Smooth muscle choristoma of the internal auditory meatus

Choristomas of the internal auditory meatus are very uncommon tumors. Because of their rarity and the lack of a consistent clinical and radiological pattern, they are usually misdiagnosed as vestibular schwannomas. Surgical exploration usually shows involvement of the vestibular, cochlear or facial nerve by the tumor, representing a diagnostic and therapeutic challenge to the surgeon. In this report, a case of a smooth muscle choristoma of the internal auditory meatus is presented. The lesion involved the vestibular and cochlear nerves and was extremely adherent to the facial nerve. Microscopic examination of the tumor revealed nerve fibers, smooth muscle and a small amount of adipose tissue. No striated muscle was found. The contemporary terminology, diagnosis and management of this infrequent lesion are analyzed.     

Neuromuscular hamartoma of the cochlear nerve: a rare occurrence in the internal auditory meatus

The authors present a case of neuromuscular hamartoma of the cochlear nerve, an unusual occurrence in the internal auditory meatus (IAM). A review of the literature shows no previous report of neuromuscular hamartoma of the cochlear nerve. This tumour was clinically and radiologically difficult to distinguish from acoustic neuroma. It is important to consider the diagnosis of these rare small tumours pre-operatively, as it may be appropriate to manage this conservatively. Received: 28 June 2001 / Accepted: 21 September 2001     

中颅窝进路内听道毗邻结构的解剖学研究

目的 :针对中颅窝手术进路 ,以面神经裂孔为标记 ,对内听道的毗邻结构进行测量 ,为临床手术操作提供应用解剖学基础。方法 :采用甲醛固定的头颅标本 2 4具 (4 8侧 ) ,分别暴露棘孔、岩浅大神经、岩浅小神经、面神经裂孔和弓状隆起 ,并对其相互之间的位置关系进行测量。结果 :8.3%面神经迷路段和膝状神经节骨管型缺如 ,面神经裂孔到膝神经节的距离变异较大。结论 :该研究提供的测量数值 ,对临床进行中颅窝手术进路的内听道定位有较大的参考价值。     

Atypical haemangioma of the internal auditory meatus: a case report

Haemangiomas involving the internal auditory meatus (IAM) are rare and can mimic other frequent lesions of the IAM such as schwannomas by their clinical and imaging aspects. The case of a patient with an atypical IAM haemangioma fluctuating in size is reported to highlight this diagnostic possibility. A 36-year-old female presented with a sudden and recurrent left sensorineural hearing loss (SNHL). Three consecutive MRIs were performed in a 10-month period of preoperative observation. They showed a fluctuation of the tumour signal and size. The surgical removal was performed via a translabyrinthine approach. Pathological findings were consistent with the diagnosis of a heamangioma. MRI and CT findings suggested the diagnosis of IAM heamangioma, but the rapid variation in size and signal was misleading. This phenomenon may be due to haemorrhage or oedema, and can be accompanied by a deterioration of the hearing function. Early surgical resection is the treatment of choice and allows to confirm the diagnosis.     

Scanning electron microscopy of cochlear blood vessels in the mouse

Summary Resin replicas of the microvasculature of the cochlear lateral wall of the mice were studied by scanning electron microscopy. The vascular system of the mouse cochlea showed a similar architecture to that of the guinea pig, cat, and rat. Several thin connecting branches were found between the vessels of the osseous spiral lamina and the cochlear lateral wall at the apical end. The apical turn and the basal part of the lower basal turn were innervated by several radiating arterioles originating from a single stem arteriole. The hook portion and the apical end had a particular vascular meshwork different from other parts of the cochlea.     

