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Sixty-five patients with suspected acoustic neuromas were examined by CT and MR; the optimal diagnostic procedures are discussed. Extrameatal acoustic neuromas (11 cases) were all diagnosed by CT and MR, but only 82% of intrameatal tumours could be diagnosed by CT combined with air cisternography. Using special surface coils and the paramagnetic contrast medium Gd-DTPA, the accuracy of MR was 100%. All tumours greater than 4 mm were demonstrated. Following clinical and neurological examination, MR is the primary diagnostic method in the investigation of acoustic neuromas.

Auditory brain stem responses (ABR, BSR) were obtained in 16 patients with acoustic neurinoma. The pattern of ABR was studied with reference to the tumor size and the pure tone audiogram in each case.As a result, the 16 cases were classified into 4 types. In 2 patients, wave I, III and V were clearly recorded but wave III and V were prolonged in latency (type I). In 4, wave I and V were recorded but all other components of ABR were markedly obscured and wave V was more prolonged in latency than in type I (type II). In 5, only wave I was recognized (type III). No ABR response was obtained in remaining 5(type IV).The diameters of the tumors were as follows; 0.8cm and 2cm in type I, 2.5cm to 3.5cm (mean: 3cm) in type II, 3cm to 5cm (mean: 3.8cm) in type III, and 4cm to 6cm (mean: 4.8cm) in type IV.From these results, it was considered that the pattern of ABR reflects the size of the tumor to some extent. However, no definite tendency was found concerning the relationship between the pure tone audiogram and the ABR pattern.

Case 1: A 54-year-old female had complained of bilateral complete hearing loss, left facial palsy and gate disturbance. A diagnosis of cholesteatoma was given from the findings of left ear drum, X-ray, vestibular function test, C-T scanning, and so on. Cholesteatoma was removed as completely as possible from the left temporal bone by a left paramedian suboccipital craniotomy. Histopathological examination confirmed it to be cholesteatoma.Case 2: A 33-year-old male had complained of right severe hearing loss and facial palsy. A diagnosis was made as cholesteatoma in the right temporal bone from the X-ray, vestibular function test, C-T scanning, and so on. Cholesteatoma was removed as completely as possible by a right middle cranial fossa approach. Histopathological examination revealed the mass to be cholesteatoma.Cholesteatoma of the temporal bone is rare. It is difficult to diagnose it before surgery. We could differenciate it from the cerebellopontine angle lesions, particularly acoustic neurinoma in two cases with temporal bone cholesteatoma.We conclude from our experience of present cases that trans-labyrinthine approach is best in case of the temporal bone cholesteatoma with ipsilateral complete hearing loss and facial palsy and trans-labyrinthine approach plus suboccipital craniotomy or suboccipital-trans-temporal combined approach is better in such a case.

• We studied the vestibular system of 30 patients with eighth nerve schwannoma. Preoperatively, cold and warm calorizations were performed. At operation, the utriculus and the ampulla of the horizontal semicircular canal as well as the eighth nerve were identified and removed for study. The sensory epithelium of utricular macula and ampullar crista appeared fairly normal in most cases. In one, there was tumor invasion to the labyrinth and in another patchy necrosis of the sensory epithelium. The number and quality of sensory cells varied from case to case. In cases with intact superior vestibular nerve, on light microscopy the histopathologic features of sensory epithelia did not differentiate between groups with symmetrical caloric reactions and with reduced or absent caloric reactions. ( Arch Otolaryngol 106:723-726, 1980)

In order to find out how otologists contribute to the diagnosis of acoustic neurinoma, a questionnaire was sent to 80 neurosurgical departments of university hospitals. Answers were obtained from 71 departments.1) Acoustic neurinomas represented 7.8% of all brain tumors in Japan. The rate varied from 0% to 24% in university hospitals. 2) 48.8% of acoustic neurinomas were diagnosed by otologists. The rate varied from 0% to 100% in university hospitals.Since in most cases, the first symptom of acoustic neurinoma is unilateal progressive hearing loss, it was presumed that more than 48.8% of acoustic neurinoma patients had visited an otologist's clinic.In order to prevent wrong diagnosis, problems which frequently rise in diagnosing acoustic neurinomas are discussed.

