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.     

Cochlear changes in chronic otitis media

OBJECTIVES/HYPOTHESIS: The objective was to describe the morphological changes in the cochlea in chronic otitis media. STUDY DESIGN: Retrospective human temporal bone analysis. METHODS: Fifteen temporal bones with unilateral chronic otitis media were selected and compared with contralateral normal temporal bones. Standard cytocochleograms and spiral ganglion cell reconstructions were performed on all temporal bones. Spiral ligament was divided into four segments according to the locations of different types of fibrocytes. The average loss of fibrocytes in each segment was estimated. Morphometric measurements of areas of stria vascularis and spiral ligament were made in all turns of the cochlea on mid modiolar sections. RESULTS: Loss of outer and inner hair cells was common in the basal turn of the cochlea in temporal bones with chronic otitis media compared with control ears. There was no difference in the number of spiral ganglion cells in the chronic otitis media and contralateral ears. The areas of stria vascularis and spiral ligament in the basal turn decreased significantly in the ears with chronic otitis media compared with control ears. There were no significant differences between the ears with chronic otitis media and the contralateral ears for any of the regions characterized by the presence of types I-IV fibrocytes. CONCLUSION: The results of the study are consistent with the hypothesis that chronic otitis media causes cochlear disease.     

Effect of cochlear implantation on residual spiral ganglion cell count as determined by comparison with the contralateral nonimplanted inner ear in humans

It is generally assumed that at least a minimal number of spiral ganglion cells is essential for successful speech perception with a cochlear implant. Although the insertion of a multichannel cochlear implant frequently results in loss of residual hearing in the implanted ear, this outcome does not imply that significant damage to residual populations of spiral ganglion cells has occurred. The purpose of the current study was to compare spiral ganglion cell counts in implanted and nonimplanted cochleas in 11 patients for whom both temporal bones were available and in whom a multichannel cochlear implant had been placed unilaterally. The temporal bones were processed for light microscopy by standard techniques. The cochleas were reconstructed by 2-dimensional methods. Spiral ganglion cell counts of the implanted and nonimplanted sides were compared by a paired t-test (2-tailed). The mean spiral ganglion cell counts for implanted and nonimplanted ears were not statistically different in the most basal three segments of the cochlea. However, the mean spiral ganglion cell count in segment 4 (apical segment) and the mean total spiral ganglion cell count were lower in the implanted cochleas than in the nonimplanted cochleas (p < .01). The results of this study suggest a modest decrease in the total spiral ganglion cell count in the implanted ears as compared to the nonimplanted ears, principally in the apical segment. Possible interpretations of this finding are discussed.     

Anomaly of the round window a histopathological study using a graphic reconstruction method

Although literature to date has reported that anomalies of the round window occur infrequently, no study to our knowledge has investigated such anomalies quantitatively. Thus, we developed a graphic reconstruction method and used it to study histology sections of the temporal bones. By this method we studied quantitatively the morphology of the round window of individuals with Mondini dysplasia of the inner ear and compared it to that of individuals with no anomaly. Iit was found that in 3 of 19 individuals with dysplasia, the total area of the round window was more than two standard deviations below the mean, thus small enough to be called anomalous. Moreover, the area of the round window was statistically significantly smaller in the ears from individuals with Mondini dysplasia, as a group, than in normal ears. This round window anomaly seems to be due to interruption of the normal development of the round window early in fetal life, as the result of poor development of the cartilage bar between the tympanic cavity and the subarachnoid space and also of the otic capsule in the hook portion of the basal turn of the cochlea.     

