Electron Microscopic Temporal Bone Histopathology in Experimental Pneumococcal Meningitis

Abstract

Bacterial meningitis is one of the most common causes of acquired profound sensorineural deafness in children. Measurement of hearing and examination of the cochlea is limited in patients suffering from acute meningitis. A rabbit model of pneumococcal meningitis was developed to identify the temporal bone histopathologic changes that occur in meningogenic labyrinthitis caused by Streptococcus pneumoniae. Light microscopy was previously performed on temporal bones from acutely meningitic rabbits with profound hearing loss as determined electrophysiologically. Extensive inflammation of the cochlea with endolymphatic hydrops was observed. The organ of Corti, however, showed preserved architecture in the majority of these animals. In order to further investigate these findings, a protocol was used to create meningitic rabbits with hearing loss ranging from early high-frequency loss to profound deafness. The temporal bones from 7 rabbits were examined by transmission electron microscopy. In cases of mild hearing loss, partial degeneration of the inner row of outer hair cells, as well as edema of efferent cochlear nerve endings and marginal cells of the stria vascularis, was seen. With increasing degrees of hearing loss, the remainder of the organ of Corti and intermediate cells of the stria showed ultrastructural abnormalities. Spiral ganglion cells and basal cells of the stria vascularis remained intact in all subjects. This study provides unique information regarding the histology and pathophysiology of meningogenic deafness. The clinical implications of these findings are discussed, with an emphasis on potentially reversible changes and therapeutic intervention.

Doxycycline Reduces Mortality and Injury to the Brain and Cochlea in Experimental Pneumococcal Meningitis

“…If this is the case, the withdrawal of neurotrophins normally produced by the hair cells might further aggravate neuron loss in the spiral ganglion (30). This hypothesis is supported by the fact that significant differences in the neuron density of the spiral ganglion between infected and mockinfected animals can only be observed weeks after the cured infection (20,37). Together, our results support further investigation of the beneficial effects of adjunctive doxycycline on the loss of spiral ganglion neurons caused by bacterial meningitis.…”

Meningitis‐associated hearing loss: Protection by adjunctive antioxidant therapy

“…Damage to the organ of Corti is a wellrecognized event during suppurative labyrinthitis, 12,13,37 and hair cell loss can induce spiral ganglion neuronal death due to inactivity. 38,39 Therefore, it is conceivable that peroxynitrite-mediated damage to hair cells can indirectly lead to neuronal loss in the spiral ganglion and thus to permanent meningitis-associated hearing loss.…”

Nitrogen and Oxygen Molecules in Meningitis-Associated Labyrinthitis and Hearing Impairment

“…Using electron microscopy, severe damage to the organ of Corti could be demonstrated in cochlea of guinea pigs and rabbits with meningitis-associated hearing loss [18,32]. In more detail, partial degeneration of the inner row of outer hair cells with craters of the apical surface and disruption of inner hair cell stereociliae was seen.…”

“…Besides structural damage of the spiral limbus, the spiral ligament, and the stria vascularis that was seen by light microscopy [20,32], functional damage of the blood-labyrinth barrier during bacterial meningitis-associated labyrinthitis was detected by the systemic administration of the tracer substance Evans blue. Evans blue is bound to albumin and therefore, it does not cross an intact blood-brain or blood-labyrinth barrier [33,34].…”