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

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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. more than 30 or 40 decibels.

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Tone decay test (TDT)8 must be adapted so that short bursts of sound The purpose of the tone decay test is to show of the same frequency are superimposed on a the stability of the auditory threshold over 60 constant test frequency which is supplied to seconds. The test is administered by present- the ear under test at 20 decibels above its ing a signal 5 decibels above the threshold for threshold. These short bursts of sound are the ear under test. The patient is instructed 1 decibel above the test frequency level. The to hold up his hand as long as he hears the patient is instructed to listen carefully for sound. Each time his hand lowers to indicate any increase in loudness and responds with a loss of the tone, the signal is increased by 5 hand signal each time he perceives an increase decibels until it is audible again. This proce- in loudness. Twenty 1-decibel increments dure is followed for the full minute as timed are presented for each frequency selected for by a stopwatch. The amount of tone decay test, and each time the patient recognizes an that occurs while the signal is perceivable is increase a mark is made on a score sheet. The determined by subtracting the intensity level final test score is the number of correct re- at the start of the test from the level at the sponses divided by the number of 1-decibel close of the test. The difference represents the increments presented to the patient (N/20). amount of intensity necessary to maintain Each correct response, thus, is equal to 5 threshold audibility over 1 minute. percent. The foregoing procedure is repeated for A final score of less than 20 percent is nega- other frequencies in the ear under test and tive for cochlear deficit. A score between 20 also in the other ear. In the interpretation and 55 percent is in the questionable range, of this test it has been found that a difference and a score above 55 percent is considered of from 0 to 15 decibels represents normal to positive for cochlear deficit. A low SISI score mild decay; from 15 to 30 decibels, moderate with normal or near-normal pure-tone audio- decay; and more than 30 decibels, severe de- gram thresholds and a markedly reduced cay. Patients showing mild or moderate decay speech discrimination score is strongly sug- usually have cochlear lesions. Patients show- gestive of a retrocochlear lesion. If the SISI ing severe decay may have retrocochlear le- score is above 20 percent and is accompanied sions. Most patients with retrocochlear lesions, by decreased threshold levels, a deficit local- even with secondary cochlear involvement, ized to the cochlea is suggested. Comparison of have severe decay. SISI scores for high and low frequency gives much information concerning the integrity of Short-increment sensitivity index (SISI)9 the auditory mechanism. The purpose of the SISI test is to locate a lesion by the use of a standardized version of Belasy test (automatic audiometry) °.11 the difference limen test. The test is based on Bekesy audiometry requires a social audi- the ability of patients with cochlear lesions ometer which permits the patient to trace his to perceive extremely small changes in signal own threshold by adjusting a response switch intensity. which is connected to a motor-driven atten- The test is administered by first selecting a uator. This attenuator changes the intensity specific frequency and determining the thresh- of the signal, which may be presented at a old for the ear under test. The audiometer fixed or specific frequency or across the full

786/72 frequency range from 125 to 10,000 cycles per ing to Bekesys classification. An interweaving second. The attenuator is connected to a pen- pattern is seen in a Type I tracing and indi- writing graph drum so that the responses of cates normal function of the cochlea or a mild the patient are recorded permanently in end-organ deficit. graphic form. The degree of separation of the continuous Interrupted and continuous signals are re- and intermittent tone tracings may be helpful corded on the same graph, and the interpre- in localization of lesions. When the separation tation is dependent on whether the response extends from 5 to 20 decibels at frequen- lines interweave or separate. If they separate, cies of 500 or more cycles per second, the then the degree of separation must be con- pattern may be classified as of Type II; such sidered. The amplitude of marking pen excur- separation at frequencies below 500 cycles sion is dependent on the response time, end- per second is of Type IV. Type II patterns are organ "on-effect," and tonal adaptation. The present with cochlear lesions or conductive response time is variable from patient to pa- deafness with early sensorineural involvement. tient, and a standard amplitude cannot be Type IV patterns occur with cochlear lesions determined. The "on-effect" is the spike re- which are advanced and severe and with retro- sponse of the auditory mechanism to a signal cochlear lesions with secondary cochlear in- and is thought to be reflected in the ampli- volvement. tude of the threshold tracing. When the separation is greater than 30 If the cochlea is not functioning properly, decibels at frequencies of 500 cycles per sec- the "on-effect" will be reduced and with it ond or less, the tracing is classified as of Type the amplitude of the tracing. Therefore, if the III, which is almost pathognomonic of a retro- amplitude of the continuous tracing is smaller cochlear lesion. than the amplitude of the interrupted tracing, there probably is cochlear involvement in the Other diagnostic measures frequency areas where this difference is noted. Localization and verification of the lesion site With retrocochlear lesions, the "on-effect" may be further refined in specific cases by con- for continuous tones usually remains un- ventional x-ray study of the skull and temporal changed unless there is also cochlear involve- bone, polytomography, cerebral angiography,12 ment. Tonal adaptation, the amount of tone air pneumoencephalography, isotope brain decay shown over some time, is reflected in scans, and posterior fossa myelography. These the degree of separation of the two tracings. are highly specialized types of investigation In the normal cochlea, recovery from stimula- and require the services of skilled radiologists tion is rapid, and there is little or no tone and neurosurgeons. If there is any vertigo or decay and thus little or no separation. If there nystagmus, then the use of warm and cold is cochlear disease, the tonal adaptation may caloric tests with the electronystagmograph vary between 5 and 20 decibels, depending on may show directional preponderance and thus the nature and extent of the lesion. With retro- aid in localizing the lesion site. cochlear lesions, tonal adaptation is rapid and excessive, and there will be a separation in the Summary low frequencies beyond 20 decibels. This is Most lesions causing hearing deficits may be characteristic of the Type III tracing accord- accurately localized and verified by the correla-

