Surgical approaches to inner ear therapies

Drug delivery to the cochlea has been hampered by the very mechanisms that exist to protect its delicate neurosensory epithelium from pathogens. The blood-brain barrier restricts the distribution of systemic therapies, while local administration is constrained by basal to apical gradients. As we progress towards restorative and regenerative therapies, precise delivery of therapeutics to their target site is required. This review discusses the surgical approaches to cochlear therapeutic delivery that can overcome these barriers.

Recent advancements in microneedle technology have facilitated nondestructive round window membrane penetration that overcomes restrictive diffusion. Direct intracochlear catheterisation provides a solution to traditional basal to apical gradients along the cochlear duct, particularly when combined with fenestration for allowance of efflux. Drug-eluting implants present a unique opportunity for direct intrascalar administration, which may be extended in a sustained-release format. Finally, surgical approaches for direct injection to the modiolus have been detailed, allowing maximum survival of stem cell grafts.

The evolution of precise pharmacotherapy to specific subsites of the cochlea demands precise methods of administration. These novel strategies often require a surgical approach and can overcome the protective barriers of the cochlea that traditionally restrict pharmacodynamics and pharmacokinetics.