The suboccipital fossa approach to the fundus of the internal auditory canal (IAC) at acoustic neurinoma surgery was investigated in 32 temporal bones. A microdissection was done under the operating microscope in a specially constructed holder so that the surgeon's exposure and angles of view through the craniotomy were mimicked. It was possible to obtain an unobstructed view of the transverse crest and the vestibular nerves in all specimens without the bony labyrinth being opened in the process. A prerequisite was that, as the posterior wall of the IAC was removed, drilling did not extend lateral to a line running through the midpoint of the craniotomy to the transverse crest. The distances of major structures from the posterior and superior pyramid surface were measured, using a special impression technique that made it possible to measure the thickness of the bony layer removed.
Light and electromicroscopic investigations of Reissner's membrane were undertaken on 10 cochleae from 6 patients with normal hearing for their age. The membrane consisted of two layers, an epithelium and a mesothelium separated by a basement membrane. The mesothelium was formed by a single thin layer which was intermittently discontinuous. The melanocytes were localized on the mesothelial side of the basement membrane. Their numbers was 2-4 times greater in the upper half of the basal turn and in the middle turn than elsewhere. The epithelium was much thicker and had more irregular features than the mesothelium. It was composed of two types of epithelial cells, flat and rounded. The flat cells were more regular in shape than the rounded cells and they were mainly distributed in the middle and apical turns. Judging from their structure they were in a resting state. The rounded cells covered a smaller area than the flat ones and had numerous microvilli. They assumed three different shapes, cuboidal, spindle-form and spherical and were arranged in four different patterns, namely bands, strands, whorls and clusters. The rounded cells were the most active according to the composition of the cytoplasm and dominated the cell population in the hook and the lower half of the basal turn where the age-related sensorineural degeneration is most apparent.
In 24 temporal bones from patients with otosclerosis prepared by the method of microdissection and surface preparations, otosclerotic foci could be clearly seen during removal of the otic capsule. The state of activity of each focus was estimated on the basis of its consistency and vascularity. Small anterior foci constituted the most common form of involvement of the otic capsule. All were judged to be inactive, and none of them appeared to have caused obvious sensorineural degeneration. No cases of “pure cochlear otosclerosis” were seen. Sensorineural degeneration was associated with large anterior foci which reached the upper basal turn. One specimen displayed a circumscribed sensorineural degeneration in the upper basal turn, with an almost exact correspondence between the location and extent of the cochlear lesion and the site of invasion by the otosclerotic process in the bone and endosteum bordering on scala media and scala tympani. It is postulated that a toxic factor had diffused from the focus and acted directly on the organ of Corti. When multiple foci were present they were usually poorly defined. The otosclerotic process involved the round window, with new lamellar bone formation in the scala tympani of the lower half of the basal turn. The most extensive sensorineural degeneration in the entire material was seen in this group. One specimen also had severe cochlear hydrops. In three specimens large shunts were observed to connect the otosclerotic foci with the cochlear vasculature, which was severely dilated. Where otosclerosis involved the endosteum of the scala tympani, loss of vessels was observed. One specimen with extensive active capsular otosclerosis had severe sensorineural degeneration of the vestibular system. Vestibular pathology in fenestrated ears is also described. In a specimen from a patient with no caloric reaction, numerous hair cells were present in the macular organs.
Ceramic stems, their lateral end capped with a modelled ossicle, or ceramic prostheses manufactured with a cap-shaped head were used as a columella from the stapes footplate to the tympanic membrane or a fascia graft in 41 ears operated on during 1982-1985. Six ears had no membrane perforations and no severe disease of the tympanic mucosa. Twelve ears underwent primary operations for cholesteatoma and 23 ears had revision surgery. Good hearing improvement occurred in well-aerated ears while hearing in ears with extensive tympanic disease did not improve after surgery. No tissue reactions to the ceramic prosthesis were observed and no prosthesis was extruded. Ceramic can be regarded as an acceptable alternative to bone for columella grafts used in surgery for chronic middle ear disease when the stapes superstructure is missing.
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