Electrical impedance measurements of cochlear structures using the four-electrode reflection-coefficient technique

In individuals with severe-to-profound hearing loss, cochlear implants (CIs) bypass normal inner ear function by applying electrical current directly into the cochlea, thereby stimulating surviving auditory nerve fibers. Although cochlear implants are able to restore some auditory sensation, they are far from providing normal hearing. It has been estimated that up to 75% of the current injected via a CI is shunted along scala tympani and is not available to stimulate auditory neurons. The path of the injected current and the consequent population of stimulated spiral ganglion cells are dependent upon the positions of the electrode contacts within the cochlea and the impedances of cochlear structures. However, characterization of the current path remains one of the most critical, yet least understood, aspects of cochlear implantation. In particular, the impedances of cochlear structures, including the modiolus, are either unknown or based upon estimates derived from circuit models. Impedance values for many cochlear structures have never been measured. By combining the hemicochlea preparation, a cochlea cut in half along its mid-modiolar plane, and the four-electrode reflection-coefficient technique, impedances can be measured for cochlear tissues in a cochlear cross section including the modiolus. Advantages and disadvantages of the method are discussed in detail and electrical impedance measurements obtained in the gerbil hemicochlea are presented. The resistivity values for the cochlear wall in Ωcm are, 528 (range: 432–708) for scala media 3rd turn, 502 (range: 421–616) for scala tympani 3rd turn and scala vestibuli 2nd turn, 627 (range: 531–759) for scala media 2nd turn, 434 (range: 353–555) for scala tympani 2nd turn and scala vestibuli basal turn, 434 (range: 373–514) for scala media basal turn, and 590 (range: 546–643) for scala tympani basal turn. The resistivity was 455 Ωcm (range: 426–487) for the modiolus.     

CT-scanning of the cochlea in Pendred's syndrome

The inner ears of 5 adult patients with Pendred's syndrome were investigated using a Siemens SOMATOM DRG. Five normal hearing adults participated in the investigation as a control group. The CT-scanning comprised 10-15 consecutive scans of the cochlea. The CT evaluation was performed using both a special bone setting and a soft tissue setting. The cochlear content was quantitatively evaluated by drawing an irregular region of interest on the bone pictures. The region of interest was then transferred to the soft tissue pictures by means of the standard program of the CT-scanner. The resulting mean values of attenuation expressed in Hounsfield Units were significantly lower in the Pendred cochleas than in the normal cochleas. At the same time a typical Mondini malformed cochlea was demonstrated in all patients with Pendred's syndrome. The lower values of attenuation of the cochlea in Pendred's syndrome reflect the rudimentarily developed infra-cochlear osseous structures in this disease. We conclude that CT-scanning of the cochlea using this procedure is reliable enough to replace the conventional axial-pyramidal tomography when a Mondini cochlea is suspected.     

Mondini-like malformation mimicking otosclerosis and superior semicircular canal dehiscence

In 2003, it was reported that superior semicircular canal dehiscence can mimic otosclerosis because of low-frequency bone conduction hearing gain and dissipation of air-conducted acoustic energy through the dehiscence. We report the case of a 17-year-old girl with left-sided combined hearing loss thought to be due to otosclerosis. Bone conduction thresholds were -10 dB at 250 and 500 Hz and she had a 40 dB air-bone gap at 250 Hz. When a tuning fork was placed at her ankle she heard it in her left ear. Acoustic reflexes and vestibular evoked myogenic potentials could be elicited bilaterally. Imaging of the temporal bones showed no otosclerosis, superior semicircular canal dehiscence or large vestibular aqueduct, but a left-sided, Mondini-like dysplasia of the cochlea with a modiolar deficiency could be seen. Mondini-like cochlear dysplasia should be added to the causes of inner-ear conductive hearing loss.     

