Round window membrane in serous and purulent otitis media. Structural study in the rat

Gentamicin delivery to the inner ear: Does endolymphatic hydrops matter?

Introduction

Middle ear application of gentamicin is a common medical treatment for uncontrolled Ménière’s disease. The objective of the study was to evaluate the impact of endolymphatic hydrops on inner ear delivery.

Methods

Perilymph gentamicin concentrations and correlation with endolymphatic hydrops in an animal model were assessed. A group of 24 guinea pigs was submitted to surgical obstruction of the endolymphatic sac and duct of the right ear. Gentamicin was applied either to the right ear’s round window niche or through a transtympanic injection. Perilymph specimens were collected at different times. Histologic morphometry was used to evaluate both turn-specific and overall hydrops degree.

Results

In animals with endolymphatic hydrops, lower concentrations of gentamicin were observed after 20 or 120 minutes of exposure and in both types of administration, when compared to controls. This difference reached statistical significance in the round window niche application group (Mann-Whitney, p = 0,007). A negative correlation between perilymphatic gentamicin concentration and hydrops degree could be observed in both groups, after 120 minutes of exposure (Spearman correlation, round window niche p<0,001; TT p = 0,005).

Conclusions

The study indicates that the endolymphatic hydrops degree has a negative interference on the delivery of gentamicin into the inner ear following middle ear application.

Change in cochlear response in an animal model of otitis media with effusion

Our previous studies confirm that middle ear mobility is reduced in the presence of otitis media with effusion (OME). Variations in middle ear function may result in changes in cochlear response in OME ears. With the long-term goal of evaluating cochlear function in OME ears, the aim of this study was to measure the displacement of the basilar membrane (BM) in guinea pig ears with OME. Vibrations of the BM at the apex and basal turn were measured in an in vitro preparation extracted 3 and 14 days after injection of lipopolysaccharide in the middle ear of guinea pigs. The results show that the displacement sensitivity of the BM at the apex and the basal turn to sound pressure in the ear canal was reduced up to 25 dB at their characteristic frequencies, respectively. Cochlear gain with respect to umbo movement was also changed in ears with OME in both groups. This study provides data for analysis of the change of BM vibration in a guinea pig OME model.

Visualization of endolymphatic hydrops in patients with Meniere's disease

OBJECTIVE

Recently, there have been many reports of intratympanic gentamicin therapy for the treatment of intractable Meniere's disease. Intratympanic administration of steroids has also been used to treat sudden sensorineural hearing loss. We attempted to visualize how the intratympanically administered drug enters the inner ear.

METHODS

Gadolinium hydrate diluted eightfold with saline was injected intratympanically through the tympanic membrane using a 23 G needle in nine patients with inner ear diseases. With a 3 Tesla magnetic resonance imaging (MRI) unit, three-dimensional fluid-attenuated inversion recovery (3D-FLAIR) imaging was performed.

RESULTS

3D-FLAIR MRI clearly revealed that the gadolinium entered the perilymphatic space and delineated the perilymphatic and endolymphatic spaces of the inner ear. In patients with endolymphatic hydrops, the perilymphatic space surrounding the endolymph was small or had disappeared. Gadolinium appeared first in the scala tympani of the basal turn of the cochlea and the perilymphatic space of the vestibule. One day after the intratympanic injection of gadolinium, the gadolinium was observed in almost all parts of the perilymph. Six days after the intratympanic injection, the gadolinium had almost disappeared from the inner ear.

CONCLUSION

We reported the first visualization of endolymphatic hydrops in patients with Meniere's disease. The relationship between the image of the endolymphatic space and functional tests, such as electrocochleography and vestibular-evoked myogenic potential, must be examined in the near future. It is important for the development of intratympanic drug therapies for inner-ear diseases to investigate how the drugs enter and leave the inner ear.

Ventral approach to rat inner ear preserves cochlear function

CONCLUSION

This technique enabled us to visualize the cochlea without causing damage.

OBJECTIVE

The mammalian inner ear is difficult to approach surgically. This is particularly true in the cases of the rat and mouse, which both have small cochleae. Rat and mouse research is particularly important because their genomes are well characterized, and significantly similar to that of the human. The aim of the present study was to develop a method of accessing the rat cochlea without affecting its function.

MATERIALS AND METHODS

In the ventral approach, a small hole was made for access to the scala tympani. Cochlear function was assessed through auditory brainstem response (ABR) threshold measurements.

RESULTS

The ventral approach enabled the direct visualization of the tympanic bulla. Thus, the tympanic bulla could be easily opened in a manner that was benign to cochlear function. There was no significant difference in ABR threshold before and after surgery.

[Cochlear involvement in acute otitis media]

OBJECTIVE

An experimental design with mice has been realized to understand the origin of sensorial hearing loss related to infectious processes in the middle ear. Our aim is to study if the cilliated cells in the Corti organ's are lost after one or more acute otitis media.

