Regulation of alcohol oxidase gene expression in methylotrophic yeast Ogataea minuta

Ogataea minuta is a methylotrophic yeast that is closely related to Ogataea (Hansenula) polymorpha. Like other methylotrophic yeasts, O. minuta possesses strongly methanol-inducible genes, such as AOX1. We have focused on O. minuta as a host for the production of heterologous glycoproteins. However, it remained unknown how the AOX1 promoter is regulated in O. minuta. To elucidate regulation mechanisms of the AOX1 promoter, we adopted an assay system to quantitate AOX1 promoter activity using the PHO5 gene, which encodes an acid phosphatase, of Saccharomyces cerevisiae. The promoter activity assay revealed that glycerol, as well as glucose, cause strong catabolite repression of AOX1 expression in O. minuta. To investigate what factors are involved in transcription of the AOX1 promoter in O. minuta, we cloned three putative transcription factor genes, TRM1, TRM2, and MPP1, as homologues of other methylotrophic yeast species. Deletion mutants of these genes all showed decreased induction of the AOX1 promoter when methanol was added as the sole carbon source, indicating that these genes are indeed involved in AOX1 promoter regulation in O. minuta. Double deletion and constitutive expression of these transcription factor genes indicated that TRM1 and MPP1 regulate the transcription of AOX1 in the same pathway, while TRM2 regulates it in another pathway. By reverse transcription-qPCR, we also found that these two pathways compensate for each other and have crosstalk mechanisms with each other. A possible model for regulation of the AOX1 promoter in O. minuta was shown.

Lipid moiety of glycosylphosphatidylinositol-anchored proteins contributes to the determination of their final destination in yeast

Yeasts have two classes of glycosylphosphatidylinositol (GPI)-anchored proteins; one is transferred to the cell wall, whereas the other is retained on the plasma membrane. The lipid moieties of the GPI in Saccharomyces cerevisiae consist of either phosphatidylinositol (PI) or inositolphosphorylceramide (IPC). Cwh43p is involved in the remodeling of lipid from PI to IPC. We found that the GPI lipid moiety of Cwp2p in wild-type cells is PI. To elucidate the physiological role of the lipid remodeling by Cwh43p, we investigated the distribution of Gas1p and Cwp2p by immunoblotting and found that Gas1p with the PI-form GPI lipid moiety in cwh43∆ mutant cells tends to be localized to the cell wall, suggesting that the IPC species in the GPI lipid moiety contributes to the retention of GPI-anchored proteins on the plasma membrane. We also found that CWH43 is genetically related to TED1, which encodes a protein involved in the removal of the ethanolamine phosphate from the second mannose residue in GPI glycan moieties. We propose possible models for the physiological function of Cwh43p and Ted1p in the transfer of GPI-anchored proteins from the plasma membrane to the cell wall.

Mating type switching, formation of diploids, and sporulation in the methylotrophic yeast Ogataea minuta

Ogataea minuta is a methylotrophic yeast that is closely related to Ogataea (Hansenula) polymorpha. Like other methylotrophic yeasts, O. minuta also possesses strongly methanol-inducible genes, such as AOX1. We have focused on O. minuta as a host for the production of therapeutic glycoproteins. However, genetic methods, which are required for the construction of strains by breeding, have not yet been established in this organism. In this study, we investigated the O. minuta mechanisms of mating and sporulation, which would facilitate genetic analysis in this species. Specifically, we determined DNA sequences around the MAT locus in O. minuta strain NBRC 10746, and found that two MAT loci were flanked by a pair of inverted repeat sequences, as reported in O.polymorpha (Maekawa and Kaneko, PLOS Genet., 10, e1004796, 2014). As in O. polymorpha, mating type in O. minuta appears to be switched by inversion of the chromosomal region between the two MAT loci. We successfully obtained O. minuta diploid cells, which showed vegetative growth on rich medium. The size of the diploid cells was 1.3-fold larger than haploid cells of this species. Diploid cells formed ascospores, which contained 2-4 spores, under nutrient starvation conditions. Phenotypes of the resultant haploid cells exhibited Mendelian segregation, indicating that genetic approaches are applicable to O. minuta.

PER1, GUP1 and CWH43 of methylotrophic yeast Ogataea minuta are involved in cell wall integrity

In eukaryotes, the glycosylphosphatidylinositol (GPI) modification of many glycoproteins on the cell surface is highly conserved. The lipid moieties of GPI-anchored proteins undergo remodelling processes during their maturation. To date, the products of the PER1, GUP1 and CWH43 genes of the yeast Saccharomyces cerevisiae have been shown to be involved in the lipid remodelling. Here, we focus on the putative GPI remodelling pathway in the methylotrophic yeast Ogataea minuta. We found that the O. minuta homologues of PER1, GUP1 and CWH43 are functionally compatible with those of S. cerevisiae. Disruption of GUP1 or CWH43 in O. minuta caused a growth defect under non-permissive conditions. The O. minuta per1Δ mutant exhibited a more fragile phenotype than the gup1Δ or cwh43Δ mutants. To address the role of GPI modification in O. minuta, we assessed the effect of these mutations on the processing and localization of the O. minuta homologues of the Gas1 protein; in S. cerevisiae, Gas1p is an abundant and well-characterized GPI-anchored protein. We found that O. minuta possesses two copies of the GAS1 gene, which we designate GAS1A and GAS1B. Microscopy and western blotting analysis showed mislocalization and/or lower retention of Gas1Ap and Gas1Bp within the membrane fraction in per1Δ or gup1Δ mutant cells, suggesting the significance of lipid remodelling for GPI-anchored proteins in O. minuta. Localization behaviour of Gas1Bp differed from that of Gas1Ap. Our data reveals, for the first time (to our knowledge), the existence of genes related to GPI anchor remodelling in O. minuta cells.

