) had either unilateral (n ϭ 33, 40%) or bilateral (n ϭ 49, 60%) internal auditory canal diverticula. The coincidence of otosclerosis and internal auditory canal diverticula was 34% (n ϭ 28). There was no correlation between patient age and diverticulum size on either side. Among the index cases with isolated unilateral internal auditory canal diverticula and complete audiometric data, word recognition scores and the prevalence and severity of sensorineural hearing loss were not significantly different comparing the internal auditory canal diverticulum side to its contralateral control. CONCLUSIONS: This study did not find a statistically significant association between ears with internal auditory canal diverticula and worsening sensorineural hearing loss or word recognition. Internal auditory canal diverticula most likely represent a normal anatomic variant in ears without otosclerosis. ABBREVIATIONS: CHL ϭ conductive hearing loss; HL ϭ hearing loss; IAC ϭ internal auditory canal; IQR ϭ interquartile range, MHL ϭ mixed hearing loss; SNHL ϭ sensorineural hearing loss

Morphological comparison of internal auditory canal diverticula in the presence and absence of otospongiosis on computed tomography and their impact on patterns of hearing loss

“…There remains lack of clarity over the implication of IAC diverticula in patients with and without OS. Our finding of a 5.5% prevalence for isolated IAC diverticula on CT is in keeping with previous studies [ 5 , 6 ]. We also demonstrated IAC diverticula to be present in 23% of patients with additional CT features of OS, as compared with 10–39% incidence of cavitary OS at this site in previous studies [ 3 , 4 , 9 – 11 ].…”

“…Morphological imaging features were partly based on those investigated in previous reports [ 6 , 7 ] and for their potential ease of assessment in clinical reporting. The following morphological criteria were evaluated (Figs.…”

“…Focal low attenuation diverticula have been demonstrated to arise from the antero-inferior margin of the internal auditory canal (IAC) fundus on CT [ 1 – 5 ]. Isolated IAC diverticula are seen in approximately 5% of temporal bone CT studies but their clinical significance remains uncertain [ 5 , 6 ]. Such IAC diverticula are also described in the context of cavitary otospongiosis (OS) [ 3 , 4 ] where diverticula associated with cavitary plaques are typically demonstrated in a similar location at the fundus of the IAC [ 4 ] (Fig.…”

“…It has been observed that IAC diverticula have a variable appearance on CT with respect to their depth, degree of definition and shape. Mihal et al showed that the depth of the IAC diverticula differed between patients with and without OS [ 6 ] whilst Muelleman et al found no relationship between diverticulum size and hearing loss [ 7 ]; however, the full implications of the different morphological characteristics is yet to be explored. We therefore aimed to ascertain whether there were particular morphological features of IAC diverticula which were associated with the presence of additional CT features of fenestral or pericochlear OS, and whether the morphology of the IAC diverticula influenced patterns of hearing loss in patients with or without OS.…”

Histopathologic Characteristics of Internal Auditory Canal Diverticula

“…This study also compared unilateral diverticula to their contralateral control side to show that IAC diverticula are not associated with a worse pure tone average or worse recognition score. 16 Given the preponderance of IAC diverticula independent of otosclerosis, we suspect that IAC diverticula may be congenital. Bast and Anson described endochondral otic capsule development in detail.…”