Vestibular pathophysiologic changes in experimental perilymphatic fistula

Histopathological reaction in the vestibule after cochlear implantation in Macaca fascicularis

Cochlear implantation surgery (CI) is considered a safe procedure and is the standard treatment for the auditory rehabilitation in patients with severe-to-profound sensorineural hearing loss. Although the development of minimally traumatic surgical concepts (MTSC) have enabled the preservation of residual hearing after the implantation, there is scarce literature regarding the vestibular affection following MTCS. The aim of the study is to analyze histopathologic changes in the vestibule after CI in an animal model (Macaca fascicularis). Cochlear implantation was performed successfully in 14 ears following MTCS. They were classified in two groups upon type of electrode array used. Group A (n = 6) with a FLEX 28 electrode array and Group B (n = 8) with HL14 array. A 6-month follow-up was carried out with periodic objective auditory testing. After their sacrifice, histological processing and subsequent analysis was carried out. Intracochlear findings, vestibular presence of fibrosis, obliteration or collapse is analyzed. Saccule and utricle dimensions and neuroepithelium width is measured. Cochlear implantation was performed successfully in all 14 ears through a round window approach. Mean angle of insertion was >270° for group A and 180-270° for group B. In group A auditory deterioration was observed in Mf 1A, Mf2A and Mf5A with histopathological signs of scala tympani ossification, saccule collapse (Mf1A and Mf2A) and cochlear aqueduct obliteration (Mf5A). Besides, signs of endolymphatic sinus dilatation was seen for Mf2B and Mf5A. Regarding group B, no auditory deterioration was observed. Histopathological signs of endolymphatic sinus dilatation were seen in Mf 2B and Mf 8B. In conclusion, the risk of histological damage of the vestibular organs following minimally traumatic surgical concepts and the soft surgery principles is very low. CI surgery is a safe procedure and it can be done preserving the vestibular structures.

Bifenestral surgical and chemical labyrinthectomy, a new effective ablative surgical approach to intractable vertigo in Ménière Disease elderly Patients

INTRODUCTION

In this article, the bi-fenestral surgical chemical labyrinthectomy is introduced as a surgical demolition technique for treating resisting incurable forms of Meniere's disease in patients aged over 70 and/or with low hearing residues refractory to medical treatment.

MATERIALS AND METHODS

The results on participants fitting the inclusion criteria (n = 16) were reported using anamnesis (frequency of the crisis), Dizziness Handicap Inventory (DHI) and Functional Level Scale (FLS) before and after the intervention.

RESULTS

Vertigo control was achieved in all patients of this case series. A difference of 57 and 3.67 in mean DHI (from 68 (SD 16,7) to 11 (SD 14)) and FLS (from 4,68 (SD 0,7) to 0,1 (SD 0,3)) scores respectively were seen after an average of 16.28 months. Contextually tinnitus was reported to improve in seven patients (43,75%), aggravate in three (18,75%) and remain unchanged in the remaining six(37,5%).

CONCLUSION

Bi-fenestral surgical chemical labyrinthectomy appears a safe, immediate, and effective demolition treatment for vertigo control in a restricted class of patients affected by intractable Meniere disease.

Direction-fixed positional nystagmus following head-roll testing: how is it related with a vestibular pathology?

OBJECTIVE

The goal of this study is to analyze the clinical view of patients with direction-fixed positional nystagmus (DFPN) following head-roll maneuver.

METHODS

Sixty patients with DFPN were reviewed retrospectively. Patients were categorized into 3 groups according to the direction of nystagmus based on rotation side. Associated problems were documented, and cumulative data were compared between groups. One-way analysis of variance (ANOVA test) was used for statistical analysis (P < 0.05).

RESULTS

Thirty-three patients (55%) had stronger nystagmus beating towards the direction of head-roll (Group-A). Three patients developed geotropic LC-BPPV. Fourteen patients had inner ear disease. Sixteen patients (27%) had stronger nystagmus beating against the direction of head roll (Group-B). Nine patients had inner ear disease. None of the patients tested with head-shaking had change of direction of nystagmus. Eleven patients (18%) had DFPN with equal velocity during right or left head-roll maneuver (Group-C). Of those, nine patients had inner ear disease. None of the patients had change of direction of nystagmus. Comparison of the incidence of associated problems (migraine, vestibular neuronitis, Meniere's disease etc.) in each group was not statistically significant (P˃0.05).

CONCLUSION

Patients with DFPN should be followed for a possibility of vestibular pathology since vestibular problem was documented for more than half of the patients in the follow-up. On the other hand, DFPN could be related with a temporary reason (thermal, physical or drug effect etc.) in some patients who do not exhibit any associated disease. Head-shaking testing is recommended to expose the lateral canal BPPV. But the incidence is low.