MATERIAL AND METHODS

For that, thirty Sprague-Dawley mice have been divided in two groups. In the first one, we have induced one acute otitis media, in the second group we have induced two infections of this kind.

RESULTS

The statistic study shows that the loss of the cilliated cells is greater in the basal turn of the mice is cochlea, in the first group (alpha=0,020) and also in the second (alpha=0,038). We've noticed in the first group the near absence of injury in the middle turn, but in all samples of the second group we found that injury (alpha=0,002).

CONCLUSIONS

In acute otitis media, the loss of ciIliated cells are mainly in the basal turn of the mice is cochlea, and affects the middle turn when the infection is repeated.

Ventral approach to the rat middle ear for otologic research

OBJECTIVE

To describe a simple approach to the rat middle ear because there are few clear descriptions of this technique with minimal morbidity and mortality.

STUDY DESIGN AND SETTING

Six male Long-Evans rats were used in this study. We designed a cervical approach to the middle ear with the purpose of creating an experimental model of ossiculoplasty that permits the postoperative survival of the animal.

RESULTS

It was possible in all cases to visualize the majority of structures of the tympanic cavity: promontory, round window, stapedial artery, stapes, incus, and tympanic membrane. There were no cases of postoperative infection or facial paralysis.

CONCLUSIONS AND SIGNIFICANCE

The ventral approach to the rat middle ear is a rapid and simple technique that makes the rat the animal of choice for many otologic investigations.

A surgical approach appropriate for targeted cochlear gene therapy in the mouse

Therapeutic manipulations of the mammalian cochlea, including cochlear gene transfer, have been predominantly studied using the guinea pig as the experimental model. With the significant developments in mouse genomics and the availability of mutant strains of mice with well-characterized hearing loss, the mouse justifiably will be the preferred animal model for therapeutic manipulations. However, the potential advantages of the mouse model have not been fully realized due to the surgical difficulty of accessing its small cochlea. This study describes a ventral approach, instead of the routinely used postauricular approach in other rodents, for accessing the mouse middle and inner ear, and its application in cochlear gene transfer. This ventral approach enabled rapid and direct delivery of liposome-transgene complex to the mouse inner ear while avoiding blood loss, facial nerve morbidity, and mortality. Transgene expression at 3 days was detected in Reissner's membrane, spiral limbus, spiral ligament, and spiral ganglion cells, in a pattern similar to that previously described in the guinea pig. The successful access and delivery of material to the mouse cochlea and the replication of gene expression seen in the guinea pig demonstrated in this study should promote the use of the mouse in future studies investigating targeted cochlear therapy.

Uncommon and unusual complications of otitis media with effusion

Some complications of otitis media with effusion (OME) are not obvious and not always associated with otitis media by physicians and patients; the authors propose to call them 'unusual complications', although they may be quite frequent. Complications such as dizziness, clumsiness and behavioural disorders are classified in this group. Other complications are rare and uncommon such as sensorineural hearing loss and cholesteatoma. Some of these sequelae are structural, others more functional. The impact of OME on complex functions such as language, learning or behaviour is still controversial but seems to have been underestimated until now. Not only withholding treatment in children with OME may cause complications but also the treatment of OME may lead to sequelae, although serious side effects caused by the treatment of OME are rare. In this literature review, the epidemiology, importance and diagnosis of the uncommon and unusual complications of OME will be discussed.

Antibiotics in chronic suppurative otitis media: a bacteriologic study

Conservative medical management of chronic suppurative otitis media (CSOM) is an important step in achieving a dry ear. Topical antibiotic ear drops and aural toilet form the mainstay of medical management of noncholesteatomatous CSOM. This study analyzes the causal organisms and their sensitivity to various antibiotics. Out of 382 swabs examined, the major organisms isolated were Pseudomonas aeruginosa (27.2%), followed by Staphylococcus aureus (23.6%). The sensitivity of P. aeruginosa was 100% to ceftazidime, 98.9% to ciprofloxacin, 96.3% to gentamicin, and 95.4% to polymyxin B, whereas the sensitivity of S. aureus was 98.6% to ciprofloxacin, 97.4% to cloxacillin sodium, 96.5% to cotrimoxazole, and 90.7% to gentamicin. Pseudomonas aeruginosa was almost completely resistant to ampicillin (97.6%) and chloramphenicol (96.6%), whereas S. aureus was almost completely resistant to ampicillin (73.8%) and polymyxin B (98.3%). Among the available topical antibiotic preparations for use in the ear, we found that ciprofloxacin and gentamicin are the best choices.

Experimental cholesteatoma in the rat

The etiology of cholesteatoma is still enigmatic. Of the current theories, none has been confirmed with adequately convincing evidence. A completely suitable animal model has not hitherto been available and there is still a need for further experimental studies of this entity. As a possible experimental model we suggest dimethyl-benzanthracene induced cholesteatoma in the rat.