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Pediatric and Adult Cochlear Implantation¹

¹ From the Departments of Radiology (R.J.W., J.I.L., M.A.B., A.K.) and Otolaryngology (C.L.W.D.), Mayo Clinic, 200 First Street SW, Rochester, MN 55905; and the Departments of Otolaryngology (L.B.L.) and Radiology (A.L.K.), Mayo Clinic, Jacksonville, Fla. Recipient of a Certificate of Merit award for an education exhibit at the 2001 RSNA scientific assembly. Received March 5, 2002; revision requested April 24; final revision received February 13, 2003; accepted February 19. Address correspondence to R.J.W. (e-mail: witte.robert@mayo.edu).

View larger version (78K): [in a new window]   Figure 1.  Drawing illustrates hearing aid function. Sound waves are amplified by the hearing aid (1). The tympanic membrane and ossicles convert the sound waves into mechanical energy (2). Pressure waves generated in the perilymphatic fluid pass from the scala vestibuli to the scala tympani (3). The hair cells in the organ of Corti convert this mechanical-pressure energy into an electrical impulse (4). The impulse travels through the spiral ganglia to the ventral and dorsal cochlear nuclei, located in the lateral brainstem adjacent to the foramen of Luschka (5). Crossed and uncrossed fibers carry the impulse through the lateral lemniscus, inferior colliculus, and medial geniculate body, and finally to the auditory cortex of the Heschl transverse temporal gyri (6).

View larger version (56K): [in a new window]   Figure 2.  Drawings illustrate cochlear implant function. The microphone receives the sound (1). The sound is sent to the speech processor, which analyzes and digitizes the sound into coded signals (2). The coded signals are sent to the transmitter, which sends the code across the skin to the internal implant (3). The implant converts the code into electrical signals (4). The signals are sent to the electrodes to stimulate the nondegenerated cochlear nerve spiral ganglia-axons (5). The electrical impulse travels normally along the remaining auditory pathway (6).

View larger version (83K): [in a new window]   Figure 3.  Drawing illustrates a cochlear implant. E = stimulator electrode array, G = ground electrode, M = magnet (which "binds" transcutaneously to the transmitter), R = receiver-stimulator. A U.S. quarter is shown for size comparison.

View larger version (46K): [in a new window]   Figure 4.  Drawings illustrate ABI function. The microphone receives the sound (1). The sound is sent to the speech processor, which analyzes and digitizes the sound into coded signals (2). The coded signals are sent to the transmitter, which sends the code across the skin to the internal implant (3). The implant converts the code into electrical signals (4). The signals are sent to electrodes to stimulate the cochlear nuclei in the brainstem (5). The electrical impulse travels normally along the remaining auditory pathway (6).

View larger version (30K): [in a new window]   Figure 5.  Drawings illustrate surgical technique. In A, a skin flap incision is made behind the ear. In B, after an intact canal wall mastoidectomy is performed, the facial recess is opened. A cochleostomy is then created by drilling anteriorly (arrow) from the round window into the basal turn of the cochlea. A = antrum, C = chorda tympani, F = facial nerve, HSC = horizontal semicircular canal, I = incus, R = round window, S = stapes. In C, an electrode array is placed (arrow) in the cochlea with an introducer.

View larger version (70K): [in a new window]   Figure 6.  Cochlear aplasia. Coronal CT scan of the temporal bone demonstrates bilateral cochlear aplasia.

View larger version (40K): [in a new window]   Figure 7.  Sequential 3D oblique sagittal constructive interference in the steady state (CISS) images of the lateral (top left) to middle (bottom right) IAC show the cochlear nerve (C) in the anteroinferior canal to be similar in size to the facial nerve (F). The closely approximated superior and inferior vestibular nerves (VN) are seen in the posterior canal.

View larger version (108K): [in a new window]   Figure 8a.  Absence of the cochlear nerve. (a) On a sagittal two-dimensional (2D) fast spin-echo MR image of the right IAC, the cochlear nerve is absent. Arrow indicates its expected location. (b) Coronal CT scan demonstrates a severely dysplastic cochlea (arrow).

