Spatiotemporal dynamics of brain-derived neurotrophic factor mRNA induction in the vestibulo-olivary network during vestibular compensation.
Vestibular compensation, which is the behavioral recovery from vestibular dysfunction produced by unilateral labyrinthectomy (UL), is attributed to functional and structural reorganization of neural networks in the central vestibular system. To assess the possible contribution of brain-derived neurotrophic factor (BDNF) to this recovery process, we investigated changes in mRNA expression levels in the central vestibular system after UL. We evaluated BDNF mRNA expression levels by quantitative reverse transcription-PCR and in situ hybridization. We found that BDNF mRNA is differentially induced in the medial vestibular nucleus ipsilateral to UL and in the prepositus hypoglossi and inferior olive on the contralateral side. The BDNF mRNA induction lasted for at least 24 hr and returned to the basal expression level within 72 hr after UL. In contrast to BDNF mRNA induction, the expression of an immediate-early gene, c-fos, quickly reached the maximum level at 3 hr and decreased to the basal level within 24 hr after UL. Neither BDNF or c-fos induction was observed in sham-operated animals. The persistent induction of BDNF after UL temporally corresponded to early behavioral manifestations of vestibular compensation. We further found that trkB mRNA was expressed in the central vestibular network at high levels, although its expression levels did not change over time after UL. Because BDNF is implicated in regulating synaptic structure and function, these results provide support for the hypothesis that BDNF is involved in neuronal reorganization that allows vestibular compensation. (+info)
Prognostic significance of changes in the internal acoustic meatus caused by vestibular schwannoma.
The prognostic significance of the variety of changes in the internal auditory meatus (IAM) caused by vestibular schwannoma was retrospectively analyzed in 69 consecutive patients with vestibular schwannoma. Preoperative bone-window computed tomography was used to classify IAM changes into extensive destruction (17%), widening (46%), and normal IAM (36%). Extensive destruction (47 +/- 19 years) and widening (48 +/- 13) occurred in significantly younger patients than normal IAM (59 +/- 9). Preoperative hearing was significantly more severely disturbed in patients with extensive destruction than in those with widening or normal IAM. IAM change was significantly related to the tumor consistency, as normal IAM was more common in patients with cystic tumor than in those with solid tumor. Postoperative hearing and facial function were worse in patients with severe IAM change, although the relationship between the IAM change and the surgical result was not significant. One patient with extensive destruction developed postoperative cerebrospinal fluid (CSF) leakage through the air cells around the IAM, and needed surgical repair. Severe IAM change occurs with solid tumor and causes severely disturbed preoperative hearing in younger patients, which reflects the tumor aggressiveness. Severe IAM change increases the technical difficulty of tumor removal and the risk of postoperative CSF leakage, and is associated with a poorer prognosis for patients with vestibular schwannoma. (+info)
Unilateral labyrinthectomy modifies the membrane properties of contralesional vestibular neurons.
Vestibular compensation after a unilateral labyrinthectomy leads to nearly complete disappearance of the static symptoms triggered by the lesion. However, the dynamic vestibular reflexes associated with head movements remain impaired. Because the contralesional labyrinth plays a prominent role in the generation of these dynamic responses, intracellular recordings of contralesional medial vestibular nucleus neurons (MVNn) were done after 1 mo of compensation. Their firing properties and cell type were characterized at rest, and their response dynamics investigated using step, ramp, and sinusoidal current stimulations. The sensitivity of the contralesional MVNn firing rates to applied current was increased, which, along with increased phase leads, suggests that significant changes in active conductances occurred. We found an increased proportion of the phasic type B neurons relative to the tonic type A neurons in the contralesional MVN. In addition, the remaining contralesional type A MVNn response dynamics tended to approach those of type B MVNn. Thus the contralesional MVNn in general showed more phasic response dynamics than those of control MVNn. Altogether, the firing properties of MVNn are differentially modified on the ipsilesional and contralesional sides of the brain stem 1 mo after unilateral labyrinthectomy. Ipsilesional MVNn acquire more "type A-like" tonic membrane properties, which would contribute to the stabilization of the spontaneous activity that recovers in the deafferented neurons during vestibular compensation. The bilateral increase in the sensitivity of MVNn and the acquisition of more "B-like" phasic membrane properties by contralesional MVNn should promote the restoration of the vestibular reflexes generated by the remaining, contralesional labyrinth. (+info)
Microscopic anatomy of the carotid canal and its relations with cochlea and middle ear.
The knowledge of the relations between the noble and vital structures of temporal bone is still a great challenge for the otologic surgeon. The microscopic anatomic studies of the temporal bone are one of the greatest help to prevent lesions during surgical intervention. AIM: To study the anatomic correlations between the carotid canal and the cochlea, and the occurrence of dehiscence of the carotid canal in the middle ear tympanic cavity. MATERIAL AND METHODS: Microscopic study of 122 human temporal bones. RESULTS: The average distance between the carotid canal and the cochlea were: the shortest distance, 1.05 mm; basal turn, 2.04 mm; middle turn, 2.32 mm; and apical turn, 5.70 mm. The occurrence of dehiscence of the carotid canal inside the tympanic cavity was 35.2%. CONCLUSION: The small distances between the cochlea and carotid canal, and the high incidence of dehiscence in the tympanic cavity remind us that anatomical knowledge of the temporal bone is required for the best qualification of otologists. (+info)
The translabyrinthine approach for acoustic neuroma and its common complications.
