Noninflammatory Diseases of the Labyrinth Primary involvement of the cochlea, vestibular apparatus, or the eighth cranial nerve with spread to the contiguous structures is characteristic of this group of diseases. Unfortunately, the common involvement of the vestibular labyrinth and its widespread central nervous connections in systemic illness makes difficult the differentiation of symptoms due to this cause from those due to specific vestibular disease. The principal subjective symptoms---vertigo(眩晕), deafness, and tinnitus--are all common to this group of disorders, again creating problems of diagnosis. Rapid progress in methods of examination of cochlear and vestibular function has greatly aided in the differentiation of these diseases and thus removed a great deal of the confusion which was present in the past. Vertigo and Dizziness Vertigo is defined as a hallucination of movement. This may be a sensation of turning, spinning, falling, rocking, etc. Dizziness, although commonly used by the patient as a term to describe the above sensations, refers to less severe and distinct sensations of giddiness, faintness, confusion, blankness, or unsteadiness. This differentiation is important, since vertigo arises from disturbance of the vestibular end-organ, vestibular nerve, or vestibular nucleus. Dizziness may arise from mild disturbance of the vestibular apparatus but usually indicates disturbance in other regions. An analogy given by Cawthoru helps to clarify the types of disturbance of the poripheral vestibular apparatus resulting in vertigo. This mechanism may be likened to a twin-engined airplane. When both engines are running normally and the controls are properly operating, the airplane flies on a straight course. If one engine suddenly fails, the plane is violently diverted off its course by the unopposed action of the normally running engine. By readjusting the controls, after a short period the pilot is able to fly on a straight course again, though turning or a sudden gust of wind will have a more disturbing effect than when the two engines are working normally. In another situation the faulty engine may start up again, and even if it does not return to its normal speed, all is well provided it runs steadily. However, should the faulty engine repeatedly fail and recover, the result will be more disturbing than having a dead engine. In another situation one engine may fail to work properly only when the airplane is in a certain position, such as in a steep bank to the left, but will return to normal as soon as the airplane straightens out. Finally, if one engine loses power slowly, the pilot almost imperceptibly is able to readjust the controls without deviating from his course. The airplane engines may be directly compared to the set of vestibular end-organs in each. labyrinth, Each of the types of failure may occur in man, resulting in each case with loss of equilibrium and a type of vertigo. In evaluating vertigo, the history is of great importance. The following information should be elicited (引出): 1. Whether the symptom experienced is true vertigo. If the complaint does consist of a sensation of motion or turning, the origin lies in the vestibular apparatus; otherwise, other regions must be subjected to examination and evaluation 2. The pattern of the vertigo. It is important to note whether the attacks are spontaneous or precipitated(突如其来的) by movement. The presence of paroxysmal attacks separated by periods of relative freedom from symptoms indicates a different pathologic condition than more or less continuous dizziness. 3. The degree of vertigo. Vertigo arising in the labyrinth is usually accompanied by nausea and often vomiting. Less specific forms may be milder and may arise from any part of the body. 4. The association of hearing loss or tinnitus with dizziness is a definite aid to localization. Complete audiometric evaluation is essential to the examination of the dizzy patient, since these diseases may affect the vestibular apparatus alone, the cochlear apparatus alone, or both together. Tinnitus This may be objective in rare instances (a sound which may be heard by the examiner) but is usually a subjective sensation of sound arising from within the head. Tinnitus may vary in intensity and may be continuous or intermittent. Subjectively loud and continuous tinnitus may produce a severe handicap(阻碍) to the individual. Tinnitus is associated with hearing loss arising from disorders of the sound conduction system, the cochlea, or the neural pathways of the cochlear nerve. Patients describe the sound in various ways, but the examiner should attempt to obtain a description of the sound with which both the patient and the doctor is familiar. In general the sounds experienced will range from predominantly（主要地） low frequencies (like a ventilating fan or sea shell sound) to wide-range white noise (a rushing sound commonly experienced in Meniere's disease) or high-pitched noise, whistles, or insect sounds (which frequently may be matched