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tion of the results of special auditory tests 8. Rosenberg, P.E.: Tone decay. Maico Audiological Library Series. Vol. VII, Report 6. Maico Hearing Instruments, Chicago, 1969 with a careful and complete history and phys- 9. Jerger, J., Shedd, J.L., and Harford, E.: On the detection of ical evaluation. To increase the precision of extremely small changes in sound intensity. Arch Otolaryng 69:200- 11, Feb 59 localization of retrocochlear and central le- 10. Von Bekesy, G.: A new audiometer. Acta Otolaryng 35:411-22, sions, special x-ray and isotope examinations 47 11. Jerger, J.: Bekesy audiometry in analysis of auditory dis- beyond the scope of the otologist may be re- orders. J Speech Hearing Res 3:275-87, Sep 60 quired. The close cooperation of the patient, 12. Hodges, F.J.. III: Developments in cerebral angiography. Cur- rent application and future utilization. Radiol Clin N Amer 2:515- audiologist, otologist, radiologist, and neuro- 41, Dec 64

surgeon facilitates early and accurate localiza- Jerger, J.: Audiological manifestations of lesions in the auditory tion of lesions causing hearing deficits. nervous system. Laryngoscope 70:417-25, Apr 60 Naunton, R.: An introduction to audiometry. Maico Hearing In- struments. Chicago, 1963 Portmann, M., and Portmann, C.: Clinical audiometry. Charles C Thomas, Springfield, III., 1961 1. Myers. D. Schlosser, W.D., and Winchester. R.A.: Otologic diagnosis and the treatment of deafness. Clin Sympos 14:39-73, Pulec, J.L.: When to suspect the possibility of an acoustic neuroma. Apr-Jun 62 Diagnostic tests. Otol Clin N Amer 1:176-90, Feb 69 2. Campbell, P.A.: Aero-otology. In Otolaryngology, edited by G.M. Coates and H.P. Schenck. W.F. Prior Co., Hagerstown, Md., 1960 This paper was prepared in partial 3. House, H.P.: Congenital fixation of the stapes footplate. Otol fulfillment of the requirements for Clin N Amer 1:35-51, Feb 69 residency training and for certification by the American Osteopathic Board of 4. Shambaugh, G.E.: Surgery of the ear. Ed. 2. W.B. Saunders Ophthalmology and Otorhinolaryngol- Co.. Philadelphia. 1967 ogy. The paper was prepared at Kirks- 5. Glorig, A.: Audiometry. Principles and practice. Williams ville Osteopathic Hospital, under the Wilkins Co.. Baltimore, 1965 direction of Arthur A. Martin, D.O., 6. Dix, M.R., Hallpike, C.S., and Hood. J.D.: Observations upon FOCOO, chairman of the Department the loudness recruitment phenomenon with special reference to the of Ophthalmology and Otorhinolaryn- differential diagnosis of disorders of the internal ear and VIIIth gology. nerve. J Laryng 62:671-86, Nov 48 7. Dr. Kent, 666 Brighton Ave., Portland, Jerger, J.F.: Recruitment and allied phenomena in differential Me. 04102. diagnosis. J Auditory Res 1:145-52, Jan 61

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