Structural modeling and mutagenesis of endo-β-N-acetylglucosaminidase from Ogataea minuta identifies the importance of Trp295 for hydrolytic activity

Endo-β-N-acetylglucosaminidase from the methylotrophic yeast Ogataea minuta (Endo-Om) is a glycoside hydrolase family 85 enzyme that has dual catalytic activity in the hydrolysis and transglycosylation of complex N-glycans, in common with the enzymes from the eukaryotic species. In this study, we have conducted mutagenesis of Endo-Om at Trp295, to determine the effect on hydrolytic activity. Structural modeling predicted that Trp295 forms an important interaction with the α-1,3-linked mannose residue of the trimannosyl N-glycan core, rather than being directly involved in catalytic activity. Our results showed that an aromatic amino acid is required at position 295 for the hydrolytic activity of this enzyme. Notably, the tryptophan residue is highly conserved in eukaryotic endo-β-N-acetylglucosaminidases that show activity toward complex oligosaccharides. Accordingly, our results strongly suggested that Trp295 is involved in the recognition of oligosaccharide substrates by Endo-Om.

A short-wavelength infrared emitting multimodal probe for non-invasive visualization of phagocyte cell migration in living mice

For the non-invasive visualization of cell migration in deep tissues, we synthesized a short-wavelength infrared (SWIR) emitting multimodal probe that contains PbS/CdS quantum dots, rhodamine 6G and iron oxide nanoparticles. This probe enables multimodal (SWIR fluorescence/magnetic resonance) imaging of phagocyte cell migration in living mice.

Auditory brainstem implants: current state and future directions with special reference to the subtonsillar approach for implantation

In this article, the authors describe the current state of the auditory brainstem implant (ABI), comparing it to that of the cochlear implant (CI). The CI restores hearing by stimulating the cochlear nerve in the cochlea in patients whose deafness has been caused by inner ear disease; the ABI restores hearing by stimulating the cochlear nucleus of the brainstem in patients who are deaf because of bilateral cochlear nerve dysfunction. Up to now, about 500 patients worldwide have undergone ABI and had their hearing restored, most of whom suffer from neurofibromatosis type 2. Hearing performance, however, is not as good as that offered by the cochlear implant. To improve the quality of hearing, new techniques such as advanced coding strategies and penetrating electrodes, are now being introduced.

Subtonsillar placement of auditory brainstem implant

A 26-year-old female with NF2 underwent removal of an acoustic schwannoma via extended retrosigmoid approach with subtonsillar placement of the auditory brainstem implant. The patient had already shown palsy of the lower cranial nerves on the opposite side due to previous surgery. Differing from conventional routes such as the translabyrinthine and the retrosigmoid, the subtonsillar approach enabled us to observe the entire cochlear nucleus and avoid injury to the 9th and 10th cranial nerves when applying the electrode. Hearing in pure tone average was maintained almost at the preoperative level. We present a new use of this approach in placing the electrode and discuss its advantages.

Audiological findings in patients with myoclonic epilepsy associated with ragged-red fibres

Sensorineural hearing loss is a common symptom in patients with myoclonic epilepsy associated with ragged-red fibres (MERRF), one of the mitochondrial encephalomyopathies, although the lesion causing hearing loss in such cases remains unknown. Here we describe the audiological features in three MERRF patients, all of whom exhibited a point mutation in their mitochondrial DNA at nucleotide 8344. Pure-tone threshold audiometry revealed bilateral, sloping-type, sensorineural hearing loss in all three patients. Distortion product otoacoustic emissions, electrocochleography, and auditory brainstem responses were variable, even differing between the right and left ears of the same patient. Taken together, our findings suggest that the primary lesion underlying hearing loss in MERRF patients is in the cochlea, although a retrocochlear lesion may be involved in some patients.

Cross-sectional shapes of the internal auditory canal in patients with acoustic neuromas

Cross-sectional images of the internal auditory canal (IAC) were investigated in 23 patients with acoustic neuroma in order to clarify the widening of the IAC. The area of the IAC and the ratio of areas (neuroma side:normal side) were calculated. The shape of the IAC was fitted by an ellipse to obtain the length of the axes and the direction of the long axis. The area of the IAC was 34.2+/-12.2 mm2 in the neuroma side and 18.1+/-4.8 mm2 in the normal side. The neuroma side was larger than the normal side in all patients, and the mean ratio of areas was 1.9. However, the degrees of cochlear and vestibular damage did not correlate with the ratio of areas. The mean ratio of axes of the approximated ellipse was 1.17+/-0.09 in the neuroma side and 1.14+/-0.10 in the normal side; however, no significant difference was seen between the ratio of axes. The directions of the long axes were not always consistent with the positions of the originating nerves of the tumour. Referring to hypothetical models of enlargement of the IAC, our data suggest that the widening of the IAC in the acoustic neuroma was expansive. The data also indicated that symptoms of the acoustic neuroma were caused not only by compression of the nerves but also by other mechanisms, such as vascular insufficiency to the inner ear.

