Impact of inner ear malformation and cochlear nerve deficiency on the development of auditory-language network in children with profound sensorineural hearing loss

Profound congenital sensorineural hearing loss (SNHL) prevents children from developing spoken language. Cochlear implantation and auditory brainstem implantation can provide partial hearing sensation, but language development outcomes can vary, particularly for patients with inner ear malformations and/or cochlear nerve deficiency (IEM&CND). Currently, the peripheral auditory structure is evaluated through visual inspection of clinical imaging, but this method is insufficient for surgical planning and prognosis. The central auditory pathway is also challenging to examine in vivo due to its delicate subcortical structures. Previous attempts to locate subcortical auditory nuclei using fMRI responses to sounds are not applicable to patients with profound hearing loss as no auditory brainstem responses can be detected in these individuals, making it impossible to capture corresponding blood oxygen signals in fMRI. In this study, we developed a new pipeline for mapping the auditory pathway using structural and diffusional MRI. We used a fixel-based approach to investigate the structural development of the auditory-language network for profound SNHL children with normal peripheral structure and those with IEM&CND under 6 years old. Our findings indicate that the language pathway is more sensitive to peripheral auditory condition than the central auditory pathway, highlighting the importance of early intervention for profound SNHL children to provide timely speech inputs. We also propose a comprehensive pre-surgical evaluation extending from the cochlea to the auditory-language network, showing significant correlations between age, gender, Cn.VIII median contrast value, and the language network with post-implant qualitative outcomes.

A 3-Year Follow-Up and Radiological Analysis of Cochlear Implantation Patients with Cochlear Nerve Deficiency and Modiolar Deficiency-Type Malformations

OBJECTIVE

Cochlear nerve deficiency (CND) is often combined with modiolar deficiency-type inner ear malformations, which cause variable cochlear implantation (CI) outcomes. We aimed to assess the postoperative development of auditory and speech perception in CND patients with modiolar deficiency-type malformations after 3 years of follow-up to determine the factors correlated with CI outcomes.

METHODS

Sixty-seven CND patients with modiolar deficiency-type malformations who underwent CI surgery were retrospectively reviewed. Modiolar deficiency-type malformations included common cavity (CC), cochlear hypoplasia (CH) (including CH-I and CH-II) and incomplete partition-I (IP-I). Categorical auditory performance (CAP) and the infant-toddler meaningful auditory integration scale (MAIS) were used to assess auditory ability. The speech intelligibility rating (SIR) and meaningful use of speech scale (MUSS) were used to assess the speech intelligibility of these CI patients. The CI outcomes were evaluated at 0, 12, 24 and 36 months after implant activation.

RESULTS

All patients demonstrated improvements in auditory ability and speech intelligibility after CI. There were no significant differences in CI outcomes at any time point according to the malformation type. The number of nerve bundles within the internal auditory canal (IAC) showed significant differences at 12, 24 and 36 months after CI ( p < 0.05). Patients with one nerve bundle had relatively poor CI outcomes.

CONCLUSIONS

CND patients with modiolar deficiency-type malformations showed continuous improvement in auditory and speech abilities after CI. Compared with malformations, the number of nerve bundles should be given more attention when selecting the side for CI.

[Cochlear nerve continuity preservation during retrosigmoid ablative osteotomy of the internal auditory canal for advanced vestibular schwannomas]

The data of 86 patients with retrosigmoid microsurgical resection of vestibular schwannoma in tumor stage Koos II-IV were evaluated. In more than two thirds of the cases it was shown that the cochlear nerve followed the facial nerve, which is easily identified by electroneurography, in recurrent similar patterns in the region of the internal auditory canal. Starting from the fundus, this facilitated early identification and thus preservation of continuity of the cochlear nerve in the course of the internal auditory canal. This was of particular importance when safe functional preservation could not be guaranteed due to tumor size or formation despite intraoperative derivation of somatosenoric potentials, but when the possibility of subsequent hearing rehabilitation with a cochlear implant should be granted. Preoperative MRI sequences gave an indication of the possible nerve courses in some cases, but intraoperative imaging in the internal auditory canal was superior to MRI.

Audiological Features in 63 Patients With Cochlear Nerve Deficiency

OBJECTIVE

We aimed to investigate the clinical features of cochlear nerve deficiency (CND), and in particular, the long-term course of hearing disability and audiogram shapes.

STUDY DESIGN

Retrospective observational nonrandomized group study.

SETTING

Academic medical center.

PATIENTS/INTERVENTIONS

The subjects were 63 children with congenital hearing loss who visited our hospital between 2009 and 2019 and underwent MRI, based on which they were diagnosed with CND. There were 61 cases of unilateral CND and two cases of bilateral CND.

MAIN OUTCOME MEASURES

Imaging tests by MRI and CT and audiometric assessments by pure-tone audiometry and distortion product otoacoustic emission were performed.

RESULTS

Among the cases of CND diagnosed by assessing the cochlear nerve on MRI, approximately 20% of the bony cochlear nerve canals that could be assessed on CT were normal. Of the 61 cases diagnosed with unilateral CND, 55 cases had cochlear nerve aplasia (90.2%), and six had cochlear nerve hypoplasia (9.8%), with a mean hearing ability of 92.2 and 94.6 dB HL, respectively. Thus, the majority of cases had severe-to-profound hearing loss. The overall audiometric patterns were 78.7% flat, 9.8% cookie-bite, and 9.8% high-frequency. Six of 61 cases (9.8%) had a distortion product otoacoustic emission (DPOAE) response based on the affected side, and none of the cases lost the response during follow-up.

