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Bacterial Invasion of the Inner Ear in Association With Pneumococcal Meningitis

Møller, Martin Nue*; Brandt, Christian; Østergaard, Christian; Caye-Thomasen, Per

doi: 10.1097/MAO.0000000000000305
Basic Science

Objective To examine the pathways of bacterial invasion and subsequent spreading in the inner ear during pneumococcal meningitis.

Study Design A well-established adult rat model of Streptococcus pneumoniae meningitis was used.

Methods Thirty rats were inoculated intrathecally with S. pneumoniae serotype 1, 3 or 9 V and received no additional treatment. The rats were sacrificed when reaching terminal illness or on Day 7 and then prepared for serial sectioning and PAS-Alcian blue staining for light microscopy.

Results During the first few days after inoculation, bacteria invade the inner ear through the cochlear aqueduct, into the scala tympani of the cochlea (perilymphatic space). From here, bacteria spreads apically toward the helicotrema and subsequently basally through the scala vestibuli, toward the vestibule and the vestibular system. When the bacteria after 5 to 6 days had reached scala vestibuli of the basal turn of the cochlea, hematogenous spreading occurred to the spiral ligament and into the cochlear endolymph, subsequently to the vestibular endolymph. We found no evidence of alternative routes for bacterial invasion in the inner ear. Several internal barriers to bacterial spreading were found within the inner ear. Bacterial elimination was evidenced by engulfment by macrophages within the inner ear.

Conclusion From the meninges, pneumococci invade the inner ear through the cochlear aqueduct during the first days of infection, whereas hematogenous invasion via the spiral ligament capillary bed occur at later stages. Although internal barriers exist within the inner ear, the spreading of bacteria occurs via the natural pathways of the fluid compartments. Bacterial elimination occurs by local macrophage engulfment.

*Department of Oto-Rhino-Laryngology, Head and Neck Surgery, University Hospital, Rigshospitalet/Gentofte, Copenhagen; †Department of Infectious Diseases, Copenhagen University Hospital Hvidovre; ‡Department of Clinical Microbiology, Copenhagen University Hospital Hvidovre, Hvidovre; and §The Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen Denmark

Address correspondence and reprint requests to Martin Nue Møller, M.D., Department of Oto-Rhino-Laryngology, Head and Neck Surgery, University Hospital, Rigshospitalet/Gentofte, 2100 Copenhagen, Denmark; E-mail:

Disclosure: The authors report no conflicts of interest.

Copyright © 2014 by Otology & Neurotology, Inc. Image copyright © 2010 Wolters Kluwer Health/Anatomical Chart Company