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Localization of Lesion in Hearing Loss Hearing Disorders

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Localization of Lesion in Hearing Loss Hearing Disorders Localization of lesion in hearing loss Hearing disorders HAROLD W. KENT, D.O. Portland, Maine The site of most lesions that cause The otologist frequently is presented with the hearing deficits can be problem of localization of the lesion causing hearing loss. Accurate localization permits ini- localized with a high degree of accuracy. tiation of appropriate treatment and is im- To accomplish this, the portant in reducing the morbidity and mor- results of special auditory tests must be tality associated with serious disease, such as correlated with a complete acoustic neurinoma, which may progress slow- history and careful physical examination. ly over several months or years. After a pure-tone audiogram This paper will discuss the diagnostic meth- ods and modalities that make it possible to is obtained, the history is taken. Careful localize the site of a lesion with a high degree questioning of the patient of accuracy. Audiometric localization will be regarding the onset, nature, and considered in detail. progression of symptoms is It should be emphasized that in many pa- emphasized. Throughout, the physician tients it may be relatively easy to find the must be aware of the lesioned area, but in others a variety of tests may be required. For all patients it is essen- characteristics of pure precochlear, tial to correlate the information gained from cochlear, and retrocochlear several tests with the history and physical lesions. The general physical status is findings before localization can be considered then determined and the head valid. and neck region evaluated thoroughly. On the patients first visit with a complaint Procedures for performing of hearing deficit it is desirable to obtain a pure-tone audiogram of bone and air conduc- and evaluating the results of several tion thresholds and perform the Weber and tests, all readily available Rinne tests. 1 This routine serves four impor- to the otologist, are described : the tant functions: (1) It establishes the hearing alternate binaural loss; (2) it may suggest malingering; (3) it loudness-balance test, the tone decay guides the otologist in questioning as to his- test, the short increment tory; and (4) it has medicolegal value. After the audiogram the patient should be sensitivity index, and the Bekesy test. questioned concerning the complaint which If more precise localization brought him to the otologist, which is some de- of the lesion site is necessary, special gree of hearing loss possibly accompanied with x-ray and isotope tinnitus or vertigo or both. The onset, char- examinations may be required. acter, and progression of symptoms should be carefully determined. The type of onset of the symptoms and the sequence of their ap- pearance may have a direct bearing on local- ization or verification of the site of the lesion. Careful questioning should be directed to symptoms of brain or cranial nerve deficits and Journal AOA/vol. 70, April 1971 783/69 Localization of lesion in hearing loss their possible relation to sequelae of acute in- conduction levels. fectious diseases or cephalic trauma. The pos- Patients with conductive deafness have bet- sibility of familial or congenital hearing dis- ter understanding of speech over the tele- orders should be investigated. The patient phone than in face-to-face conversation, and should be questioned regarding his occupation they hear better than others in noisy sur- and possible exposure to noise or change of roundings. barometric pressure. 2 Evidence of present or Patients with cochlear and retrocochlear past exposure to drugs and chemical ototoxic (sensorineural) lesions have audiograms which agents, including hypotensive or anticoagulant run downhill between frequencies of 256 and medicaments, should be sought. The general 2,048, with subnormal bone conduction thresh- physical condition should be determined, with olds. With pure cochlear lesions the overall particular attention to the cardiovascular hearing loss is from 20 to 40 percent, with an status, carbohydrate metabolism, and symp- abrupt downhill change in the audiogram. toms or signs suggesting areas of infection or With retrocochlear lesions there is gradual toxicity, such as chronic urinary tract infec- high tone loss of from 20 to 80 percent. tion, dental caries, or chronic tonsillitis. Mixed Patients with sensorineural lesions generally types of deafness often present difficulties in have poorer understanding of telephone speech localization of lesioned areas. However, in than of face-to-face conversation, and their evaluation of the audiogram and interroga- hearing is diminished in noisy surroundings. tion of the patient, the physician should keep After the history, the patient should have a in mind the following characteristics of pure complete physical evaluation of the head and precochlear, cochlear, and retrocochlear le- neck, and the blood pressure should be checked sions. if this is indicated from the history. Patients with precochlear lesions