Postoperative vestibular-evoked myogenic potentials in cases with vestibular schwannomas

Although still the subject of discussion, vestibular-evoked myogenic potentials (VEMPs) have been considered to reflect the function of the saccular and, more recently, the cochlear tracts. To accurately determine the precise afferent pathway carrying VEMPs, we studied the outcomes of VEMPs and other examinations in patients with unilateral vestibular schwannomas. Eleven patients with unilateral vestibular schwannomas resected using a middle cranial fossa approach were included in the study. Patients underwent pure-tone threshold audiometry, caloric tests and analysis of auditory brainstem responses (ABRs) and VEMPs pre- and postoperatively. The results were compared with those obtained in patients with intact superior or inferior vestibular and cochlear nerves. Among the 11 patients studied, 4 retained their VEMPs postoperatively. Three of the 10 patients with inferior vestibular schwannomas exhibited normal VEMPs, preserved hearing levels (20 dB HL) and anatomically intact superior vestibular nerves. In all of these cases, ABRs more closely correlated with VEMPs than with caloric responses. In one of the cases with inferior vestibular schwannomas, VEMPs were preserved postoperatively and VEMP latencies were shortened, which indicates the preoperative presence of a conduction block in either the cochlear or superior vestibular nerve. VEMPs may be conducted in both the superior vestibular and cochlear nerves, as well as in the inferior vestibular nerve. Thus, evaluation of saccular nerve function should be performed carefully, especially in cases where hearing is preserved. It appears that cochlear conduction may proceed along two pathways, one direct and the other via the brainstem, but this remains to be verified.

Three-dimensional image for the middle fossa approach and its anatomical considerations

OBJECTIVE

To investigate the usefulness and significance of three-dimensional images in the middle cranial fossa approach.

STUDY DESIGN

Retrospective study.

METHOD

Three-dimensional images of 12 patients with acoustic neuromas were made for surgical guidance. An image showing an ideal surgical view was prepared, which showed no overlap between the labyrinthine bone and internal auditory canal (IAC) with a slight gap between them. The IAC was located and opened referring to this image.

RESULTS

Directions of the images in the ideal surgical view were anterior from lateral position in all cases. Viewing toward the vestibule, angle from lateral plane was 24 degrees +/- 12 degrees (mean +/- standard deviation). In 11 of 12 patients, the IAC was safely opened; in one patient the IAC could not be opened because of bleeding. Overall hearing preservation rate was 82%.

CONCLUSION

Our method facilitated not only in the identification of the IAC but also in avoiding inner ear damage. Our data indicated that the center of craniotomy should be made anterior to the external auditory canal and surgery should be viewed from an anterolateral position for a safe procedure.

[Speech perception ability in a patient with a 8-channel auditory brainstem implant]

Auditory brainstem implant (ABI) is a central prosthesis that directly stimulates the cochlear nucleus in the brainstem for those who have interrupted auditory nerves and cannot benefit from the cochlear implantation. Speech perception in a recipient of the Nuclues 8 channel ABI, the first in Japan, is reported. A 25-year-old man with bilateral acoustic nerve tumors postlingually deafened due to tumor resection received auditory sensations with 5 channels. The correct answer using a coding strategy, SPEAK, was 35% for 5 vowels and 36% for 5 monosyllables. The use of ABI also improved his lip-reading ability on monosyllables and open-set words. This indicated that he benefited from ABI, although it was limited. Even after 1 year and 3 months of follow-up, he had no serious side effects such an infection or implant rejection.

Nerve origin of the acoustic neuroma

Two hundred and seventy-one Japanese patients who underwent surgical removal of neuroma from the cerebello-pontine angle using the translabyrinthine approach were retrospectively reviewed in order to investigate the nerve origin on an anatomical basis. In 269 out of the 271 cases, the origin of the neuromas was identified. Among these cases, 84.8 per cent of tumours originated from the inferior vestibular nerve (IVN), followed by the superior vestibular nerve (SVN) (8.9 per cent). Of the 5.6 per cent of tumours arising from the vestibular nerve, however, it could not be determined whether they originated from the SVN or IVN. Two cases of neuromas originating from the facial nerve were seen (0.7 per cent). No neuroma arose from the cochlear nerve. Currently, the diagnosis of acoustic neuromas is best made with Gd-enhanced magnetic resonance imaging (MRI). However, our data indicate that the development of a functional test of the individual IVN can be useful for screening most cases of acoustic neuroma and in facilitating their early diagnosis.

Relationship between cystic change and rotatory vertigo in patients with acoustic neuroma

Acoustic neuromas are benign neoplasms that most often arise from the vestibular nerve. Many patients with this tumor experience some degree of vestibular symptoms. However, patients rarely complain of rotatory vertigo. Acoustic neuromas are known to exhibit a cystic appearance in some patients. It was hypothesized that cystic change might be a causative factor for rotatory vertigo. A retrospective study of 178 patients with unilateral acoustic neuroma who underwent surgery in the Department of Otolaryngology at Tokyo Medical and Dental University was carried out. The cystic appearance of the tumors was detected preoperatively by magnetic resonance imaging and confirmed at surgery. The relationship between cystic change of the tumor and presentation with rotatory vertigo was examined. Of the 178 patients studied, only 10 had both cystic change of the tumor and rotatory vertigo, and 120 had neither cystic tumor nor rotatory vertigo. Of the remaining 48 patients, 24 experienced rotatory vertigo with negative findings for cystic tumor and the other 24 had evidence of cystic tumor but no rotatory vertigo. Tumor with cystic change was observed in 34 patients, accounting for 19.1% of all patients studied. Rotatory vertigo was also experienced in 34 patients (19.1%). Of the 34 patients with cystic lesions, 29.4% (10) had rotatory vertigo. The difference in percentage of the two groups did not reach statistical significance. It is suggested that there may be other factors causing rotatory vertigo in patients with acoustic neuromas than cystic change of the tumor.

Three-dimensional imaging of the internal auditory canal in patients with acoustic neuroma

Three-dimensional imaging of the internal auditory canal (IAC) was carried out in 21 patients with acoustic neuromas using helical computed tomography. The IAC was widened in 20 patients, but no irregularities of the canal walls were seen. In addition, the shape of the enlarged IAC corresponded to that of the tumor on magnetic resonance imaging. The data suggest that widening of the IAC in acoustic neuroma patients is due to enlargement of the tumor. Other mechanisms, for example, tumor invasion or destruction caused by release of a specific mediator from the tumor, are unlikely to explain these findings; however, further investigation is needed.