Case Report: Could Hennebert's Sign Be Evoked Despite Global Vestibular Impairment on Video Head Impulse Test? Considerations Upon Pathomechanisms Underlying Pressure-Induced Nystagmus due to Labyrinthine Fistula

We describe a case series of labyrinthine fistula, characterized by Hennebert's sign (HS) elicited by tragal compression despite global hypofunction of semicircular canals (SCs) on a video-head impulse test (vHIT), and review the relevant literature. All three patients presented with different amounts of cochleo-vestibular loss, consistent with labyrinthitis likely induced by labyrinthine fistula due to different temporal bone pathologies (squamous cell carcinoma involving the external auditory canal in one case and middle ear cholesteatoma in two cases). Despite global hypofunction on vHIT proving impaired function for each SC for high accelerations, all patients developed pressure-induced nystagmus, presumably through spared and/or recovered activity for low-velocity canal afferents. In particular, two patients with isolated horizontal SC fistula developed HS with ipsilesional horizontal nystagmus due to resulting excitatory ampullopetal endolymphatic flows within horizontal canals. Conversely, the last patient with bony erosion involving all SCs developed mainly torsional nystagmus directed contralaterally due to additional inhibitory ampullopetal flows within vertical canals. Moreover, despite impaired measurements on vHIT, we found simultaneous direction-changing positional nystagmus likely due to a buoyancy mechanism within the affected horizontal canal in a case and benign paroxysmal positional vertigo involving the dehiscent posterior canal in another case. Based on our findings, we might suggest a functional dissociation between high (impaired) and low (spared/recovered) accelerations for SCs. Therefore, it could be hypothesized that HS in labyrinthine fistula might be due to the activation of regular ampullary fibers encoding low-velocity inputs, as pressure-induced nystagmus is perfectly aligned with the planes of dehiscent SCs in accordance with Ewald's laws, despite global vestibular impairment on vHIT. Moreover, we showed how pressure-induced nystagmus could present in a rare case of labyrinthine fistulas involving all canals simultaneously. Nevertheless, definite conclusions on the genesis of pressure-induced nystagmus in our patients are prevented due to the lack of objective measurements of both low-acceleration canal responses and otolith function.

Inner ear test battery in guinea pig models - a review

OBJECTIVE

This study reviewed the development of the inner ear test battery comprising auditory brainstem response (ABR), and caloric, ocular vestibular-evoked myogenic potential (oVEMP), and cervical vestibular-evoked myogenic potential (cVEMP) tests in guinea pig models at our laboratory over the last 20 years. Detailed description of the methodology for testing the small animals is also included.

METHODS

Inner ear disorders, i.e. ototoxicity, noise exposure, or perilymph fistula were established in guinea pig models first. One to four weeks after operation, each animal underwent ABR, oVEMP, cVEMP, and caloric tests. Then, animals were sacrificed for morphological study in the temporal bones.

RESULTS

Inner ear endorgans can be comprehensively evaluated in guinea pig models via an inner ear test battery, which provides thorough information on the cochlea, saccule, utricle, and semicircular canal function of guinea pigs. Coupled with morphological study in the temporal bones of the animals may help elucidate the mechanism of inner ear disorders in humans.

CONCLUSIONS

The inner ear test battery in guinea pig models may encourage young researchers to perform basic study in animals and stimulate the progress of experimental otology which is in evolution.

Effect of Intratympanic Application of Aminoglycosides on Click-Evoked Myogenic Potentials in Guinea Pigs

OBJECTIVES

Although numerous studies have identified damage to the cochlear and vestibular end organs as the primary site of aminoglycoside-induced ototoxicity, the effect on the saccule remains poorly understood, possibly due to lack of monitoring saccular function in experimental animals. Therefore, this study applied three kinds of aminoglycosides into the tympanic space of guinea pigs to examine their toxic impact on the saccule by way of click-evoked myogenic potential test coupled with morphologic assessment.

DESIGN

Albino guinea pigs were treated with saline, gentamicin, tobramycin, or amikacin, with 10 animals assigned to each group. Each compound was injected directly overlying but not through the round window membrane on the left ear, with the right ear serving as a control. One week after injection, each animal underwent auditory brain stem response, caloric test, and click-evoked myogenic potential test. Animals were then killed for morphologic assessment through the use of light and electron microscopic examinations.

RESULTS

The animals treated with saline, gentamicin, tobramycin, or amikacin exhibited abnormal auditory brain stem response in 0%, 30%, 100%, and 30% of cases; abnormal caloric responses were found in 0%, 100%, 40%, and 40% of cases; absent click-evoked myogenic potentials were found in 0%, 100%, 30%, and 40% of cases, respectively. Gentamicin and other groups differed significantly in abnormal rates of caloric responses and click-evoked myogenic potentials. Morphologic study of the gentamicin-treated animals confirmed that the absence of click-evoked myogenic potential originated from the lesion in the saccular macula.