or conduc- The external ear and auditory meatus should tive deafness present an audiogram which be examined for possible obstruction by neo- does not run downhill between frequencies of plasms, plugs of cerumen, foreign bodies, or 256 and 2,048 cycles per second (from left to congenital anomalies. The eardrums should be right). Bone conduction thresholds are nor- carefully evaluated for scars, perforations, mal, and the average hearing loss is not more and normal landmarks. Politzer inflation than 50 percent over the entire hearing range. and examination with the Siegle otoscope If the lesion involves the ear canal, tympanic should be performed. Anterior rhinoscopy membrane, ossicular chain (except with fix- should be followed by nasopharyngoscopy, in ation of the stapes footplate3 ), or eustachian which allergic signs, neoplasms, infections, and tube, there will be a general hearing loss of other obstructive mechanisms at the orifice of not more than 40 percent, and bone conduction the eustachian tubes should be sought. The usually will remain less than air conduction mouth and pharynx should be examined, with at the 2,048 frequency even when disease is careful evaluation of the teeth, tonsillar fos- advanced. This results in a characteristic sae, and possible congenital anomalies. The "peaking" of the audiogram at 2,048 frequen- temporomandibular joints should be evaluated, cy. Fixation of the stapes footplate results in and the dental occlusion checked. The lymphat- a flat audiogram with a 40 to 50 percent hear- ic vessels in the neck should be palpated care- ing loss over all frequencies and normal bone fully, and the carotid artery pulsations should 784/70 be evaluated, with comparison of pulse inten- The test consists of presenting to the ref- sity on the right and left. erence ear a signal 20 decibels above its thresh- The eyes should be evaluated for size, equal- old. The patient then is asked to concentrate ity, and function of pupils, nystagmus, tropias, on the ear under test, and the signal is ad- and condition of the fundi. Lid function should justed until it seems equally loud in both ears. be noted and sensitivity of both corneas de- Signals then are increased in units of 20 termined. decibels until the laddergram is plotted. It is customary to use the levels of 20, 40, and 60 Auditory tests decibels above threshold in the reference ear. In the interpretation of the test, if the lines Certain auditory tests are of great importance on the laddergram remain parallel, then the in location of the site of the lesion in the pres- growth of loudness is equal in the two ears, ence of loss of hearing. These tests are readily and recruitment is absent. If the lines tend to available to the otologist and therefore will converge, then the ear under test is showing be discussed in detail. recruitment. When recruitment is present, the site of the lesion generally is cochlear, since Alternate binaural loudness-balance test this phenomenon usually is not present with (ABLB) 6-7 retrocochlear lesions unless there are secon- The purpose of the test is to compare the dary cochlear disturbances. Recruitment usu- levels of sensation of loudness between the two ally is not present with a conductive lesion un- ears when exposed to equal changes in in- less the lesion has invaded the cochlea and tensity of a pure tone signal. Changes are in- there is a mixed deficit. It has been demon- dicated on a graph called a "laddergram." By strated that recruitment always is associated comparing the growth of loudness in one ear with some cochlear impairments. However, with that in the other, the otologist may gain this phenomenon is not present with all coch- information concerning the integrity of sen- lear impairments. The extent and the dura- sorineural functions. The test is performed by tion of the pathologic condition have a direct selecting a specific frequency on the audiom- bearing on the presence or absence of recruit- eter and having the patient switch the ear- ment. phone from one ear to the other. On dual- The ABLB test has some limitations and dis- channel audiometers it is necessary to change advantages. A high degree of manual dex- only the input selector on the audiometer, terity is necessary for rapid presentation and and this probably increases the reliability. alteration of tones and intensities. If changes The ear for which the site of the lesion is to are not carried out properly, extraneous noises be determined is called the "ear under test," which can alter the judgment of loudness may and the other ear is called the "reference ear." be introduced. If presentation is not quick and Threshold levels are then determined for both of short duration, the patient may forget a ears and are plotted as base lines from which loudness level, or auditory fatigue may occur the growth of loudness is measured. The ref- above threshold levels. The test is most useful erence ear must have normal hearing or mild when the reference ear is normal and is not conductive or sensorineural loss without tol- possible if the difference between the ears is erance problems or reduced dynamic range.
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