Tumor volume measurements of acoustic neuromas with three-dimensional constructive interference in steady state and conventional spin-echo MR imaging

The purpose was to compare three-dimensional (3D) constructive interference in steady state (CISS) and conventional spin-echo (SE) MR imaging in tumor volume measurements of acoustic neuromas. Twenty-two patients with acoustic neuromas were examined using high-resolution 3D-CISS and SE imaging at a 1.5-T system. Tumor volume determined by SE imaging with the ellipsoid formula was overestimated by 692 mm(3)(35%) on average as compared with that at 3D-CISS with the voxel-count method (the reference standard). Intra- and interobserver variations in SE imaging were poor as compared with 3D-CISS imaging. However, tumor volume results with SE imaging showed a high correlation with those using 3D-CISS imaging (P <. 0001). On the basis of diameters shown on SE images, the tumor volume could be assessed using the following equation (P <.0001): (Tumor volume) = -26.407 + 0.387 x (maximum diameter along the pyramid) x(maximum diameter perpendicular to the pyramid) x (maximum height). J. Magn. Reson. Imaging 2000;12:826-832.

Restoration of hearing with an auditory brainstem implant in a patient with neurofibromatosis type 2--case report

A 25-year-old male with neurofibromatosis type 2 had hearing restored with an auditory brainstem implant (ABI) after removal of an acoustic schwannoma. The ABI allows the patient to discern many different environment sounds and is a significant adjunct to lip-reading, enabling conversation with people who have clear pronunciation without the necessity for writing.

Prediction of the nerves of origin of vestibular schwannomas with vestibular evoked myogenic potentials

OBJECTIVE

To determine whether the nerves of origin of vestibular schwannomas can be predicted using vestibular evoked myogenic potentials (VEMPs).

STUDY DESIGN

The study was a retrospective analysis.

SETTING

The ear, nose, and throat department of Tokyo Medical and Dental University.

PATIENTS

Twenty-eight patients undergoing removal of vestibular schwannomas were included in the study.

INTERVENTIONS

Patients underwent pure tone audiometry, VEMP testing, caloric testing, and magnetic resonance imaging preoperatively. Hearing level, caloric weakness, maximum tumor size, and the nerves of origin of tumors were compared with VEMP testing.

MAIN OUTCOME MEASURE

Results of VEMP testing.

RESULTS

Comparisons between VEMPs and results of the other three examinations revealed no correlations. Complete disappearance of VEMPs was observed only in patients with tumors arising from inferior vestibular nerves. Patients in whom hearing was preserved tended to have preserved VEMPs. Some patients showed damaged hearing and normal VEMP results, although with inferior vestibular schwannomas. A patient with a tumor arising from a cochlear nerve exhibited preservation of VEMP, preserved caloric response, and moderate hearing loss.

CONCLUSIONS

Inferior vestibular nerve function and hearing level were reflected in VEMP results. Prediction of the nerve of origin of a tumor was possible only in certain restricted cases.

A clinically oriented video-based system for quantification of eyelid movements

A field-worthy system was developed to quantify the eyelid movements in clinical sites. The system consists of a home-use charge-coupled device video camera, a processing unit, and a personal computer. A white marker of 4-mm diameter and 30-mg weight is attached to the lower margin of the upper eyelid. The processing unit automatically detects the vertical displacement of the upper edge of the marker. One marker is attached to each eye so that the movements of the both eyelids are measured with one camera simultaneously. The measurement error of the system was evaluated in experiments on eight healthy subjects and eight patients with eyelid paralysis. The mean of the absolute error of peak amplitudes occurring in 2 min was 0.81 mm, with the worst error being +1.7 mm. The reproducibility of the mean peak amplitude measured on five consecutive days was within 1 mm. The mean peak amplitudes of both eyes were measured preoperatively and postoperatively for approximately three months for three patients who were operated on to remove vestibular schwannoma. The results demonstrated basic clinical utility of the system.

Detection of antibody to sialyl-i, a possible antigen in patients with Meniere's disease

An autoimmune hypothesis for the etiology of Meniere's disease has been proposed. In this study, we focused on gangliosides as potential antigens for autoantibodies in Meniere's disease patients. In an attempt to investigate ganglioside antigens which respond to the serum of patients with Meniere's disease, we analyzed gangliosides of human acoustic neurinomas, and used them as antigens to broadly explore gangliosides that react to serum. All the acoustic neurinoma samples used in the present study showed a similar ganglioside profile on TLC (thin-layer chromatography). For the microscale ganglioside analysis, a newly developed TLC blotting/secondary ion mass spectrometry (SIMS) system together with TLC immunostaining method was employed. Most of the ganglioside bands could be analyzed, and they were identified as GM3, GM2, SPG, GM1a, GD3, S-i (sialyl-i ganglioside) and GD1a. GD1a was the predominant ganglioside and many neolactoseries gangliosides were recognized by immunological analysis. Next, the immune reactivity of serum samples, from patients with Meniere's disease, with the acoustic neurinoma gangliosides was studied by TLC immunostaining. The result showed that five of 11 patients with Meniere's disease and one of eight normal subjects reacted with a specific band, which was identified as S-i by the TLC blotting/SIMS system. The findings of the present study indicate that S-i ganglioside is an autoantigen and possibly involved in the pathogenesis of Meniere's disease.

