Seung Ha Oh

Cross-modal plasticity and cochlear implants.

Hearing in profoundly deaf people can be helped by inserting an implant into the inner ear to stimulate the cochlear nerve. This also boosts the low metabolic activity of the auditory cortex, the region of the brain normally used for hearing. Other sensory modalities, such as sign language, can also activate the auditory cortex, a phenomenon known as cross-modal plasticity. Here we show that when metabolism in the auditory cortex of prelingually deaf children (whose hearing was lost before they learned to talk) has been restored by cross-modal plasticity, the auditory cortex can no longer respond to signals from a cochlear implant installed afterwards. Neural substrates in the auditory cortex might therefore be routed permanently to other cognitive processes in prelingually deaf patients.

Pyriform Sinus Fistula: Management with Chemocauterization of the Internal Opening:

A branchial remnant originating in the pyriform sinus causes a recurrent fistula or abscess in the neck. In spite of excision, recurrence may result from inadequate removal of the fistula tract. We attempted chemocauterization of the internal opening of the fistula tract with trichloroacetic acid (TCA) on direct endoscopy. This is a 6-year review of 18 patients with pyriform sinus fistula. Medical history, barium esophagography, computed tomography scans, operative findings, and treatment results were analyzed. By direct endoscopy, all patients were found to have a fistula opening in the pyriform sinus, exclusively on the left side. In only 9 patients, the fistula tract was identified by barium esophagography before operation. Computed tomography revealed a suspicious fistula tract originating from the pyriform sinus in 8 of 10 patients. Sixteen patients were initially managed by TCA chemocauterization. There were no serious intraoperative or postoperative complications. Four patients had recurrent masses, which were managed by simple excision in 2 patients and repeated TCA cauterization in the other 2 patients with unobliterated internal openings. We recommend barium swallow study and direct endoscopy for all patients presenting with a recurrent lateral neck abscess, especially on the left side. Our results suggest that initial chemocauterization of the internal opening can be a reasonable alternative procedure for the management of pyriform sinus fistula.

Immunohistochemical study of the distribution of sodium-dependent vitamin C transporters in adult rat brain

Sodium‐dependent vitamin C transporters (SVCTs) is known to transport the reduced form of ascorbic acid into the cell, whereas the oxidized form of vitamin C (VC) is moved through a facilitative sugar transporter, such as glucose transporter (GLUT). With regard to the distribution of SVCT1 and ‐2 within the various organs, they were reported to be expressed in different types of cells. Especially in the central nervous system, only SVCT2 mRNA was expressed mainly in neurons and some types of neuroglial cells. However, data on the expression of SVCT proteins in the brain are scant. Therefore, we tried to develop comprehensive data on the distribution of SVCT proteins in adult rat brain by using immunohistochemical techniques for the first time. In our study, SVCT2 immunoreactivities (IRs) were intensely localized in the neurons of cerebral cortex, hippocampus, and Purkinje cells of cerebellum, and much weaker SVCT2 IRs were found in the other brain regions. Judging from double‐immunohistochemical data, most of the cells expressing SVCT2 IRs were likely to be neurons or microglia, even though the cells in choroids plexus or ependymal cells around the ventricles also exhibited SVCT2 IRs. Complete mapping of the distribution of SVCT2 IRs was available by using a semiquantitative method. The subcellular localization of SVCT proteins is necessary for understanding the exact role of the protein, so the current overall mapping of SVCT IRs in the rat brain could be the basis for further studies on related subjects.

Design for a Simplified Cochlear Implant System

A simplified cochlear implant (CI) system would be appropriate for widespread use in developing countries. Here, we describe a CI that we have designed to realize such a concept. The system implements 8 channels of processing and stimulation using the continuous interleaved sampling (CIS) strategy. A generic digital signal processing (DSP) chip is used for the processing, and the filtering functions are performed with a fast Fourier transform (FFT) of a microphone or other input. Data derived from the processing are transmitted through an inductive link using pulse width modulation (PWM) encoding and amplitude shift keying (ASK) modulation. The same link is used in the reverse direction for backward telemetry of electrode and system information. A custom receiver-stimulator chip has been developed that demodulates incoming data using pulse counting and produces charge balanced biphasic pulses at 1000 pulses/s/electrode. This chip is encased in a titanium package that is hermetically sealed using a simple but effective method. A low cost metal-silicon hybrid mold has been developed for fabricating an intracochlear electrode array with 16 ball-shaped stimulating contacts

Bone morphogenetic protein 4 (BMP4): A regulator of capsule chondrogenesis in the developing mouse inner ear

