Acoustic neuromas. Diagnostic efficiency of various test combinations

The diagnostic value of vestibular-evoked myogenic potential in patients with vestibular schwannoma

OBJECTIVE

This study examined the diagnostic value of the vestibular-evoked myogenic potential (VEMP) in comparison with the caloric test in patients with vestibular schwannoma (VS).

METHODS

Data were retrospectively collected from 803 consecutive patients who visited our vertigo clinic and underwent vestibular tests. Amongst them, 78 patients were diagnosed as having untreated unilateral VS. VEMP was performed using click and short-tone burst stimulation. The caloric test was performed using ice water. The sensitivity and specificity of each test were evaluated.

RESULTS

Of the 78 patients with VS, 63 had abnormal VEMPs as well as abnormal caloric responses. Of the 725 patients without VS, 382 had normal VEMPs and 416 had normal caloric responses. The sensitivity and specificity of VEMP were 80.8% (95% CI: 72.0-89.5%) and 52.7% (95% CI: 49.1-56.3%), respectively; those of the caloric test were 80.8% (95% CI: 72.0-89.5%) and 57.4% (95% CI: 53.8-61.0%), respectively.

CONCLUSIONS

The sensitivity and specificity of VEMP and the caloric test showed no significant differences.

SIGNIFICANCE

In patients with VS, although the specificity of VEMP was not very high, its sensitivity was high and comparable to that of the caloric test.

Phase audiometry in neuroaudiological practice

Six groups of subjects, altogether 107 in number, were studied with phase audiometry. Three control groups were studied (normal-hearing healthy controls, persons with cochlear hearing losses, and patients with neurological disease not affecting the auditory system), and three patient groups were studied (patients with cerebellopontine angle tumours, with brainstem lesions, and with temporal lobe lesions). Two phase audiometers were used. The sensitivity was 85% for patients with cerebellopontine angle tumours, 71% for patients with brainstem lesions, and 69% for patients with temporal lobe lesions. There was good agreement between the phase audiometers, though one of them (BIAB Phase Audiometer) had better results for two of the patient groups. Phase audiometry can be recommended in neuroaudiological practice.

Vestibular investigations in acoustic neuroma

Forty-eight patients with surgically proven acoustic neuroma were examined preoperatively with a comprehensive battery of vestibular tests. In 87% of the patients, reduced caloric responses were measured on the side of the lesion. In 60% of the patients a non-responsive labyrinth was found. Spontaneous nystagmus was observed in 29% of the patients. A significant correlation with the size of the tumour was found in the occurrence of abnormal saccades in the calibration test, pathological smooth pursuit movements and the occurrence of gaze nystagmus, respectively. There was no correlation between the magnitude of the caloric response reduction and the mean hearing loss, which suggests that the hearing loss and the vestibular function loss do not occur synchronously. This study shows that in most cases of acoustic neuroma, the peripheral part of the vestibular system is severely disturbed. Abnormalities in the central and peripheral part of the vestibular system are more easily recognized with increasing tumour size. We conclude that a complete battery of vestibular tests is essential in combination with audiometric, neurologic and radiologic analysis for the early clinical diagnosis of acoustic neuroma.

Audiovestibular tests in the diagnosis of cerebellopontine angle tumours

Symptoms and signs were recorded in a series of 78 patients with a cerebello-pontine-angle (CPA) tumour and in 92 patients with symptoms and signs suggestive of such a lesion but with a negative CT scan. Variable symptomatology was found in the tumour cases. A substantial proportion of the patients had experienced sudden phenomena such as rotatory vertigo and/or sudden hearing loss. A CPA tumour must therefore be considered in almost every case of unilateral auditory or vestibular disturbances. Unfortunately, conventional audiovestibular tests have a low sensitivity of around 50%, with the exception of stapedial reflex threshold elevation (89%). The specificity on the other hand is quite low for this test, whereas other test results, like a genuinely pathological stapedial reflex decay, carry a high specificity of 60%. However, brainstem response audiometry (BRA) exhibited a very high sensitivity (100%) coupled with a reasonable specificity (54%), making it a suitable single test for screening patients suspected of having a CPA tumour. A program for the diagnostic work-up is suggested.

Diagnostic strategies in search for acoustic neuromas. Findings in 300 acoustic neuroma patients

The diagnostic findings in 300 patients with acoustic neuromas are reported. Because of a centralized treatment of acoustic neuromas, we have a uniform work-up of all the patients, which enables us to make a non-selected comparison of the diagnostic efficiency of the various tests. Diagnostic dilemmas in patients with normal hearing, anakusis, normal auditory brainstem recordings, normal vestibular function and normal tomography of the internal acoustic meatus are discussed. In patients with hearing better than 80 dB, a normal ABR, the presence of recruitment and a normal caloric reaction can exclude the presence of a tumour, making tomography superfluous. In patients with poor hearing, the need for tomography is imperative. We perform CT if two procedures among the following produce tumour-positive results: ABR, recruitment tests, caloric test, and tomography. Those who have only one tumour-positive finding at the screening are re-examined after one year. If, even with contrast enhancement, CT proves negative, we continue to perform air CT. Only then do we know for sure whether the patient has a tumour or not. An advantage with using many tests for the same physiological function is that they complement each other, though, on the other hand this often adds to the confusion. With fewer tests, the confusion is reduced, but the requirements regarding technical quality must be very stringent. ABR, the Metz recruitment test and tomography are purely objective, while the caloric test is subjective on the part of the investigator. The Hallpike procedure, however, has stood the test of time in separating pathologic from normal.

The Audiologic Evaluation of Cerebellopontine Angle Tumor Suspects: A Review of Tumor and Non-Tumor Suspects

In an initial study from January 1981 through December 1983, audiologic data were gathered on 41 patients with proven cerebellopontine angle (CPA) tumors and 82 tumor suspects who revealed no tumor on computed tomography with air cisternography of the internal auditory canal. The acoustic reflex threshold and decay, performance intensity function for phonetically balanced (PB) words, and several auditory brainstem response (ABR) variables were examined. Sensitivity, specificity, and diagnostic efficiency were calculated for each test. The ABR was better than the other tests. The interaural wave V latency difference (IT5) had a sensitivity of 100%, specificity of 80%, and diagnostic efficiency of 87%. In a subsequent study, from January 1984 to June 1985,52 patients with abnormal IT5 values were examined to determine the predictive value of a positive IT5 in detection of a CPA tumor. Nineteen of these patients had CPA tumors, for a detection rate of 36%. The high diagnostic efficiency of the ABR, coupled with the prevalence of a CPA tumor in a tumor suspect population, will translate into a yield of approximately one tumor for every three abnormal IT5 tests.

Auditory evoked cortical responses to frequency glides in subjects with retrocochlear hearing impairment

Auditory cortical responses evoked by stimulation with frequency glides of a continuous tone have been recorded from 44 subjects with intracranial tumours affecting auditory function. Response latencies obtained when stimulating the ear on the side of the tumour were different from the non-tumour ear as well as from groups with cochlear impairment and normal hearing. Tumours caused a reduction of a specific sensitivity to the frequency glide stimulation, affecting further processing of the dynamic change in tone frequency. The test appears to have diagnostic potential.