Auditory brainstem response. A comparison of different interpretation strategies for detection of cerebellopontine angle tumors

In this retrospective study (111 tumor; 1370 non-tumor patients), the effectiveness of the auditory brainstem response for identifying cerebellopontine angle tumors was studied using different criteria to interpret the test. Individual ABR features were examined. The I-V was best (sensitivity = 82%; specificity = 97%) but present for only 44% of the population; I-III (sensitivity = 50%; specificity = 96%) and III-V (sensitivity = 30%; specificity = 97%) were worst. Ninety-three percent of patients had V and ILDV, with good results (sensitivity = 74% and 81% respectively; specificity = 93% each). Three interpretation strategies were compared: (1) included the latencies of V, ILDV, I-V, III-V and I-III and ILDI-V, (2) excluded III-V and I-III, (3) used I-V and ILDI-V when available; V and ILDV otherwise. When corrected for hearing loss, strategy 3 provided significantly better specificity (91%) than strategy 1 (87%), with no significant difference in sensitivity (92% and 93%, respectively).

The burden of screening for acoustic neuroma: asymmetric otological symptoms in the ENT clinic

The rising numbers of legal cases relating to delay in the diagnosis of acoustic neuroma, combined with the increasing availability of magnetic resonance, is increasing pressure on otologists to make an early definitive diagnosis of cerebellopontine angle tumours. Unilateral or asymmetrical otologic symptoms not explained by external or middle ear disease are elicited in 16.6% of 500 consecutive attenders to an otolaryngology clinic. An agreed policy of risk stratification of patients with unexplained asymmetric otological symptoms is required if expense is to be limited and litigation minimized.

Work-related, noise-induced hearing loss: evaluation including evoked potential audiometry

This article reviews the evaluation of 246 workers (492 ears) who underwent otologic and audiologic testing as part of a worker's compensation claim for work-related, noise-induced hearing loss. Tinnitus was present in 58% of the patients, but was rarely a major symptom. Other otologic symptoms or a history of ear disease were virtually nonexistent. Standard audiometry showed a downsloping, high-frequency sensorineural hearing loss in 85% of the ears tested, with only 37% having a characteristic "noise notch" at 4000 or 6000 hertz. Asymmetric hearing loss was not uncommon, with 48 patients (20%) undergoing magnetic resonance scanning, all of whom showed no central lesion responsible for the loss. Proven malingering was surprisingly uncommon (9%). In this study, evoked response audiometry was a valuable adjunct to confirm behavioral thresholds in the evaluation of possible work-related, noise-induced hearing loss. The middle latency response was more effective than the auditory brainstem response as a result of the high-frequency steepness of the audiometric curve.

Clinical and financial audit of diagnostic protocols for lesions of the cerebellopontine angle

OBJECTIVE

To assess the diagnostic efficiency and costs of protocols used for investigating patients with suspected lesions of the cerebellopontine angle.

DESIGN

Prospective evaluation of tests of auditory brain stem responses and acoustic reflex thresholds, electronystagmography, and calorics. Positive test results were confirmed or refuted by high resolution computed tomography with intravenous enhancement.

SETTING

Single general otolaryngology clinic in a teaching hospital.

PATIENTS

270 consecutive patients with sensorineural hearing loss requiring investigation to exclude a lesion of the cerebellopontine angle.

MAIN OUTCOME MEASURES

Estimated costs of various diagnostic protocols and performance in detecting tumours of the cerebellopontine angle.

RESULTS

Protocols including tests of auditory brain stem responses and acoustic reflex thresholds as sifting tests before computed tomography were clinically acceptable and presented considerable savings over the use of computed tomography in all patients (74,000 pounds or 84,000 pounds v 122,000 pounds). The use of electronystagmography and calorics could not be justified on clinical or financial grounds.

CONCLUSIONS

Audiological tests of auditory brain stem responses and acoustic reflex thresholds followed by computed tomography constitute the most cost effective protocol for determining suspected lesions of the cerebellopontine angle.

IMPLICATIONS

The cost effectiveness of diagnostic protocols should be evaluated throughout the health service.

Strategy for the diagnosis of small acoustic neuromas

Twenty small (extra-meatal size less than 15 mm) acoustic neuromas have been diagnosed since high-resolution (HR) magnetic resonance imaging (MRI) became available in our clinic. Among these tumors, 18 had sensorineural hearing loss and 16 enlarged internal auditory meatus in X-ray photo, but only 8 tumors out of 18 tested showed diminished caloric response. Auditory brainstem responses (ABR) has been believed as the most reliable test for the diagnosis of acoustic neuroma despite several reports of false-negatives. In our series, 4 tumors out of 18 tested had normal ABR. The false-negative rate was 22%, which is much higher than expected. In CT, only 11 tumors were recognized. Although the total number is not large, present results clearly suggest the limits of these examinations. At present, HR-MRI is the most reliable diagnostic method for acoustic neuromas with no false-negative reported; ordinary MRI may have false-negatives. For the effective use of MRI, the results of audiometry, X-ray photo, ABR and other examinations must be evaluated properly.

Diagnostic vetting of individuals with asymmetric sensorineural hearing impairments

Audiological and vestibular tests were administered conjointly in a neurological or general ORL clinic to exclude cerebellopontine angle (CPA) tumours. This study aimed to assess the efficiency of various tests in achieving that exclusion with the minimum of unnecessary investigations. All patients received the full battery of auditory brainstem responses, acoustic reflex thresholds and decay, alternate binaural loudness balance and ENG and caloric testing. All patients who did not have normal auditory brainstem responses proceeded to high resolution CT scanning. One hundred and fifteen patients were investigated and four acoustic neuromas were diagnosed. The efficiency of these tests in a general ORL clinic is very much poorer than often suggested, due largely to the number of occasions on which the tests cannot be done, and to the very small proportion of the test population who have CPA tumours.

Screening for retrocochlear pathology

In 1982, 135 patients were screened for possible retrocochlear pathology, by means of an investigation protocol consisting of caloric test, impedance audiometry and brainstem response audiometry (BRA). A combination of the first two of these procedures had an unacceptably low prognostic accuracy. BRA indicated retrocochlear pathology in 8 and was inconclusive in 4 cases. Enhanced computer tomography revealed an intracranial tumour in 4 of the former, while no space-occupying lesion could be demonstrated in the remainder nor in the 4 patients with inconclusive BRA. BRA is the best single test for screening of this patient category.