Comparisons were made of contralateral stapedius reflex recordings obtained by means of two different electroacoustic impedance devices, the commercial Grason-Stadler 1723 (G-S 1723) impedance meter and a laboratory equipment, in patients with acoustic neurinoma. With the latter, acoustically elicited reflex responses were noted in 11 of the 21 tumour ears studied. The recordings with the G-S 1723 showed deflections indicating stapedius reflex responses in all 21 cases. Three of these deflections proved to be artefacts. The stapedius reflex threshold test indicated a retrocochlear lesion in all 21 pathological ears when the laboratory equipment was used. The G-S 1723 produced recordings indicating a cochlear lesion in two of these tumour ears. Furthermore, five of 15 normal contralateral ears were classified as having a retrocochlear lesion with the G-S 1723, as opposed to one with the laboratory equipment. The reflex decay test could be applied in 15 normal and six tumour ears. Only minor discrepancies in the degree of reflex decay were found between the two instruments. As the G-S 1723 displayed a low rate of detection for acoustic neurinomas (90%) and led to a large number of false-positive interpretations (33%), it is concluded that this instrument is less useful for diagnostic purposes than the laboratory equipment in differentiating between cochlear and retrocochlear lesions.

Recently, we encountered three patients in whom episodic vertigo and fluctuating deafness was associated with cerbellopontine-angle tumors or an acoustic tumor.We wish to emphasize the association between Meniere's disease and cerebello-pontine-angle tumors or acoustic neurinoma by describing the case history of three patients who presented complaints of fluctuating hearing loss and recurrent vertigo.

Vestibular findings were studied in 27 patients with acoustic neurinoma. Four of them had experienced vertigo and/or dizziness at the onset of the disease, and 14 other patients had these complaints during the course. Vestibular symptoms were more prominent with middle-sized tumors which extended to the posterior cranial fossa than with those in the internal auditory canal. Although most acoustic neurinomas originate from the vestibular nerve, the incidence of vestibular symptoms is rather infrequent. This is probably due to a compensating mechanism of the central nervous system while the tumor grows slowly. Therefore, the growth rate of the tumor is considered to be most important for the concomitance of vestibular symptoms. The origin of the tumor was identified in 13 cases; in 3 it was from the inferior vestibular nerve and in 10 from the superior vestibular nerve. No significant difference in caloric test results could be seen between the tumors of different origins. The incidence of vestibular symptoms was more frequent when the tumor originated from the superior vestibular nerve than from the inferior vestibular nerve. The recover time required from the dysequilibrium after extirpation of the tumor depended on the degree of preoperative vestibular function.

Article, 信州医学雑誌 26(4): 393-401(1978)

Two patients with intracranial glossopharyngeal neurinoma are described. In both patients, neurologic signs and findings of conventional radiologic and computed tomography examinations suggested a diagnosis of acoustic neurinoma. Magnetic resonance imaging, however, definitely indicated that the mass had actually arisen from the lower cranial nerves. This was confirmed at operation. The superb sensitivity and specificity of magnetic resonance imaging in the diagnosis of posterior fossa extraaxial mass are emphasized.

The clinical and neurological features of four siblings (2 male, 2 female) affected by syringomyelia are described. A fifth sister was affected by an acoustic neurinoma. Since neither parent showed signs of syringomyelia, this is considered to be a datum substantiating the dysembryogenetic theory of the syringomyelia syndrome.

One case of spontaneous subarachnoid haemorrhage due to acoustic neurinoma is presented. The literature regarding this subject is reviewed and the pathogenesis of haemorrhage from neurinoma is discussed.

Five cases of von Recklinghausen's disease were found in one family. In three of them, bilateral acoustic neurinoma were observed. The pure tone audiometry was performed repeatedly in two of them and the changes of audiograms were studied.Clinical signs and symptoms of these cases seem quite different from those in unilateral acoustic neurinoma.The changes in audiograms revealed the two periods in the progress of hearing loss. They were rapidly increasing periods and slowly increasing periods.These results suggest the etiology of the bilateral acoustic neurinoma in von Recklinghausen's disease is different from other acoustic neurinoma.

