Noise level of drilling instruments during mastoidectomy. (1/118)

Exposure to intense noise has been identified as a potential risk in the development of hearing impairment. Social concern about excessive noise is increasing and this also extends to the operating room. A noise level study was performed in the operating room during mastoidectomy with a sound level meter and it was analyzed by a sound-analyzing program. The drilling instruments used included the Stryker, Midas, M.P.S. and Med-Next. The operator was exposed to sound levels from 69 to 83 dBA. The loudest drilling instrument was the Midas and it produced an average sound level of 83 dBA to the operator. The mean exposure time was 41 minutes during mastoidectomy. This is below the occupational noise-level regulations in Korea. However, considering that individual susceptibility to noise varies and that the otologic surgeon is repeatedly exposed to prolonged drilling noise, ear protection is recommended for the operators of high-speed drilling instruments.  (+info)

Random errors in localization of landmarks in postero-anterior cephalograms. (2/118)

The aim of the present study was to evaluate the random error in localization of the most common landmarks in postero-anterior cephalograms (PAC). The study took place at the Department of Orthodontics of Aarhus University during the period 1993-1995. The material consisted of 30 standardized PAC taken in natural head position. Five examiners had to identify 34 landmarks on each cephalogram. Subsequently, all examiners had to identify again the same 34 landmarks on one randomly selected cephalogram five times with a time interval of at least 24 hours. All landmarks were digitized, related to an X-Y co-ordinate system, and an arithmetical mean was calculated. The accuracy of digitizing was evaluated by digitizing one randomly selected cephalogram 10 times. The main findings of this study are: (1) The digitizing error is negligible compared to the errors introduced by landmark identification. (2) Each landmark has its own characteristic pattern of variance, which is very similar on both sides. (3) Significant differences in accuracy exist between the various postero-anterior landmarks. The six most accurate landmarks are mastoid left (l) and right (r), latero-orbitale (l) and (r), and antegonion (l) and (r). The six least accurate landmarks are coronoid (l) and (r), condylar (l) and (r), and mandibular foramen (l) and (r). (4) A significant difference in the accuracy of landmark identification between the five examiners was only seen for seven of the 34 landmarks. (5) No evidence was found that one examiner was consistently better/worse than the others. (6) No improvement in the accuracy was found after repeated identification, thus there seems to be no short-term 'learning process'. Refereed Paper  (+info)

Multisensory cortical signal increases and decreases during vestibular galvanic stimulation (fMRI). (3/118)

Functional magnetic resonance imaging blood-oxygenation-level-dependent (BOLD) signal increases (activations) and BOLD signal decreases ("deactivations") were compared in six healthy volunteers during galvanic vestibular (mastoid) and galvanic cutaneous (neck) stimulation in order to differentiate vestibular from ocular motor and nociceptive functions. By calculating the contrast for vestibular activation minus cutaneous activation for the group, we found activations in the anterior parts of the insula, the paramedian and dorsolateral thalamus, the putamen, the inferior parietal lobule [Brodmann area (BA) 40], the precentral gyrus (frontal eye field, BA 6), the middle frontal gyrus (prefrontal cortex, BA 46/9), the middle temporal gyrus (BA 37), the superior temporal gyrus (BA 22), and the anterior cingulate gyrus (BA 32) as well as in both cerebellar hemispheres. These activations can be attributed to multisensory vestibular and ocular motor functions. Single-subject analysis in addition showed distinctly nonoverlapping activations in the posterior insula, which corresponds to the parieto-insular vestibular cortex in the monkey. During vestibular stimulation, there was also a significant signal decrease in the visual cortex (BA 18, 19), which spared BA 17. A different "deactivation" was found during cutaneous stimulation; it included upper parieto-occipital areas in the middle temporal and occipital gyri (BA 19/39/18). Under both stimulation conditions, there were signal decreases in the somatosensory cortex (BA 2/3/4). Stimulus-dependent, inhibitory vestibular-visual, and nociceptive-somatosensory interactions may be functionally significant for processing perception and sensorimotor control.  (+info)

Unexpected reflex response to transmastoid stimulation in human subjects during near-maximal effort. (4/118)

1. In human subjects, a high-voltage electrical pulse between electrodes fixed over the mastoid processes activates descending tract axons at the level of the cervico-medullary junction to produce motor responses (cevicomedullary evoked responses; CMEPs) in the biceps brachii and brachioradialis muscles. 2. During isometric maximal voluntary contractions (MVCs) of the elbow flexors, CMEPs in the biceps brachii and brachioradialis muscles are sometimes followed by a second compound muscle action potential. This response can be observed in single trials (amplitude of up to 60 % of the maximal M wave) and follows the CMEP by about 16 ms in both muscles. The response only occurs during very strong voluntary contractions. 3. The second response following transmastoid stimulation appears with stimulation intensities that are at the threshold for evoking a CMEP in the contracting muscles. The response grows with increasing stimulus intensity, but then decreases in amplitude and finally disappears at high stimulation intensities. 4. A single stimulus to the brachial plexus during MVCs can also elicit a second response (following the M wave) in the biceps brachii and brachioradialis muscles. The latency of this response is 3-4 ms longer than that of the second response observed following transmastoid stimulation. This difference in latency is consistent with a reflex response to stimulation of large-diameter afferents. 5. The amplitude of the second response to transmastoid stimulation can be reduced by appropriately timed subthreshold transcranial magnetic stimuli. This result is consistent with intracortical inhibition of the response. 6. We suggest that transmastoid stimulation can elicit a large transcortical reflex response in the biceps brachii and brachioradialis muscles. The response travels via the motor cortex but is only apparent during near-maximal voluntary efforts.  (+info)

