Abstract
Objective: We used synchrotron radiation phase contrast imaging (SR-PCI) to study the 3D microanatomy of the basilar membrane (BM) and its attachment to the spiral ligament (SL) (with a conceivable secondary spiral lamina [SSL] or secondary spiral plate) at the round window membrane (RWM) in the human cochlea. The conception of this complex anatomy may be essential for accomplishing structural preservation at cochlear implant surgery.Material and methods: Sixteen freshly fixed human temporal bones were used to reproduce the BM, SL, primary and secondary osseous spiral laminae (OSL), and RWM using volume-rendering software. Confocal microscopy immunohistochemistry (IHC) was performed to analyze the molecular constituents.Results: SR-PCI reproduced the soft tissues including the RWM, Reissner’s membrane (RM), and the BM attachment to the lateral wall (LW) in three dimensions. A variable SR-PCI contrast enhancement was recognized in the caudal part of the SL facing the scala tympani (ST). It seemed to represent a SSL allied to the basilar crest (BC). The SSL extended along the postero-superior margin of the round window (RW) and immunohistochemically expressed type II collagen.Conclusions: Unlike in several mammalian species, the human SSL is restricted to the most basal portion of the cochlea around the RW. It anchors the BM and may influence its hydro-mechanical properties. It could also help to shield the BM from the RW. The microanatomy should be considered at cochlear implant surgery.
Highlights
The osseous spiral lamina (OSL) and the basilar crest (BC) form a ‘hammock’ to support the basilar membrane (BM) and the organ of Corti in the human cochlea
The BM was well-defined from the spiral limbus to the narrowing wedge of the BC at the lateral wall
The relationship between the round window membrane (RWM) and the BM was examined on serial synchrotron radiation phase contrast imaging (SR-phase contrast imaging (PCI)) sections in three specimens where the entire RWM was included (1637R, 1512R, and 1552R)
Summary
The osseous spiral lamina (OSL) and the basilar crest (BC) form a ‘hammock’ to support the basilar membrane (BM) and the organ of Corti in the human cochlea. A secondary spiral lamina (SSL) forms a ridge on the outer wall that projects inward from the bony tube toward the primary lamina, leaving a narrow cleft for the BM. In the bat, which can perceive intense high-frequency sounds, the SSL is wide and supports the BM fibers firmly to the lateral wall (LW) [1]. In the mouse and guinea pig, it is prominent [2]; in man, a species less adapted to perceive high-frequency sounds, it varies and is limited to the lower part of the basal turn [3] around the posterior and superior margins of the round window (RW) [4]. Hearing preservation cochlear implantation motivates further analysis of the intricate microanatomy at the cochlear base
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