on the audiometer). Conductive hearing loss usually produces a low-pitched continuous sound which, if combined with inflammation, becomes pulsating. High-pitched continuous or intermittent tinnitus is associated with high tone hearing loss and is an important and early sign of drug intoxication (aspirin, digitalis洋地黄, quinine, dihyclrostreptomycin, etc.). Pulsating low-pitched tinnitus without hearing loss is an important early symptom of glomus jugulare tumors of the middle ear. It is also associated with occlusive disease of the carotid artery, which will at times produce an audible bruit. Other than relieving a conductive hearing loss, there is no effective treatment of tinnitus. Even section of the eighth nerve in most cases does not result in cessation(停止) of tinnitus. Patients suffering from this symptom deserve a full and honest explanation of the nature of the disorder so that natural anxiety does not cause exaggeration of the severity of the symptoms. Barbiturates and tranquilizers are rarely indicated for use in this condition, for in most instances patients are able to adapt to the presence of tinnitus and ignore it. Examination and Differential Diagnosis The main causes of vertiginous labyrinthine disturbance are: 1. Acute toxic labyrinthitis 2. Meniere's disease 3. Paroxysmal positional vertigo (postural vertigo) 4. Vestibular neuronitis（前庭神经元炎） 5. Vertebral-basilar artery insufficiency(椎基底动脉供血不足) 6. Trauma 7. Tumor (Acoustic neurinoma) The main types of disturbances to be differentiated from these diseases are the following: 1. Disease of the cerebellum, especially vascular disease and tumors 2. Disease of the proprioceptive system 3. Cerebral anoxemia, particularly mild arteriosclerosis, postural hypotension, and anemia 4. Endocrine disease, particularly hypothyroidism; and female hormonal disturbance 5. Epilepsy（癫痫） Nonvertiginous labyrinthine disease affects primarily the cochlea and includes the following: 1. Congenital and neonatal hearing loss 2. Familial deafness 3. Presbycusis(老年性耳聋). 4. Drug toxicity 5. Ototropic viral disease(耳带状疱疹) 6. Noise-induced hearing loss 7. Sudden idiopathic hearing loss（突发性耳聋） 8. Otosclerosis （耳硬化症） Examination of the patient with labyrinthine symptoms (vertigo, hearing loss, and tinnitus) should include caloric examination and hearing evaluation. The latter should consist of air and bone audiometry; speech audiometry; Bekesy audiometry, when indicated; and determination of recruitment. If the examiner does not have the equipment to perform these tests, the patient should be referred to a Speech and Hearing center where they may be performed. In general, all patients with unilateral symptoms or findings or with widely differing findings in the two ears should have the complete battery of tests described above. In recent times, electronystagmography(眼震电图描记法) has enabled accurate quantitative measurement of the ocular responses to caloric and rotatory tests of the vestibular apparatus and should be employed when available. Radiographic examination of the inner ear includes the Stenvers view and the Town-Chamberlain view. These projections enable visualization of the petrous bone and internal auditory canal. In most instances CT or MR is essential in the work-up of these problems. In many cases complete neurologic examination and spinal fluid analysis are necessary to provide an exact diagnosis. MENIERE'S DISEASE In 1848 Prosper Meniere described the symptom complex bearing his name, illustrating the report by citing (引用) the case of a young girl who died from labyrinthine hemorrhage in order to prove definitely the anatomic origin of the symptoms. Knowledge of the pathologic process (although anticipated by G. Portmann, who likened the disease to glaucoma) was provided by Hallpike and Cairns in 1938, who reported the changes of dilatation of the endolymphatic system accompanied by degeneration(恶化) of the sensory elements of the cochlea and vestibular apparatus. Since that time, microscopic examination of many involved temporal bones has clarified the exact pathologic picture, while the etiology remains obscure. Pathology. Knowledge of the pathologic process in Meniere's disease has been gained by study of temporal bones of individuals suffering from this disease. The earliest findings are dilatation of the scala media(中阶) of the cochlea and the saccule(球囊). This dilatation in the cochlea is evidenced by stretching of Reissner's membrane rather than of the basilar membrane. As the disease progresses, there is degeneration of the organ of Corti with loss of hair cell population. Tearing of Reissner's membrane with rcattachment further out on the scala vestibuli（前庭阶） has been demonstrated in a few temporal bones. Dilatation of the utricle（椭圆囊） and membranous semicircular canals is not often found, occurring late in the disease or in severe cases. It has been demonstrated by electron microscopic study that the normal secretory endothelium of the endolymphatic sac has disappeared and been replaced with a