Perilymph/Modiolar Communication Routes in the Human Cochlea

Abstract

To analyze communication routes between perilymph spaces and the modiolus in the human cochlea. Such pathways are of potential importance with regard to local inner ear drug delivery and pharmacokinetics. We analyzed the surface structure of the human cochlea, using high-resolution scanning electron microscopy (SEM) in macerated and freshly obtained specimens together with light microscopy of celloidin-embedded temporal bones. Combined SEM and light microscopy showed that perilymph and fluid spaces in the modiolar periphery form a common system. The modiolar wall of the scala vestibuli and tympani in the first and second turn is porous, forming a perilymphatic communication route to the perivascular and perineural spaces in the modiolus. A "perimodiolar lymph" or fluid space can be identified in the modiolar periphery. It communicates through a trabecular meshwork of porous membrane and web of connective tissue with the perilymph. The thin mesothelial cell sheets showed pores and displayed signs of vesicular activity. This canalicular system may play a role in the circulation of perilymph in the human cochlea. We suggest that this system may represent an important fluid communication route between modiolus and perilymph and may represent a pathway for future drug and cell-based therapy to the inner ear.