The arcuate eminence is not a protrusion of the superior semi-circular canal but a trace of sulcus on the temporal lobe

Thirteen cadavers (26 temporal bones) were examined to show the arcuate eminence, especially its correspondence to the superior semicircular canal and inferior surface of the temporal lobe. Arc-like eminences on the petrous bone were observed in 92 per cent of specimens, however, they did not exactly correspond to the superior semi-circular canal. Some eminences corresponded to sulci of the temporal lobe of which most were traces of the occipitotemporal sulcus. On the other hand, a dull, smooth and even domed eminence existed in nine temporal bones independently of the arc-like eminence. Those eminences corresponded to each superior semi-circular canal in only three out of nine specimens. The arcuate eminence was listed as an important landmark in the middle cranial fossa approach. However, in order to drill out the internal auditory canal safety, surgeons should rely on other landmarks or apply other methods from our data.

Electrocochleographic study in patients with vestibular schwannomas and U-shaped audiograms

To determine the nature of sensorineural hearing loss in the middle-frequency range (U-shaped audiogram), we compared the differences in electrocochleographic findings for 15 ears with vestibular schwannomas and 10 ears without tumours. Short-tone bursts of 0.5, 1, 2, and 4 kHz were used to evoke cochlear microphonics (CM). Ears with tumours had normal or lower CM detection thresholds than ears without tumours. Input-output curves for 1-kHz frequency were normal in 10 ears with tumours and in 1 ear without tumours. These indicate that tumour ears have no or mild cochlear dysfunction. In addition, CM detection thresholds of ears with tumours were lower than audiometric thresholds, particularly at the 1- and 2-kHz region. These findings suggest that the loss seen by audiometry in ears with vestibular schwannomas was from a retrocochlear component.

Progressive sensorineural hearing impairment in professional fishery divers

There have been many reports of a high rate of hearing impairment in divers. A prospective study was performed to determine whether sensorineural hearing acuity in the same divers deteriorated faster than in a normal population as they continued diving. After an observation period of approximately 5 years, audiometric examination was performed on a group of professional fishery divers who had normal hearing or sensorineural hearing loss at the time of initial study. Thirty-three ears of 18 divers were included in statistical analyses. The average hearing deterioration in the divers in 5 years, after elimination of the aging effect, was 6.6 dB (SD 4.5) and was statistically significant. We concluded that the hearing acuity of our subjects deteriorated faster than that of normal Japanese.

Cochlear microphonics for hearing preservation in vestibular schwannoma surgery

OBJECTIVES

To determine whether cochlear function is beneficial in decision-making concerning the selection of hearing preservation surgery for vestibular schwannoma.

STUDY DESIGN

Retrospective review of 44 patients undergoing tumor resection with a middle fossa approach.

METHODS

Cochlear microphonics in electrocochleography together with tumor size, pure-tone average (PTA), speech discrimination score (SDS), auditory brainstem response (ABR), and compound action potentials were examined. As acoustic stimuli, short tone-bursts with frequencies of 0.5, 1, and 2 kHz were employed to measure cochlear microphonics and a click was used to obtain compound action potentials. We determined detection thresholds of cochlear microphonics and action potentials.

RESULTS

The overall rate of preservation of serviceable hearing was 59.1% (26/44). There were significant differences between patients with and without serviceable postoperative hearing in PTA, SDS, finding of ABR, compound action potential detection threshold, and mean cochlear microphonic detection threshold (at 0.5, 1, and 2 kHz). However, tumor size was unrelated to hearing outcome. Serviceable hearing was preserved in 23 (76.7%) of 30 patients, with a mean cochlear microphonic detection threshold of 40 dB nHL or less, suggesting normal or slightly impaired cochlear function. Hearing recovery was recognized in three patients, who also had a mean cochlear microphonic detection threshold of 40 dB nHL or less. Of the three patients, two had lower cochlear microphonic detection thresholds than audiometric thresholds, demonstrating the existence of a retrocochlear component in their hearing loss.

CONCLUSIONS

The cochlear microphonic detection threshold predicts not only hearing preservation but also hearing improvement in patients with vestibular schwannomas.

Meningioma of the internal auditory canal with extension into the vestibule

Meningiomas account for approximately 18 to 19 per cent of all brain tumours. Although they can arise in numerous locations, meningiomas of the internal auditory canal (IAC) are rare. Most tumours that originate in the IAC are schwannomas of the VIIIth cranial nerve (acoustic neuromas). We report a case of a meningioma which appears to originate from the IAC and extends into the vestibule. The clinical findings and the radiographical features of meningiomas of the IAC are similar to those of acoustic neuromas. Pre-operative differentiation between acoustic neuromas and meningiomas of the IAC may be difficult.

Hearing impairment in patients with acoustic neuroma--analysis by electrocochleography

OBJECTIVE

In patients with acoustic neuroma, the site and severity of hearing impairment are important in discussing surgical approaches. Since the effectiveness of conventional auditory psychological testing is limited, we studied objectively hearing impairment of the cochlea and the cochlear nerve due to the tumor.

METHODS

Electrocochleography (ECochG) was carried out in 21 patients with acoustic neuroma. Cochlear microphonic potential (CM) and action potential (AP) in ECochG evoked with clicks and short tone bursts were recorded through a transtympanic needle electrode technique. Cochlear function was studied using the detection thresholds of CM, and cochlear nerve involvement was analyzed by differences between AP and CM detection thresholds.

RESULTS

The 1 kHz CM detection threshold was elevated in 17 (81.0%) of 21 patients indicating cochlear impairment. Of seven patients with normal hearing or mild sensorineural hearing loss in pure tone audiometry, three had a slightly elevated CM detection threshold. Of five patients with pronounced pure tone levels, four showed a CM response and were thought to have mild cochlear dysfunction. Cochlear nerve impairment was confirmed in three of four patients with well-developed CM based on elevated AP detection thresholds. Three patients had CM response but no AP response, suggesting severe cochlear nerve impairment.

