Morphological changes in the round window membrane associated with Haemophilus influenzae-induced acute otitis media in the chinchilla

Abstract

Objective The round window membrane (RWM) encloses the round window, the opening into the scala tympani (ST) from the middle ear. During the course of acute otitis media (AOM), structural changes of the RWM can occur that potentially affect sound transmission into and out of the cochlea. The relationship between such structural changes and conductive hearing loss during AOM has remained unclear. The focus of the current study was to compare the thickness distribution across the RWM surface between normal ears and those with AOM in the chinchilla. We the occurrence of AOM-associated histological changes in this membrane compared to uninfected control animals after AOM of two relatively short durations. Material and methods AOM was induced by transbullar injection of the nontypeable Haemophilus influenzae strain 86-028NP into two groups of adult chinchillas (n=3 each). Bullae were obtained from the two infected groups, at 4 days or 8 days post challenge. Structures and thickness of these RWMs were compared between the two infected treatment groups and to RWMs from uninfected control animals (n=3) at seven different RWM locations. Results RWM thickness in infected chinchillas increased significantly at locations along the central line on the 4th day post bacterial challenge compared to values found for uninfected control animals. Lymphocyte infiltration and edema were the primary contributors to these thickness increases. No significant further increases in RWM thickness were observed when RWMs from chinchillas ears infected for 4 and 8 days were compared. Thickness and structural changes at the RWM lateral and medial areas were less visually obvious and not statistically significant among the three treatment groups. These latter RWM regions clearly were less affected during AOM than the central areas. Conclusions This histological study establishes that H. influenzae-induced AOM causes significant acute changes in chinchilla RWM structure that are characterized by region-specific increases in thickness. Our new morphological findings comparing normal and diseased chinchilla RWMs identify yet another biomechanical mechanism by which nontypeable H. influenzae may contribute to hearing loss in AOM.

Three-Dimensional Analysis of Round Window Membrane in the Chinchilla Model with Acute Otitis Media Induced with <i>Streptococcus Pneumoniae</i> 7F

“…In the presented study, we found in the 2D measurements that the thickness of the RWM was significantly higher in the experimental group compared to those in the control group. In accordance with our results, Jiang et al ( 10 ) observed that the membrane was significantly thickened in the chinchillas with AOM created by Haemophilus influenzae inoculation compared to the control group in four days after inoculation. In both their and our studies, the thickening of the RWM, which may be explained by the intracellular edema and cell proliferation occurring in the membrane, may be interpreted as part of the body’s defense system to protect the inner ear and other related structures from inflammation in the middle ear.…”

“…While a normal chinchilla RWM has a more convex shape, the RWM of the infected ears showed a more flattened shape in our study, in accordance with the findings of previous studies ( 10 , 12 ). Most researchers assume that this difference in the shape of RWM is related with the negative middle ear pressure due to inflammatory cell and exudate infiltration in the tympanic cavity due to acute onset of OM as well as with the inflammatory changes in the layers of the membrane ( 10 , 19 ). But in all circumstances, the contraption involving the change in the shape of RWM may affect the whole interaction between the middle and the inner ears, hence the hearing mechanism.…”

“…Each section was measured from three different points. The first measurement was made from the center of the round window, while the other two measurements were performed 0.2 mm anterior and inferior ( 10 , 11 ).…”

“…The round window membrane (RWM), which separates the middle ear and the scala tympani of the basal turn of the cochlea, has an important role in several pathologies involving the middle and the inner ears in that it is a semi-permeable membrane allowing bacterial toxins, inflammatory mediators, and antibiotics to pass through ( 7 , 8 ). As RWM takes part in the body’s defense system and plays a role in the transport of mechanical energy between the ear ossicles and the inner ear fluid; the structural changes that occur in the RWM with the thickening of the membrane give rise to the pathology of many diseases involving the middle and the inner ears including hearing loss ( 3 , 8 , 9 , 10 ). Therefore, analyzing any changes in RWM plays an important role in determining the pathogenesis of possible complications that may arise from otitis media and labyrinthitis.…”

Mucosal Type of Chronic Suppurative Otitis Media and the Long-Term Impact on Hearing Loss

“…To apprehend better the pathogenesis of inner ear impairment caused by middle ear inflammation or infection, the RWM structure was best investigated in rat models [23]. Several studies reported inflammatory cell infiltration and penetration of bacteria into the RWM and neighboring scala tympani [24,25].…”