Surgical Transcanal Procedure for Injection of Cells and Substances into the Human Cochlear Modiolus

Cochlear implants (CIs) enhance hearing by stimulating spiral ganglion neurons (SGNs) but are less effective in individuals with compromised SGN functionality. Advances in regenerative medicine suggest that local delivery of medical drugs or cell therapy could regenerate the auditory nerve. This study evaluates a minimally invasive technique for precise delivery of cell-sized beads, simulating cell therapy, into the cochlear modiolus of human temporal bones.

Ten fresh-frozen human temporal bone specimens were used. Five bones served to establish the injection trajectory using a tungsten rod probe, and the remaining five for injecting microbeads into the modiolus. The surgical procedure involved accessing the middle ear via the external ear canal, performing a cochleostomy at the first cochlear turn, and drilling into the modiolus. Beads were injected into the modiolus using a Hamilton syringe connected to an injection pump, followed by micro-computed tomography imaging and histological assessment.

Accurate placement of the tungsten rod probe within the modiolus was achieved in four out of five bones. Microbead injections indicated 89 to 97% retention within the modiolus, with minimal leakage. The technique showed consistent trajectory with low variability.

The study demonstrates the feasibility of a minimally invasive, precise injection method for delivering and retaining cell-sized beads into the cochlear modiolus. This technique enables future local delivery of medical drugs or cell therapy drugs aimed at hearing restoration, benefiting both current CI users and CI candidates. Further research is necessary to evaluate precision, reproducibility, and long-term outcomes of the procedure.