CONCLUSIONS

Herein, we report the largest study on CND and performed CND image and audiometric assessments. Accurately in diagnosing CND requires not only CT but also MRI assessment. Hearing loss is often severe to profound; however, various audiometric patterns have been observed. CND includes a small number of cases that respond to DPOAE, indicating that some CND cases are clinically diagnosed with auditory neuropathy spectrum disorder (ANSD). A sustained DPOAE response might help in differentiating CND from other ANSDs. Children with congenital deafness who have passed the newborn hearing screening by DPOAE should be examined by MRI to rule out CND.

[The imaging characteristics and prognosis of patients with cochlear implants whose cochlear nerves are not shown on MRI]

Objective: To analyze the temporal bone CT and inner ear magnetic resonance imaging characteristics of cochlear implant patients with no cochlear nerve display in the inner auditory canal under MRI. To retrospectively analyze the long-term hearing and speech rehabilitation effects of such patients after cochlear implant. And to analyze the correlation between the results of imaging examinations and the postoperative effects of cochlear implant patients with this type of cochlear nerve deficiency. Methods: A total of 88 children with cochlear nerve deficiency, who underwent cochlear implantation in Shandong Provincial ENT Hospital from May 2014 to October 2018, were enrolled. Patients with cochlear malformations were excluded,only the patients with cochlear nerve deficiency whose cochlear structure was normal and no cochlear nerve displayed in inner auditory canal under MRI were enrolled. There were 64 patients, including 4 bilaterally implanted, 68 ears in total, with an average age of (2.8±1.7) years (range 1-6 years) at the time of implantation. The implanted product was Cochlear, including 24RECA and 512 models. All patients underwent inner ear magnetic resonance imaging and temporal bone CT scan before operation. Auditory speech function assessments were performed at 12 months, 24 months, and 36 months after surgery, including categories of auditory performance (CAP), speech intelligibility rating (SIR) and hearing aid threshold test. The imaging evaluation content included the width of the cochlear nerve canal of temporal bone CT, the width of the internal auditory canal, the width of the auditory nerve at the cerebellopontine angle of the inner ear MRI, and the ratio of the facial nerve to the width of the auditory nerve at the cerebellopontine angle. The correlations between the results of postoperative hearing aid hearing threshold, CAP, SIR and imaging results were analyzed. Results: Among the 64 cases of cochlear nerve not shown under MRI, 56 ears with CT data showed that the width of the cochlear nerve canal in temporal bone CT was (0.72±0.30) mm (mean±standard deviation, the same below), and the width of the internal auditory canal was (4.07±1.10) mm; 66 ears with MRI data showed that the diameter of the auditory nerve at the cerebellopontine angle of the inner ear MRI was (1.58±0.27) mm, the diameter of the facial nerve was (1.57±0.27) mm, and the ratio of the diameter of the facial nerve to the auditory nerve was (1.02±0.23). The average hearing thresholds at 12, 24, and 36 months after surgery were (46.8±2.5) dB HL, (40.7±0.8) dB HL, and (36.8±1.5) dB HL, respectively. The preoperative and postoperative CAP scores at 12, 24 and 36 months were (1.0±1.0), (3.8±1.4), (4.5±1.4) and (5.1±0.7) points, respectively. The preoperative and postoperative SIR scores at 12, 24, and 36 months were (1.1±0.3), (1.9±0.9), (2.5±0.9), and (2.9±0.6) points, respectively. The hearing threshold at 24 months after surgery was negatively correlated with the width of the internal auditory canal of temporal bone CT (r=-0.349, P=0.037), and the hearing threshold at 36 months after surgery was positively correlated with the ratio of the diameter of the facial nerve to the auditory nerve at the cerebellopontine angle of the inner ear MRI (r=0.740, P=0.001). Conclusions: Children with cochlear implants whose cochlear nerves are not shown on MRI can benefit from cochlear implantation, and their speech and auditory functions can improve significantly after surgery. The width of the internal auditory canal in the temporal bone CT and the ratio of the diameter of the facial nerve to the auditory nerve at the cerebellopontine angle of the inner ear MRI may be related to the long-term hearing threshold after surgery.

[The analysis of the characteristics of hearing loss in patients with cochlear nerve aphasia identified by MRI]

Objective:To explore the characteristics of hearing loss in patients with cochlear nerve aphasia（CNA） and to provide evidences for diagnosis and treatment of cochlear nerve aphasia. Methods:A retrospective study was performed. A total of 51 cases were included in the study. The data of hearing test, inner auditory canal MRI and temporal HRCT were analyzed. Results:77.19% of the affected ears had extremely severe hearing loss, and 7.02% of the affected ears had moderate hearing loss. The residual hearing was concentrated in low-medium frequency. A CNA ear with bone cochlear nerve canal atresia can exhibited moderate hearing loss. Conclusion:The patient with CNA may still present residual hearing function. CNA could not be excluded in patients with moderate hearing loss. The "three-dimensional integration" comprehensive evaluation system, which includesinternal auditory canal MRI, temporal thin-layer CT scan and audiology evaluation, could be helpful to the diagnosis of cochlear nerveaphasia.

Bilateral cochlear nerve absence in a 3 year old child with VACTERL association

We report a case of a 3 year old boy with bilateral profound sensorineural hearing loss diagnosed from New Born Hearing Screening, with severe form of VACTERL association. He was referred to our Cochlear Implant Unit for assessment with regard to the possibility of cochlear implantation. MRI findings have showed bilateral vestibulocochlear cystic abnormalities. Only single nerve noted within the IAM on the right and likely single nerve within the IAM on the left. Hence, decision was made not to offer cochlear implantation. This is the first report of severe bilateral cochleovestibular nerve abnormalities to be associated with VACTERL.

