Cochlear nucleus stimulation.
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Brain Stem↗
Biomedical subjects
L I Terr
Publications and source records attributed to L I Terr.
Cochlear nucleus anatomy related to central electroauditory prosthesis implantation.
The central electroauditory prosthesis is now used to stimulate the cochlear nuclei to obtain auditory perception in patients with bilateral cochlear nerve transection who are undergoing bilateral acoustic tumor removal. In this study, we used fixed cadaver specimens to identify visible landmarks for accurate placement of the central electroauditory prosthesis through a combined suboccipital-translabyrinthine opening. Histologic features of the regions of probable implantation of the central electroauditory prosthesis were also investigated. We found that the following landmarks might have surgical significance: (1) the tenia of the inferior velum of the fourth ventricle, which crosses the surface of the ventral cochlear nucleus and the vestibulocochlear nerve; (2) the angle between the vestibulocochlear and glossopharyngeal nerves; and (3) the foramen of Luschka. It is suggested that an incision be made in the tenia for insertion of the prosthesis into the lateral recess and eventual placement on the ventral cochlear nucleus surface. To study regions of potential stimulation, we injected ink into different sites on the exposed surface of the cochlear nuclei. We then histologically examined neuronal populations adjacent to the sites. We found that a portion of the ventral cochlear nucleus localized within the lateral recess might be the most appropriate location for placement of the central electroauditory prosthesis.
Cochlea↗
Effects of stimulation by cochlear implant on the cochlear nerve.
Degeneration of the cochlear nerve before and after placement of the cochlear implant might influence the efficacy of the device. We examined histological characteristics, including the caliber of the cochlear nerve fibers of the central segment proximal to the porus acusticus, in three profoundly deaf patients. Two of them used a cochlear implant for many years longer in one ear than in the other, and one used an implant in one ear only. No qualitative or quantitative differences between the two sides were found. However, in all three cases we found that the cochlear nerves on both sides were substantially degenerated. These results indicated no noticeable effects of stimulation by the cochlear implant on the central portion of the cochlear nerve.
Adult↗
Biocompatibility of the central electroauditory prosthesis and the human cochlear nuclei.
Previous studies from the House Ear Institute have reported the possibility of sound sensation from the central electroauditory prosthesis (CEP) implanted in patients during removal of bilateral acoustic neuromas. This study describes histologic features of tissues formed around a CEP that was removed due to infection in the area of the electrical plug on the external surface of the skull. We found a layer of compact collagen tissue around the CEP. The tissue penetrated spaces of the Dacron mesh matrix, preventing our determination of the precise place of the electrode-tissue interface. We also found a layer of connective tissue on the Silastic covering on the CEP leads. Histopathologic analysis showed no unusual pathologic changes around the CEP except for degeneration of the abdominal fat used for placement and stabilization of the CEP on the surface of the cochlear nuclei.
Biocompatible Materials↗
Histopathologic study of the cochlear nuclei after 10 years of electrical stimulation of the human cochlea.
This report provides histologic data on the cochlear nuclei of a patient who used a cochlear implant in the right ear for about 10 years and in the left ear for about 1 year. The most pronounced abnormality in the cochlear nuclei is sites of gliosis. However, since areas of necrosis with similar size, shape, and content of cells were observed outside the nuclei, the gliosis was not specific to the nuclei. There were no other unusual changes in the cochlear nuclei, such as excessive chromatolysis, excessive accumulation of lipofuscin, swollen neurons, or accumulation of glial cells. Comparison showed no statistically significant differences in sizes of cell bodies, size of nuclei, and total density of neurons in cochlear nuclei between the right and left sides. However, the density of normal-looking neurons (with visible nucleoli and without visible pathologic features) was noticeably less on the longer-stimulated side. Some differences between the longer- and shorter-stimulated sides may be due to differences before implantation or other factors, as well as to effects of stimulation.
Cochlea↗
Computer-aided three-dimensional reconstruction of the cochlear nerve root.
Computer-aided three-dimensional reconstruction techniques have been used for reconstruction of the cochlear nuclei and the cochlear nerve root. The cochlear nuclei, the nerve root, and the other adjacent structures were studied in serial frontal and horizontal sections. Boundaries of these structures were digitized into a computer and eight three-dimensional models were produced. Two solid models (reconstructions) showed the spatial surface topography, while the others revealed the appearance of the nerve root within the nuclei. The reconstructions also showed the position of the tenia of the tela choroidea on the surface of the nuclei and its relation to the root. This knowledge makes it possible to use the tenia as a landmark for determination of the root position within the nuclei. As the nerve enters the nucleus and forms the root, there is an appreciable reduction in its thickness. At the same time, the distance between the nuclei surface and the root, which has a cone shape, increases. The cone is curved along its longitudinal axis toward the inferior cerebellar peduncle. The top of the root borders the dorsal cochlear nucleus. This study stems from work in this institution on placement of the central electroauditory prosthesis on the cochlear nuclei surface. The results obtained further knowledge of the anatomy of the nuclei, specifically the areas used for the prosthesis implantation and the underlying tissue.
