Faculty Bibliography

Neurogenic tumors consist of schwannomas, neurofibromas, and neurosarcomas that arise from the Schwann cell of a peripheral nerve. Their occurrence in the larynx is rare, with only 115 cases having been reported. Three new cases are presented, the literature is reviewed, and the first computed tomographic (CT) scan of a benign schwannoma of the larynx is demonstrated. The diagnosis and treatment of these tumors and the CT scan analysis are discussed

Audiometric tests were conducted on 19 subjects with hypophosphatemic bone disease to investigate whether auditory impairment like that reported in affected adults occurs in young patients. No hearing loss or significant auditory findings were noted among the children or young adult patients. However, sensorineural hearing loss of cochlear origin was identified in the three oldest subjects (40 to 58 years), although a history of noise exposure in two of them could explain the observations. The results indicate that if an association exists between hypophosphatemic bone disease and hearing impairment, the auditory signs will not develop until adulthood in treated patients. Additional studies of large populations of affected adults are needed to identify the incidence and mechanism(s) of the auditory system abnormalities and to assess any effect of medical therapy for the metabolic bone disease.

Measurements of functional gain were compared first to coupler gain for 57 subjects using one of three hearing aid-earmold combinations and second to probe-tube gain for 12 subjects using in-the-ear hearing aids. The average difference between functional and coupler gain plotted as a function of frequency yielded results that were similar to previous reports, with the greatest effects occurring at 3000 and 4000 Hz. Significant differences were seen among hearing aid-earmold combinations at 3000, 4000, and 6000 Hz. Standard deviations for measurements between 750 and 2000 Hz were less than 5 dB and could be explained by variability of functional gain measures associated with test-retest variability of thresholds measured in a sound field. Below 750 Hz and above 2000 Hz, standard deviations exceeded 5 dB. The greater variability may be explained by differences in earmold venting, acoustic characteristics of the ear canal, and stimuli used to measure functional and coupler gain. Neither room nor hearing-aid noise appeared to affect the results significantly. When functional gain was compared to insertion gain measured with a probe-tube system, the average difference across frequencies was less than 1 dB. The variability of the differences at all frequencies, with the exception of 6000 Hz, was within the range reported for functional gain measurements. It was concluded that functional gain can be accurately estimated using probe-tube measurements.

Determination of the drug susceptibility of Mycobacterium tuberculosis by conventional methods using an agar-based medium may take 3 weeks or more to complete. On the other hand, results on positive cultures are generally available in 4 to 7 days with the radiometric (BACTEC, Johnston Laboratories, Towson, Md.) procedure. One disadvantage to the latter is the requirement to determine the quantity of 14CO2 in each test vial on a daily basis from the day of inoculation. Growth index readings often must be made over weekends, adding to the work load of clinical laboratories during periods of reduced staff or necessitating compensatory pay or time. Susceptibility tests with streptomycin, isoniazid, ethambutol, and rifampin against 104 M. tuberculosis strains were performed by the submerged disk method, the recommended BACTEC method with daily growth index readings, and the radiometric procedure with readings delayed for 2 days after inoculation. Criteria for interpretation of "delayed" tests were established. Drug concentrations tested included some modifications of those available commercially. Overall agreement for the four drugs by the three methods was greater than 90%. We conclude that under our test conditions a schedule of inoculation of radiometric test vials on Friday with growth index readings commencing on Monday gives susceptibility results that correlate well with the daily BACTEC method and with a conventional 7H10 agar method.

Nuclear magnetic resonance imaging, a relatively new diagnostic instrument, is a noninvasive imaging method which, among its many advantages, uses no ionizing radiation. There are a few limitations and contraindications to its use. There may be displacement of intracerebral aneurysm clips and metallic implants, and cardiac pacemakers can be disabled because of the high magnetic field created by this device. We studied the effects of a magnetic field on metallic middle ear prosthetics and concluded that nuclear magnetic resonance imaging should offer no risks to hearing or otologic function in patients with nonferromagnetic metallic middle ear prosthetics. Nuclear magnetic resonance imaging is contraindicated in patients with cochlear implants