Abstract
Purpose
To determine histopathological findings in the cochlea of human temporal bones with serous labyrinthitis.
Materials and methods
We compared human temporal bones with serous labyrinthitis (20 cases) associated with silent otitis media and without serous labyrinthitis (20 cases) to study location of serous labyrinthitis, the degree of endolymphatic hydrops, number of spiral ganglion cells and hair cells, loss of fibrocytes in the spiral ligament, and areas of the spiral ligament and stria vascularis.
Results
The serous labyrinthitis caused significant loss of outer hair cells in the lower basal ( P = 0.006), upper basal ( P = 0.005), and lower middle ( P = 0.011) cochlear turns, and significant increase in the degree of endolymphatic hydrops than the control group ( P = 0.036). No significant difference was found in the loss of inner hair cells, in the number of spiral ganglion cells and fibrocytes in the spiral ligament, and in areas of the stria vascularis and spiral ligament ( P > 0.05).
Conclusions
Serous labyrinthitis resulted in significant loss of outer hair cells and significant increase in the degree of endolymphatic hydrops.
1
Introduction
Middle ear inflammation and interaction between the middle and inner ears can cause inner ear damage and hearing loss secondary to otitis media. Serous labyrinthitis (SL) is an inflammation of the labyrinth in the absence of bacteria, or viruses . The underlying problems of serous labyrinthitis may include cochlear damage due to middle and inner ear interaction, perilymph contamination during surgery, the presence of inflammatory mediators (meningogenic/otogenic), perilymph fistula, or neoplasia . SL and some other inner ear complications can occur due to otitis media when bacterial products, viruses, and inflammatory mediators enter the inner ear through the round window membrane . In this study, we investigated histopathological changes in human temporal bones with SL. In contrast to widespread opinion , our hypothesis is that SL can cause permanent pathologic damage in the cochlea.
2
Materials and methods
We obtained samples from the human temporal bone collection at the University of Minnesota. All temporal bones had previously been removed at autopsy, fixed in formalin solution, decalcified, embedded in celloidin, and serially sectioned in the horizontal plane at a thickness of 20 μm. Every 10th section was stained with hematoxylin–eosin (H&E) and mounted on a glass slide for light-microscopic observation. This study was approved by the institutional review board of the University of Minnesota (0206M26181).
We specifically defined SL as the presence of serous fluid in the labyrinth, with fibrous or granular precipitate in the inner ear in the absence of bacteria, viruses, or inflammatory cells. Silent otitis media has been described as a chronic pathologic condition behind an intact tympanic membrane . For our study, we selected only temporal bones from patients with SL associated with silent otitis media. We excluded temporal bones from patients who had a history of acoustic trauma, meningitis, systemic autoimmune disorders, otosclerosis, Meniere’s disease, or metastatic tumors, because all of those conditions can contribute to changes in the inner ear.
The SL group included 20 temporal bones from 16 patients (12 men and 4 women) associated with silent otitis media; their age ranged from 5 months to 88 years (mean, 31.4 ± 27.6 years). The control group included 20 temporal bones from 16 healthy patients (9 men and 7 women) who did not have SL; their age ranged from 4 days to 64 years (mean, 37.3 ± 20.5 years). We investigated the location of SL in the inner ear, the degree of endolymphatic hydrops, the number of spiral ganglion cells and hair cells, mean loss of fibrocytes in spiral ligament, and the areas of the stria vascularis and spiral ligament.
2.1
Spiral ganglion cells
We divided Rosenthal’s canal into 4 segments as described previously: segment I (from base to 6 mm); II (6 to 15 mm); III (15 to 22 mm) and IV (22 mm to apex) . All nuclei were counted in each section. The number of ganglion cells was determined for each segment and for the cochlea as a whole by multiplying their summed counts by 10 to account for the unmounted sections and by a factor of 0.9 to account for cells that would be counted because of their location at the interface between sections.
2.2
Hair cells
We assessed the presence of outer and inner hair cells in each cochlear turn. The percentage loss of cochlear hair cells was counted to compare 2 groups.
2.3
Endolymphatic hydrops
We subdivided our temporal bone samples according to the degree of endolymphatic hydrops, per the classification of Cureoglu et al. ; (1) slight hydrops, i.e., bulging of Reissner’s membrane without contact with the bony wall of the scala vestibuli; (2) moderate hydrops, i.e., displacement of Reissner’s membrane with contact with the wall of the scala vestibuli but with an angle with the osseous spiral lamina of less than 90 degrees; and (3) profound hydrops, i.e., displacement of Reissner’s membrane with bony contact, with an angle with the osseous spiral lamina of more than 90 degrees.
2.4
Stria vascularis
In all of the cochlear turns at the midmodiolar level, as well as on the adjacent 2 sections, we obtained morphometric measurements of the stria vascularis. We acquired each image with a digital camera at a magnification of × 200. Using a computer, we quantified the areas of the cut surfaces of the stria vascularis. For the measurements, we used image analyses software (SPOT Advanced, SPOT Imaging Solutions, Sterling Heights, MI). Excluded from the area of the stria vascularis were any secondary changes, such as cystic-like structural areas or concretions.
2.5
Spiral ligament
We subdivided the spiral ligament into 4 segments according to the appearance of different types of fibrocytes, per previous studies by Spicer and Schulte : Type I fibrocytes lie circumferentially aligned between the stria vascularis and bone. Type II fibrocytes occupy the superficial inferior spiral ligament between the basilar crest and the stria. Type III fibrocytes are longitudinally located in the deepest part of the inferior spiral ligament. Type IV fibrocytes lie radially oriented, inferior to the basilar crest.