A new classification for cochleovestibular malformations

OBJECTIVE: The report proposes a new classification system for inner ear malformations, based on radiological features of inner ear malformations reviewed in 23 patients. STUDY DESIGN: The investigation took the form of a retrospective review of computerized tomography findings relating to the temporal bone in 23 patients (13 male and 10 female patients) with inner ear malformations. The subjects were patients with profound bilateral sensorineural hearing loss who had all had high-resolution computed tomography (CT) with contiguous 1-mm-thick images obtained through the petrous bone in axial sections. METHODS: The CT results were reviewed for malformations of bony otic capsule under the following subgroups: cochlear, vestibular, semicircular canal, internal auditory canal (IAC), and vestibular and cochlear aqueduct malformations. Cochlear malformations were classified as Michel deformity, common cavity deformity, cochlear aplasia, hypoplastic cochlea, incomplete partition types I (IP-I) and II (IP-II) (Mondini deformity). Incomplete partition type I (cystic cochleovestibular malformation) is defined as a malformation in which the cochlea lacks the entire modiolus and cribriform area, resulting in a cystic appearance, and there is an accompanying large cystic vestibule. In IP-II (the Mondini deformity), there is a cochlea consisting of 1.5 turns (in which the middle and apical turns coalesce to form a cystic apex) accompanied by a dilated vestibule and enlarged vestibular aqueduct. RESULTS: Four patients demonstrated anomalies involving only one inner ear component. All the remaining patients had diseases or conditions affecting more than one inner ear component. Eight ears had IP-I, and 10 patients had IP-II. Ears with IP-I had large cystic vestibules, whereas the amount of dilation was minimal in patients with IP-II. The majority of the semicircular canals (67%) were normal. Semicircular canal aplasia accompanied cases of Michel deformity, cochlear hypoplasia, and common cavity. In 14 ears, the IAC had a defective fundus at the lateral end. In two ears the IAC was absent. In all seven cases of common cavity malformations, there was a bony defect at the lateral end of the IAC. In five of them the IAC was enlarged, whereas in two the IAC was narrow. All patients with IP-I had an enlarged IAC, whereas in patients with type II disease, four had a normal IAC and 10 had an enlarged IAC. All cases of IP-II had an enlarged vestibular aqueduct, whereas this finding was not present in any of the cases of IP-I. In all cases, the vestibular aqueduct findings were symmetrical on both sides (simultaneously normal or enlarged). No patient demonstrated enlargement or any other abnormalities involving the cochlear aqueduct. CONCLUSIONS: Radiological findings of congenital malformations in the present study suggested two different types of incomplete partition. Cystic cochleovestibular malformation (IP-I) and the classic Mondini deformity (IP-II). The type I malformation is less differentiated than the type II malformation. Classic Mondini deformity has three components (a cystic apex, dilated vestibule, and large vestibular aqueduct), whereas type I malformation has an empty, cystic cochlea and vestibule without an enlarged vestibular aqueduct. Mondini deformity represents a later malformation, so the amount of dysplasia is much less than in type II. Therefore, it is more accurate and useful for clinical purposes to classify these malformations (in descending order of severity) as follows: Michel deformity, cochlear aplasia, common cavity, IP-I (cystic cochleovestibular malformation), cochlear hypoplasia, and IP-II (Mondini deformity). Only in this way can these complex malformations be grouped precisely and the results of cochlear implantation compared.     

The Mondini defect in Turner's syndrome. A temporal bone report

The histopathology of the right temporal bone of a 47 year old deaf woman with Turner's Syndrome (gonadal dysgenesis) is described. The appearances are of the Mondini deformity, the cochlea consisting of a single basal turn with a bulbous apical dilatation. The organ of Corti was absent. The remainder of the bony labyrinth save for the cochlear aqueduct was normal. The patient's death was due to a cerebral astrocytoma. Previous reports concerning the co-existence of gonadal dysgenesis, congenital deafness and non-gonadal neoplasia are discussed.     

