Surface microstructure of the perilymphatic space: implications for cochlear implants and cell- or drug-based...

To study the surface microstructure of the scala tympani and scala vestibuli in humans and cats using scanning electron microscopy.

Cochleas from 8 humans and 4 cats were harvested and the otic capsule and soft tissue removed before the cochleas were prepared for scanning electron microscopy. Micrographs were taken of the bony surface of both the scala tympani and scala vestibuli in each cochlear turn. The diameter and density of the micropores (canaliculi perforantes) and the thickness of the osseous spiral lamina (OSL) adjacent to Rosenthal's canal was measured.

The human cochlea exhibits numerous canaliculi on the surface of the scala tympani, particularly associated with the OSL. There was a large range of diameters in the modiolar region of the OSL (0.2-23.0 micro m). The OSL was also very thin, with a mean thickness of 26.8 micro m in the base, tapering to 8.4 micro m in the apical turn. Far fewer canaliculi were evident in the scala vestibuli. Examination of the cat cochleas showed a similar distribution of canaliculi to that seen in the human; however, they were smaller in diameter and the OSL was thicker than in the human cochleas.

The OSL is a thin and highly porous bony lamina that would appear to provide an open and extensive fluid communication channel between the scala tympani and Rosenthal's canal. These findings have important implications for the design and application of perimodiolar cochlear implant electrode arrays and may provide a potential route for drug- and cell-based cochlear therapies delivered via the scala tympani.