Restudy of malformations of the internal auditory meatus, cochlear nerve canal and cochlear nerve

The present study aims to restudy the correlation between the internal auditory meatus (IAM), the cochlear nerve canal (CNC), the cochlear nerve (CN) and inner ear malformations. In this retrospective study design, the abnormal diameter of the IAM, CNC and CN in patients with any kind of inner ear malformations was evaluated using multi-slice spiral computed tomography (MSCT) (37 patients) and magnetic resonance imaging (MRI) (18 patients). Of 37 MSCT-diagnosed patients, 2 had IAM atresia, 11 IAM stenosis, 22 enlarged IAM, and 2 normal IAM with an abnormal CN. MRI diagnoses of 18 patients revealed 8 cases of aplastic CN, 6 hypoplastic CN, and 4 normal CN. CNC stenosis was associated with CN hypoplasia (P < 0.001). Patients with absent or stenotic IAM had less CN development than those with normal or enlarged IAM (P = 0.001). We propose a modification of the existing classification systems with a view to distinguishing malformations of the IAM, CNC and CN.

Sudden deafness and facial diplegia in Guillain-Barré Syndrome: radiological depiction of facial and acoustic nerve lesions

We herein report a 26-year-old man with Guillain-Barré Syndrome (GBS) coexisting facial nerve palsy (FP) and deafness. He developed deafness, facial weakness, and limb weakness and numbness. Neurological examination showed facial diplegia, bilateral hypoacusia, areflexia and sensorimotor deficits in the distal limbs. The nerve conduction study findings supported the diagnosis of the demyelinating polyneuropathy. An audiogram revealed sensorineural hearing loss of 40-50 dB. Auditory brainstem responses disclosed no elicitation of waves I to IV on both sides. Magnetic resonance imaging depicted abnormal enhancement in bilateral facial and acoustic nerves. Physicians should pay more attention to auditory dysfunction in GBS patients with FP.

[Observation of foramina hypoplasia within internal auditory canal fundus with CT virtual endoscopy]

OBJECTIVE

To observe normal and abnormal findings of foramina within internal auditory canal (IAC) fundus with Virtual Endoscopy of multisection helical Computed Tomography.

METHOD

CT scanning of temporal bone was undergone in 25 volunteers (50 ears) in the normal group, in 8 cases (13 ears) with foramina hypoplasia within IAC fundus which were shown on CT and MRI images. CT virtual endoscopy (CTVE) findings were observed in the normal and abnormal groups. The lower threshold value was 900-1200 HU, the upper value was 3,071 HU in CTVE definitions.

RESULT

The shape and position of foramina within IAC fundus were shown on the CTVE image, 50 foramina within IAC fundus were shown in all normal cases. In abnormal group, 9 ears were shown as IAC fundus disorder and foramina absent, only 1 foramina was shown in 1 ear, 2 foramen in 4 ears, 3 foramen in 2 ears, 4 foramen in 2 ears; Abnormal shape of cochlear nerve foramina was seen in 4 ears. Other malformations were also shown, including IAC malformations in 3 ears and inner ear malformations in 8 ears.

CONCLUSION

CTVE is useful to show the shape and position of normal foramina and pathological changes in the patients with foramina hypoplasia within IAC fundus.

Isolated cochlear nerve hypoplasia with various internal auditory meatus deformities in children

OBJECTIVES

We report neuro-otological findings in isolated congenital cochlear nerve hypoplasia with various bony deformities and evaluate relationships between functional impairment and the radiologic dimensions of the internal auditory meatus (IAM).

METHODS

We performed imaging and functional analyses on consecutive juvenile or adolescent patients between 2001 and 2005 with "isolated" unilateral hypoplasia of the cochlear nerve, without inner ear anomaly or other deformities.

RESULTS

Among 20 patients with unilateral profound deafness who underwent imaging studies, 10 (50%) passed the inclusion criteria. In all affected ears, auditory brain stem responses were absent and the speech discrimination score was very poor (0% to 5%). Distortion product otoacoustic emissions were good in 2 ears, fair in 1 ear, and poor in 7 ears. Caloric responses were absent in 2 ears, reduced in 3 ears, and normal in 5 ears. Inferior vestibular nerve function and facial nerve function were normal in all ears. Distortion product otoacoustic emissions and caloric responses tended to be better in ears with less severe narrowing of the IAM.

CONCLUSIONS

The risk of co-involvement of the inner ear and superior vestibular nerve functions is higher in the presence of a narrower bony IAM. Cochlear nerve hypoplasia is proposed as one of the most important causes of juvenile unilateral deafness because of its unexpectedly high incidence.

Value of Computed Tomography in the Evaluation of Children With Cochlear Nerve Deficiency

OBJECTIVE

To assess the predictive value of high-resolution computed tomography (HRCT) in the evaluation of children with cochlear nerve deficiency (CND).

STUDY DESIGN

Retrospective review of medical records.

SETTING

: Tertiary referral center, hospital setting.

PATIENTS

Nineteen children (31 ears) with CND.

INTERVENTIONS

Magnetic resonance imaging (MRI), HRCT, and audiologic evaluation.

MAIN OUTCOME MEASURES

Comparisons of the morphology of the internal auditory canal (IAC), the bony cochlear nerve canal (BCNC) as seen on HRCT, and audiologic data.

RESULTS

Of 12 ears with MRI evidence of an absent cochlear nerve (CN) and a normal-size IAC, all had a patent BCNC as revealed by HRCT. Four of these ears failed auditory stimulation after cochlear implantation, confirming clinically significant CND. Of 15 ears with a narrow IAC and a single nerve visible on MRI, 2 (13.3%) had a normal-size BCNC, 4 (26.7%) were narrow, and 9 (60.0%) were absent. One ear with a narrow IAC, normal BCNC, and a single nerve as revealed by MRI has benefited from cochlear implantation.

CONCLUSION

Using BCNC patency, as revealed by HRCT, as a means of identifying CND would miss all cases of absent CNs in the setting of a normal-size IAC. Thus, MRI should be the primary modality for imaging children with severe to profound sensorineural hearing loss. When MRI demonstrates a single nerve within a narrow IAC, the addition of HRCT can further identify more than half of these cases as involving absent CNs because of an absent BCNC. In a subset of patients, CN status remains indeterminate.