Brain Stem↗
Anatomical relationships of the cochlear nuclei and the pontobulbar body: possible significance for neuroprosthesis placement.
The pontobulbar body (PBB) is located in the cerebellopontine angle caudally to the cochlear nuclear complex (CN). We found the common boundary between these two structures on the surface of the brain stem as well as within it. We used the Kluver-Barrera staining technique to characterize different neuronal types adjacent to the boundary. Although the majority of them in the CN were globular, we also saw a substantial number of spherical neurons. Neurons in the PBB were substantially different in shape and were mainly angular. The boundary between the PBB and CN at their closest contact runs around the caudal side of the ventral cochlear nucleus and the most proximal part of the eighth nerve. In the more dorsal region, the PBB is completely separated from the CN by the brain stem tissue. In the ventral region, the PBB runs between the seventh and eighth nerves, and it is adjacent to both. These results might aid accurate placement of the central electroauditory prosthesis and further understanding of the general anatomy of the cerebellopontine angle.
Adult↗
Topography of vestibulocochlear nerve fibers in the posterior cranial fossa.
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.
Adult↗
Three-dimensional computer-aided reconstruction of the pontobulbar body.
The pontobulbar body (PBB) has a crescent-like shape and runs along the caudal border of the cochlear nuclei (CN) on the lateral surface of the brain stem and then extends rostrally to the root of the trigeminal nerve. Three-dimensional computerized reconstruction methods have been used to produce two models that show the surface topography of the PBB and CN together, while other models revealed the appearance of different sides of the PBB only. The models accurately localized the common boundaries between the PBB and CN. Inside the brain stem, the boundary between the ventral CN and PBB was not always clear in sections stained for cell bodies and myelinated fibers. Close relationships between the PBB and pontine nuclei in the ventral portions of the pons were demonstrated. The reconstructions also showed the position of the tenia of the inferior velum of the fourth ventricle in relation to the PBB and CN. In contrast to the CN, only a relatively small portion of the PBB was located within the fourth ventricle. Results may be useful to work underway in this institution on implantation of the central electro-auditory prosthesis. Results might also be useful for further development of the surgical anatomy of the cerebellopontine angle.
Computer Simulation↗
Demonstration of lipofuscin and Nissl bodies in crystal violet stained sections using a fluorescence technique or pyronin Y stain.
This paper presents two simple, reliable methods for identification of lipofuscin and Nissl bodies in the same section. One method shows that lipofuscin stained with crystal violet retains its ability to fluoresce and can be observed under the fluorescence microscope after the stain has faded. Fading is accompanied by a gradual increase in the intensity of the fluorescence and is complete in about 5 min. Exciting illumination from this part of the spectrum also substantially fades staining of other autofluorescing tissue elements, such as lipids. Nonfluorescing structures, such as Nissl bodies, remain stained. By changing from transillumination with tungsten light to epifluorescent illumination and vice versa, both types of structures--Nissl bodies and lipofuscin--can be identified in the same section. The second technique uses pyronin Y for staining Nissl bodies in preparations previously stained with crystal violet. Nissl bodies are stained pink but lipofuscin remains violet. Lipofuscin in these sections also remains autofluorescent after the crystal violet stain has faded under violet or near-UV light.
Brain↗
Neurons of the inferior medullary velum in the cerebellopontine angle.
The edge of the inferior medullary velum (tenia) is attached in part to the surface of several structures localized in the cerebellopontine angle, including the cochlear nuclear complex and the pontobulbar body. Since superficial layers of these structures contain numerous neurons, we examined the possibility that neurons are also present within the velum. On light microscopy, we found groups of neurons accumulated immediately under the pia mater covering the tenia. The number of groups in different specimens varied from one to three, and the groups were rounded or oval in shape. A bundle of fibers running from the main mass of the brain stem toward these groups was revealed with a myelin-staining technique. The majority of neurons in the groups were angular in shape. These findings may contribute to our understanding of the general and surgical anatomy of the cerebellopontine angle.
Adult↗