View larger version (74K): [in a new window]   Figure 8b.  Absence of the cochlear nerve. (a) On a sagittal two-dimensional (2D) fast spin-echo MR image of the right IAC, the cochlear nerve is absent. Arrow indicates its expected location. (b) Coronal CT scan demonstrates a severely dysplastic cochlea (arrow).

View larger version (129K): [in a new window]   Figure 9a.  Absent and hypoplastic cochlear nerves. (a) Axial 3D CISS image shows a severely atretic right IAC with only a sliver of signal intensity (arrow). The cochlear nerve cannot be identified. B = adjacent basal cochlear turn. (b) Adjacent image shows the middle cochlear turn (M). (c) On a maximum-intensity-projection (MIP) image of the left inner ear, the left IAC (I) is narrowed. The cochlea (C) is unremarkable. (d) Sagittal 3D CISS image depicts a hypoplastic left cochlear nerve (C).

View larger version (121K): [in a new window]   Figure 9b.  Absent and hypoplastic cochlear nerves. (a) Axial 3D CISS image shows a severely atretic right IAC with only a sliver of signal intensity (arrow). The cochlear nerve cannot be identified. B = adjacent basal cochlear turn. (b) Adjacent image shows the middle cochlear turn (M). (c) On a maximum-intensity-projection (MIP) image of the left inner ear, the left IAC (I) is narrowed. The cochlea (C) is unremarkable. (d) Sagittal 3D CISS image depicts a hypoplastic left cochlear nerve (C).

View larger version (137K): [in a new window]   Figure 9c.  Absent and hypoplastic cochlear nerves. (a) Axial 3D CISS image shows a severely atretic right IAC with only a sliver of signal intensity (arrow). The cochlear nerve cannot be identified. B = adjacent basal cochlear turn. (b) Adjacent image shows the middle cochlear turn (M). (c) On a maximum-intensity-projection (MIP) image of the left inner ear, the left IAC (I) is narrowed. The cochlea (C) is unremarkable. (d) Sagittal 3D CISS image depicts a hypoplastic left cochlear nerve (C).

View larger version (140K): [in a new window]   Figure 9d.  Absent and hypoplastic cochlear nerves. (a) Axial 3D CISS image shows a severely atretic right IAC with only a sliver of signal intensity (arrow). The cochlear nerve cannot be identified. B = adjacent basal cochlear turn. (b) Adjacent image shows the middle cochlear turn (M). (c) On a maximum-intensity-projection (MIP) image of the left inner ear, the left IAC (I) is narrowed. The cochlea (C) is unremarkable. (d) Sagittal 3D CISS image depicts a hypoplastic left cochlear nerve (C).

View larger version (133K): [in a new window]   Figure 10a.  Cochlear dysplasia. (a) Axial CT scan of the left temporal bone shows incomplete partition (Mondini dysplasia) of the middle and apical cochlear turns (arrow). (b) Axial CT scan of the right temporal bone shows more severe cochlear dysplasia (black arrow) with associated vestibular and semicircular canal anomalies (white arrow). (c) Axial CT scan demonstrates a cochlea with a normal middle and apical turn (arrow) for comparison.

View larger version (124K): [in a new window]   Figure 10b.  Cochlear dysplasia. (a) Axial CT scan of the left temporal bone shows incomplete partition (Mondini dysplasia) of the middle and apical cochlear turns (arrow). (b) Axial CT scan of the right temporal bone shows more severe cochlear dysplasia (black arrow) with associated vestibular and semicircular canal anomalies (white arrow). (c) Axial CT scan demonstrates a cochlea with a normal middle and apical turn (arrow) for comparison.

