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Jian Wang, Fumitaka Yoshioka, Wonil Joo, Noritaka Komune, Vicent Quilis-Quesada, and Albert L. Rhoton Jr.

T he cochlea is the most anterior and medial part of the vestibulocochlear labyrinth. It lies anteromedial to the vestibule and semicircular canals, where it is embedded in the petrous part of the temporal bone adjacent to the petrous segment of the internal carotid artery , facial nerve , geniculate ganglion, internal acoustic meatus , and semicircular canals. The middle fossa surgical approaches directed through the temporal bone to the internal acoustic meatus, cerebellopontine angle, and petroclival region pass near but usually spare the cochlea

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Seong Min Kim, Ho Yun Lee, Han Kyu Kim, and Joseph M. Zabramski

/or combined middle fossa posterior approach, which both provide similar surgical fields. 1 To perform the anterior petrosal approach more safely, the use of possible anatomical landmarks, including the maxillary branch of the trigeminal nerve (V3), gasserian ganglion, greater superficial petrosal nerve (GSPN), petrous internal carotid artery (ICA), cochlea, geniculate ganglion, dura mater of the internal acoustic canal (IAC), labyrinthine portion of the facial nerve, vestibule, and superior semicircular canal can also be put to good use. Of these, the cochlea is well

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Nicolas Massager, Ouzi Nissim, Carine Delbrouck, Isabelle Delpierre, Daniel Devriendt, Françoise Desmedt, David Wikler, Jacques Brotchi, and Marc Levivier

fibers (eighth cranial nerve damage); compression or thrombosis of the internal auditory artery, leading to ischemic injury of the cochlea; or direct radiation injury to inner ear structures. 1 It has been shown that the components of the cochlea are likely to be damaged by radiation exposure after fractionated radiation therapy. 6 Although the purpose of radio-surgery is to deliver a high dose of radiation with a steep gradient into the tumor volume, structures located near the irradiated target will nevertheless receive a significant amount of radiation. Therefore

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Burak Sade and Joung H. Lee

(left) and postoperative (right) audiograms showing the marked improvement in the low-frequency range as well as the SRT and SDS. F ig . 2. Preoperative contrast-enhanced axial (A and B) and coronal (C and D) T1-weighted MR images demonstrating the middle fossa mass along the course of the GSPN and extending into the cochlea. Operation A left temporal craniotomy was performed. The initial intradural exploration revealed the tumor to be completely extradural. Therefore, the dura was closed and was then dissected off the petrous bone. The tumor was

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Hideyuki Kano, Douglas Kondziolka, Aftab Khan, John C. Flickinger, and L. Dade Lunsford

Common hypotheses for the development of hearing loss include direct compression of cochlear nerve fibers by an adjacent AN, the development of a conduction block followed by the degeneration of nerve fibers, compression and/or thrombosis of the internal auditory artery, and/or ischemic injury to the cochlea. 3 , 12 Therapeutic options include observation, microsurgical removal, SRS, SRT, or other forms of fractionated radiation therapy. Presently, radiosurgery is a well-established alternative to microsurgical removal of an AN. 10 In a recent study in which Gamma

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Johannes Kuchta, Steven R. Otto, Robert V. Shannon, William E. Hitselberger, and Derald E. Brackmann

S peech perception is dependent on both temporal and spectral (frequency) cues. In normal hearing the different frequencies of incoming sounds create a displacement at different points along the basilar membrane of the cochlea. This way the cochlea acts like a spectrum analyzer. It decomposes complex sounds into their frequency components. In auditory implants, the speech processor and the individual electrodes have to take over this task. There has been an intensive discussion in recent years regarding how many individual channels of spectral information are

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Noritaka Komune, Satoshi Matsuo, Koichi Miki, and Albert L. Rhoton Jr.

ear structures were exposed after removal of the posterior wall of the external acoustic canal and the tympanic membrane. E: Removal of the promontory, ossicles, and chorda tympani exposed the basal turn of the cochlea. F: Removing the bone inferior to the cochleariform process exposed the middle and apical turns of the cochlea. A. = artery; Ac. = acoustic; Ant. = anterior; Car. = carotid; CN = cranial nerve; Coch. = cochlea; Cochlear. = cochleariform; Cond. = condylar; Emin. = eminence; Endolymph. = endolymphatic; Eust. = eustachian; Ext. = external; For

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Shinya Watanabe, Masaaki Yamamoto, Takuya Kawabe, Takao Koiso, Tetsuya Yamamoto, Akira Matsumura, and Hidetoshi Kasuya

impacts of these factors. In addition to the aforementioned factors, cochlear dose was recently recognized as likely to be related to a decrease in hearing acuity after SRS. 2 , 3 , 9 , 16 , 21 , 22 , 25 , 33–35 Several in vivo studies have examined radiation effects on the cochlea, as previously reported. Hulcrantz et al. stated that in a pregnant mouse model, scanning electron microscopy revealed that both inner and outer hair cells were missing in large numbers of exposed animals, irrespective of the irradiation dose, and that remaining hair cells, as well as pillar

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Tomio Sasaki, Makoto Taniguchi, Ichiro Suzuki, and Takaaki Kirino

T he combined supra- and infratentorial approach or the transpetrosal—transtentorial approach has afforded the surgeon wide exposure of the petroclival region. 2–5 In those approaches, surgeons radically drill the petrous bone and the mastoid process, taking care not to injure the facial nerve. If hearing is to be preserved, care should be taken to avoid injuring the cochlea and the semicircular canals. Such drilling is a formidable procedure for neurosurgeons who are not conversant with the anatomy of temporal bone. Even performed by a neurootologist versed

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Carys Thomas, Salvatore Di Maio, Roy Ma, Emily Vollans, Christina Chu, M.Math., Brenda Clark, Richard Lee, Michael McKenzie, Montgomery Martin, and Brian Toyota

–Robertson. Determining Prognostic Factors for Posttreatment Hearing Deterioration Dosimetric, volumetric, and patient-related factors were analyzed; radiation doses to the cochlea and cochlear nucleus, ITV, GTV, PTV, preradiation Gardner–Robertson grade, patient age, and sex were retrospectively analyzed to determine the relationship with postradiation hearing status. The position of the cochlea was determined on bone window CT scans. The position of the cochlear nucleus was identified on the axial T1-weighted magnetization-prepared rapid acquisition gradient echo sequence images