Nine cases of acoustic neurinoma were treated by stereotactic radiosurgery between 1969 and 1974. The follow-up period can now be regarded as sufficiently long for a preliminary evaluation of the results. An arrest of growth or shrinkage of the tumour was observed in 8 of the 9 cases. In one case open surgery was performed 2 years after irradiation and histological examination showed regressive changes of the type expected after irradiation. Audiological examination revealed that in the majority of cases radiosurgery could be performed without causing serious damage to the hearing function. The average hearing loss present before treatment increased on average only 20.0 dB in the most successful 7 cases. None of the patients suffered facial nerve involvement. In small and medium-sized acoustic tumours this method offers a satisfactory therapeutic alternative worthy of consideration.

We describe the case of a patient who had a right acoustic neurinoma and a right temporal anaplastic astrocytoma that were diagnosed and operated on 7 months apart. Reports of 2 other cases of neurinomas associated with a glioma appear in the literature; neither of these 2 patients underwent surgical intervention for either of their tumors. In a careful survey of the literature, we encountered 86 cases of multiple primary intracranial tumors of different cell types. Clinical presentations and locations and types of tumors are discussed.

A case of atypical acoustic neurinoma is presented. The initial symptom was sudden deafness. This was followed by hearing threshold fluctuation.The tumor was an internal type with a cystic lesion. These two factors caused various symptoms and made the precise diagnosis difficult.The necessity of taking atypical acoustic neurinomas into consideration, detailed history taking and neuro-otological findings are discussed.

After a review of electrophysiological studies in 1,500 cases concerning different types of lesions of the trigeminal nerve, the acousticofacial complex, and the brain stem, one can conclude that beside the intensive clinical examination which most often allows a precise topographic diagnosis, study of trigeminofacial and facial reflexes appears to be an essential diagnostic method to determine the topography of the lesions. On the other hand, this study can sometimes contribute to the prognostic evaluation as well as the choice of the approach in some lesions concerning the acousticofacial complex.

Auditory brain stem responses (BSR) were studied in five cases including 2 acoustic neurinomas, degenerative type of myoclonus epilepsy, pontine glioma and the 4-th ventricle tumor.They showed typical BSR suspecting of brain stem lesions, and the BSR patterns were compared with those of animal experiments for discussion of the topographical differential diagnosis. In two patients with acoustic neurinoma, nothing but wave I was recognized at the pathologic side, and normal BSR was recorded at the healthy side. The BSR was similar to that of a cat destructed ipsilateral cochlear nucleus.In the patient with degenerative type of myoclonus epilepsy, wave I was reconized only in both sides.In the patient with pontine glioma, wave 1, 2 and 3 at the right side and wave 1 and 2 at the left side were recognized, but the following components were obscured in both sides. The right side response was considered similar to BSR of a cat destructed bilat. inf. colliculus, and the left side one was similar to that of a cat with destruction of bilat. Sup. olivery nucleus complex.In the patient with the 4-th ventricle tumor, wave 1, 2, 3 and 4 were recognized in both sides, and probably wave 5 was depressed in both sides. BSR was considered similar to that of a cat with destruction of contralateral inf. colliculus or contralateral sup. olivery nucleus complex. It was considered that the BSR pattern was suggestive of a medial lesion of the upper portion of the brain stem.The data of animal experiments could not be applied to the clinical use, but it could be very useful for topographical differential diagnosis of the brain stem lesions.

Article, 信州医学雑誌 31(5): 408-416(1983)

A 77-year-old female was found to have a small acoustic neurinoma which was removed totally with a translabyrinthine approach. The surgical treatment should be determined in consideration of the general condition, tumor size, and the contralateral hearing level. When these conditions permit, even in elderly patients the total removal is desirable.

Twenty two cases of acoustic neurinoma were operated upon in the lateral position under an operating microscope during the past three years. Anatomical and physiological preservation of the facial nerve was successfully achieved in 19 cases. Electrical stimulation of the facial nerve using bipolar forceps proved to be very useful. Sound monitoring with tremorgraphy pick-ups on the face was designed for observation of facial movement driven by nerve stimulation. Hearing acuity could be preserved postoperatively in three large sized neurinomas with the aid of direct recording of action potentials on the cochlear nerve during surgery. Advantages of the lateral position and some instrumental improvements for surgery are discussed.

