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Bacterial tympanogenic labyrinthitis, meningitis, and sensorineural damage
P A Schachern1, M M Paparella, R Hybertson
1University of Minnesota Otitis Media Research Center, Minneapolis.
Abstract:
Pathologic changes (sensorineural hearing loss, labyrinthitis, meningitis) can follow otitis media. Various macromolecular substances demonstrably enter the inner ear via the round window membrane, but its permeability to bacteria is less known. We inoculated Streptococcus pneumoniae type 7F bilaterally into the middle ears of two groups of chinchillas, with and without grafted round window membranes. Inner ears of inoculated animals were observed by light and electron microscopy. None with continuous grafts had labyrinthitis. Bacteria penetrated all three layers of nongrafted round window membranes and into all cochlear turns, entering Schuknecht's channels and following neuronal pathways; nerves were often degenerated, hair cells were damaged or missing, and the stria vascularis was edematous and hemorrhagic. The neural damage suggests a mechanism for the hearing loss that can follow otitis media. Absence of labyrinthitis and meningitis in grafted animals suggests a tympanogenic pathway for the bacteria.
Insights
Streptococcus pneumoniae can invade the inner ear through the round window membrane, causing neural damage and hearing loss in otitis media. Grafting the membrane prevented bacterial entry and subsequent labyrinthitis.
Area of Science:
- Otolaryngology
- Microbiology
- Pathology
Background:
- Otitis media can lead to serious complications like sensorineural hearing loss, labyrinthitis, and meningitis.
- The round window membrane is a known entry point for macromolecular substances into the inner ear, but its permeability to bacteria remains unclear.
Purpose of the Study:
- To investigate the permeability of the round window membrane to Streptococcus pneumoniae.
- To determine if bacterial entry through the round window membrane contributes to inner ear pathology following otitis media.
Main Methods:
- Bilateral inoculation of Streptococcus pneumoniae type 7F into the middle ears of chinchillas.
- Comparison between animals with and without grafted round window membranes.
- Microscopic examination (light and electron) of inner ear structures.
Main Results:
- Bacteria successfully penetrated all layers of non-grafted round window membranes.
- Inoculated bacteria reached all cochlear turns, entering neuronal pathways and causing nerve degeneration and hair cell damage.
- Animals with continuous round window membrane grafts showed no signs of labyrinthitis or meningitis.
Conclusions:
- The round window membrane is permeable to Streptococcus pneumoniae, providing a pathway for bacteria to reach the inner ear.
- Bacterial invasion via the round window membrane can cause significant neural damage and hair cell loss, explaining hearing loss associated with otitis media.
- Grafting the round window membrane effectively prevents bacterial translocation and subsequent inner ear inflammation.