Endolymphatic sac involvement in bacterial meningitis.

The commonest sequelae of bacterial meningitis are related to the inner ear. Little is known about the inner ear immune defense. Evidence suggests that the endolymphatic sac provides some protection against infection. A potential involvement of the endolymphatic sac in bacterial meningitis is largely unaccounted for, and thus the object of the present study. A well-established adult rat model of Streptococcus pneumoniae meningitis was employed. Thirty adult rats were inoculated intrathecally with Streptococcus pneumoniae and received no additional treatment. Six rats were sham-inoculated. The rats were killed when reaching terminal illness or on day 7, followed by light microscopy preparation and PAS-Alcian blue staining. The endolymphatic sac was examined for bacterial invasion and leukocyte infiltration. Neither bacteria nor leukocytes infiltrated the endolymphatic sac during the first days. Bacteria invaded the inner ear through the cochlear aquaduct. On days 5-6, the bacteria invaded the endolymphatic sac through the endolymphatic duct subsequent to invasion of the vestibular endolymphatic compartment. No evidence of direct bacterial invasion of the sac through the meninges was found. Leukocyte infiltration of the sac occurred prior to bacterial invasion. During meningitis, bacteria do not invade the endolymphatic sac through the dura, but solely through the endolymphatic duct, following the invasion of the vestibular system. Leukocyte infiltration of the sac occurs prior to, as well as concurrent with bacterial invasion. The findings support the endolymphatic sac as part of an innate immune defense system protecting the inner ear from infection.

The development of endolymphatic hydrops following CMV inoculation of the endolymphatic sac.

The effect of inoculation of cytomegalovirus (CMV) into the endolymphatic sac was examined in CMV-seronegative and seropositive animals. Seronegative animals developed hearing loss, infection in the epithelial cells of the endolymphatic sac and perisaccular connective tissue, and endolymphatic hydrops. Control animals inoculated with inactivated CMV showed no hearing loss, viral infection, or endolymphatic hydrops. Seropositive animals showed complete protection from hearing loss and viral infection, yet a monocytic infiltrate was seen surrounding the endolymphatic sac. Associated with this localized immune response was mild evidence of endolymphatic hydrops in 40% (2/5) of the animals. Control seropositive animals inoculated with inactivated CMV showed no hearing loss or morphological changes. CMV then, can infect cells of the endolymphatic sac resulting in hearing loss and endolymphatic hydrops. The immune response to CMV in seropositive animals is protective, but is associated with endolymphatic sac inflammation.