Formation of the cartilaginous otic capsule is directed by otic epithelial–periotic mesenchymal interactions. In response to induction by otic epithelium, condensations of mesenchyme appear in the periotic region and form a chondrified otic capsule that serves as the template for the subsequent formation of the endochondral bony labyrinth. Previous studies indicate that members of the transforming growth factor beta superfamily, including transforming growth factor beta1, participate in guiding these tissue interactions. In this study, we report the localization of bone morphogenetic protein 4 (BMP4) to the mesenchymal and epithelial‐derived tissues of the mouse inner ear between 10.5 and 14 days of embryonic development. We demonstrate modulation of chondrogenesis in cultured mouse periotic mesenchyme by exogenous BMP4 protein and investigate the function of endogenous BMP4 in otic capsule chondrogenesis. We show that in the presence of the BMP antagonist, Noggin, otic capsule chondrogenesis is suppressed in culture in a dose‐dependent manner. Consistent with this finding, addition of BMP4‐specific antisense oligonucleotide to cultures of mouse periotic mesenchyme containing otic epithelium decreases levels of endogenous BMP4 protein and suppresses the chondrogenic response of the cultured periotic mesenchyme, providing evidence of the necessity for BMP4 in mediating otic capsule chondrogenesis. Supplementation of either Noggin‐ or BMP4 antisense oligonucleotide‐treated cultures with BMP4 protein can restore the extent of chondrogenesis to normal levels. Our findings support BMP4 as an essential mediator of chondrogenesis in the developing otic capsule in situ. Developmental Dynamics 226:000–000, 2003.

Expression of Heat Shock Protein 72 in Rat Cochlea with Cisplatin-induced Acute Ototoxicity

Cisplatin ototoxicity is known to involve mainly the organ of Corti. Outer hair cells (OHCs), especially in the basal turn, are preferentially involved. One possible mechanism of ototoxicity might be alteration of the antioxidant system causing an increase in free radicals. It has been demonstrated that heat shock proteins (HSPs), which are believed to protect cells by dissolving and refolding misfolded or denatured protein are induced by various form of stress. HSP is also demonstrated to be induced by free radicals. The purpose of this study was to evaluate HSP 72 induction in cochlea following cisplatin injection in the animal model. Sprague-Dawley (SD) rats were injected intraperitoneally with normal saline as control or cisplatin at a dose of 5, 10 or 20 mg/kg. Cochleae were harvested 1, 3, 6 and 12 h after injection and compared with those of controls. Immunocytochemical study with surface preparation and Western blotting were performed to investigate the expression of HSP 72. Auditory brainstem response (ABR) was also recorded to assess functional change according to the dosage of cisplatin and duration after injection. In the 5 and 10 mg/kg groups, immunostaining for HSP 72 in the OHCs reached a plateau level at 3 h, which was maintained until 12 h after injection. The amount of immunoreactive OHCs in the 20 mg/kg group was smaller than those in 5 and 10 mg/kg groups and declined after 6 h. The bands for HSP 72 became less intense as the cisplatin dosage increased from 5 to 10 and 20 mg/kg in Western blotting. The change in ABR threshold was small in the 5 and 10 mg/kg groups and a marked change in threshold was observed in the 20 mg/kg group. Detection of HSP 72 after cisplatin injection could confirm the OHCs as one of the major injured cells in the cochlea. With a lethal dosage of cisplatin (20 mg/kg), HSP 72 expression was less prominent and declined after 6 h.Cisplatin ototoxicity is known to involve mainly the organ of Corti. Outer hair cells (OHCs). especially in the basal turn, are preferentially involved. One possible mechanism of ototoxicity might be alteration of the antioxidant system causing an increase in free radicals. It has been demonstrated that heat shock proteins (HSPs), which are believed to protect cells by dissolving and refolding misfolded or denatured protein are induced by various form of stress. HSP is also demonstrated to be induced by free radicals. The purpose of this study was to evaluate HSP 72 induction in cochlea following cisplatin injection in the animal model. Sprague-Dawley (SD) rats were injected intraperitoneally with normal saline as control or cisplatin at a dose of 5, 10 or 20 mg/kg. Cochleae were harvested 1, 3, 6 and 12 h after injection and compared with those of controls. Immunocytochemical study with surface preparation and Western blotting were performed to investigate the expression of HSP 72. Auditory brainstem response (ABR) was also recorded to assess functional change according to the dosage of cisplatin and duration after injection. In the 5 and 10 mg/kg groups, immunostaining for HSP 72 in the OHCs reached a plateau level at 3 h, which was maintained until 12 h after injection. The amount of immunoreactive OHCs in the 20 mg/kg group was smaller than those in 5 and 10 mg/kg groups and declined after 6 h. The bands for HSP 72 became less intense as the cisplatin dosage increased from 5 to 10 and 20 mg/kg in Western blotting. The change in ABR threshold was small in the 5 and 10 mg/kg groups and a marked change in threshold was observed in the 20 mg/kg group. Detection of HSP 72 after cisplatin injection could confirm the OHCs as one of the major injured cells in the cochlea. With a lethal dosage of cisplatin (20 mg/kg), HSP 72 expression was less prominent and declined after 6 h.

Prognosis of ramsay hunt syndrome presenting as cranial polyneuropathy

Ramsay Hunt syndrome is known to be accompanied with cranial polyneuropathy very occasionally. We reviewed our experience to analyze the clinical manifestations and prognosis of these cases.

Unilateral sensorineural hearing loss in children: the importance of temporal bone computed tomography and audiometric follow-up.

