A case for further quantification of the stapedius reflex

Clinical stapedius reflex determinations presently include only threshold and decay measurements. Recent observations indicate that reflex latency, amplitude, and rise and relaxation times are sensitive to cochlear and brain stem disorders. Our investigations using a chronic animal model of an experimental acoustic tumor show that reflex amplitude, latency, and rise time are exquisitely sensitive to extrinsic pressure on the auditory nerve. Because of our observations and those of others, we suggest that further quantification of the reflex test will increase its sensitivity and reliability. Quantification can be achieved by an interface between an impedance bridge and a small computer to provide on-line averaged values for each reflex parameter.

Brainstem audiometry in neurotologic diagnosis

Brainstem electric response audiometry (BERA) has been found to be a valuable adjunct to the neurotologic diagnosis. Ninety-eight percent of patients with surgically confirmed acoustic neuromas has positive BERA findings. We report six cases that illustrate the value of this technique in examining patients with suspected retrocochlear lesions.

[Topographic diagnosis of lesions of the acoustico-facial nerve complex using the winking reflex]

An electrophysiological study in close to 1,500 cases of various lesions of the trigeminal nerve, the acoustico-facial complex and the brain stem was presented. It was concluded that following a detailed clinical examination which, most often, allows precise topographical diagnosis, the study of the trigemino-facial and facial reflexes appears to be an essential diagnostic tool to determine the topography of a lesion. Moreover, this method may give prognostic evaluation as well as facilitate the choice of surgical approach to the lesions of the acoustico-facial complex.

[Audiological findings in cases of acoustic neuromas, cerebellopontine angle and brain tumors (author's transl)]

The study contributes to improve, audiological diagnostics of central auditory path lesions and attempts, through the comparison of audiological and neurosurgical findings of 15 patients, to refer certain auditory lesions caused by cerebral tumors to topodiagnostically characteristic audiological symptoms. The audiological findings obtained through 7 generally accepted test methods from 6 patients with an acusticus neurinoma indicate a labyrinthine but not a central symptomatic picture while 4 patients with a pontine-angle tumor present a chiefly central hearing defect which, as regards the constellation of findings, clearly differs from the central hearing defect of 3 patients with a pontine tumor. Two patients with tumors in the lateral ventricle area merely show, from the audiological point of view, a lack of contralateral dichotic discrimination.

A new acoustic reflex pattern

A new crossed-vs-uncrossed acoustic reflex pattern has been observed in four patients with retrocochlear disorder. The new reflex pattern is characterized by a unique "uni-box" configuration. Reflexes are abnormal with sound to the affected ear on crossed stimulation only. In one additional patient, a variation of the uni-box pattern was found on suprathreshold reflex amplitude measures. WE observed a large ear difference between reflex amplitude functions in the crossed condition, but not in the uncrossed condition. This observation suggests that reflex amplitude measures may be a valuable addition to threshold measures in some patients.

Human auditory nerve action potentials and brain stem evoked responses

Latency-intensity (L-i) functions for (1) the auditory nerve action potential (AP) N1 peak, (2) the brain stem evoked response (BER) V peak, and (3) the N1-V interval were related to hearing level and lesion location. The AP L-l curves tended to steepen with increasing 4 to 8 kHz hearing level. This relationship was identical for cochlear and retrocochlear ears, except for a few retrocochlear ears with "inappropriate AP perservation." Both high-frequency cochlear loss and retrocochlear abnormality prolonged peak V latency, but retrocochlear abnormality generally prolonged it more. Among cochlear-loss ears, as 4 to 8 kHz hearing levels increased, N1-V intervals decreased and L-i curve slopes increased. In contrast, retrocochlear abnormality greatly prolonged N1-V intervals. As a retrocochlear sign, N1-V prolongation was slightly more reliable than V prolongation.

Cochlear nerve in neurilemomas. Audiology and histopathology

Correlative data between the histopathologic changes in the cochlear nerve and audiologic findings are reported in 16 cases of neurilemomas. Poor speech discrimination, positive or absent recruitment, excessive adaptation, or separation of forward vs reverse continuous tone Bekesy tracings did not correlate with the number of preserved nerve fibers. There were several cases with profound hearing loss in which the nerve fiber population approached normal. Histologically, pathologic changes included dilated fibers and increased interfibrillary collagen. In many specimens the fibers were further apart than normally, especially in the immediate vicinity of the tumor, and many lay between tumor cells. The tumor-nerve interface was usually gradual and no abrupt change appeared at the transition from the nerve to the tumor, the Schwann cells appearing to continue as tumor cells. Nonspecific changes apparently due to specimen handling were seen in some areas of most specimens.

Computerized screening of the human vestibulospinal system

The vestibular nerve projects rostrally via the ascending medial longitudinal fasiculus (MLF) to eventually supply the ocular muscles and also projects caudally via the descending MLF to eventually supply the spinal and limb musculature. Electronystagmographic techniques are designed to evaluate only portions of the vestibulo-ocular and oculomotor systems. Vestibular lesions affecting only the caudal vestibular nerve distributions or lesions affecting both neural distributions, therefore, cannot be objectively assessed except for the vestibulo-ocular component. A promising recording technique for the evaluation of the vestibulospinal system has been developed and tested in the Raymond E. Jordan Human Vestibular Systems Laboratory. A comparison of two data analysis techniques in normal subjects, unilateral vestibular lesion patients and patients with unilateral lesions of the cerebellar hemispheres have provided pilot data which indicate that the vestibulospinal stability test technique holds considerable promise for both research and clinical evaluation of the human vestibulospinal system.

Vestibular responses to bithermal caloric and harmonic acceleration

Vestibulo-oculomotor responses from 33 patients with either peripheral labyrinthine or central pathology were compared using the standardized Fitzgerald-Hallpike bithermal caloric and harmonic accelerations. In numerous cases (40%), patients with normal caloric responses reflected abnormalities in either their phase relationships or labyrinthine preponderance to sinusoidal acceleration. Results clearly indicate that harmonic acceleration provides additional information to the clinician in the evaluation of vestibulo-oculomotor pathology that is not reflected in the responses to standard caloric tests.

Enlarging optic chiasmal glioma with stable visual acuity

A 13 1/2-year-old girl with stable, reduced visual acuity, nystagmus and Small, pale optic discs initially noted at age nine months, developed signs and symptoms of increased intracranial pressure. At craniotomy, an intrinsic glioma of the optic chiasm and both optic nerves extended into both frontal lobes, the hypothalamus and the third ventricle.