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accurate physical three-dimensional reconstruction of the cochlear nuclear complex (CN), we used light microscopy to analyze the CN boundaries, cell types, and myelinated nerve bundles and transferred traced contours from enlarged photographs of serial sections onto acrylic plates. We produced two models, one demonstrating the CN in relation to the brain stem and the other showing the CN completely dissected out of the brain stem. The models localized the CN boundaries on the brain-stem surface and revealed topographic characteristics of the CN and a part of the eighth nerve adjacent to the brain stem. The major parts of the CN, namely, the ventral and dorsal cochlear nuclei, are located mainly within the lateral recess. The models produced are currently used in our institution to determine the optimal surgical and electrophysiologic approach to the CN. (Arch Otolaryngol 1985;111:495-501) It is well known that the cochlear nuclear complex (CN) is the first major relay center that processes information received through syn¬ apses with the cochlear nerve and then transmits it toward the cortex.The nuclei have been the subject of several intensive investigations that mainly studied carnivores1'7 and CA 90057 (Dr Terr). rodents.811 Primates, however, have received less attention, with only a few articles describing the CN in humans.1222The CN is a highly complicated heteromorphic formation consisting of several relatively well-separated divi¬ sions, namely, the dorsal (DCN) and ventral (VCN) cochlear nuclei, with smaller subdivisions of the latter.Although a part of the CN surface can be seen by the naked eye, gross analy¬ sis makes it difficult to appreciate the shape and dimensions of the cochlear nuclei in humans. The difficulty is due to the small size of the nuclei and the fact that the CN is almost completely hidden within the brain tissue and inseparable from it as a structural entity. At the same time, it may be equally difficult to understand the CN general spatial organization by study¬ ing individual or even serial histologie sections without specific reconstruc¬ tion methods. Three-dimensional re--· construction of the CN and the accu¬ rate characterization of the CN orien¬ tation have not been done yet. The morphology of the human CN is of substantial interest to us, since evaluation of the geometry of the nuclei is essential to further develop techniques for the electrical stimula¬ tion of the CN. Our institution cur¬ rently uses electrical stimulation of the cochlear nuclei as a form of rehabilitation of individuals deafened from the bilateral loss of the auditory nerves.23 MATERIALS AND METHODSTissue blocks were dissected from post¬ mortem, normal brains of adults. Macroexamination was completed on 20 brains. Detailed histologie examination was done on six brains (left and right sides). Varia¬ tions in the shape of the CN and adjacent structures, namely, root of the eighth nerve and inferior cerebellar peduncle, were not observed. One brain was utilized for three-dimensional reconstruction.The brai...

In the posterior cranial fossa, the separation of the vestibular and cochlear subdivisions of the eighth nerve is clear in about 75% of cases. Although in the remaining cases the vestibulocochlear cleavage plane is not visible macroscopically, the large‐fibered vestibular subdivision and the small‐fibered cochlear subdivision are well recognized in histological sections. Within the cochlear subdivision, some fibers of large caliber are mixed with fibers of small caliber in a region we named the “overlapping zone.” We studied, histologically, cross sections of the intracranial portion of six eighth nerves at about 5 mm proximal to the porus acusticus. A computerized video system was used to measure the diameters of the fibers of the vestibular and cochlear subdivisions localized at different distances from the vestibulocochlear cleavage plane. The overlapping zone is located within the cochlear subdivision adjacent to the vestibulocochlear cleavage plane. It has a pear‐like shape, with the larger part occupying the anterosuperior part of the cochlear subdivision. The mean cross‐sectional area of this zone in our six samples is about 0.4 mm2, which is approximately 23% of the area of the cochlear subdivision. The thickness of the zone in the superior‐inferior direction ranges from 0.23 mm to 0.55 mm. The parameters of the described overlapping zone should be taken into consideration in vestibular neurectomy, in which complete sectioning of the vestibular fibers is important.

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