CONCLUSION

Disorders of the cochlea and the cochlear nerve can be evaluated with ECochG AP and CM measurement. The findings of ECochG are thought to be important information to judge hearing prognosis, thereby enhancing its clinical utility.

Three-dimensional reconstruction of the incudostapedial joint with helical computed tomography

Three-dimensional images of the incudostapedial joint (I-S joint) were reconstructed using helical computed tomography (CT). The images of the joint were most often reconstructed when threshold values were selected at -500 to -700 Hounsfield Units. These shapes were changed by choosing various threshold values. Histological examinations of the cadaver specimen indicate that these changes are due to structure of the I-S joints. We conclude that these 3-D images may be useful in assessing pathology of the I-S joint.

67Ga whole-body scintigraphy in the evaluation of head and neck squamous cell carcinoma

The diagnostic accuracy of 67Ga-citrate whole-body scintigraphy for the evaluation of primary tumours, local recurrences, cervical node metastases and distant metastases was investigated in patients with head and neck squamous cell carcinoma (SCC). Altogether, 102 67Ga-citrate whole-body scans were performed on 83 patients with head and neck SCC using a dual-headed gamma camera. The results were compared with those of computed tomography (CT) and final diagnosis. 67Ga scintigraphy correctly diagnosed 28 of 29 primary lesions, a sensitivity of 97% (CT = 97%). For tumour recurrence, 67Ga scintigraphy correctly diagnosed 13 of 15 recurrences and 53 of 58 instances of no recurrence, giving a sensitivity of 87% and a specificity of 91% (CT = 80 and 62%, respectively). Scintigraphy correctly diagnosed 23 of 31 metastatic sides of the neck and all 173 negative sides of the neck, giving a sensitivity of 74% and a specificity of 100% (CT = 90 and 84%, respectively). Finally, scintigraphy correctly diagnosed all 12 distant metastases as well as 86 of 90 cases of no metastasis, resulting in a sensitivity of 100% and a specificity of 96%. Furthermore, in five patients, distant metastases were initially detected on 67Ga scintigraphy. In conclusion, 67Ga whole-body scintigraphy with a dual-headed camera resulted in a high sensitivity and specificity for the detection of primary lesions, recurrences and distant metastases of head and neck SCC. Although the sensitivity for detecting neck node metastases was relatively low, the specificity was high. Thus, 67Ga scintigraphy is an effective technique for the evaluation of head and neck SCC, especially tumour recurrence and distant metastases.

A group of schwannomas with interstitial deletions on 22q located outside the NF2 locus shows no detectable mutations in the NF2 gene

Schwannomas are tumors arising mainly at cranial and spinal nerves. Bilateral vestibular schwannoma is the hallmark of neurofibromatosis type2 (NF2). The NF2 gene has been cloned and comprehensive analysis of its mutations in schwannomas shows that up to 60% of tumors carry inactivating mutations. Thus, the genetic mechanism behind the development of more than 40% of schwannomas without NF2 mutations is unknown. We have therefore studied tumor tissue from 50 human schwannomas by allelotyping and have found chromosome 22 deletions in over 80% of the cases. We detected 14 cases (27%) that revealed partial deletions of one copy of chromosome 22, i.e., terminal and/or interstitial deletions. We sequenced the NF2 gene in seven of these tumors and detected only one case with mutations. The deletion mapping of chromosome 22 in tumors with partial deletions indicates that several regions, in addition to the NF2 locus, harbor genes involved in schwannoma tumorigenesis. Our findings suggest that heterogeneity in the mechanisms leading to the development of schwannomas probably exists. These findings are in agreement with the recent analysis of schwannomas from familial and sporadic cases of schwannomatosis and point to a possible role of an additional gene, which, in cooperation with the NF2 tumor suppressor, causes schwannomas.

A comparison of extratympanic versus transtympanic recordings in electrocochleography

Detection thresholds, amplitudes and input output curves of cochlear microphonics (CMs), and action potentials (APs) determined by extratympanic electrocochleography (ET ECochG) were compared with those determined by transtympanic (TT) ECochG in the same ears. Two groups were studied: 12 ears in 9 volunteers with normal hearing, and 6 ears in 6 subjects with sensorineural hearing loss. Short tone bursts with frequencies of 0.5, 1, 2 and 4 kHz were used as acoustic stimuli to evoke CMs, and a click was presented to measure the APs. In both groups, although the two approaches produced large differences in amplitudes, nearly identical values were obtained for the CM and AP detection thresholds. The CM and AP input-output curves obtained from mean amplitudes at each intensity in normally-hearing ears had similar slopes with the two approaches. These findings demonstrate the clinical usefulness of ET ECochG.

An adequate parameter evaluating the galvanic body sway test: comparison with the caloric test in patients with vestibular schwannomas

It has been reported that the galvanic body sway test does not correlate with the caloric test. We evaluated the galvanic body sway test in patients with vestibular schwannomas using three parameters: the angle of deviation response onset, the maximum value of the deviation response, and the area of deviation. These parameters reflect velocity, position, and locus of the centre of pressure, respectively. Among these parameters, only the angle of deviation response onset showed unilateral weakness of the response correlating with the canal paresis value, which indicates that velocity is responsible for conduction in the vestibular nerve. However, the galvanic body sway test is apt to be preferred to the caloric test. This might be attributed to the decreased sensitivity of this test.