Objectives: The first objective of this study was to identify rates, types, and laterality of clinically relevant inner ear malformations in children with unilateral sensorineural hearing loss (USNHL). The second objective was to assess the change of the ipsilesional and contralesional hearing thresholds of the patients with USNHL and the association between hearing change with time and the findings on high-resolution temporal bone computed tomography (TBCT). Study Design: Retrospective case review. Setting: Tertiary referral center. Patients: A total of 322 children diagnosed with USNHL on initial audiometry were included. Interventions: Otologic examination, pure-tone audiometry or auditory brainstem response, and high-resolution TBCT. Main Outcome Measures: Radiologic findings demonstrating clinically relevant bony or soft tissue malformations of the inner ear. Audiologic findings of change in thresholds. Results: In a series of 322 consecutively investigated children with USNHL, 93 TBCT scans (28.9%) were identified as abnormal. The abnormal CT findings included cochleovestibular malformations (49 cases; 52.7%), vestibular malformations (27 cases; 29.0%), and malformations of vestibular or cochlear aqueducts (17 cases; 18.3%). Of these abnormal CT findings, 18 cases (19.4%) showed bilateral malformations. Incomplete partition type II was the most common type of malformation (28 cases), followed by narrow internal auditory canal (23 cases) and subsequently followed by enlarged vestibular aqueduct syndrome (17 cases). Of 244 patients, 77 (31.6%) in the profound USNHL group accompanied malformations, which was significantly higher than 23.8% (15 of 78) in the nonprofound (mild to severe) USNHL group (p = 0.036). Of 115 patients who were regularly followed up for more than 6 months, 7 (6.1%) had hearing decrement (including 3 cases of bilateral decrement). Of 85 patients in the normal TBCT group, 4 (4.7%) revealed hearing decrement, and considering there were only 27 patients with nonprofound USNHL in this group, the rate of decrement was as much as 14.8% (4 of 27). Of 24 patients in the unilateral malformation group, 1 patient (4.2%) showed worsening of hearing, and 2 of 6 (33.3%) patients showed worsening of hearing in the bilateral malformation group. Conclusion: Based on the results, we propose all children with USNHL should have a TBCT scan because management, including genetic counseling and prognostic predictions of these cases, may be significantly influenced by the CT outcome. Moreover, the non-negligible rate of progressive nature of ipsilateral and contralateral SNHL in normal-looking TBCT group and in groups with inner ear malformations mandates longitudinal audiologic assessments for both ears.

Management of intratemporal facial nerve schwannoma.

Objective The aim of this study was to report a series of 18 facial nerve schwannomas, including 2 infantile cases. Study Design Retrospective case review. Setting Tertiary referral center. Patients Eighteen patients with facial nerve schwannoma, operated on between 1980 and 2000. Intervention Surgical treatments were performed in all cases. Main Outcome Measures The presenting symptoms and facial nerve function were graded using the House-Brackmann scale and eye closure. Results Facial nerve paralysis was the most common symptom, presenting in 94% of cases, followed by hearing loss and mass lesion. In one case, the tumor was shaved, leaving the facial nerve intact. In the other cases, the facial nerve reconstruction with hypoglossal-facial anastomosis or interposition graft was performed. The postoperative facial function was House-Brackmann grade IV in most cases (88.2%). In terms of the functional recovery classified by complete or incomplete eye closure, the moderate preoperative facial nerve palsy group showed a better functional outcome than severe group. Conclusion In cases with good facial nerve function, it would be better to consider an alternative method for preserving the facial nerve. Furthermore, when facial nerve paralysis has developed to more than House-Brackmann grade III, an immediate operation is recommended to obtain a good postoperative facial functional recovery.

Prevalence of p.V37I Variant of GJB2 in Mild or Moderate Hearing Loss in a Pediatric Population and the Interpretation of Its Pathogenicity

A p.V37I variant of GJB2 has been reported from subjects with moderate or slight hearing loss especially in East Asian populations. This study aimed to estimate the prevalence of the p.V37I variant among such subjects and prove, epidemiologically, its pathogenic potential to cause mild hearing loss. A total of 380 subjects from 201 families with hearing loss were enrolled. From them, 103 families were selected who had autosomal recessive inheritance or sporadic occurrence of hearing loss and who were younger than 15 years old. GJB2 sequencing was carried out for the probands of all 103 families. The prevalence of the p.V37I variant was compared between the subtle, mild or moderate hearing loss (group I) and the severe or profound hearing loss (group II) groups. Where possible, a targeted next generation sequencing of 82 deafness genes was performed from the p.V37I carrier to exclude the existence of other pathogenic genes. Five (4.8%) of 103 probands were found to carry p.V37I. The carrier frequency of p.V37I among group I (18.2%) was significantly higher than that of group II (1.2%) or the reported Korean normal hearing control group (1.0%). Detection of the p.V37I variant of GJB2 in 18.2% of Koreans with mild hearing loss strongly suggests its contribution to the pathogenesis of milder hearing loss, which might justify sequencing of GJB2 from these subjects in the Korean population.