A retrospective analysis of 15 cases intracanalicular acoustic neuroma that undergone tumour excision by translabyrinthine approach spanning from August 1996 until December 2002 is presented. The main presenting complaints are unilateral hearing loss (100%) and tinnitus (86.7%). The mean age of presentation was 48.5 years old. Magnetic resonance imaging is the most important investigation tool to diagnose acoustic neuroma. At six months post operatively, the facial nerve was normal or near normal (grade I and II) in 46.6%, grade III to IV in 46.6% and grade V to VI in 6.7% of the cases respectively. There were also four cases of post operative cerebrospinal fluid leak, which was successfully managed with conservative measures. The translabyrinthine approach is the most familiar surgical technique employed by otologist. It is the most direct route to the cerebellopontine angle and internal auditory canal. It requires minimum cerebellar retraction. However, it sacrifices any residual hearing in the operated ear. (+info)
Canal wall reconstruction and mastoid obliteration with composite multi-fractured osteoperiosteal flap.
We used inferior pedicled composite multi-fractured osteoperiosteal flap (CMOF), our original and new surgical approach, to obliterate the mastoid cavity and reconstruct the external auditory canal (EAC) to prevent the open cavity problems. CMOF was used to obliterate the mastoid cavity and reconstruct the EAC in 24 patients (13 women, 11 men; age span 12-51 years) who underwent radical mastoidectomy to treat the chronic otitis media between 1998 and 2004. Small meatoplasty was done in all 24 patients to relieve their aesthetical concerns. Temporal bone CT scanning was done to observe the neo-osteogenesis in the mastoidectomy cavity and the CMOF, and the EAC volume was measured postoperatively. All our patients were followed-up for 2 years. The epithelization of the new EAC in our patients was complete at the end of the second month. Cholesteatoma, granulation, and recurrence of osteitis did not occur in any of the patients. We saw the new bone formation filling the mastoid cavity in the postoperative temporal bone CT scanning images. The mean volume of the new EAC on the 24th month was 1.83 +/- 0.56 cm(3). We had an almost natural EAC, which owed its existence to the neo-osteogenesis that grows behind the CMOF, which we use to obliterate the mastoid cavity and to reconstruct the EAC. (+info)
The mastoid as a functional rate-limiter of middle ear pressure change.
INTRODUCTION: The physiological function of the mastoid air cell system (MACS) with respect to middle ear (ME) pressure-regulation remains controversial because predictive mathematical models and experimental data to formulate and test hypotheses are lacking. OBJECTIVE: A mathematical description of MACS volume effects on the rate of ME pressure change is presented; the agreement between published data and model prediction is examined for consistency with the hypothesis that the MACS acts as a functional rate-limiter of ME pressure change, and an explanation for the relationship between MACS volume and otitis media is discussed. METHODS: The mathematical description shows that the value of a single, free parameter, termed the "MACS buffering efficiency" (M) determines if MACS volume affects the rate of ME pressure change caused by diffusive gas exchange. The MACS serves no rate-limiting function for M=0, acts as a gas sink for M>1 and acts as a gas reserve (rate-limiter) for M<1. RESULTS: Fitting the model equation to published adult human data yielded an estimate for M of 0.2. This implies that larger MACS volumes are associated with lesser rates of change in ME pressure caused by diffusive gas exchange and lesser required frequencies of effective Eustachian tube openings to maintain near ambient ME pressures. CONCLUSION: If well-controlled studies confirm M<1 for children and adults, larger MACS volumes will increase the time required to develop sufficient ME underpressures to cause otitis media by hydrops ex vacuo during transient or prolonged periods of Eustachian tube dysfunction. (+info)
Comparison of microtia reconstructive surgery with autograft versus homograft.
BACKGROUND: Microtia is a congenital abnormality with low incidence but considerable morbidities. Reconstruction of the microtia deformity is a complex and difficult process that requires a proper planning. The primary technique of reconstruction employs patient's own rib cartilage. Irradiated homograft cartilages previously have been used in facial reconstruction but its application in microtia surgery has not been reported yet. This study is designed to compare the results of autograft versus homograft auriculoplasty. METHODS: Between 1992 - 2002, 23 patients underwent auricular reconstructive surgery by the senior author in our department. Autograft implantation was performed in one stage but homograft auriculoplasty was done in two stages. RESULTS: Auricular deformity was right-sided in 13, left-sided in 8, and bilateral in 2 cases. Implanted graft was autograft in 9 patients and homograft in 14 patients. During mean follow-up of 4 years, cartilage graft resorption was detected in two cases, one in autograft and one in homograft group (P > 0.05). No postoperative infection was observed. Status of postauricular sulcus was optimal in 85.7% of homograft and 77.8% of autograft groups (P > 0.05). The satisfaction score of the patients and/or parents was excellent in 66.7% of autograft and 92.9% of homograft groups (P < 0.01). CONCLUSION: Based on better satisfaction score, equivalent aesthetic appearance, and absence of complications such as scaring and pain on the chest wall, homograft auriculoplasty is an appropriate option for reconstructive surgery in patients with microtia. (+info)