Ultrastructural aspects of the microvasculature of the cochlea: the internal spiral network.

We performed a study of the microvasculature of the cochlea with scanning electron microscopy on corrosion casts in the guinea pig. This study was performed in 140 cochleas from healthy adult guinea pigs. Different microvascular techniques were used, including injection-microdissection in 53 cases, injection-diaphanization in 27 cases, a histologic technique in 34 cases, injection-microdissection-diaphanization in 32 cases, and scanning electron microscopy on corrosion casts in 14 cases. The internal radiating arterioles branch off as collateral branches of the spiral modiolar artery, as first-order collateral branches. We detail the morphology, caliber, trajectory, and collateral branches. Among their collateral branches, are third-order arterioles, the arterioles to the spiral ganglia, and the arterioles of the tympanic lip. The arterioles of the tympanic lip form, through their anastomosis, a rich capillary network at the edge of the spiral lamina, called the internal spiral network. We emphasize the glomeruli of Schwalbe, which arise near the scala tympani as third-order arterioles with a medium caliber of 14 microm. The upper glomeruli, situated in the bony wall, and the lower glomeruli, situated in the width of the osseous spiral lamina, form vascular loops made of anastomosed capillaries with a caliber of less than 10 microm. These loops play an important role as efficient devices, or "relay stations," for regulation of cochlear blood flow. The comparison of results obtained with each technique gave the perspective of the cochlear microvasculature with great accuracy.