A surgical approach to the internal auditory canal is presented which has proved useful in the following circumstances: 1) as a destructive procedure in Ménière's disease, 2) as a diagnostic procedure in patients in whom an acoustic neurinoma is suspected and a labyrinthectomy is indicated. In this situation the tumor may be removed during the same operative procedure, 3) for the removal of small, mobile, intracanalicular neurinomas, and 4) for complete facial nerve decompression in patients with no vestibular response and no serviceable hearing.

Using 240 true positive brain scans, a computer system for the differential diagnosis of brain lesions has been evaluated. Eighty-six parameters were extracted from brain scan findings without relationship to neurological signs and symptoms, and the likelihood method was adopted as an example of mathematical logic. The results of our experiment indicated that the overall accuracy was 77 per cent for the maximum likelihood method. The digital computer gave satisfactory results, particularly for diseases such as infarct, meningioma, acoustic neurinoma, and subdural hematoma. In spite of several problems to be solved, this method could provide invaluable help in differential diagnosis of brain lesions.

In patients with acoustic neuronoma or space-occupying lesion in the region of the brainstem we recorded preoperatively the brainstem potentials as well as the late potential N1. With one exception all patients investigated showed changes in the brainstem potential pattern. When stimulating monaurally there exists a clear side difference, that means the changes in the potential pattern are more distinct on the side of the tumour than on the opposite side and then only if an obstructive hydrocephalus exists. Moreover we could demonstrate in patients with tumours in the region of the brainstem that the brainstem potential IV is no longer suitable for measuring the hearing threshold. On the other hand in these patients an exact determination of the hearing threshold is possible with the late potential N1. Altogether the findings show, that the recording of the brainstem potentials when stimulating monaurally is an important additional diagnostic tool to recognize impairment of the acoustic pathways within the brainstem and probably affords the possibility of perceiving pathological pressure within the brain.

A 35-year-old male with bilateral acoustic tumors (case 1) and a 48-year-old male with a left acou-stic tumor (case 2) had severe hearing loss on the affected sides but caloric test results were normal.At operation a well-preserved vestibular nerve was confirmed in the auditory meatus in case 1 In case 2 vestibular and facial nerves could be preserved after total removal of the tumor. Those findings explain why the caloric responses were normal in both cases.

Four cases of typical “Patulous Canal” are presented. Two of the patients had von Recklinghausen's disease. Patulous canal is defined as bilateral dilatation of the internal auditory canal without an accompanying acoustic neurinoma.Bilateral perceptive deafness may rarely accompany this syndrome.Etiologies of bone changes of von Recklinghausen's disease may be summarized as:1. Changes in the bone secondary to mass effect of neurofibromas.2. Intrinsic factors in the initial stage of ontogenesis.Among the latter, abnormalities of mesodermal tissues are found frequently.Ontogenitically the skull, especially the temporal bone including the internal auditory canal, are derived from the peri-otic capsule of the cartilaginous neurocranium which is of mesenchymal origin.The inner ear is derived from the otic vesicle which separates from the epidermal ectoderm.The presence of bone changes such as dilatation of the internal auditory canal in von Recklinghausen's disease and in other illnesses may suggest that bony changes are accompanied by mesenchymal abnormalities ontogenetically.The rarity of the complication of deafness may be explained by the low incidence of coincidental involvement of both mesenchymal and ectodermal tissues in congenital and intrinsic abnormalities.Attention has been focused on the occurrence of similar bony changes, such as dilatation of the internal auditory canal in von Recklinghausen's disease. The possible mechanisms causing these changes are discussed from the embryological viewpoint.

Five cases of large acoustic neurinomas (diameter 2.5 cm) with involvement of the facial nerve in the tumour capsule are presented. The preoperative function of the facial nerve was normal. During surgery, in order to achieve a radical tumour removal, the facial nerve was severed juxtapontine. Reconstruction was performed at the same procedure using a 5-6 cm long sural nerve graft. Thus the central juxtapontine stump was joined to the peripheral stump in the facial nerve canal of the petrous bone. After six months, all five patients exhibited a well functioning mimic and a good eyelid function. At the one year control four patients had normal nerve function clinically and one patient still showed asymmetrical mimic.