Interaction of Cochlear Nucleus Explants With Semiconductor Materials

OBJECTIVE/HYPOTHESIS

Implantable hearing devices such as cochlear implants and auditory brainstem implants deliver auditory information through electrical stimulation of auditory neurons. The combination of microelectronic electrodes with auditory nerve cells may lead to further improvement of the hearing quality with these devices. Whereas several kinds of neurons are known to grow on semiconductor substrates, interactions of cochlear nucleus (CN) neurons with such materials have yet to be described.

MATERIALS AND METHODS

To investigate survival and growth behavior of CN neurons on different semiconductor materials. CN explants from postnatal day 10 Sprague-Dawley rats were cultured for 96 hours in Neurobasal medium on polished and unpolished silicon wafers (p-type Si [100] and p-type Si3N4[100]) as well as plastic surface. These surfaces had been coated with poly-L-lysine and laminin. Neuronal outgrowth was examined using image analysis software after immunohistologic staining for neurofilament. Neurite length and directional changes were quantified. Additionally, neurite morphology and adhesion to the semiconductor material was evaluated by scanning electron microscopy.

RESULTS

Although proper adhesion of CN explants was seen, no neurite growth could be detected on unpolished silicon wafers (Si and Si3N4). Compared with the other test conditions, polished, laminin-coated Si3N4 wafers showed best biocompatibility regarding neurite length and number per explant. CN explants developed a mean of eight neurons with an average length of 236 mum in 96 hours of culture on these wafers.

CONCLUSION

The results of this study demonstrate the general possibility of CN neuron growth in culture on semiconductors in vitro. The differences in neuron length and number per explant indicate that the growth of CN neurons is influenced by the semiconductor substrate as well as extracellular matrix proteins, with laminin-coated p-type Si3N4[100] being a preferable material for future hybrid experiments on auditory-neuron semiconductor chips.

A case of cochlear implant with internal mechanical failure

Cochlear implantation has been performed since the 1970s and has been proven to be an effective treatment for profoundly deaf people. In some cases re-implantation has also been reported due to trauma causing implant damage, mechanical failure, extrusion, and wound infections, or device upgrade. We present a case of a 9-year-old boy with a cochlear implant in which mechanical failure occurred after a blow to his temporal region. The clinical presentation and radiographic imaging findings suggested that the cause of mechanical failure was internal failure. We performed cochlear re-implantation to the same ear and it worked well. The explanted device analysis by the manufacturer concluded that the device had failed due to a cracked hybrid integrated circuit.

Evaluation of Cochlear Nerve Imaging in Severe Congenital Sensorineural Hearing Loss

The route of the cochlear nerve can be imaged using computed tomography (CT) or magnetic resonance imaging (MRI). To gain information about the cochlear nerve, we conducted a trial measuring the width of the cochlear nerve canal (CNC) using CT. When we examined images of the route of the cochlear nerve on MRI, both in ears with congenital sensorineural hearing loss (SNHL) and normal ones, we found that in ears in which the CNC was narrower than 1.5 mm with CT, images of cochlear nerve deficiency could be seen in that ear with MRI.

Role of CT and MRI in the preoperative evaluation of auditory brainstem implantation in patients with congenital inner ear pathology

PURPOSE

The purpose of this study was to evaluate the reliability of computed tomography (CT) and magnetic resonance imaging (MRI) in characterising cochlear nerve anomalies in auditory brainstem implant candidates with congenital hearing loss.

MATERIALS AND METHODS

Seventeen patients affected by congenital sensorineural hearing loss were examined by CT and MRI. Inner ear malformations eligible for auditory brainstem implants were classified according to the Casselman classification. All patients subsequently received auditory brainstem implants.

RESULTS

Suspected congenital anomalies were confirmed by CT and MRI in all 17 patients. There were 5/17 bilateral cochlear nerve aplasias and 12/17 cochleovestibular anomalies. Of these, 5/12 patients had a common cochleovestibular cavity, 2/12 had bilateral cochlear aplasia and cochlear nerve agenesis, 1/12 had type I incomplete partition, 2/12 had type II incomplete partition and 2/12 had cochlear hypoplasia.

CONCLUSIONS

Preoperative CT and MRI assessment of patients with sensorineural hearing loss is reliable. MRI provided additional information, identifying the possible absence of cochlear nerve and excluding other central nervous system (CNS) diseases.

Pre-perioperative, transtympanic electrically evoked auditory brainstem response in children

The purpose of this study was to characterize the transtympanically evoked, perioperative electrically evoked auditory brainstem response (EABR) and define its relationship with preoperative hearing, age and hearing loss etiology in 59 children (10-60 months of age) who had received cochlear implants. The results indicate that there was no difference between wave V latency obtained from the younger (10-36 months) and the older (37-60 months) children. There was a statistically significant difference in the preoperative pure-tone average between the higher-EABR threshold group (650 microA and above) and the lower-EABR threshold group (600 microA or less). Patients with post-meningitic deafness exhibited the longest EABR wave V latencies. Perioperative, transtympanic, promontory EABR is an effective clinical procedure which can decrease the likelihood of placing a cochlear implant in a non-stimulable ear, and may provide the clinician with a valuable tool for selecting the most appropriate ear for implantation.

Preoperative imaging protocol for cochlear implant candidates

OBJECTIVE

To formulate and test a CT imaging protocol for preoperative scanning of the temporal bone in cochlear implant candidates.

MATERIAL AND METHODS

A human head was scanned in three CT planes: axial, axiopetrosal and semilongitudinal. Multiplanar reformats (MPRs), based on axial slices, were created and compared with the corresponding images obtained by direct scanning in the respective planes. All scans were analyzed on a viewing workstation.