simple flattened epithelium in patients with Meniere's disease. Some but not all human temporal bone specimens have demonstrated various degrees of narrowing and fibrosis of the vestibular aqueduct（前庭导水管）, reducing or obliterating the functional lumen of the endolymphatic duct（内淋巴管）. Valvassori has developed projections to visualize the vestibular aqueduct by polytomography and, together with others, has reported a high incidence of narrowing or nonvisualization of this structure in patients with Meniere's disease. The pathology is usually unilateral, but may become bilateral in as many as 25% of patients with longer durations of observation. Etiology. Although it is clear that this is a disease affecting the fluid physiology of the endolymphatic system, the origin of this disturbance has not been defined. It is not as yet known whether the primary disturbance is one of hypersecretion, hypoabsorption, or a disturbance of balance between both secretion and absorption. Also possible is a deficit（不足额） of membrane permeability（渗透性） or alteration of osmotic pressure（渗透压） relationships. It is clear that all the energy required for the function of the cochlea is supplied by the stria vascularis（血管纹） and transported by the endolymph, showing that a rapid production of this fluid is needed. The exact site of absorption is not known, but most workers consider it to take place either in the endolymphatic sac or in the stria vascularis. The most popular theories of etiology have been: 1. Local disturbance of salt and water balance, leading to "edema" of the endolymph. 2. Disturbance of the autonomic regulation of the endolymphatic system. 3. Local allergy of the inner ear, causing edema and disturbance in autonomic control. 4. Vascular disturbance of the inner ear especially of the stria vascularis(血管纹). 5. Local labyrinthine manifestation of systemic metabolic disease involving either thyroid or glucose metabolism or both. 6. Alteration in the relationship between perilymphatic, and endolymphatic pressure dynamics, which may be related to anatomic alterations in both the endolymphatic duct（内淋巴管） and, the cochlear aqueduct（耳蜗导水管）. 7. Disturbance of the endolymphatic duct or sac, Causing interference with absorption of endolymph. H. House has described a case with an otosclerotic focus blocking the endolymphatic duct which also showed distention of the membranous labyrinth. This author's experience has led to yet another hypothesis concerning the pathogenesis of Meniere's disease. The concept is of primary (undefined) or inflammatory or metabolic process acting on the endolymphatic sac and duct, which causes involution of the endothelium and functional narrowing or obliteration of the endolymphatic duct as seen by x-ray examination. These changes may be latent for varying periods of time but become manifest when stress acts upon the fluid systems of the inner ear. This stress will then result in hydrops because of the grossly impaired resorptive apparatus of the endolymphatic duct and sac. The more common stresses appear to be upper respiratory infection, particularly nasopharyngeal; metabolic alteration of thyroid or insulin function; allergic reaction, especially to food or tobacco; and acute emotional problems. Treatment based on this hypothesis has been successful in most patients in affording control of the symptomatology. Symptoms. Meniere's disease has its onset usually in the third or fourth decade, affecting both sexes equally. It is characterized by active periods of variable length interspersed with longer periods of remission also of a variable, length. The pattern of attacks and remissions is impossible to predict in the individual case, although the symptoms tend to become less severe over a period of years. The symptoms experienced by the patient with Meniere's disease are typical and almost diagnostic. There is usually a period of intra-aural fullness or pressure which the patient may experience for weeks, days, or hours prior to the attack. This sensation is forgotten, however, because of the spontaneous, sudden onset of severe vertigo accompanied by nausea and vomiting. There is an almost unnoticed depression of hearing in the involved ear due to loud roaring tinnitus occurring with the onset of vertigo. The initial episode usually lasts for 2 to 4 hours, at which time the vertigo subsides, although there will be a persistent dizziness with head movement lasting for several hours. The hearing improves and the tinnitus lessens but does not disappear with the subsidence of the vertigo. There is now a period of freedom from vertigo, during which the patient may notice increasing intra-aural pressure, fluctuation in hearing, and roaring tinnitus. These symptoms are then interrupted by another episode of spontaneous vertigo similar to the first but not as severe. The frequency of these episodes varies but usually they occur as often as once or twice a week or as little as once a month or less. In extreme cases they can occur daily. Commonly following