Clinical correlates of acoustic neuroma volume

Cerebellopontine angle tumor presenting as acute audiovestibular syndrome

BACKGROUND

Acute audiovestibular deficits may be a harbinger of vestibular schwannoma (VS).

OBJECTIVE

To investigate clinical and laboratory features of 25 consecutive patients with VS presenting with acute audiovestibular deficits.

METHODS

A symptomatic combination of acute audiovestibular deficits was investigated. Audiometric and vestibular function tests, and internal auditory canal magnetic resonance imaging (IAC MRI) results were evaluated.

RESULTS

Varying combinations of symptoms may develop in VS patients with acute audiovestibular deficits, of whom sudden hearing loss (HL) without acute vertigo or acute facial nerve palsy (FNP) was most common. The most common audiometric configuration was high-tone hearing loss, and no patient showed low-tone hearing loss. IAC MRI demonstrated that the tumor had an intracanalicular portion and attachment to the bony IAC wall in all patients and widened the IAC wall in some patients.

CONCLUSION

Different symptomatic combinations of acute audiovestibular deficits may develop in patients with VS. Awareness about the possibility of VS as a cause of sudden HL, acute vertigo, and acute FNP, as well as subsequent IAC MRI scanning is vital to earlier diagnosis of VS in these patients.

Audiovestibular Function Deficits in Vestibular Schwannoma

Introduction. Vestibular schwannomas (VS) are benign tumours of the vestibular nerve and can lead to hearing loss, tinnitus, vertigo, facial palsy, and brainstem compression. Audiovestibular diagnostic tests are essential for detection and treatment planning. Methods. Medline was used to perform a systematic literature review with regard to how audiovestibular test parameters correlate with symptoms, tumour size, and tumour location. Results. The auditory brainstem response can be used to diagnose retrocochlear lesions caused by VS. Since hearing loss correlates poorly with tumour size, a retrocochlear lesion is probably not the only cause for hearing loss. Also cochlear mechanisms seem to play a role. This can be revealed by abnormal otoacoustic emissions, despite normal ABR and new MRI techniques which have demonstrated endolymphatic hydrops of the inner ear. Caloric and head impulse tests show frequency specific dynamics and vestibular evoked myogenic potentials may help to identify the location of the tumour regarding the involved nerve parts. Conclusion. In order to preserve audiovestibular function in VS, it is important to stop the growth of the tumour and to avoid degenerative changes in the inner ear. A detailed neurotological workup helps to diagnose VS of all sizes and can also provide useful prognostic information.

Sporadic vestibular schwannomas associated with good hearing secrete higher levels of fibroblast growth factor 2 than those associated with poor hearing irrespective of tumor size

HYPOTHESIS

We hypothesize that the severity of hearing loss (HL) associated with sporadic vestibular schwannomas (VS) is correlated with tumor secretion of proteins with ototoxic or otoprotective potential.

BACKGROUND

Because the recognition that HL associated with VS is not solely due to compression of the auditory nerve, elucidating the mechanism by which VS cause HL has been an important task. We previously showed that VS stratified by hearing have differential gene expression. We now focus on identifying differentially expressed proteins in tumor secretions.

METHODS

Fresh surgical specimens of VS were incubated in sterile PBS at 37°C to collect secretions. The specimens were divided into a group associated with good hearing (GH, word recognition ≥ 70% and pure-tone average ≤ 30 dB, n = 11) or poor hearing (PH, n = 10). The groups were compared using a customized cytokine array. Statistically significant results were verified with an enzyme-linked immunosorbent assay on a different set of secretions (n = 8 for GH and n = 10 for PH group).

RESULTS

Of the 37 molecules we studied, 9 were significantly expressed in secretions from VS compared with secretions from control nerves. Secretion of fibroblast growth factor 2 (FGF2) was 3.5-fold higher in VS associated with GH versus PH based on cytokine array analysis (p = 0.02), which was validated with enzyme-linked immunosorbent assay.

CONCLUSION

This study highlights FGF2, a mitogen known to protect the auditory nerve, as a potential tumor-secreted mediator of hearing protection in VS. If FGF2's significant role in hearing protection in patients with VS is validated, then FGF2 could be used as a biomarker for HL in VS, and therapeutic targeting of the FGF2 signaling pathway may reduce HL due to VS.

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

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.

The relationship between pure tone thresholds and the radiological dimensions of acoustic neuromas

A retrospective analysis of 109 consecutive patients presenting with acoustic neuromas between 1986 and 1997 were undertaken. Sufficient data were available in 104 cases for comparison. In 65 cases patients had undergone surgery and the radiological diagnosis of acoustic neuroma was confirmed histologically. In this group there were 25 large and 40 small tumors when a maximal radiological diameter of 2.5 cm was used to subdivide the groups. When pure tone thresholds were compared at specific frequencies, in those with hearing ears, there was no significant difference between the two groups. Our results are compared with recent series and the causes of hearing loss associated with acoustic neuroma are discussed.