View larger version (125K): [in a new window]   Figure 10c.  Cochlear dysplasia. (a) Axial CT scan of the left temporal bone shows incomplete partition (Mondini dysplasia) of the middle and apical cochlear turns (arrow). (b) Axial CT scan of the right temporal bone shows more severe cochlear dysplasia (black arrow) with associated vestibular and semicircular canal anomalies (white arrow). (c) Axial CT scan demonstrates a cochlea with a normal middle and apical turn (arrow) for comparison.

View larger version (128K): [in a new window]   Figure 11.  Electrode extrusion through the cochlear wall. Slightly off-axis axial reformatted CT scan of an extruded electrode array shows the stimulator electrode (E) protruding through the basal cochlear turn (B).

View larger version (131K): [in a new window]   Figure 12.  Postoperative anteroposterior radiograph of a left cochlear implant shows the normal position of the electrode array within the basal and middle cochlear turns (arrows).

View larger version (123K): [in a new window]   Figure 13.  Oblique axial reformatted image generated from a 3D CISS data set clearly delineates the entire cisternal portion of the vestibulocochlear trunk (arrow).

View larger version (137K): [in a new window]   Figure 14.  On an MIP image of the left inner ear generated from a 3D CISS data set, the cochlear turns and scalar chambers are readily discerned. A = apical turn, B = basal turn, M = middle turn, S = semicircular canal, V = vestibule.

View larger version (97K): [in a new window]   Figure 15a.  Otomastoiditis. (a) Axial CT scan demonstrates increased attenuation of the mastoid process (black arrows) and middle ear (white arrow). (b) Axial CT scan demonstrates dense mastoid sclerosis (arrows).

View larger version (110K): [in a new window]   Figure 15b.  Otomastoiditis. (a) Axial CT scan demonstrates increased attenuation of the mastoid process (black arrows) and middle ear (white arrow). (b) Axial CT scan demonstrates dense mastoid sclerosis (arrows).

View larger version (175K): [in a new window]   Figure 16a.  Labyrinthitis. (a) Axial 3D fast-recovery fast spin-echo image demonstrates replacement of the normally bright endolymphatic signal intensity of the basal turn of the cochlea (arrow). (b) On an axial contrast material-enhanced T1-weighted MR image, the basal turn of the cochlea demonstrates enhancement (arrow).

View larger version (151K): [in a new window]   Figure 16b.  Labyrinthitis. (a) Axial 3D fast-recovery fast spin-echo image demonstrates replacement of the normally bright endolymphatic signal intensity of the basal turn of the cochlea (arrow). (b) On an axial contrast material-enhanced T1-weighted MR image, the basal turn of the cochlea demonstrates enhancement (arrow).

View larger version (103K): [in a new window]   Figure 17.  Labyrinthine ossification in a patient with a history of meningitis and sensorineural hearing loss. Coronal CT scan shows dense cochlear ossification (arrow).

View larger version (112K): [in a new window]   Figure 18.  Facial nerve dehiscence. Coronal CT scan demonstrates a dehiscent left facial nerve (arrow), which is at risk for injury during cochleostomy performed prior to electrode array implantation.

View larger version (111K): [in a new window]   Figure 19.  Bilateral retrofenestral otosclerosis in a 60-year-old patient. Axial CT scan of the right temporal bone demonstrates the typical osteopenic appearance of the bony labyrinth in retrofenestral otosclerosis (arrows). Such a finding does not preclude implantation.

View larger version (185K): [in a new window]   Figure 20a.  Absent right facial nerve in a 3-year-old cochlear implant candidate with bilateral sensorineural hearing loss and right facial paralysis. (a) On a sagittal 3D fast spin-echo MR image of the right IAC, the right facial nerve is absent (F). Although sensorineural hearing loss was most severe on the right side, the cochlear nerve (C), albeit small, is present. VN = vestibular nerve. (b) Sagittal 3D fast spin-echo MR image demonstrates a normal left IAC. C = cochlear nerve, F = left facial nerve, VN = vestibular nerve.