内耳疾病基因治疗方法的研究

目的:探讨一种高效、安全和简便的内耳疾病基因转移和导入方法。方法:将30只健康豚鼠随机分为A、B、C 3组,每组10只。用Ad—GFP报告基因分别由圆窗、耳蜗底回和脑脊液三种途径导入30只豚鼠内耳,在术前和术后测定听性脑干反应(ABR)阈值和畸变产物耳声发射(DPOAE)振幅改变。再行耳蜗铺片,观察AdGFP在内耳组织中的转染表达和耳蜗毛细胞的形态结构。结果:三种途径导入Ad—GFP在耳蜗螺旋神经节、血管纹和Corti器上均有转染和表达。在术后3 d的表达产物最高,7 d后减弱,10 d后更弱。圆窗和耳蜗底回钻孔导入手术可引起蜗内出血,凝血块淤积在耳蜗顶回的中阶,造成顶回毛细胞损害。而脑脊液给药途径无此现象。ABR阈值在各组动物手术前后无明显改变,而圆窗和耳蜗底回给药途径造成DPOAE幅度明显下降,脑脊液给药组无DPOAE改变。结论:应用腺病毒载体进行基因转移通过圆窗和耳蜗底回钻孔途径可引起蜗内出血,影响DPOAE幅度,而应用脑脊液给药途径则相对安全和方便。     

蜗轴缺失内耳形态学表现与人工耳蜗植入入路的选择

目的：总结人工耳蜗植入手术患者耳蜗蜗轴缺失的类型和人工耳蜗植入手术入路的选择,为掌握人工耳蜗植入手术的适应证提供参考。方法：人工耳蜗植入患者按术前颞骨高分辨CT检查,将存在的耳蜗蜗轴发育缺失分为3种类型：1耳蜗发育不良形成的蜗轴缺失（Mondini畸形）;2耳蜗前庭半规管发育不良（Common cavity畸形）;3内耳道与耳蜗共腔（IP-Ⅲ）畸形。将蜗轴缺失的内耳畸形人工耳蜗植入手术入路分成3种类型：Ⅰ型,常规面神经隐窝入路将圆窗扩大开放入耳蜗内;Ⅱ型,常规面隐窝入路后鼓岬表面开放入畸形的耳蜗腔内,电极沿侧壁摆放;Ⅲ型,乳突侧开放外半规管突入共腔将电极摆放于耳蜗侧的腔内骨壁。结果：1246例内耳畸形中耳蜗蜗轴发育缺失共166例,其中Mondini畸形的215例患者中存在蜗轴缺失135例;Conmon cavity畸形18例,全部存在耳蜗蜗轴缺失;内耳道与耳蜗共腔（IP-Ⅲ）畸形13例,全部存在耳蜗蜗轴缺失。2内耳畸形存在耳蜗蜗轴缺失的人工耳蜗植入手术入路的选择：Ⅰ型136例,其中Mondini畸形123例,内耳道与耳蜗共腔（IP-Ⅲ）畸形13例;Ⅱ型12例,全部为Mondini畸形存在蜗轴缺失患者;Ⅲ型18例,全部为Conmon cavity畸形。33种内耳畸形人工耳蜗植入术后效果：Mondini畸形声场测试平均为65dB,单韵母言语识别为95%,单声母言语识别为25%;Conmon cavity畸形声场测试平均为80dB,单韵母言语识别为60%,单声母言语识别为0;内耳道与耳蜗共腔（IP-Ⅲ）畸形声场测试平均为55dB,单韵母言语识别为100%,单声母言语识别为45%。结论：耳蜗蜗轴缺失的内耳畸形人工耳蜗植入术后患者听觉言语识别效果很差,Conmon cavity畸形最差,Mondini畸形次之,内耳道与耳蜗共腔（IP-Ⅲ）畸形较前两者好。     

Temporal bone findings in trisomy 13 with cyclopia

Temporal bone findings in a fetus with trisomy 13 syndrome and cyclopia may be histopathologically characterized by the dysplasia of bony and membranous labyrinth and of the nervous system. In the left ear, there was a shortened cochlea housing a malformed Corti's organ appearing as a ribbonlike structure, an unexpected canal running obliquely through the scala tympani, a peculiar shape of the utricular macula and posterior canal crista, and a delayed ossifying process in the otic capsule. The poor development of the structures in the seventh and eighth nerves and their ganglions was observed in both ears. The type of anomaly can be classified as Mondini or Mondini-Alexander. The several anomalies might involve the organs that begin to develop during the period from five to eight gestational weeks.     

