Evaluation of the internal structure of normal and pathological Guinea pig cochleae using optical coherence tomography

Optical coherence tomography (OCT) makes it possible to visualize the internal structures of several organs, such as the eye, in vivo. Although visualization of the internal structures of the inner ear has been used to try and identify certain pathological conditions, attempts have failed mainly due to the thick bony capsule surrounding this end organ. After decalcifying the bony wall of the cochlea with ethylenediamine tetraacetic acid, we could clearly visualize its internal structures by using OCT. We identified endolymphatic hydrops, strial atrophy and damage to the organ of Corti, evident as a distention of Reissner's membrane, thinning of the lateral wall and flattening of the organ of Corti, respectively. When specimens embedded in paraffin, sliced and stained with hematoxylin and eosin (HE) were examined under a light microscope, the OCT images of normal and pathological cochleae were virtually identical with those of the HE specimens, except that the HE specimens exhibited several artifacts unrecognized in OCT images, which were considered to be induced during the preparation process. Since OCT enables one to obtain arbitrary plane images by manipulating the slice axis of the specimens and avoids any misinterpretation due to artifacts induced during histological preparation, our technique would be useful for examining cochlear pathologies without or prior to histological evaluations.