Introducing a translationally relevant mouse model of radiosurgery-induced unilateral hearing loss

Stereotactic radiosurgery (SRS) is widely used to treat vestibular schwannomas but may cause irreversible hearing loss due to cochlear toxicity. The underlying mechanisms are not fully understood, and no effective otoprotective therapies exist. We aimed to establish a mouse model that replicates the clinical pattern of radiation-induced hearing loss.

C57BL/6J mice (n = 31) received 8 Gy (n = 3), 16 Gy (n = 5), 24 Gy (n = 8), or 32 Gy (n = 15) using the Leksell Gamma Knife ICON system. Targeting was based on the built-in cone-beam CT, co-registered with MRI and CT-based mouse atlases, to guide unilateral cochlea targeting. A single isocenter was placed lateral to the right cochlea, with the 80% isodose line traversing its medial edge. Auditory brainstem response (ABR) was measured at baseline and at 1 and 4 weeks post-SRS. A 32 Gy subgroup (n = 7) was evaluated at 16 weeks. Histological analysis of cochleae was performed at 4 weeks in all groups and at 16 weeks in the long-term 32 Gy group.

SRS was well tolerated, and the contralateral cochlea received a very low radiation dose. No ABR shifts were observed at 8 or 16 Gy, with only minimal histological changes. At 32 Gy, ABR threshold shifts at 22.6 and 32 kHz were evident by week 1 and worsened by week 4. Similar but milder effects occurred at 24 Gy. In the 32 Gy long-term subgroup, hearing loss progressed across all frequencies, most severely at high frequencies, alongside a sustained wave I amplitude decline. At 32 Gy, outer hair cells were reduced by 14 and 44% at 32 and 45.2 kHz, respectively, at 4 weeks, and by 38 and 80% at 16 weeks. Ribbon synapses were mildly reduced at 4 weeks and more markedly at 16 weeks in corresponding high-frequency regions. Spiral ganglion neuron density was mildly reduced at the basal and middle turns. All reported changes were statistically significant when compared to the contralateral ear.

This new model reproduces key features of SRS-induced cochlear toxicity, including unilateral, dose-dependent, and progressive hearing loss. It thus provides a valuable platform for investigating mechanisms and testing otoprotective strategies.