Temporal bone histopathologic findings in a case of interstitial deletion of the long arm of chromosome 2 [del(2) (q31q33)].

The temporal bones of a 24-day-old female neonate with an interstitial deletion of the long arm of chromosome 2 [del(2)(q31q33)] were studied histopathologically, focusing mainly on the inner ear. This is, to our knowledge, the first report of a temporal bone study in a case of this chromosomal aberration. The abnormalities included a shortened cochlea with underdeveloped modiolus in both ears. Total absence of the spiral ganglion cells and the cochlear nerve bundle, accompanied by obliteration of the fundus of the internal auditory meatus by a bony plate, and dislocation of some geniculate ganglion cells to the internal auditory meatus were also observed in the right ear. The absence of the spiral ganglion cells is considered to be the result of some complication in the early fetal life, such as dysgenesis or early degeneration of the neuronal cells. The organ of Corti in the right ear was well-developed and preserved in the middle turn, suggesting that the differentiation of the cochlear sensory epithelium in humans is not dependent upon the innervation, at least on the gross level.     

Distortion products in early stage experimental hydrops in the guinea pig

The swelling of the endolymphatic spaces in experimental hydrops is likely to induce mechanical changes all along the cochlea. The selective atrophy of short and middle stereocilia on the outer hair cell above the first cochlear turn is expected to alter micromechanics and transduction. Two tone stimuli were employed in the present study to investigate cochlear distortion products in hydropic ears. Despite a substantial low frequency sensitivity loss on the CAP audiogram, 2f1-f2 distortion products recorded in the RWCM and the CAP were similar in hydropic ears and normal control ears which reflect the probable common origin of these responses--the base of the cochlea where no threshold shifts can be detected. On the other hand this distortion product in the otoacoustic emissions was considerably reduced in hydropic cochleas when the primary tones lay within the pathological part of the audiogram. The reduction of CDT emissions cannot be accounted for by hair cell loss since at the early stage of hydrops described here there is only discrete hair cell loss which is restricted to the apex of the cochlea. On the other hand the reduction in the amplitude of the CDT might reflect disturbance in hair cell function and/or cochlear mechanics above the first cochlear turn.     

Total deafness from aminoglycoside overdosage: histopathologic case study

A 57-year-old patient became totally deaf two days after receiving excessive doses of the aminoglycosidic antibiotic lividomycin parenterally for 14 days; she died four and a half months later. Her temporal bones were examined by microdissection, surface preparation, and serial sectioning of the modiolus. Loss of inner and outer cochlear hair cells was virtually complete. Refractile concretions were scattered along the atrophic stria vascularis, especially in the middle turn. The distal half of the radial cochlear nerve fibers in the osseous spiral lamina had degenerated, but closer to the modiolus they appeared to be intact. The spiral ganglion in the basal turn showed partial loss of neurons. Scanning electron microscopy revealed hair cell loss from the vestibular end-organs, more severe in the ampullar cristae than in the utricular macula. The dark cells of the utricular wall appeared to be altered.     

