Causes
See the list below:
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The most common cause of labyrinthitis ossificans (LO) is bacterial infection of the inner ear that results in suppurative labyrinthitis. Bacterial invasion of the labyrinth can occur via 3 routes: hematogenic spread through the cochlear vasculature, a sequela to otitis media that passes through the round window membrane, or meningogenic spread from the subarachnoid space in meningitis. Labyrinthitis ossificans associated with meningitis is seen in the image below.
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Based on data from 1995, the 3 most common organisms responsible for bacterial meningitis in the United States are H influenzae (0.2 cases per 100,000 population), S pneumoniae (1.1 cases per 100,000 population), and Neisseria meningitidis (0.6 cases per 100,000 population). With the success of conjugate vaccines in preventing invasive H influenzae type b (Hib) disease, S pneumoniae has become the leading cause of bacterial meningitis in the United States. Children younger than 1 year have the highest incidence of pneumococcal meningitis (approximately 10 cases per 100,000 population).
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Woolley et al performed a retrospective study of 432 patients with meningitis and determined that 59 (13.7%) developed hearing loss. [12] Forty-six (78%) of these children with hearing loss had stable auditory thresholds over time, and 13 (22%) exhibited deterioration or fluctuation of acuity over time. The authors determined that significant predictors of future hearing loss included increased intracranial pressure (revealed with CT scan), male sex, low cerebrospinal fluid glucose levels, S pneumoniae as a causative organism, and the presence of nuchal rigidity.
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The cells and mechanisms responsible for ossification in labyrinthitis ossificans (LO) are unknown; however, several hypotheses have been proposed.
In 1967, Paparella and Sugiura hypothesized that bone-lining cells of the cochlea are pluripotent mesenchymal stem cells that remain uncommitted until stimulated to differentiate into osteoblasts. [5]
In 1985, Kotzias and Linthicum hypothesized that this type of bone originates from osteoblasts within the otic capsule. [13] They suggested that ectopic bone forms on the endosteal layer after inflammatory insult, but the bone is not incorporated beyond the surface.
Additionally, pericytes associated with blood vessels that supply the modiolus and spiral ligament fibroblasts have been hypothesized as cells of origin.
In an antemortem analysis of labyrinthitis ossificans (LO) in a human case report, metaplastic bone was reported to have formed within serofibrinous exudate; however, the cell of origin for the osteoneogenesis has not been identified. Because the new bone deposition occurs in continuity with endosteal bone, postmortem studies are not able to differentiate metaplastic bone from osteoplastic bone within the cochlea. The cells and mechanisms responsible for ossification in labyrinthitis ossificans (LO) remain undefined.
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Fibrosis and ossification of the scala tympani are shown. F, fibrosis; O, osteoneogensis (hematoxylin and eosin stain).
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Stages of ossification are shown. This histological specimen was obtained 3 months after induction of labyrinthitis. F, fibrosis; O, osteoid; C, calcospherite deposition (calcification); B, normal endochondral bone. (hematoxylin and eosin stain)
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Ossification of the scala tympani is shown.
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Labyrinthitis ossificans is depicted with right cochlea enhancement.
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Labyrinthitis ossificans is shown on axial CT scan.
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Labyrinthitis ossificans associated with meningitis is shown.