RESULTS

The axial plane image allowed for an overview of the temporal bone. The width of the facial recess and the cochlear nerve canal could be studied on combined axial and axiopetrosal images. Cochlear patency could be evaluated using combined axial and semilongitudinal images. Axiopetrosal and semilongitudinal MPRs were able to replace the images obtained by direct scanning in the respective planes.

CONCLUSION

The combination of the axial CT plane image and MPRs was found to be sufficient for preoperative analysis of the temporal bone morphology.

[CT of the temporal bone in the study of the inner ear structures in detection of the causes of neurosensory hypoacusis]

Computed tomograms of the inner ear structures (n=175) of 150 patients (age 0-75 years) with unaffected temporal bones were studied in detail. It is shown that polyposition CT of the temporal bone is a non-invasive method of visualization of the osseous labyrinth structures: cochlea, vestibule, semicircular canals, aqueducts of the labyrinth and internal acoustic meatus which are reflected on tomograms in 100% cases irrespective of the patient age. Their age-related features are analysed. CT imaging was made in 65 patients with neurosensory hypoacusis of inherited and acquired genesis. The following causes of neurosensory hypoacusis and deafness were revealed: congenital malformation of the labyrinth of Mondini type, common cavity of the labyrinth, cochlear hypoplasia, dysplasia of the vestibule and semicircular canals, a wide aqueduct of the vestibule, stenosis of the internal acoustic meatus, bulboform enlargement of the inner acoustic meatus, neurinoma (schwannoma) of the hearing nerve, Langerhans-cell histiocytosis with affection of the labyrinth capsule, atypical cholesteatoma. The detected changes in the inner ear structures determine further treatment policy.

Lipochoristomas (Lipomatous Tumors) of the Acoustic Nerve

Context.—Lipochoristomas (lipomatous choristomas) are rare tumors of the acoustic nerve (cranial nerve VIII/vestibulocochlear nerve) within the internal acoustic canal and sometimes the cerebellopontine angle, and are histogenetically believed to be congenital malformations. Their clinically indolent behavior has recently prompted a more conservative management protocol in a quest for maximal nerve/hearing preservation. This approach contrasts sharply with that for the common internal acoustic canal/cerebellopontine angle tumors, the neuroepithelial neoplasms (acoustic schwannomas and meningiomas), which behave more aggressively and have more prominent clinical manifestations. Owing to their rarity, the clinicopathologic features of cranial nerve VIII lipochoristomas have been obtained mainly through case reports.

Objective.—We present the clinicopathologic features of 11 cases of lipochoristomas of cranial nerve VIII.

Design.—The 11 cases were documented between 1992 and 2003. We performed complete clinical reviews with histologic, histochemical, and immunohistochemical analyses of formalin-fixed, paraffin-embedded tumor samples.

Results.—The patients were 8 men and 3 women with hearing loss of the right ear (5 patients) or the left ear (6 patients). No patient had bilateral tumors. All lipochoristomas histologically possessed mature adipose tissue admixed with varied amounts of mature fibrous tissue, tortuous thick-walled vessels, smooth muscle bundles, and skeletal muscle fibers, the latter verified with immunohistochemistry.

Conclusions.—The histomorphologic and immunophenotypic evidence showed that these tumors are better characterized as choristomas than as simple “lipomas,” as they have been labeled in the past. Their overall nonaggressive clinical nature in addition to the characteristic radiologic and histomorphologic findings are important clinicopathologic features for the pathologist to recognize and differentiate, especially during frozen section evaluations, in order to direct the neurosurgeon to a more appropriate conservative therapeutic intervention.

Development of a novel eighth-nerve intraneural auditory neuroprosthesis

OBJECTIVES/HYPOTHESIS

Cochlear nerve stimulation using a linear array of electrodes, the cochlear implant, has become an accepted treatment for profound deafness. Major limitations of this technology are high threshold of stimulation, poor performance in a noisy background, cross-talk between electrodes, unsatisfactory channel selectivity, and variable reconstruction of frequency space. A novel auditory neuroprosthesis is proposed that is expected to overcome these problems by implanting an array of three-dimensional microelectrodes, the Utah Electrode Array, directly into the cochlear nerve.

STUDY DESIGN

We have conducted acute, extending for up to 12 hours and semichronic, extending for up to 52 hours, electrophysiological experiments, radiologic and histologic studies in 12 cats.

METHODS

The electrically evoked auditory brainstem response was used as a means to characterize the threshold, dynamic range, and stability of cochlear nerve stimulation through the implanted Utah Electrode Array neuroprosthesis. Plain film, computed tomographic, and histological studies were conducted to determine the result of the implant.

RESULTS

The electrically evoked auditory brainstem response thresholds were approximately one to two orders of magnitude lower than those evoked with conventional cochlear implants. We were able to close the cochleostomy, bring the cat into normal anatomical position, and obtain stable electrically evoked auditory brainstem responses for up to 52 hours. Plain film and computed tomographic studies indicated that the Utah Electrode Array neuroprosthesis was in the intended position in the nerve. Histological studies did not reveal hemorrhage or significant damage to the nerve.

CONCLUSION

Because the presented stimulation paradigm appears to significantly mitigate some of the problems of conventional cochlear implants, it may offer a new therapeutic approach to profound deafness.

Clinical and audiological features in auditory neuropathy

OBJECTIVE

To medically and audiologically characterize a population of children diagnosed as having auditory neuropathy (AN).

STUDY DESIGN

Retrospective medical chart review.

SETTING/SUBJECTS

We identified 22 patients from a pediatric otology clinic in a tertiary care pediatric hospital setting.

