Læknablaðið : fylgirit - 01.06.2005, Blaðsíða 38

ABSTRACTS / XXIX CONGRESS OF THE NORDIC ASSOCIATION OF OTOLARYNGOLOGY
initiated successful results in allografting and xenografting in
many human organ systems. It is now possible to replace a large
number of organs or tissues by using organic or non-organic mate-
rials. In the inner ear the cochlear prosthesis (CI) has initiated a
new era of inner ear treatment as the damaged hair cells can now
be bypassed. The function of the CI is however dependant of
the integrity of the spiral ganglion cells (SGCs). Recent studies
have illustrated that fetal dorsal root ganglion neurons (DRGs)
implanted into the inner ear can survive and send axons towards
the SGCs. Further, these axons have a tendency to approach
the CNS. Stem cells implanted into the inner ear have migrated
towards the cochlear nucleus, which can be stimulated by exog-
enous factors.
These findings demonstrate the feasibility of a new strategy
to repair or replace the inner ear. Further, the future outcome
of these experiments may lead to a replacement of the auditory
nerve. If so, tissues implanted into the inner ear may regain
auditory function in e.g. acoustic neuroma patients where the
auditory nerve has been severed by the disease or its treatment.
Abstract no.: 097
Expression of TNF-a and VEGF in injured Guinea Pig
Cochlea
E Toppila, J Zou, I Pyykkö
Department of Otolaryngology, University Hospital of Tampere
Transcranial vibration was applied for seven animals at frequency
of 250 Hz for 15 minutes, and 5 animals were used as controls
to investigate molecular mechanism linked to surgery-induced
hearing loss in animal model. Compound action potential (CAP)
was measured. Expression of tumour necrosis factor alpha (TNF-
a) and its receptors (TNF Rl, TNF R2), vascular endothelium
growth factor (VEGF) and its receptors (VEGF Rl, VEGF R2)
were analysed. Vibration caused expression of TNF-a, TNF R1
and TNF R2 in the cochlea and the expression of TNF R2 was
stronger than that of TNF Rl. Vibration also induced VEGF
and VEGF R2 expression in the cochlea. The average immediate
hearing loss was 62 dB and after three days still 48 dB. Human
cadaver experiments were conducted with drilling of the tem-
poral bone with cutting and diamond drills of different size (1-6
mm). Responses were evaluated by measuring the skull vibration
Noise level was measured at the external ear canal. Diamond
burs caused less vibration and noise than cutting burs, but the
difference was less than is generally believed. The drill revolution
determined the hazardousness of the vibration. Temporal bone
drilling causes high cochlear share forces, leading easily to dam-
ages of hearing.
Abstract no.: 098
Brain maps of promontorial stimulation in normal hearing
Vejby Mortensen M, Madsen S, Gjedde A
Aarhus University Hospital
Electrical stimulation with a transtympanic electrode on the
promontory of the middle ear commonly is used to assess audi-
tory nerve function prior to cochlear implantation in deaf adults.
The promontorial test includes gap detection and temporal dif-
ference limen (TDL), a measure of discriminatory processing
of sound duration. In a series of studies of objective predictive
measures of outcome in cochlear implantation, we used positron
emission tomography (PET) to map cortical activity in normally
hearing subjects undergoing promontorial stimulation. We tested
the hypothesis that the ability to discriminate short duration
differences is correlated positively with activity in the right
posterior temporal region. The stimulus was perceived differ-
ently by the subjects, suggesting variable stimulation of multiple
sensory modalities, but this had no effect on brain activity. TDL
raised blood flow in the posterior middle temporal gyri. This
area is active during duration discrimination in different sensory
modalities and in the perception of words containing manipulated
phonemes. We conclude that recruitment of this part of the right
hemisphere is important for comprehension of speech containing
mostly temporal cues. The study also shows that stimulus-induced
activation reflects the goal of the task rather than the nature of
the stimulus.
Abstract no.: 099
Brain maps of promontory stimulation in cochlear implant
candidates
Vejby Mortensen M, Madsen S, Gjedde A
Aarhus University Hospital
Prediction of outcome is a challenge to the field of cochlear
implantation (CI). In previous studies, measures of gap detection
and duration discrimination in the promontory test were shown
to predict the extent of open-set speech perception accomplished
after CI. Previous neuroimaging of normal hearing revealed a
region in the right posterior temporal lobe that is crucial to dura-
tion discrimination and known to be active in Cl-users capable
of excellent speech perception. The present study tested the
hypothesis that this area is recruited only by postlingually deaf
CI candidates who are able to make subtle temporal discrimina-
tions in the promontory test. Fourteen postlingually deaf adult
Cl-candidates were stimulated in the ear chosen for implantation
and altered cerebral activity was recorded with positron emission
tomography as incremental 15-O-labelled water uptake. On stim-
ulation with tone bursts, we found bilateral activity close to the
primary auditory cortex in all subjects. In contrast, group-specific
differences of brain activity emerged in the temporal tasks and
the findings suggest that the ability to discriminate small duration
differences, important for speech perception, can be evaluated
preoperatively.
Abstract no.: 100
Endolymphatic hydrops and diplacusis - a case report
Brannström J, Malrnö University Hospital, Grenner J
Lund University Hospital
Endolymphatic hydrops causes increased pressure in the endo-
lymphatic sac, affecting the mechanical properties of the basilar
38 Læknablaðið/Fylgirit 51 2005/91