To estimate and evaluate the mean loss of fibrocytes in the spiral ligament, we used a rating scala: 0, within normal limits (missing less than 1/3 of the fibrocytes); 1, missing 1/3 of the fibrocytes; 2, missing 2/3 of the fibrocytes; and 3, severe or complete loss of the fibrocytes on sections at the midmodiolar level, per the methods of Hequembourg and Liberman . The calibrated image was obtained at an original magnification of × 40.
Morphometric measurements of spiral ligament’s area were made in all turns of the cochlea at the midmodiolar level and the adjacent two sections. The image was obtained with a charge-coupled device camera that was connected to a personal computer. The calibrated image was obtained at an original magnification of × 40. The areas of spiral ligament were quantified by determining the areas of their cut surfaces, with the aid of the computer. Measurements were made using commercially available image analysis software (SPOT Advanced, SPOT Imaging Solutions, Sterling Heights, MI).
2.6
Statistical analysis
To analyze any differences between the temporal bones with the SL and the control groups, we used Student t test. Significance was defined as P < 0.05.
2
Materials and methods
We obtained samples from the human temporal bone collection at the University of Minnesota. All temporal bones had previously been removed at autopsy, fixed in formalin solution, decalcified, embedded in celloidin, and serially sectioned in the horizontal plane at a thickness of 20 μm. Every 10th section was stained with hematoxylin–eosin (H&E) and mounted on a glass slide for light-microscopic observation. This study was approved by the institutional review board of the University of Minnesota (0206M26181).
We specifically defined SL as the presence of serous fluid in the labyrinth, with fibrous or granular precipitate in the inner ear in the absence of bacteria, viruses, or inflammatory cells. Silent otitis media has been described as a chronic pathologic condition behind an intact tympanic membrane . For our study, we selected only temporal bones from patients with SL associated with silent otitis media. We excluded temporal bones from patients who had a history of acoustic trauma, meningitis, systemic autoimmune disorders, otosclerosis, Meniere’s disease, or metastatic tumors, because all of those conditions can contribute to changes in the inner ear.
The SL group included 20 temporal bones from 16 patients (12 men and 4 women) associated with silent otitis media; their age ranged from 5 months to 88 years (mean, 31.4 ± 27.6 years). The control group included 20 temporal bones from 16 healthy patients (9 men and 7 women) who did not have SL; their age ranged from 4 days to 64 years (mean, 37.3 ± 20.5 years). We investigated the location of SL in the inner ear, the degree of endolymphatic hydrops, the number of spiral ganglion cells and hair cells, mean loss of fibrocytes in spiral ligament, and the areas of the stria vascularis and spiral ligament.
2.1
Spiral ganglion cells
We divided Rosenthal’s canal into 4 segments as described previously: segment I (from base to 6 mm); II (6 to 15 mm); III (15 to 22 mm) and IV (22 mm to apex) . All nuclei were counted in each section. The number of ganglion cells was determined for each segment and for the cochlea as a whole by multiplying their summed counts by 10 to account for the unmounted sections and by a factor of 0.9 to account for cells that would be counted because of their location at the interface between sections.
2.2
Hair cells
We assessed the presence of outer and inner hair cells in each cochlear turn. The percentage loss of cochlear hair cells was counted to compare 2 groups.
2.3
Endolymphatic hydrops
We subdivided our temporal bone samples according to the degree of endolymphatic hydrops, per the classification of Cureoglu et al. ; (1) slight hydrops, i.e., bulging of Reissner’s membrane without contact with the bony wall of the scala vestibuli; (2) moderate hydrops, i.e., displacement of Reissner’s membrane with contact with the wall of the scala vestibuli but with an angle with the osseous spiral lamina of less than 90 degrees; and (3) profound hydrops, i.e., displacement of Reissner’s membrane with bony contact, with an angle with the osseous spiral lamina of more than 90 degrees.
2.4
Stria vascularis
In all of the cochlear turns at the midmodiolar level, as well as on the adjacent 2 sections, we obtained morphometric measurements of the stria vascularis. We acquired each image with a digital camera at a magnification of × 200. Using a computer, we quantified the areas of the cut surfaces of the stria vascularis. For the measurements, we used image analyses software (SPOT Advanced, SPOT Imaging Solutions, Sterling Heights, MI). Excluded from the area of the stria vascularis were any secondary changes, such as cystic-like structural areas or concretions.
2.5
Spiral ligament
We subdivided the spiral ligament into 4 segments according to the appearance of different types of fibrocytes, per previous studies by Spicer and Schulte : Type I fibrocytes lie circumferentially aligned between the stria vascularis and bone. Type II fibrocytes occupy the superficial inferior spiral ligament between the basilar crest and the stria. Type III fibrocytes are longitudinally located in the deepest part of the inferior spiral ligament. Type IV fibrocytes lie radially oriented, inferior to the basilar crest.
To estimate and evaluate the mean loss of fibrocytes in the spiral ligament, we used a rating scala: 0, within normal limits (missing less than 1/3 of the fibrocytes); 1, missing 1/3 of the fibrocytes; 2, missing 2/3 of the fibrocytes; and 3, severe or complete loss of the fibrocytes on sections at the midmodiolar level, per the methods of Hequembourg and Liberman . The calibrated image was obtained at an original magnification of × 40.
Morphometric measurements of spiral ligament’s area were made in all turns of the cochlea at the midmodiolar level and the adjacent two sections. The image was obtained with a charge-coupled device camera that was connected to a personal computer. The calibrated image was obtained at an original magnification of × 40. The areas of spiral ligament were quantified by determining the areas of their cut surfaces, with the aid of the computer. Measurements were made using commercially available image analysis software (SPOT Advanced, SPOT Imaging Solutions, Sterling Heights, MI).
2.6
Statistical analysis
To analyze any differences between the temporal bones with the SL and the control groups, we used Student t test. Significance was defined as P < 0.05.
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