Cochlear microphonic potentials in patients with vestibular schwannomas

We evaluated the cochlear function of 44 patients with unilateral vestibular schwannomas by measuring cochlear microphonic potentials (CM) in electrocochleography. We used short tone bursts with 0.5-, 1-, 2-, and 4-kHz frequencies as acoustic stimuli to evoke CMs, and determined CM detection thresholds. The CM detection thresholds in vestibular schwannomas ranged from normal to no response. Cochlear dysfunction was seen in 35 (79.5%) of the 44 cases; these patients had higher CM detection thresholds than normal subjects. Although a significant correlation was found between mean hearing level (0.5-4 kHz) and mean CM detection threshold (0.5-4 kHz), 20 patients had lower CM detection thresholds than were found using audiometry. This suggests that there is an additional retrocochlear component responsible for this hearing loss.

Aberrant jugular bulb vein obstructing approach to intracanalicular vestibular schwannoma

In cases of jugular bulb anomalies, such as a high jugular bulb, troublesome bleeding may occur during surgery. We report an unusual case with a vestibular schwannoma, in which we recognized an additional branch arising from the jugular bulb. Three-dimensional computed tomography (3-D CT) revealed this anomaly beforehand, enabling us to avert excessive bleeding upon resection of the tumour. The abnormal vein was thought to be a remnant of the petrosquamosal sinus in the embryonic stage.

A CT study of the course of growth of the maxillary sinus: normal subjects and subjects with chronic sinusitis

We measured the maxillary sinus volume of normal children and those with bilateral chronic sinusitis by coronal CT scan of the paranasal sinus, and compared the results with findings previously obtained from adult patients. The distribution of mean maxillary sinus volume by age group from 4-9 to 70-79 years exhibited a monomodal pattern with a peak in the 20s in both the normal group and the surgical therapy group. The maxillary sinus volumes of children aged 10-15 years and adults tended to be smaller in the surgical therapy group than in the normal group; this tendency was more prominent in the adult group. These findings appear to support the hypothesis that the ethmoid infundibulum and middle meatus are narrowed by inflammation of the ostiomeatal complex and by various bony anatomic variations in the nasal cavity, leading to impaired pneumatization of the maxillary sinus.

The furosemide test and vestibular status in Meniere's disease

A total of 62 ears of patients with typical Meniere's disease was examined by the furosemide test to detect endolymphatic hydrops. In 95% of the normal control group, the per cent change in the maximum velocity of the slow phase of caloric nystagmus (MVS) after injection of furosemide was under 10%. Therefore, a positive furosemide test was defined as a change in MVS of more than 10%. Thirty-five (56%) of the 62 ears with typical Meniere's disease showed a positive furosemide test. When the affected ears were divided into two groups according to vestibular symptoms, only 11 (38%) of 29 inactive ears were positive while 24 (73%) of 33 active ears were positive. There was a significant difference in the positive rate of the furosemide test between the ears with clinically inactive and active vestibular disease. The per cent canal paresis (CP%) was determined to assess canal excitability and a CP%> 25% was defined as canal paresis. There was no significant difference in the furosemide test positive rate between ears with canal paresis and ears with a normal CP%, although the former tended to show a greater MVS change. The response to the furosemide test showed no relationship to the results of pure tone audiometry. In conclusion, the furosemide test appears to indicate the vestibular status in various stages of Meniere's disease.

A new electrode (HN-5) for CM measurement in extratympanic electrocochleography

A new electrode (HN-5) for measuring cochlear microphonics (CMs) in extratympanic (ET) electrocochleography (ECochG) has been developed. The HN-5 electrode consists of a silver wire 2 mm in diameter and 5.0 cm in length connected to a low noise cable. The HN-5 electrode showed low impedance and excellent frequency characteristics. Using the dummy ear, artefact contamination tests, such as electromagnetic induction and mechanical vibration, were performed with the HN-5 electrode and various other electrodes. In the HN-5 electrode, artifact contaminations were kept within acceptable noise levels, whereas in the smaller electrodes, the measurable artifact contaminations were larger. The CMs were measured from subjects with normal hearing. CM findings obtained using the HN-5 electrode did not differ from those obtained by transtympanic (TT) ECochG, apart from their amplitude. HN-5 overcame the major disadvantage of the ET ECochG and provided a very favourable signal-to-noise ratio, resulting in repeatable response signals averaged from the same relatively small number of samples as those of TT ECochG. This resulted in successful CM measurements of ET ECochG.

Influence of phylogeny on jugular fossa shape and otological disorders

We examined the shape of the jugular fossa and its protrusion into the tympanic cavity in 51 human skulls and in 355 various monkey skulls. All human specimens had a done-shaped fossa, and the right fossa was larger than the left in 60 per cent of the specimens. Fossae protruded into the tympanic cavity in 20 per cent of these specimens. In contrast, none of the monkey specimens had a dome-shaped fossa. Some monkeys had saucer-shaped jugular fossa; the frequency of such fossa became higher as phylogeny progressed. Furthermore, the jugular fossae in monkeys did not protrude into the tympanic cavity. The shapes of both the jugular fossa and sulcus of the transverse sinus were generally symmetrical. The shape of the jugular fossa and its positional relationship to the tympanic cavity were considered from the viewpoint of the influence of phylogeny and the possible relationship to various otological problems.

Intraoperative measurements of auditory-evoked potentials in three patients with acoustic neuroma

Auditory brainstem responses (ABRs), electrocochleograms and the evoked potentials from the internal auditory canal were recorded simultaneously in 3 acoustic neuroma (AN) patients. The neural conduction in the internal auditory canal was examined by recording the compound action potentials of the cochlear nerve. In an AN patient with wave I only in the ABR, the neural conduction of the excitement in the cochlear nerve was blocked within the internal auditory canal. In 2 AN patients with elongated interpeak latency differences between waves I and V in ABRs, the neural conduction velocity of the cochlear nerve was lower than that of normal subjects. These results provide neurophysiological evidence that low neural conduction velocity in the cochlear nerve results in the abnormal ABR.