View larger version (170K): [in a new window]   Figure 20b.  Absent right facial nerve in a 3-year-old cochlear implant candidate with bilateral sensorineural hearing loss and right facial paralysis. (a) On a sagittal 3D fast spin-echo MR image of the right IAC, the right facial nerve is absent (F). Although sensorineural hearing loss was most severe on the right side, the cochlear nerve (C), albeit small, is present. VN = vestibular nerve. (b) Sagittal 3D fast spin-echo MR image demonstrates a normal left IAC. C = cochlear nerve, F = left facial nerve, VN = vestibular nerve.

View larger version (133K): [in a new window]   Figure 21a.  Enlarged endolymphatic sac. (a) Axial 3D fast-recovery fast spin-echo MR image shows an enlarged left endolymphatic sac (arrow). (b) Surface-rendered reformatted image generated from the same data set also shows the enlarged sac (arrows).

View larger version (164K): [in a new window]   Figure 21b.  Enlarged endolymphatic sac. (a) Axial 3D fast-recovery fast spin-echo MR image shows an enlarged left endolymphatic sac (arrow). (b) Surface-rendered reformatted image generated from the same data set also shows the enlarged sac (arrows).

View larger version (103K): [in a new window]   Figure 22a.  (a) Dilated vestibular aqueduct in a patient with bilateral sensorineural hearing loss (worse on the right side). Axial CT scan of the right temporal bone shows a dilated vestibular aqueduct (white arrow). The diameter of the duct is greater than that of the adjacent posterior semicircular canal (black arrow). (b) Axial CT scan obtained in a different patient demonstrates a normal-sized vestibular aqueduct (white arrow). The posterior semicircular canal (black arrow) is shown for comparison.

View larger version (128K): [in a new window]   Figure 22b.  (a) Dilated vestibular aqueduct in a patient with bilateral sensorineural hearing loss (worse on the right side). Axial CT scan of the right temporal bone shows a dilated vestibular aqueduct (white arrow). The diameter of the duct is greater than that of the adjacent posterior semicircular canal (black arrow). (b) Axial CT scan obtained in a different patient demonstrates a normal-sized vestibular aqueduct (white arrow). The posterior semicircular canal (black arrow) is shown for comparison.

View larger version (99K): [in a new window]   Figure 23.  Aberrant carotid artery. On a coronal CT scan of the right temporal bone, the right internal carotid artery (arrow) has an aberrant course and overlies the cochlear promontory.

View larger version (115K): [in a new window]   Figure 24a.  Brainstem infarct resulting in profound sensorineural hearing loss. (a) Axial T2-weighted MR image shows an unsuspected infarct of the left pons and brachium pontis (arrow). (b) More inferior axial T2-weighted MR image shows atrophy of the left medulla at the level of the eighth nerve nuclei (arrow).

View larger version (114K): [in a new window]   Figure 24b.  Brainstem infarct resulting in profound sensorineural hearing loss. (a) Axial T2-weighted MR image shows an unsuspected infarct of the left pons and brachium pontis (arrow). (b) More inferior axial T2-weighted MR image shows atrophy of the left medulla at the level of the eighth nerve nuclei (arrow).

View larger version (137K): [in a new window]   Figure 25.  Hemosiderosis in a patient whose primary presenting symptom was bilateral sensorineural hearing loss, although other cranial neuropathies were also present. Axial gradient-echo MR image accentuates dark hemosiderin deposits that line the brainstem and adjacent cisterns (arrows).

View larger version (156K): [in a new window]   Figure 26.  Artifact from an MR imaging-compatible receiver-stimulator. Although there is considerable local artifact from the implant, the majority of the image is unaffected.

View larger version (156K): [in a new window]   Figure 27.  Surface-rendered virtual endoscopic image generated from a 3D CISS data set shows the interior of the IAC (superior view). F = facial nerve (anterior), V = vestibular nerve.

View larger version (55K): [in a new window]   Figure 28.  Facial and cochlear nerve measurements. Computer screen illustrates how a sagittal 3D fast-recovery fast spin-echo data set is used to generate regions of interest of the facial (red) and cochlear (green) nerves.