Anatomy of the middle-turn cochleostomy

Objective: Middle‐turn cochleostomies are occasionally used for cochlear implant electrode placement in patients with labyrinthitis ossificans. This study evaluates the anatomic characteristics of the middle‐turn cochleostomy and its suitability for placement of implant electrodes. Methods: Ten cadaveric human temporal bones were dissected using a facial recess approach. A middle‐turn cochleostomy was drilled 2 mm anterior to the oval window and just inferior to the cochleariform process. The preparations were then stained with osmium tetroxide and microdissections were performed. The location of the cochleostomy on the cochlear spiral and its path through the various cochlear compartments were evaluated in all 10 specimens. A Cochlear Corporation depth gauge was inserted in five of the specimens and insertion trauma, number of contact rings, and depth of insertion were recorded. Results: Eight of the 10 cochleostomies were placed at approximately 360° on the cochlear spiral, near the transition between the basal and middle turns. In one case, the cochleostomy was found to enter the cochlear apex and in another it entered scala vestibuli of the proximal basal turn. The cochleostomy entered scala media in six bones and scala vestibuli in four specimens. A depth gauge was inserted in five specimens. The number of contacts placed within the cochlear lumen ranged from four to nine. There was evidence of insertional trauma to the lateral wall of the cochlear duct, basilar membrane, and Reissner's membrane, but no evidence of fractures to the osseous spiral lamina or modiolus. Conclusion: This study demonstrates that electrodes inserted via a middle‐turn cochleostomy are likely to enter scala vestibuli and have access to the middle‐ and apical‐cochlear turns. It is also possible that the electrode could be directed into the descending portion of the basal turn depending on cochleostomy orientation. Middle‐turn cochleostomy seems to be a viable alternative for electrode placement when preservation of residual hearing is not a concern.     

Stria vascularis in Ménière's disease: a quantitative histopathological study.

To investigate the role of pathology of the stria vascularis in Ménière's disease, the vascularity and the cross-sectional area of the stria vascularis in a midmodiolar section of the cochlea were examined by histological observation and a computer-aided planimetric, respectively, in eight temporal bones from individuals with Ménière's disease and eight age-matched normal temporal bones. The number of vessels in the stria vascularis was significantly smaller in most of the cochlear turns in ears with Ménière's disease than in control ears, and the cross-sectional area of the stria vascularis in the same sections was significantly smaller in all the cochlear turns in ears with Ménière's disease than in controls. Furthermore, vascularity correlated significantly with the cross-sectional area of the stria vascularis in all the temporal bones examined. From these results it appears that poor vascularity of the stria vascularis is closely related to strial atrophy, and that these pathological findings might be important factors in the pathophysiology of Ménière's disease.     

Effects of type 2 diabetes mellitus on cochlear structure in humans

OBJECTIVE: To evaluate the effects of type 2 diabetes mellitus on cochlear elements in humans. DESIGN: Comparative study of the histopathologic characteristics of human temporal bones. SETTING: Otopathology laboratory in a tertiary academic medical center. PATIENTS: Temporal bones from 18 patients with type 2 diabetes mellitus were divided into 2 groups according to the method of management of diabetes: insulin in 11 patients (mean age, 51.9 years; age range, 44-65 years) and oral hypoglycemic agents in 7 patients (mean age, 54.4 years; age range, 45-64 years). The diabetic groups and 26 age-matched controls (mean age, 52.9 years) were examined using light microscopy, and the cochlear changes were compared between groups. MAIN OUTCOME MEASURES: Morphometric measurements of vessel wall thickness in the basilar membrane and stria vascularis were made in all turns of the cochlea at the midmodiolar level. Area measurements of the stria vascularis were made in all turns of the cochlea at the midmodiolar level. Cochlear reconstructions and standard cytocochleograms were prepared using an oil immersion objective. The number of spiral ganglion cells was determined for each segment of the cochlea. Comparisons were made in each segment between diabetic and control groups. RESULTS: In the insulin group, walls of the vessels of the basilar membrane and stria vascularis in all turns were significantly thicker than those of controls. Walls of the vessels of the stria vascularis in the basal turn were also significantly thicker in the oral hypoglycemic group than in controls. Atrophy of the stria vascularis in most turns of the insulin group and the lower middle turn of the oral hypoglycemic group was significantly greater than in the controls. Loss of cochlear outer hair cells was significantly greater in the lower and upper basal turns in both diabetic groups. No significant difference was found in the number of spiral ganglion cells or inner hair cells between groups. CONCLUSION: This study demonstrates that cochlear microangiopathy and degeneration of the stria vascularis and cochlear outer hair cells are found in patients with type 2 diabetes mellitus.