RESULTS

A genetic factor in AN is suggested by our identification of 3 families with 2 affected children and 2 other children with family histories that were positive for hearing loss. Clinical features common among our population included a history of hyperbilirubinemia (n = 11 [50%]), prematurity (n = 10 [45%]), ototoxic drug exposure (n = 9 [41%]), family history of hearing loss (n = 8 [36%]), neonatal ventilator dependence (n = 8 [36%]), and cerebral palsy (n = 2 [9%]). Full clinical and audiological data were available for 18 of the 22 children, including otoacoustic emissions, auditory brainstem responses with cochlear microphonics, and age-appropriate audiometric findings. Significantly, 9 of these 18 patients showed improvement in behavioral thresholds over time, indicating that a subset of children with AN may recover useful hearing levels. Also significant was the success of cochlear implantation in 4 children.

CONCLUSIONS

Management of AN in children requires serial clinical and audiometric evaluations, with a prominent role for behavioral testing. Prematurity, genetics, and hyperbilirubinemia appear to be significant factors in the development of AN; hyperbilirubinemia can be associated with spontaneous improvement of hearing thresholds. For those children not benefiting from amplification or FM systems, cochlear implantation remains a potentially successful method of habilitation.

Hearing restoration with auditory brainstem implant in three children with cochlear nerve aplasia

OBJECTIVE

To verify the possibility of auditory habilitation in children with aplasia and hypoplasia of the cochlear nerve by direct electrical stimulation of the cochlear nuclei with an auditory brainstem implant.

STUDY DESIGN

Retrospective case review.

SETTING

Study conducted at the Ear, Nose, and Throat Department of the University of Verona, Italy.

PATIENTS

Three children, aged 4, 3, and 2 years, respectively, with severe bilateral cochlear malformations and cochlear nerve aplasia have received an auditory brainstem implant at this institution in the past 2 years.

INTERVENTION

The classic retrosigmoid approach was used. Correct positioning of the electrodes was evaluated using electric auditory brainstem responses and neural response telemetry. Before the patients were discharged, high-resolution computed tomography with a bone algorithm reconstruction technique was performed to evaluate electrode placement. The auditory brainstem implant was activated 30 to 60 days after implantation.

RESULTS

No postoperative complications were observed. To date, 21, 18, and 8 electrodes, respectively, have been activated in the three children. The first patient, 12 months after activation, had achieved good environmental sound awareness, good speech detection, and some speech recognition. The second child, 8 months after activation, had achieved good environmental sound awareness and moderate speech detection. The third patient, 1 month after activation, had obtained good environmental sound awareness.

CONCLUSION

This study indicates that auditory brainstem implantation is technically feasible in children with cochlear nerve aplasia. The early results suggest the possibility of achieving auditory habilitation with auditory brainstem implantation in this population.

[Transcranial duplex scanning in estimation of cerebral hemodynamics in patients with secondary cochleovestibular neuritis]

The authors present pilot experience with transcranial duplex scanning (TCDS) of the cerebral vessels in 17 patients with secondary cochleovestibular neuritis combined with chronic leptomeningitis (primarily of the posterior cranial fossa). This method has determined extra- and intracranial hemodynamics, characterized arterial and venous blood flow qualitatively and quantitatively, outlined possible genetically determined factors in development of dyscirculatory disorders. Finally, hemodynamic defects of two types were revealed in 12 patients. Type 1 (3 patients) was characterized by asymmetric circulation in the territory of the middle, anterior and posterior cerebral arteries, by the absence of venous congestion. Type 2 (9 patients) was characterized by impaired venous outflow manifesting as higher speed of the blood flow and its phase response along the intracranial veins and sinuses. In 7 patients these defects combined with asymmetric circulation along brain stem arteries. These patients were diagnosed to have perilymphatic labyrinthine hydrops.

Dimensions of the cochlear nerve canal: a radioanatomic investigation

The purpose of this study was to determine the normal variations of cochlear nerve canal dimensions, which is useful information to have when assessing congenital malformations, i.e. during the preoperative evaluation of cochlear implant candidates. The length and diameter of the cochlear nerve canal were measured in 117 casts from randomly selected temporal bone specimens obtained from the Uppsala Temporal Bone Laboratory. In 16 of the casts the dimensions were correlated with those obtained from CT scans of the same temporal bone. Measurements were also made from CT examinations of the temporal bone of 50 patients referred for evaluation of cholesteatoma or chronic otitis media. The mean length and diameter in the axiopetrosal plane measured in casts were 1.17 and 2.58 mm, respectively. The mean diameter in the axial plane was 2.59 mm. The mean length and diameter determined from CT scans of the specimens were 1.19 and 1.98 mm, respectively. The mean length and diameter determined from CT examinations of patients were 1.08 and 1.91 mm, respectively. In conclusion, the cochlear nerve canal is short, with a circular cross-section. If the diameter of the canal is < 1.4 mm then the possibility of cochlear nerve abnormality should be considered; if it is > 3.0 mm then other anomalies may coexist.

Cochlear implant assessment: imaging issues

Cochlear implants are electronic auditory prostheses used to rehabilitate deafened persons who have lost their hair cells. They are partly worn externally and partly implanted in the ear. They provide a direct stimulation of the spiral ganglion cells of the cochlear nerve by bypassing the destroyed hair cells. The objectives of this article are to summarise what head and neck surgeons need to know before cochlear implantation and to describe the imaging study protocol used and anomalies to look for. A few explanations are resumed about placement of a brainstem implant.

Cochlear vertebral entrapment syndrome: a case report

The authors describe a patient with isolated involvement of vestibulocochlear nerve by a huge vascular loop from vertebral dolichoectasia. No other neurological deficit was found except for unilateral hearing loss. Abnormal brainstem auditory evoked potential study indicated a retrocochlear lesion. The brain computed tomography (CT) and magnetic resonance imaging (MRI) studies demonstrated an abnormally enhanced vascular lesion impinged on the left porus acusticus with a displacement of the brainstem to the right. There was no infarction in the brainstem. A cerebral angiography demonstrated a megadolichoectatic horizontal loop at the intracranial portion of the left vertebral artery. There was no thrombus or atherosclerosis in the vertebrobasilar system. A mechanical compression by a vascular loop is the only possible pathogenesis for hearing loss. The authors diagnose this condition as cochlear vertebral entrapment syndrome.

