Graeme Clark Collection
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Item3D reconstruction of the temporal bone in cochlear implant surgery( 1992)In the preoperative evaluation of prospective cochlear implant patients high resolution computed tomography (CT) is routinely performed. Sectional images of the temporal bones in the axial or coronal plane can give essential information about cochlear or mastoid pathology that will enable the surgeon to select a side for operation and alert him to surgical obstacles he might encounter. Even with the help of serial CTs it has always been very difficult to visualize the complicated anatomy of the normal temporal bone. In particular, in a patient with a malformation or a previous operation, even an experienced otologic surgeon cannot always avoid unwelcome surprises. In analyzing the CT films he must still try to form a 3-dimensional image in his mindby looking through a large number of different pictures s. Consequently, to make it easier to understand, a lot of effort has been put into the development of 3-dimensional (3D) imagingof the object. A variety of 3D graphics systems that provide multi-angled surface renderings from serial CT images have become available in recent years and proved to be useful in craniofacialreconstructive, orthopedic and neurosurgical planning. We applied our own image analysis technique to produce three-dimensional reconstructions of temporal bones in patients and in isolation on a personal computer9 We focused on the use of this method for the preoperative examination and surgical planning for cochlear implantation as well as for our research purposes. This system and the results are presented here.
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ItemSurgery for multielectrode cochlear implants( 1987)For the surgery of the NUCLEUS Cochlear Implant (CI) in general anaesthesia we use a skin cut beginning at the bottom of the entrance to the outer ear canal, following the posterior circumference to a point nearly 12 o'clock. From here the incision runs superiorly to the tragus until two or three centimetres above the pinna base and in a wide smooth circle in direction to the occiput. The wide circle is necessary to get a distance of about 2 cm away from the package and also to guarantee the blood supply by the occipital artery and by the postauricular artery as well.
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ItemHistopathology following electrode insertion and chronic electrical stimulation(Raven Press, 1985)We have examined a number of safety issues associated with cochlear implants. This work has been primarily designed to evaluate the histopathological effects of intracochlear electrode implantation and chronic electrical stimulation. The results of these studies may be summarized as follows: 1) The insertion of the banded free-fit scala tympani array into human cadaver temporal bones produces minimal damage, occurring primarily to a localized region of the spiral ligament. This damage would not result in significant neural degeneration and thus, would not compromise the efficacy of the multiple channel device; 2) chronic intracochlear electrical stimulation for continuous periods of 500 to 2000 hours, using charge balanced biphasic current pulses developing charge densities of 18-32 }?C/cm2. geom./phase, does not adversely affect the spiral ganglion cell population; 3) labyrinthine infection severely reduces the viable spiral ganglion cell population; 4) the formation of new bone present in approximately half of the animals we have implanted --is not associated with electrical stimulation per se; 5) scanning electron microscope studies of electrodes subjected to long periods of intracochlear electrical stimulation reveals minimal platinum dissolution when compared with unstimulated control electrodes, and electrodes that have been stimulated for similar periods in inorganic saline.
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ItemSelection of patients for multiple-channel cochlear implantation(Raven Press, 1985)Only profoundly, bilaterally deaf adults are considered for evaluation. It is necessary to determine that the patient's communication ability cannot be improved to any significant degree with conventional hearing aids currently available. Initial assessment consists of audiometry, hearing aid evaluation(s), otological and medical examination, and for patients with no recent experience with hearing aids, a hearing aid trial. Polytome x-rays of temporal bones is carried out to ensure that cochlea structures are not grossly abnormal. Electrical stimulation of the promontory is used to confirm the presence of residual auditory nerve fibers. Where there is an audiometric difference between ears, the poorer ear is chosen for implantation provided there are no other contraindications. Intensive counselling is carried out to enable patients to make a fully informed decision about implantation. Patients undergo a battery of speech discrimination and lipreading tests with their hearing aid after their hearing aid trial. This is to provide a baseline for comparison with postoperative results and to assess the benefit obtained from the hearing aid. Any significant improvement in test results when using a hearing aid over lipreading alone would be a contraindication for implantation. Medical assessment is carried out as for any major surgery, including pathology, respiratory function tests and cardiovascular assessment. Particular emphasis is placed on infection prevention immediately preoperatively and during surgery.