the above period, which lasts a few weeks, either spontaneous or treatment-induced remission occurs, during which time no symptoms are noted by the patient other than some loss of hearing in the involved ear. This remission does not prove to be permanent, however, with repetition of the above acute phase occurring in a few months. As this pattern of activity and remission goes on, the symptoms during the acute period are dulled by the gradual loss of responsiveness of the end-organ due to degeneration of the sensory elements. Specific symptoms related to cochlear function occurring in Meniere's disease are: 1. Fluctuating hearing loss. The increased fluid pressure in the scala vestibuli and media interferes with acoustic transmission to the hair cell so the hearing efficiency varies with the degree of pressure increase. 2. Diplacusis (the perception of a different pitch in the involved ear than in the normal ear) 复听(指用同一音频刺激时两耳的音调感受能力有差别). This sensation is due to the tightening of the basilar membrane with increased pressure, changing its "tuning" and shifting the sound to a different set of nerve endings. 3. Intolerance to loud sounds. This is evidence of recruitment and distortion occurring simultaneously in the involved ear. Examination. Tests of cochlear function present a pattern which is typical of Meniere's disease. With the tests available today, diagnosis may be made even without the presence of vertigo and treatment instituted early in its course. The tests to be employed are pure tone air and bone audiometry, speech audiometry, and recruitment testing. Middle ear function, as demonstrated by tympanometry, is normal Pure tone audiometry reveals a perceptive hearing loss which in early cases involves the low tones primarily (a rising curve). With progressive destruction of hair cells, the curve becomes flat and then falling in late cases. Speech audiometry reveals a loss of discrimination which in moderate in severity, usually, averaging between 40 and 70%. The Bekesy audiogram shows a type II tracing which indicates cochlear or hair cell damage. Recruitment tests, such as Fowler's alternate binaural loudness balance test or the SISI (short increment sensitivity index), will show compete recruitment of the involved ear. Caloric examination of the vestibular apparatus usually shows reduced function of the involved ear to both hot and cold stimuli. Treatment. This is initially medical but a number of patients may benefit from a surgical procedure. Medical treatment. Many cases can be controlled by antihistamine labyrinthine sedatives such as prochlorperazine氯丙嗪 maleate (stemetil), cinnarizne (Stugerron) or promethazine异丙嗪 theoclate (Avomine). Because many of these patients are anxious they may be helped by anxiolytics抗焦虑药 or tranquillizers镇定剂. Betahistine hydrochloride (Serc) appears to be the most useful recent addition to the medical armamentarium and is a histamine analogue and is thought to work by causing local vasodilatation and relief of tinnitus. Other vasodilators employed include nicotinic acid and thymoxamine(Opilon). Attemptts to reduce the labyrinthine hydrops by fliud and salt restriction and diuretics 利尿剂is widely practiced and is probably worth while in cases uncontrolled by other menthods. Medical treatment controls the condition in over two –thirds of patients. During the acute attack sedation is essential and vomiting may necessitate intramuscular administration of a labyrinthine sedative. Other drugs useful in the acute attacks are chlorpromazine hydrochloride (Largactil) and promethazine hydrochloride (Phenergan), while phenobarbitong and hyoscine are effective alternatives. Surgical treatment. Decompression of the endolymphatic sac（内淋巴囊减压） is gaining in popularity as a method of reducing the vertigo, with some hope of reduction of tinnitus and preservation and occasionaaly improvement in hearing. It is now being done earlier in cases uncontrolled by medical treatment where there is still useful hearing in the affected ear. Vestibular neurectomy（前庭神经切除） has been advocated. It relieves the vertigo but the hearing continues to diminish and it is an intracranial procedure. Stellate ganglioneetomy（星状神经节切除） is still practiced with some success. In the persistently vertiginous patient where there is no useful hearing in the affected ear surgical destruction of the labyrinth may have to be considered. This, however, is a last resort and should be used as such because a number of patients develop bilateral disease. Selective destruction of the vestibular labyrinth with preservation of hearing may be achieved by applying ultrasound to the affected lateral semicircular canal. Prognosis. This depends upon the response to the various form of treatment. If treatment dose not control the attacks the outlook is bad for the affected ear. At the same time remission occurs so frequently that it is difficult to be precise in prognosis after one attack. The disease may be bilateral in up to 40% of cases and therefore conservatism is essential.