Morphological evidence that impaired intraneural microcirculation is a possible mechanism of eighth nerve conduction block in acoustic neuromas

In an attempt to better understand the mechanism of eighth nerve dysfunction in acoustic neuromas (vestibular schwannomas), we have morphologically examined microvessels and nerve fibers in the intracanalicular portion of eighth nerve specimens attached to these tumors. At the light microscopic level, microvessels were well preserved in all the specimens, even in the extremely flattened or markedly small nerve fascicles. However, the density of microvessels was quite variable in the different specimens, presumably as the result of different levels of compression by the tumors and the subsequent formation of a collateral microcirculation in each nerve. Focal areas of mild endoneurial fibrosis were found in 9 out of 22 specimens examined, but severe and widespread degeneration or demyelination was not found in any of the specimens. Ultrastructural studies frequently revealed mild to moderate abnormalities in myelin sheaths, and occasionally showed endothelial hyperplasia and hypertrophy in all the specimens. These findings are consistent with the slight to moderate reduction of endoneurial blood flow in the eighth nerves. The resultant ischemic condition in the eighth nerve may account for the eighth nerve conduction block in acoustic neuromas.

Effectiveness of conservative management of acoustic neuromas

OBJECTIVE

The goal of this study was to assess the effectiveness of the conservative management in patients with acoustic neuroma (vestibular schwannoma).

STUDY DESIGN

This retrospective study was performed in a university hospital.

PATIENTS

Patients were selected for this wait-and-see policy on the basis of age, general condition, audiometric results, tumor size, and patient preference. The study group included 97 patients, 87 of whom had at least two neuroradiologic examinations. The mean age of this population was 63 years (29 to 89 years). The mean length of follow-up of this population was 31 months. Eighty-seven of these patients had at least two radiologic examinations (magnetic resonance imaging or computed tomography). The mean interval between the initial and follow-up radiologic examinations was 15 months.

MAIN OUTCOME MEASURES

Tumor size was measured by use of two-dimensional data in all patients. The mean tumor size was 12 mm. The growth rate of the tumor was estimated by comparison of the results of the measurements from the initial and follow-up neuroradiologic examinations.

RESULTS

Of the 97 patients studied, 6 patients required surgery and 6 required radiotherapy. Sixty patients (62%) were still being treated conservatively at the end of the study period. Three patients of 28 who were classified as candidates for hearing preservation surgery lost their candidacy during the observation period. The mean annual tumor growth rate was 1.52 mm/year. The tumor was stable in size in 36% of patients, regressed in 11% of patients, or grew in 53% of patients. The growth patterns of the acoustic neuroma fell into five categories: continuous growth in 15% of patients, negative growth in 5%, growth followed by negative growth in 40%, negative growth followed by growth in 20%, and no variation of tumor size in 20%.

CONCLUSION

Conservative management of acoustic neuromas carries difficulties: long-term follow-up of the patients and unpredictability of the tumor growth pattern. A reliable and reproducible radiologic method for evaluating tumor size is of great importance.

Hypoplasia of the bony canal for the cochlear nerve in patients with congenital sensorineural hearing loss: initial observations

PURPOSE

To evaluate the length and width of the bony canal of the cochlear nerve in patients with congenital sensorineural hearing loss (SNHL) who have "normal" findings at thin-section computed tomography (CT) of the temporal bone.

MATERIALS AND METHODS

The authors retrospectively evaluated the length and width of the bony canal for the cochlear nerve in two groups of patients. The first group was composed of 33 patients with profound SNHL and no demonstrable abnormality at thin-section CT. The control group was composed of 50 patients who underwent temporal bone CT for causes unrelated to SNHL. The mean value +/- SD was calculated for both cohorts. Statistical analysis consisted of the nonparametric Wilcoxon rank sum test with the NPAR1WAY program.

RESULTS

The length and width of the bony canal for the cochlear nerve were significantly smaller in patients with SNHL than in the control group (P <.05)

CONCLUSION

The hypoplastic bony canal for the cochlear nerve in patients with SNHL may be indicative of a previously unrecognized embryologic malformation of the cochlear nerve.

Cochlear nerve aplasia: its importance in cochlear implantation

OBJECTIVE

The objective of this study was to outline the possible implications and potentially valuable techniques for managing cases in which the neural integrity of the peripheral auditory system is in question.

STUDY DESIGN

This study was a retrospective case review.

SUBJECT AND METHOD

A 3-year-old child with a profound blilateral sensorineural hearing loss was assessed for suitability of cochlear implantation. Audiologic tests confirmed that the child met the audiologic criteria for cochlear implantation. Computed tomographic scanning and magnetic resonance imaging were undertaken.

RESULTS

Computed tomographic scanning showed bilateral narrow internal auditory canals. Magnetic resonance imaging showed the absence of the acousticofacial bundle on the left side and possible atrophy of the bundle on the right. After detailed discussion, the parents elected to proceed with implantation on the right ear using the Nucleus mini-22 cochlear implant. Tuning of the device resulted in myogenic facial activity with no electrically stimulated auditory sensation. Postoperative electrophysiologic testing confirmed the presence of a compound muscle action potential only.

CONCLUSIONS

Seven months after implantation, the child was explanted uneventfully. The electrical auditory nerve action potential and the electrically evoked auditory brainstem response, using intracochlear stimulation, are potentially valuable measurements to assess neural integrity before the decision to proceed with implantation is made.

