Deaf-mutism due to meningogenic labyrinthitis

Labyrinthitis ossificans: histopathologic consideration for cochlear implantation

Labyrinthitis ossificans may be a hindrance to cochlear implantation by making electrode insertion difficult. We performed a histopathologic study of 24 temporal bones with labyrinthitis ossificans from multiple causes. The organ of Corti was graphically reconstructed and the degree of obstruction was estimated for each millimeter of the cochlea. Correlations were calculated between the degree of new bone formation and the cause, patient's age and sex, and time from the original temporal bone insult. Our results demonstrate that complete cochlear ossification is rare. The scala tympani in the basal turn of the cochlea is the most frequent area of ossification, regardless of the cause of the labyrinthitis ossificans. Meningogenic labyrinthitis, usually a childhood disease, was associated with the greatest amount of ossification. When ossification resulted from tympanogenic labyrinthitis, the scala tympani was completely ossified near the round window niche in all temporal bones. Neo-ossification of the basal turn associated with otosclerosis was limited to the proximal 6 mm of the scala tympani in all cases. Three temporal bones had a patent round window niche and basal turn, but significant apical and middle-turn ossification. Peripheral sensorineural elements were severely degenerated in the region of the ossification in all specimens, and spiral ganglion cell counts were decreased.

Histopathology of profound sensorineural deafness

In all the cases of profound deafness that we examined, the sensory epithelium along the basilar membrane had severely degenerated. However, ganglion cell counts and peripheral fiber estimates demonstrated a high degree of variability when analyzed with respect to the state of the organ of Corti or the etiology of the original cochlear disorder. We conclude that a complex interplay of factors determines the number of cells remaining in the spiral ganglion at a given time. It appears impossible at present to predict which diseases or toxic states produce primarily a sensory loss while leaving a uniform and adequate number of cochlear neurons functionally intact. We would like to emphasize that although the ganglion cell counts were consistently reduced in all our cases of profound sensorineural deafness, it has always been a surprise to us to find that the actual numbers of surviving cells are considerable. Of 15 patients, all of whom were totally deaf, only 3 had ganglion cell counts less than 10,000, whereas the majority had counts well above 15,000. Observations of this kind are possible only if accurate ganglion cell counts are carried out. Estimating the number of spiral ganglion cells by only looking at microscopic sections usually results in estimates of greater cell loss than is actually present.

Later stages of development of the periotic duct and its adjacent area in the human fetus

The later stages of development (16-40 weeks in utero) of the periotic duct and its adjacent areas in the human fetus indicate that the critical stages of development occur in four specific time related stages over a six-week period (20-26 weeks). First, the petrous apex ossifies to separate th inferior cochlear vein into the canal of Cotugno and forms the medial wall of the cochlear aqueduct (22 weeks); second, the canalicular otic capsule fuses with the cochlear otic capsule to obliterate Hyrtl fissure and forms of the lateral wall of the cochlear aqueduct (24 weeks); third, progressive bone deposition to the medial surface of the membranous labyrinth and cochlea at the petrous apex elongates the periotic duct and cochlear aqueduct (32 weeks in utero); and fourth, active arachnoid tissue ingrowth into the periotic duct occurs at 20-24 weeks and 34-40 weeks in utero. The terminal event is widening of the CNS opening of the periotic duct at 32 weeks in utero. The periotic duct and cochlear aqueduct length increase with gestation from 25 weeks until term. The periotic duct width remains the same throughout the gestation. The cochlear aqueduct width diminishes with gestational age. The periotic duct remains patent throughout 16-40 weeks in utero.

Temporal bone histopathology in deafness due to cryptococcal meningitis

This paper reports on a patient who survived an attack of cryptococcal meningitis eight years prior to his death. A bilateral sensorineural hearing loss had been noted a short time before the patient was admitted to the hospital, and was the only complication after he recovered from the disease. Histopathologic study of the temporal bones showed a similar pattern of pathology in both ears, the most striking finding being a severe loss of spiral ganglion cells in Rosenthal's canal, and of cochlear nerve fibers in the osseous spiral lamina and internal auditory meatus. The vestibular nerve was mostly free from pathology. The organ of Corti was atrophic but the hair cell population appeared to be almost normal. A slight number of cryptococci were observed in limited areas of the cochlear and the saccular nerves in the internal auditory meatus. The severe pathology of the cochlear nerve was compatible with audiologic evaluations, which pointed to a retrocochlear lesion. Thus, this case demonstrates some characteristic aspects of cryptococcal infection of the temporal bone: The primary site of invasion was the cochlear nerve in the internal auditory meatus and the modiolus, leading to the loss of ganglion cells and nerve fibers, while the vestibular nerve appears to have been resistant to infection.

Radiologic diagnosis of labyrinthitis ossificans

Labyrinthitis ossificans is the pathological ossification of the membranous labyrinthine spaces in response to processes which are destructive of the membranous labyrinth or the endosteum of the otic capsule. It has been primarily a histopathologic diagnosis. Complex motion tomography however, allows a detailed view of the osseous labyrinth and permits the diagnosis in the living state. Radiologic documentation of labyrinthitis ossificans is objective evidence of a process destructive of the membranous labyrinth. It supports the likelihood of an absence of cochlear and vestibular function. It alerts the surgeon to the possible obliteration of key inner ear anatomical landmarks.

Hearing loss as a sequela of meningitis

A retrospective study of 547 cases of meningitis was performed. Of these, 236 were bacterial, 304 were viral, and 7 were fungal in etiology. Of 110 survivors of bacterial meningitis over the age of 2 1/2 years, 23 or 21% suffered partial or complete sensorineural hearing loss. The site of auditory injury in cases of partial loss was the cochlea by audiologic criteria. A positive correlation with hearing loss was found for the species of organism, delay before treatment, low CSF sugar, and CSF pleocytosis. Of 7 patients with fungal meningitis, 3 suffered hearing loss with signs of a retrocochlear site. Of 304 cases of aseptic meningitis, none developed a hearing loss. The pathophysiology of hearing loss as a sequela of meningitis and the possible explanations for absence of hearing loss in viral meningitis are discussed.

Studies on cochlear aqueduct patency

Complex studies on the patency of the cochlear aqueduct were made on 250 human cadavers and the temporal bones isolated from these, using a chemical method (staining reaction) as well as filling the aqueduct with fluid plastics and exposing the whole of its course under an operating microscope. The disappearance of patency in the cochlear aqueduct is a progressive phenomenon reflecting the biological process of aging in the organism. Patency of the cochlear aqueduct renders possible a two-way spread of infection from the cerebrospinal fluid (CSF) to the inner ear and vice versa, CSF otorrhea, and sudden sensorineural hearing inpairment through rises in CSF pressure, while in the absence of patency, the accumulation of harmful products of metabolism in the perilymph has a deleterious effect on the sensory elements of the inner ear.

Labyrinthitis ossificans due to chronic otitis media

Histopathology of two cases of unilateral labyrinthitis ossificans in the presence of bilateral chronic suppurative otitis media is presented. In both cases, ossification and fibrosis were limited to the scala tympani of the lower basal turn, apparently due to inflammation entering through the round window membrane. The round window was occluded by new bone and fibrous tissue presumably resulting in a conductive hearing loss in addition to the conductive loss due to middle ear lesions. Degeneration of the hair cells of the organ of Corti was limited to the lower basal turn where ossification and fibrosis occurred.