中鼻道粘液纤毛系统清除功能的研究

目的:探讨中鼻道粘液纤毛系统清除功能的特性。方法:取健康成人慢性化脓性鼻窦炎、慢性肥厚性鼻炎及慢性单纯性鼻炎患者男女各20例,应用糖精颗粒法测试其中鼻道粘液纤毛系统输送速率(mucociliarytransport rate,MTR)。另取相同人数及条件测试者进行总鼻道MTR的测试。取鼻息肉、慢性化脓性鼻窦炎患者和健康成年人中鼻道粘膜行电镜扫描。结果:健康人中鼻道MTR为(4.47±0.90)mm/min,总鼻道MTR为(7.00±2.21)mm/min,二者差异显著(P<0.01),男女无差异。慢性化脓性鼻窦炎、慢性肥厚性鼻炎、慢性单纯性鼻炎患者中鼻道MTR都明显低于健康人(P<0.01);且明显低于其总鼻道MTR(P<0.01)。扫描电镜观察表明:健康人中鼻道纤毛分布与形态明显好于患者。结论:中鼻道粘液纤毛输送系统功能低于总鼻道粘液纤毛系统,中鼻道粘液纤毛系统对鼻腔的保护功能较总鼻道低下。     

内听道斜矢状位磁共振成像在人工耳蜗置入术前评估中的初步应用

目的:探讨内听道(IAC)斜矢状位MRI在人工耳蜗置入术前评估中的应用价值。方法:应用斜矢状位三维快速自旋回波T2加权MRI技术对15例(30耳)拟行人工耳蜗置入术患者的IAC进行扫描。结果:所有患者顺利完成检查,IAC内神经结构显示清楚。13例蜗神经正常的患者行人工耳蜗置入术并已成功开机,2例双侧蜗神经异常者未行耳蜗置入。结论:IAC斜矢状位MRI能清晰显示IAC内蜗神经的形态、大小及IAC的大小,是人工耳蜗置入术前判断蜗神经发育状况的良好方法。     

The prevalence of exostoses in the external auditory meatus of surfers

Fifty-four surfers and 38 surf life savers were examined and questioned in order to determine the prevalence of exostoses. Seventy-three per cent had evidence of body exostoses in the external auditory meatus. Forty per cent had their ear canals narrowed by 50% or more. The relationship between the number of years spent surfing or life saving and the extent of canal stenosis was highly significant (P < 0.00001). Left and right ears were affected equally in this series and the obstruction appears to begin after approximately 7 years and is further aggravated by continued surfing. Over 90% of subjects who had participated for longer than 10 years had some evidence of exostoses. There was no significant association between the number of days per year or the number of hours per day spent surfing and the development of surfer’s ear in this sample. Those who participated in their water sport over winter had significantly more exostoses than those who did not (P < 0.0001). Those who lived in the South Island (colder water) had more surfer’s ear than those in the North Island (warmer water).     

Electrical stimulation activates two different sites within the guinea pig cochlea

This study investigates whether auditory brainstem responses (ABRs) can be used to assess the functioning of electrically stimulated cochleas. Electrically evoked auditory brainstem responses (EABRs) were recorded in guinea pigs with normal hearing and guinea pigs deafened by amikacin, a powerful ototoxic antibiotic, combined with diuretic aminooxyacetic acid (AOAA). Two different types of EABRs were observed in normal animals, depending on the electrical pulse intensity applied to the round window: long-latency brainstem responses were evoked by low stimulation intensities, short-latency brainstem responses by high intensities. The absence of effect of strychnine applied intracochlearly ruled out the possibility of medial efferents being involved in these responses. Conversely, an intracochlear application of tetrodotoxin (TTX), an Na⁺-channel blocker, resulted in the disappearance of both types of responses, attesting that the sites activated by the electrical stimulation were located within the cochlea. In AOAA/ amikacin poisoned cochleas, in which most of the hair cells were missing with apparently normal ganglion neurons, the long-latency brainstem responses evoked by low intensities were completely lacking. These findings suggest that low currents applied to the round window of the guinea pig cochlea primarily activate the hair cells, the neurons being directly excited at higher intensities.     