After a brief survey of the microsurgical methods for acoustic neurinomas, a case is described in which a successful bilateral operation has been performed. Facial nerve function could be preserved on both sides and on the side of the still functioning ear hearing could also be saved. At 12 months following the operation pure tone and speech hearing were found to be the same as before the operation.

Fourteen patients with acoustic neurinomas varying in size from 7 to 30 mm were treated by stereotactic radiosurgery and then were followed for 4 years. The tumors of eight patients decreased 1 to 10 mm in diameter, no change was found in two, and the tumor increased slightly in three patients. Loss of the ability to enhance with contrast administration on computed tomographic scan was a common effect of the treatment. One patient in poor general condition died from intercurrent disease 6 months after radiosurgery. At postmortem examination, a large central necrosis was found. Among five patients with hearing before treatment, full preservation was demonstrated in one; in the other four, the mean impairment of speech discrimination score was 43%. One patient with total unilateral deafness regained hearing and achieved a discrimination score of 60% at 1 year after treatment. There was transient facial weakness in five patients, which was detectable only by electromyography in one. Facial hypesthesia appeared in two patients and was transitory in one of them. Thirteen of the patients are in good or excellent general condition. Stereotactic radiosurgery offers the only therapeutic alternative to open operation in the management of acoustic neurinomas. It is worth considering for every patient, but especially for poor risk patients and those with bilateral tumors.

In a pilot study of patients with cochlear hearing loss and hearing loss due to acoustic neurinoma (AN), the correlation between ABR wave V-features and speech discrimination was investigated. In cochlear hearing loss no correlation of ABR features to speech discrimination was found. In 12 patients with AN the correlation between ABR wave V amplitude to speech discrimination was significant. These results suggest that the decline of speech discrimination in AN patients is due to a deterioration in temporal accuracy of eighth nerve activity.

Focused ultrasound with a frequency of 2.5 MHz and amplitude-modulated in the range of audiometric frequencies (125–8000 Hz) was employed to examine 50 normal hearing persons and in complex diagnostics of over 500 patients suffering from sensorineural deafness, otosclerosis, chronic otitis media, and acoustic neurinoma. Typical diagnostic signs of these diseases were revealed. Modulated ultrasound is shown to offer an improved diagnosis of hearing diseases. The results confirm the previous observation that amplitude-modulated ultrasound may excite not only the acoustic receptors but also the acoustic nerve fibres. Possible mechanisms of the stimulating effect of focused modulated ultrasound are discussed.

Two cases of large, cystic acoustic neurinoma are described. On computed tomographic scans, cystic acoustic neurinomas resemble, and may be confused with, other tumors of the cerebellopontine angle. A cystic acoustic neurinoma should be considered in the event of a large, cystic cerebellopontine angle tumor, especially if there is no significant hearing loss and no destruction of the internal auditory canal.

Summary The authors describe a case of calcified, organized hematoma in the cerebellopontine angle which developed 20 years after subtotal removal of an acoustic neurinoma, presenting as a recurrence of acoustic neurinoma on computed tomography. It points out the difficulty in differentiating a recurrent tumor from an organized hematoma in this particular case because of neuroradiological similarity and masked clinical symptoms by the long-standing neurological deficits, after the original surgery. MRI scanning would have been helpful in this circumstances.

✓ An example of bronchogenic carcinoma metastasizing to an acoustic neurinoma is described. The two other comparable cases reported are discussed and the eight other cases of extracranial-to-intracranial spread of tumor noted.

Acoustic neurinoma tissue in organ culture was exposed to gamma irradiation (60CO) 30-150 Gy single dose. Schwann cell degeneration occurred from the first week onward in vitro following irradiation. After 3 weeks only a limited number of surviving cells were observed in the specimens, as compared with controls. The in vitro changes in tissue morphology indicate an irreversible course even after irradiation with the lowest dose, 30 Gy single dose. As a comparison with the in vitro experimental material it has also been possible to analyse the light and electron microscopic morphology of a tumour from a patient previously treated with stereotactic radiosurgery. An similar substantial Schwann cell loss was found in the centre of the tumour treated with stereotactic irradiation prior to surgery, as compared with the in vitro material.