Dysfunction of the cochlea contributing to hearing loss in acoustic neuromas: an underappreciated entity - PubMed (original) (raw)

Multicenter Study

Dysfunction of the cochlea contributing to hearing loss in acoustic neuromas: an underappreciated entity

Christof Roosli et al. Otol Neurotol. 2012 Apr.

Abstract

Objective: Hearing loss is a common symptom in patients with cochleovestibular schwannoma. Clinical and histologic observations have suggested that the hearing loss may be caused by both retrocochlear and cochlear mechanisms. Our goal was to perform a detailed assessment of cochlear pathology in patients with vestibular schwannoma (VS).

Study design: Retrospective analysis of temporal bone histopathology.

Setting: Multi-center study.

Material: Temporal bones from 32 patients with unilateral, sporadic VS within the internal auditory canal.

Main outcome measures: Sections through the cochleae on the VS side and opposite (control) ear were evaluated for loss of inner and outer hair cells, atrophy of the stria vascularis, loss of cochlear neurons, and presence of endolymphatic hydrops and precipitate within the endolymph or perilymph. Observed pathologies were correlated to nerve of origin, VS volume, and distance of VS from the cochlea. Hearing thresholds also were assessed.

Results: VS caused significantly more inner and outer hair cell loss, cochlear neuronal loss, precipitate in endolymph and perilymph, and decreased pure tone average, when compared with the opposite ear. Tumor size, distance from the cochlea, and nerve of origin did not correlate with structural changes in the cochlea or the hearing threshold.

Conclusion: There is significant degeneration of cochlear structures in ears with VS. Cochlear dysfunction may be an important contributor to the hearing loss caused by VS and can explain certain clinically observed phenomena in patients with VS.

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Figures

Figure 1

Figure 1

100-year old woman (Case B5 in Table 1) with untreated solitary vestibular schwannoma (VS) approximately 11×8×8 cm in size located at the entrance of the internal auditory canal (IAC) in the left temporal bone. The VS was located mainly in the cerebellopontine angle and did not come close to the cochlea in any section.

Figure 2

Figure 2

Same case as Fig. 1. Photomicrographs of cochlea on VS side are shown along with similar views from the contralateral ear. The low power views demonstrate loss of neuronal cells within the modiolus on the VS side (A) compared to the opposite ear (B). High power views of boxed areas show that the organ of Corti in the basal turn was missing (C), while it was preserved on the contralateral side (D). The hair cell and neuronal losses were likely to have been caused by the VS.

Figure 3

Figure 3

Views of the distal part of the internal auditory canal (IAC), saccule and cochlea from a 75-year old man (Case B4 in Table 1). (A) shows a VS in the IAC that reached the fundus but did not invade the inner ear. The cochlea showed acidophilic precipitate within both the endolymphatic and perilymphatic spaces (*) as well as endolymphatic hydrops in all turns. There was also hydrops of the saccule. (B) shows comparable view from the contralateral ear showing lack of hydrops and lack of precipitate within inner ear fluids. Higher power views of boxed areas are shown in (C) and (D): there was hair cell loss on the VS side (C), with an intact organ of Corti in the opposite ear (D).

Figure 4

Figure 4

Comparison of pure tone average for air conduction (AC) thresholds for the tumor side and the contralateral side. Standard deviation is indicated by error bars.

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