Mastoid air sinus abnormalities associated with lateral venous sinus thrombosis: cause or consequence? (5/118)

BACKGROUND: Mastoiditis is a known cause of lateral venous sinus thrombosis (LST). We have encountered patients with LST associated with mastoid abnormality on MRI without any clinical signs of infection; the significance of these abnormalities is uncertain. This study examines the relationship of LST and mastoid air sinus abnormalities systematically. SUMMARY OF REPORT: We performed a retrospective clinical and radiological review of a series of 26 patients with cerebral venous thrombosis. Mastoid abnormalities were detected ipsilateral to 9 of 23 thrombosed lateral sinuses (39%) and 0 of 29 unaffected lateral sinuses (P<0.001). No patient had clinical evidence of mastoiditis. Eight of 9 patients with mastoid abnormalities were treated without antibiotics; all made uneventful clinical recoveries. Repeated MRI in 1 patient revealed reversal of the mastoid changes. CONCLUSIONS: The mastoid changes observed are likely to be due to venous congestion as a consequence of LST, not mastoiditis.  (+info)

Comparison of human ocular torsion patterns during natural and galvanic vestibular stimulation. (6/118)

Galvanic vestibular stimulation (GVS) is reported to induce interindividually variable tonic ocular torsion (OT) and superimposed torsional nystagmus. It has been proposed that the tonic component results from the activation of otolith afferents. We tested our hypothesis that both the tonic and the phasic OT are mainly due to semicircular canal (SCC) stimulation by examining whether the OT patterns elicited by GVS can be reproduced by pure SCC stimulations. Using videooculography we measured the OT of six healthy subjects while two different stimuli with a duration of 20 s were applied: 1) transmastoidal GVS steps of 2 mA with the head in a pitched nose-down position and 2) angular head rotations around a combined roll-yaw axis parallel to the gravity vector with the head in the same position. The stimulation profile was individually scaled to match the nystagmus properties from GVS and consisted of a sustained velocity step of 4-12 degrees /s on which a velocity ramp of 0.67-2 degrees /s(2) was superimposed. Since blinks were reported to induce transient torsional eye movements, the subjects were also asked to blink once 10 s after stimulus onset. Analysis of torsional eye movements under both conditions revealed no significant differences. Thus we conclude that both the tonic and the phasic OT responses to GVS can be reproduced by pure rotational stimulations and that the OT-related effects of GVS on SCC afferents are similar to natural stimulations at small amplitudes.  (+info)

Diffusion-weighted imaging for differentiating recurrent cholesteatoma from granulation tissue after mastoidectomy: case report. (7/118)

Identification of recurrent cholesteatoma and differentiation from postoperative granulation tissue is important in a patient who has undergone mastoidectomy for cholesteatoma. We describe the diffusion-weighted imaging findings and apparent diffusion coefficient values in a case of recurrent cholesteatoma. This case suggests possible differentiation of cholesteatoma from granulation tissue on the basis of diffusion-weighted imaging findings.  (+info)

Vibration-induced ocular torsion and nystagmus after unilateral vestibular deafferentation. (8/118)

Vibration is an excitatory stimulus for both vestibular and proprioceptive afferents. Vibration applied either to the skull or to the neck muscles of subjects after unilateral vestibular deafferentation induces nystagmus and a shift of the subjective visual horizontal. Previous studies have ascribed these effects to vibratory stimulation of neck muscle proprioceptors. Using scleral search coils, we recorded three-dimensional eye movements during unilateral 92 Hz vibration of the mastoid bone or of the sternocleidomastoid (SCM) muscle in 18 subjects with chronic unilateral vestibular deficits after vestibular neurectomy or neuro-labyrinthitis. Nine subjects had lost function of all three semicircular canals (SSCs) on one side, and the other nine had lost function of only the anterior and lateral SSCs. Vibration of the mastoid bone or of the SCM muscle on either side induced an ipsilesional tonic shift of torsional eye position of up to 6.5 degrees during visual fixation, as well as a nystagmus with horizontal, vertical and torsional components in darkness. Subjects who had lost function of all three SSCs on one side showed a larger shift in ocular torsion in response to SCM vibration than did subjects who had lost function of only two SSCs. The difference between ocular torsion produced by ipsilesional muscle or bone vibration was not significantly different from that produced by contralesional bone or muscle vibration. The vibration-induced nystagmus rotation axis tended to align with the pitch (y) axis of the head in subjects who had lost only anterior and lateral SSC function, and with the roll (x) axis of the head in subjects who had lost function of all three SSCs. We propose that the previously described vibration-induced shift of the subjective visual horizontal can be explained by the vibration-induced ocular torsion, and that the magnitude of ocular torsion is related to the extent of the unilateral vestibular deficit. While altered proprioceptive inputs from neck muscles might be important in the mechanism of vibration-induced ocular torsion and nystagmus after unilateral vestibular deafferentation, vibratory stimulation of vestibular receptors in the intact labyrinth also appears to have an important role.  (+info)