Filter function of the guinea pig cochlea after degeneration of outer hair cells

Summary After kanamycin induced degeneration of outer hair cells from guinea pigs the tuning properties of primary auditory nerve fibres are compared with those of normal untreated guinea pigs. The existence of fibres with no alteration of the tuning properties leads to the conclusion that there is no neural interaction between inner and outer hair cells needed to enhance the frequency selectivity.This study was supported by the Deutsche Forschungsgemeinschaft (Bo 421/1-3). Kanamycin was kindly provided by Chemie Grünenthal.     

豚鼠耳蜗盖膜的扫描电镜观察

目的为了更好地理解耳蜗盖膜在听觉产生过程中的作用.方法用扫描电子显微镜观察豚鼠耳蜗盖膜的超微结构.结果在盖膜上表面观察到许多纤维网,相应与内毛细胞静纤毛顶部接触的部位有一条带状结构,在耳蜗的基底圈盖膜的下面观察到外毛细胞静纤毛的压迹,外毛细胞静纤毛的W型印在盖膜下面也形成W型的压迹.结论根据扫描电镜观察的结果讨论了盖膜与内、外毛细胞之间的接触在听力形成的作用.     

Management of jugular bulb injury during drilling of the internal auditory canal (ICA) for vestibular schwannoma surgery

The retrosigmoid approach for vestibular schwannoma surgery has remained the standard approach by most neurosurgeons. Drilling the posterior wall of the internal auditory meatus (IAM) is an essential step in removing the intrameatal tumor. During IAM drilling, three anatomical structures can be encountered, including the posterior semicircular canal, vestibular aqueduct, and jugular bulb. Any of these can be injured during drilling, especially if the jugular bulb lies above the inferior edge of the IAM. Although IAM drilling is performed in most vestibular schwannoma surgeries, information on how to manage complications such as jugular bulb injury is lacking. Here we use an intraoperative video to demonstrate how to manage the inadvertent injury to the jugular bulb in order to avoid massive blood loss. We present a case of a 39-year-old woman with hearing loss, diagnosed with a cerebellopontine angle mass extending into the IAM. Surgery was required due to tumor progression. We used the retrosigmoid approach to access the tumor. During IAM drilling, the jugular bulb was injured. A thin layer of bone wax was applied under continuous suction. The margins of the wax were then gently compressed with a dissector; great care was taken to avoid pushing the wax into the jugular bulb. Excess bone wax was removed (video 1). A small diamond drill (2?mm) was used for further drilling. Our instructional video shows the surgical approach, microsurgical anatomy, and technical aspects of managing massive bleeding from jugular bulb injury. It should therefore be helpful for young neurosurgeons.     

A new model for investigating hair cell degeneration in the guinea pig following damage of the stria vascularis using a photochemical reaction

We have established a new model for investigating the relationship between cochlear lateral wall damage and sensory cell degeneration in guinea pigs by using a photochemical reaction between the systemic injection of Rose Bengal (RB) and controlled green light irradiation to the cochlea. The photochemical reaction produced a reactive oxygen species, which then damaged the endothelium. This triggered platelet adhesion and aggregation at the site of endothelial injury to produce thrombi and affect microcirculation in the lateral wall at the site of irradiation. Changes were studied under a scanning electron microscope (SEM), and compound action potentials (CAP) were measured. SEM observations after tangential illumination of the cochlear wall revealed degeneration of the stria vascuralis (SV). Specific morphological findings at 24 h included delayed degeneration of the outer hair cells concurrent with a significant increase in the CAP. Based on these findings, we suggest that degeneration of the SV was a direct result of the photochemical reaction, but CAP changes and sensory hair cell damage were secondarily caused by SV degeneration. Received: 8 September 1999 / Accepted: 11 November 1999     