CONCLUSIONS

Gentamicin represents the dominant susceptibility of aminoglycoside-induced vestibulotoxicity for eliminating both semicircular canal and saccular functions. This study further confirms the findings of human studies in which the caloric and vestibular evoked myogenic potentials responses were monitored to assess the abolition of vestibular function in patients treated with intratympanic gentamicin injection.

Click-evoked myogenic potentials recorded on alert guinea pigs

The aim of this study was to establish an animal model of acoustically evoked vestibulo-collic reflex using guinea pigs. A special clamp was applied to restrain the head and body of the guinea pigs, but leaving its four legs free. Each animal underwent vestibular evoked myogenic potential (VEMP) and caloric tests using clip electrode method without general anesthesia or decerebrate surgery. The response rates for the myogenic potentials on the neck of guinea pigs using 100, 90, 80 and 70 dB monaural acoustic stimulation with unilateral recording were 100%, 62%, 50% and 0%, respectively. The mean latencies of the positive and negative peaks for the myogenic potentials were 7.24+/-0.49 and 9.15+/-0.47 ms, 7.09+/-0.43 and 9.28+/-0.42 ms, as well as 7.03+/-0.59 and 9.14+/-0.56 ms, when elicited by 100, 90 and 80 dB acoustic stimulation, respectively. The median (minimum-maximum) peak-to-peak amplitudes were 11.93 (6.14-16.86), 10.99 (5.28-19.40), and 11.17 (5.02-20.72) microV, when elicited by 100, 90 and 80 dB acoustic stimulation, respectively. We found no significant relationship between the stimulus intensity and the mean latencies or peak-to-peak amplitude of the myogenic potentials in guinea pigs. For those treated with gentamicin unilaterally, all guinea pigs showed absent caloric responses on the lesion side, and absent myogenic potentials on the neck when using ipsi-lesional acoustic stimulation, while the hearing was preserved. Hence, the use of gentamicin-treated animals, along with normal controls and auditory brainstem responses, results in convincing results that the recorded myogenic potentials are in fact of vestibular origin.

Hyperbaric compression in the guinea pig with perilymph fistula

OBJECTIVE

The study goal was to evaluate the effects of hyperbaric therapy on the auditory and vestibular function of guinea pigs compromised by perilymph fistula (PLF).

METHODS

Twenty-four pigmented guinea pigs underwent induction of bilateral eustachian tube dysfunction before the creation of a unilateral PLF. Half of the animals were randomly assigned to receive immediate hyperbaric compression treatment of 4 "dives" each. Hearing was tested electrocochleographically, and signs of vestibulopathy were recorded before and after compression.

RESULTS

After accounting for the effects of PLF, compression was not associated with significant hearing loss (P = 0.5411). Vestibulopathy was seen only in ears with PLF, and its incidence was similar for compression and noncompression groups.

CONCLUSION

Hyperbaric compression does not compromise auditory or vestibular function in guinea pig ears with experimental PLF.

SIGNIFICANCE

Our observations support the relative safety of recompression in patients with PLF.

Recovery of caloric function in experimental perilymph fistula

Twenty of 46 guinea pigs with experimental perilymph fistula that showed canal paresis on an ice water caloric test during the first week after operation were studied on the following days to observe the progression and final outcome of the caloric test. Two weeks after operation, 12 animals showed persistent canal paresis, whereas 8 animals developed a normal caloric response. Resolution of the caloric response progressed from canal paresis, via caloric irregularity, to a final return of normal caloric response. Morphological study of animals with recovery of caloric function shows healing of the previously ruptured membrane, with preservation of the contour of the membranous labyrinth in the lateral semicircular duct, and intact sensorineural elements. Recovery of caloric function may serve not only as an important diagnostic sign in patients with healed perilymph fistula, even without surgical proof, but also as an expectation for the recovery of hearing loss.

Treatment of vertigo using laser labyrinthectomy

Benign paroxysmal positional vertigo developed in a patient with perilymph fistula 3 years after closure of the fistula which was in the lower margin of the annular ligament. The patient's symptoms were long-lasting and intractable. The macula utriculi and utriculoampullary nerve were irradiated by argon laser beams through the stapedectomized oval window. Singular neurectomy was performed using Argon laser, although the nerve could not be identified. After surgery, the patient's symptoms disappeared. Pure tone average of the operated side was 50 dB which remained unchanged after surgery. The macula utriculi may have been completely destroyed. Ocular counter-rolling was indicative of hypofunction of the irradiated utricle. The singular nerve may or may not have been sectioned. The ampullary nerves to the lateral canal and probably the anterior canal were intact, judging from the normal caloric reaction.