Vestibular schwannoma showing a dural tail on contrast-enhanced magnetic resonance images

The dural tail on contrast-enhanced magnetic resonance (MR) images, frequently observed in meningiomas, has been used to distinguish between cerebellopontine angle meningiomas and vestibular schwannomas. We report on a 66-year-old female with vestibular schwannoma showing the dural tail on contrast-enhanced MR images. Histological examination revealed that the dural tail corresponded to the thickened dura mater comprising of collagen fibres and scattered hyalinization with no tumoral invasion.

The morphological differences of stereocilia and cuticular plates between type-I and type-II hair cells of human vestibular sensory epithelia

The sensory epithelia of macula utriculi were examined by conventional and intermediate voltage transmission electron microscopy. The specimens were obtained from three cases of acoustic neurinoma who were operated on using the translabyrinthine approach. The mean diameter of the vestibular hair cell stereocilia was obtained and the cuticular plates of type-I and type-II hair cells were reconstructed three-dimensionally from the consecutive 0.5-micron-thick sections. The mean diameter of stereocilia of type-I hair cells was 488 +/- 59 nm (n = 13) and that of stereocilia of type-II hair cells was 373 +/- 21 nm (n = 14). Stereocilia of type-I hair cells numbered about 70 and those of type-II hair cells about 50. The cuticular plates of type-I hair cells were several times as thick as those of type-II hair cells. The cuticular plate of the type-I hair cell appeared to be an inverse cone and that of the type-II hair cell seemed to be a flat disc.

[Clinical study in vertiginuous patients suspected of having neurovascular compression syndrome of the eighth cranial nerve]

Neurovascular compression syndrome of the 5th and 7th cranial nerves has been recognized as the cause of trigeminal neuralgia and hemifacial spasm. On the other hand, it is still difficult to diagnose vertigo as neurovascular compression syndrome of the 8th cranial nerve. To detect some specific finding in this syndrome of the 8th cranial nerve, 5 patients with vertigo with hemifacial spasm were examined for the clinical course and neuro-otological features. In all patients MRI and/or angiography suggested vascular compression against the 8th cranial nerve. The clinical courses of these patients revealed various symptoms resembling benign paroxysmal positional vertigo, vestibular neuronitis and Meniere's disease. Audiograms showed two normal hearing patterns, bilateral high frequency hearing loss probably due to aging in one case, bilateral C5-dip in one and fluctuating unilateral hearing loss like Meniere's disease in one. The prolongation of IPL I-III on auditory brainstem response proposed as a criterion by Møller was detected in one case. No response in the caloric test was found in two cases. These abnormalities in the auditory brainstem response and caloric test appeared to be useful for diagnosis but were uncommon findings in all cases. Electronystagmographic examinations including the eye tracking test, optokinetic nystagmus and optokinetic pattern were all normal. We could not find any specific clinical findings valuable for diagnosis of neurovascular compression syndrome of the 8th cranial nerve. It is proposed that the indication of microvascular decompression should be decided carefully.

Electrically evoked auditory brainstem response by direct electrical stimulation to the cochlear nerve in acoustic neuroma patients

The electrically evoked auditory brainstem response (EABR) was recorded by direct electrical stimulation of the cochlear nerve in 8 acoustic neuroma patients. The EABR by electrical stimulation of the cochlear nerve at the fundus of the internal auditory canal was almost similar to those previously reported from cochlear implant patients in waveform morphology and wave latencies. However, the wave corresponding to wave II in human auditory ABR was not recorded in the EABRs by stimulation of the distal part of the intracranial cochlear nerve. These results suggest that the cochlear nucleus does not contribute to the generation of wave II in ABR.

Cochlear microphonics recordable at the non-shielded bedside using a new tubal transducer

A new tubal transducer (NC-3) for measuring cochlear microphonics (CM) in extratympanic electrocochleography (ECochG) was developed by improving the common hearing aid earphone. Using a human forearm as a dummy ear, the artifact contamination generated from the NC-3 tubal transducer was tested and the possibility of measuring the CM at a non-shielded bedside was studied. An HN-5 electrode was fixed to a subject's forearm, and a sound stimulus of 90 dBnHL was delivered through the tube of the NC-3. When the earphone of the transducer was placed at a right-angle to the electrode on either a vertical or horizontal plane and the electrode was placed in direct contact with the tip of the tube, contamination from electromagnetic induction and CM-like mechanical vibration were prevented. Using the HN-5 electrode and NC-3, extratympanic ECochG-CM was recorded from normal-hearing subjects in both a shielded soundproof room and a non-shielded ordinary, quiet room. No differences were found between CMs measured in the two rooms. These results suggest that the NC-3 overcomes the shortcomings of a loudspeaker system and allows CM to be recorded accurately at non-shielded bedsides.

Primary localized nodular tongue amyloidosis associated with Sjögren's syndrome

We describe a case of primary localized nodular tongue amyloidosis associated with Sjögren's syndrome in a 62-year-old woman. The presence of Sjögren's syndrome was confirmed both serologically and histologically. The amyloid tumor, which was marginally excised, recurred 3 years later and was re-excised. Immunohistochemical examination revealed that the amyloid protein was of the AL (lambda-light chain) type. Infiltration of plasma cells was observed around the minor salivary glands of the tongue surrounded by amyloid. The relationship between the plasma cells and amyloid deposition is discussed.

Solitary plexiform neurofibroma of the submandibular salivary gland

Neurofibroma affecting the major salivary gland is uncommon. This tumour is particularly rare in the submandibular and sublingual gland. Here, a case of solitary plexiform neurofibroma of the submandibular gland without any other manifestations of von Recklinghausen's disease is presented. It is probably the first case report of this tumour invading the submandibular gland in a solitary form.