Cavernous hemangioma of the internal auditory canal

Hemangiomas rarely occur in the internal auditory canal. These tumors originate from the capillary bed of the epineurium surrounding the nerve and can either compress or infiltrate the nerve. Depending on location and the nerve of origin, these lesions can cause severe and progressive sensorineural hearing loss, tinnitus, facial nerve palsy, or vertigo even when they are relatively small. The presence of a small contrast-enhancing tumor in the internal auditory canal accompanied by severe sensorineural hearing loss and facial nerve palsy, should raise the suspicion of a hemangioma. Early recognition and surgical intervention in these benign tumors may improve the chance of preserving the functional integrity of the facial nerve and provides better results after nerve reconstruction. Due to their relative small size, the temporal bone CT-scan may show no evidence of pathological widening of the internal auditory canal or the typical intralesional calcifications at the time of presentation. MRI with Gadolinium is the imaging method of choice and a high index of clinical suspicion is necessary for the diagnosis of these tumors. In this paper we report about a 51-year-old male presented with right-sided sensory-neural deafness and facial nerve palsy, accompanied by severe tinnitus and ipsilateral loss of vestibular function due to a cavernous hemangioma in the internal auditory canal.     

Scanning electron microscopy of the human cochlea — the stria vascularis

Summary The endolymphatic surface of the stria vascularis from normally hearing human ears has been studied with the scanning electron microscope. The cells in contact with the endolymph usually have a hexagonal-shaped surface and possess many microvilli, whilst depressions or pits are rarely seen. There is marked heterogeneity of these cells with variations in the size of the cells and the number of microvilli present on each cell.A transitional zone occurs between the stria vascularis and the spiral prominence. The surface of the cells of the transitional zone are larger and elongated whilst the cells of the spiral prominence have a smaller and more regular appearance.This work has been supported by grants from the Medical Research Council of Great Britain and from the Merseyside Regional Health Authority     

Combined electrophysiology and ultrastructure of acoustic trauma in the guinea pig cochlea

Summary Acoustic trauma was studied in experimental guinea pigs by combining gross auditory nerve recordings with single neurone (spiral ganglion) techniques and scanning electron-microscopy. Structural and functional changes caused by loud pure tones were assessed immediately after exposure and after varying recovery periods.This work was supported by grants from the National Health and Medical Research Council and the Australian Research Grants CommissionPresented at the 17th Workshop on Inner Ear Biology in Stockholm, June 23–25, 1980     

Rare tumors of the internal auditory canal

The study was performed to identify the incidence and histology of rare tumors with growth restricted to the internal auditory canal (IAC) that are different from vestibular schwannoma (VS). Furthermore, the question was addressed whether a preoperative diagnosis would be possible in these cases. A series of 351 patients that were operated on for IAC tumors through a transtemporal or translabyrinthine approach was investigated retrospectively. Cases with a tumor entity other than VS were analyzed for symptoms, radiological diagnosis, intraoperative findings and postoperative histolopatology to determine if a differential diagnosis to the common VS can be established prior to surgery. In 15 out of 351 cases (4.3%), uncommon processes of the IAC were determined by histology (6 lipomas, 3 hemangiomas, 2 neurofibromas, 2 menigiomas, 1 facial neuroma and 1 case of bilateral malignant lymphoma). The symptoms and the clinical manifestations were typical for patients with VS so that a preoperative differential diagnosis was not possible in the majority of cases. An analysis of the operation reports revealed that in 10 out of the 15 cases the surgeon suspected an unusual tumor of the IAC during surgery. The results of the present investigation suggest that rare lesions of the IAC can be expected in less than 5% of the cases and that preoperative diagnosis of rare IAC tumors is difficult. Intraoperative findings such as adhesion to cranial nerves and consistency of the tumor often indicate unusual processes, but histological analysis of the removed tissue is essential for the definite diagnosis.     

Effects of acoustic trauma on stereocilia structure and spiral ganglion cell tuning properties in the guinea pig cochlea

Guinea pigs were exposed to loud pure tones from 107 to 129dB SPL for 1 h. After varying recovery periods N₁ electrocochleograms and single spiral ganglion cell recordings were obtained. The exposed cochleas were examined by scanning electron microscopy. The relationships between N₁ thresholds, single neuron tuning curves and hair cell damage are described.