Impact of cochlear modiolus dose on hearing preservation following stereotactic radiosurgery for non–vestibular schwannoma neoplasms of the lateral skull base: a cohort study

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OBJECTIVE

Radiation dose to the cochlea has been proposed as a key prognostic factor in hearing preservation following stereotactic radiosurgery (SRS) for vestibular schwannoma (VS). However, understanding of the predictive value of cochlear dose on hearing outcomes following SRS for patients with non-VS tumors of the lateral skull base (LSB) is incomplete. The authors investigated rates of hearing loss following high-dose SRS in patients with LSB non-VS lesions compared with patients with VS.

METHODS

Patients with LSB meningioma or jugular paraganglioma and serviceable pretreatment hearing who underwent SRS treatment during 2007–2016 and received a modiolus dose > 5 Gy were included in a retrospective cohort study, along with a similarly identified control group of consecutive patients with sporadic VS.

RESULTS

Sixteen patients with non-VS tumors and a control group of 43 patients with VS met study criteria. Serviceable hearing, defined as American Academy of Otololaryngology–Head and Neck Surgery class A/B, was maintained in 13 non-VS versus 23 VS patients (81% vs 56%, p = 0.07). All 3 instances of hearing loss in non-VS patients were observed in cerebellopontine angle (CPA) meningiomas. Non-VS with preserved hearing had a median modiolus dose of 6.9 Gy (range 5.7–19.2 Gy), versus 7.4 Gy (range 5.4–7.6 Gy) in those patients with post-SRS hearing loss (p = 0.53). Sporadic VS patients received an overall median modiolus point-dose of 6.8 Gy (range 5.4–11.7 Gy).

CONCLUSIONS

The modiolus dose threshold of 5 Gy does not predict hearing loss in patients with non-VS tumors undergoing SRS, suggesting that dosimetric parameters derived from VS may not be applicable to this population. Differential rates of hearing loss appear to vary by pathology, with paragangliomas and petroclival meningiomas demonstrating decreased risk of hearing loss compared to CPA meningiomas that may directly compress the cochlear nerve similarly to VS.

ABBREVIATIONS AAO-HNS = American Academy of Otololaryngology–Head and Neck Surgery; CPA = cerebellopontine angle; JP = jugular paraganglioma; LSB = lateral skull base; PTA = pure tone average; SDS = speech discrimination score; SRS = stereotactic radiosurgery; TN = trigeminal neuralgia; VS = vestibular schwannoma.

Article Information

Correspondence Michael J. Link: Mayo Clinic, Rochester, MN. link.michael@mayo.edu.

INCLUDE WHEN CITING Published online July 12, 2019; DOI: 10.3171/2019.4.JNS19201.

Disclosures The authors report no conflict of interest concerning the materials or methods used in this study or the findings specified in this paper.

© AANS, except where prohibited by US copyright law.

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Figures

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    Modified Cox proportional hazards survival model analyzing hearing loss as a function of modiolus point dose, which demonstrates a linear relationship between increasing radiation exposure and hearing loss in VS patients (blue), which was not observed in non-VS patients (red). Figure is available in color online only.

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