Narrow and vacant internal auditory canal

A case of unilateral congenital deafness revealing a narrow vacant internal auditory canal and a more anterior and superior second canal where the facial and vestibulocochlear nerves are well visualised is presented. Having reviewed the scientific and embryological data, the authors consider the mechanism of this malformation.

Electromagnetic stimulation of the auditory system of deaf patients

Electromagnetically induced auditory perception was investigated in 18 deaf patients who were candidates for cochlear implants. In the extracranial magnetic stimulation (EMS) procedure, patients were stimulated with time-varying magnetic field brief pulses from a coil positioned at the i) auricle, ii) the mastoid, and iii) the temporal lobe area. EMS elicited auditory sensations in 26 ears (of 14 patients/subjects). The lowest threshold of auditory sensation (TAS) was found to be at the 20% EMS level, with a range of 20-50% of the maximum level (2.0 Tesla), and approximately equal sensitivity in each coil position. Eleven of the subjects hearing EMS-induced sound perceived changes in pitch while 6 heard "clicks" or clicks and tones. Spearman Rho correlation analysis showed a mild negative correlation between the EMS/TAS and the pre-implant FFA, best tone threshold (BTT), and direct promontorial electrical stimulation (ES) thresholds at 250 Hz and 500 Hz. No correlation was found between EMS or ES and performance on the pre-implant or post-implant psychacoustic tests (MAC VIII or 3-Digit speech tests) or the measurements of the thickness of cutaneous and osseous tissue from the stimulation sites at the mastoid and ear canal to the cochlear and 8th nerve. A fair positive correlation was found between the EMS/TAS and the post-implant (6 months) ES threshold when the electrodes allocated the 500 Hz frequency range were stimulated. A mild positive correlation between the pre-cochlear-implant promontorial electrical stimulation (ES) at 250 Hz and the four frequency tone average (FFA: 0.5, 1, 2, 4 kHz) was also found.(ABSTRACT TRUNCATED AT 250 WORDS)

The distribution of neurons labelled retrogradely with [3H]-D-aspartate injected into the colliculus inferior of the cat

It is important to know if the transmission of sound signals through the inferior colliculus is mediated by the transmitters glutamate or aspartate because of pharmacological consequences for auditory perception. In order to identify candidate's neurons, the retrograde transport for [3H]-D-aspartate, injected into the left inferior colliculus, was studied in cats. Labelled cells were found in the dorsal and intermediate lateral lemniscal nuclei, mainly on the contralateral side. The cochlear nuclei, superior olivary nuclei and the auditory cortex were not labelled in brains containing other labelled neurons at greater distances from the injection site. Labelled cells were found in the reticular formation and adjacent nucleus coeruleus, the parabrachial nuclei, raphe nuclei (magnus, dorsalis and centralis superior), nucleus prepositus hypoglossi, lateral hypothalamus and hippocampal CA1.

Direct electrical stimulation of the cochlear nucleus: surface vs. penetrating stimulation

Prosthetic stimulation of the cochlear nucleus (CN) has been used for rehabilitation of profoundly deaf patients who are not suitable candidates for cochlear implants. The goal of this article was to assess the relative effectiveness of surface vs. penetrating stimulation of the CN. Electrophysiologic and autoradiographic measures were used to study central auditory system activation elicited by direct stimulation of the CN. Eighteen pigmented guinea pigs, divided into three groups, underwent acute implantation of bipolar electrodes in the CN. One group was not stimulated and acted as a control (n = 7). Electrodes were placed on the surface of the CN in one test group (n = 4) and within the CN in a second test group (n = 7). Thresholds for electrically evoked middle latency responses (EMLR) were determined and input/output (I/O) functions were obtained. The two test groups were then pulsed with [14C]-2-Deoxyglucose (2-DG) intramuscularly and stimulated for 1 hour with biphasic; charge-balanced pulses having a total duration of 400 microseconds, a repetition rate of 100/sec, and an amplitude of 200 microA. After stimulation, animals were killed and brains were harvested and prepared for autoradiography using standard techniques. Threshold current for EMLRs in the surface-stimulated group had a mean of 67.5 +/- 23.9 microA (range, 40 to 100 microA). Thresholds for in-depth stimulated group had a mean of 11.4 +/- 3.5 microA (range, 10 to 20 microA). The saturation level of the I/O function for the surface-stimulated group had a mean of 287.5 +/- 41.5 microA (range, 250 to 350 microA). The saturation level for the in-depth stimulated group had a mean of 192.9 +/- 49.5 mciroA (range, 100 to 250 microA). The dynamic range for the surface electrodes had a mean of 13.1 +/- 2.7 dB (range, 9.9 to 15.9 dB), whereas the dynamic range for the penetrating electrodes had a mean of 24.5 +/- 2.6 dB (range, 20 to 28.0 dB). Autoradiographs generated by CNS tissue from stimulated animals demonstrated no significant difference in metabolic activity of the CN between surface and in-depth stimulated groups. However, there were highly significant differences in 2-DG uptake in the contralateral superior olivary complex, contralateral inferior colliculus, and ipsilateral and contralateral lateral lemniscus, with greater uptake in in-depth stimulated preparations. Electrophysiologic and autoradiographic data suggest that a penetrating CN prosthesis is capable of activating the auditory tract at a lower threshold, with a relatively wider dynamic range than a surface prosthesis.(ABSTRACT TRUNCATED AT 400 WORDS)

CT in the evaluation of the vestibulocochlear nerves and their central pathways. Evaluation of neurotologic disorders

CT has evolved to become an important technique for the diagnosis of neurotologic disorders. By obtaining thin sections, the central pathway of the vestibulocochlear nerve can be rather properly evaluated with satisfactory clinical correlation when pathology exists. The validity of central vestibular and audiometric signs can be best substantiated with CT. The functional neuroanatomy of the vestibulocochlear and vestibulo-oculomotor systems is discussed. Results of the assessment of endocranial lesions involving the vestibulocochlear system are presented.