Histopathologic Evaluation of Vascular Findings in the Cochlea in Patients With Presbycusis

Importance  Age-related changes in cochlear vessel wall thickness in human temporal bones have not been described previously.

Objectives  To compare thickness of the spiral modiolar artery and strial capillaries and to investigate strial atrophy and vessel loss in temporal bones with and without presbycusis.

Design, Setting, and Participants  This retrospective case-control study examined the autopsy reports of 1024 patients in the temporal bone collection at the University of Minnesota. Inclusion criteria consisted of being 60 years or older with sensorineural hearing loss and progression of hearing loss with age (presbycusis group). Age-matched controls had no record of hearing loss. All patients underwent pure-tone audiometry. Exclusion criteria included a history of otologic disease, ototoxic drug use, head or acoustic trauma, or systemic disease. Data were collected from October 1, 2013, to October 1, 2014.

Main Outcomes and Measures  Vessel wall thickness in the modiolar artery and strial vessels, the strial area, and number of strial vessels were measured under light microscopy.

Results  Among the 1024 autopsy reports examined, 11 patients (19 temporal bones) with presbycusis (7 men and 4 women; age range, 67-88 years; mean [SD] age, 78 [7] years]) and 15 controls (24 temporal bones) (7 men and 8 women; age range, 67-94 years; mean [SD] age, 79 [8] years) met the inclusion criteria. Compared with the control group, the presbycusis group had significantly increased mean (SD) thickness of vessel walls in the modiolar arteries (6.73 [2.39] vs 5.55 [0.86] μm; P = .02) and the strial capillaries in the lower basal (1.57 [0.21] vs 1.39 [0.15] μm; P = .005), upper basal (1.62 [0.28] vs 1.40 [0.13] μm; P < .001), lower middle (1.68 [0.22] vs 1.39 [0.20] μm; P < .001), upper middle (1.74 [0.39] vs 1.40 [0.19] μm; P = .01), and apical (1.70 [0.36] vs 1.47 [0.21] μm; P = .04) turns of the cochlea. Compared with the control group, the presbycusis group had significant loss of strial area in the lower basal (6614 [1559] vs 8790 [1893] μm²; P = .002), upper basal (6387 [2211] vs 9105 [2700] μm²; P < .001), lower middle (5140 [1471] vs 7269 [2181] μm²; P = .003), upper middle, (5583 [1742] vs 7206 [2258] μm²; P = .02), and apical (4286 [1604] vs 6535 [2454] μm²; P < .001) turns of the cochlea; in the vessel area in the lower basal turn (74.65 [127.74] vs 124.92 [89.04] μm²; P = .01); and in the number of vessels in the lower basal (1.00 [0.78] vs 1.94 [0.93]; P = .008) and lower middle (1.00 [0.78] vs 1.94 [0.93]; P = .04) turns of the cochlea.

Conclusions and Relevance  The histopathologic findings of increased thickness of the vascular walls of the modiolar arteries and stria vascularis, increased strial atrophy, and decreased number of strial vessels may have led to decreased cochlear microcirculation. Deficiency in the circulation and perfusion of the cochlea may be a factor in presbycusis.

Presbycusis, or age-related hearing loss, exerts a substantial socioeconomic impact, with more than 25% of people 50 years or older affected.¹ This loss manifests itself in difficulty with sound localization and speech discrimination. The cause of presbycusis is still unclear but is hypothesized to be the result of cumulative intrinsic and extrinsic damage. Intrinsic factors contributing to presbycusis include mitochondrial DNA mutation, genetic disorders, such as acute hemorrhagic leukoencephalitis; hypertension; diabetes mellitus; metabolic diseases; and other systemic diseases. Extrinsic factors include noise, use of ototoxic drugs, and diet.² The pathologic changes associated with presbycusis have been described as degeneration of hair cells,^3-5 spiral ganglion cells,^4-6 and stria vascularis.^5,7-10

Normal auditory function depends on the maintenance of inner ear fluid homeostasis by the stria vascularis. Animal studies suggested that strial atrophy is associated with thickening of the basement membrane in the strial capillaries.^11-13 However, to our knowledge, age-related changes in the thickness of vessel walls have not been previously described in human studies. We conducted a quantitative analysis of age-related histopathologic changes of the stria vascularis and vessel walls in the cochlea using a sample of human temporal bones. We hypothesized that in patients with presbycusis, the strial capillaries will have an increased vessel wall thickness and the area of the stria vascularis will be decreased compared with patients with normal hearing.

We screened the autopsy reports of 1024 patients from the temporal bone collection at the University of Minnesota to select cases with presbycusis. Inclusion criteria for the presbycusis group included age of at least 60 years, a diagnosis of sensorineural hearing loss characterized by insidious onset, bilateral symmetry, and progression of hearing loss into old age. Control individuals were selected using medical records and otologic interview sheets. Inclusion criteria for the control group consisted of age of at least 60 years, no clinical evidence of other ear disorders, and no description of hearing loss in the medical record. Pure-tone audiometry had been performed between 5 months and 18 years before death for all participants. We excluded individuals from both groups if they had a history of otologic diseases, such as otosclerosis or otitis media; ototoxic drug use; head or acoustic trauma; or systemic diseases, such as diabetes mellitus or neurologic disease. A diagnosis of atherosclerosis was noted. A total of 19 temporal bones from 11 patients with presbycusis and 24 temporal bones from 15 age-matched controls met the inclusion criteria. This study was approved by the institutional review board of the University of Minnesota.

Data were collected from October 1, 2013, to October 1, 2014. All temporal bones had been removed at autopsy and fixed in formalin solution. Each bone was 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 and mounted on a glass slide for assessment with light microscopy. Samples were observed in a double-blinded method, and randomly selected samples were checked for intraobserver and interobserver reliability.

Morphometric measurement of the wall of the spiral modiolar artery, a main end artery providing cochlear blood flow, was performed in perpendicular cross sections. The vessel that was most perpendicularly sectioned was chosen in each sample. Morphometric measurement of the thickness of the capillary walls of the stria vascularis was made in all turns of the cochlea at the midmodiolar level and on the adjacent 2 sections. Images were acquired using a digital camera (DS-Ri1; Nikon) connected to a personal computer. Thickness of the vessel walls was measured using image analysis software (NIS-Elements BR, version 4.20; Nikon Instruments, Inc) and calculated using a modification of the method described by Robison et al.¹⁴

The vessel wall area (VWA) and vessel wall length (VWL) per vessel cross section were determined using the following formulae:

VWA = T − Luand

VWL = (Outer Length of Lines Delimiting VWA + Inner Length of Lines Delimiting VWA)/2,where T indicates the total cross-sectional area of each vessel and Lu indicates the luminal area. Vessel wall thickness in each vessel is expressed as VWA/VWL.

Morphometric measurements of the stria vascularis, including area counts, vessel area, and total number of vessels, were performed in all turns of the cochlea at the midmodiolar level and 2 adjacent sections. The areas of vessels and the total number of vessels in each turn were counted as the mean of these 3 sections. The image was acquired with a digital camera connected to a personal computer. The calibrated image of the stria vascularis was obtained at an original magnification of ×200, and the area of the vessels was quantified at an original magnification of ×600. Measurements were performed using commercially available image analysis software (NIS-Elements BR, version 4.20). Secondary changes, such as cysticlike structural areas and concretions, were excluded from the analysis. The number of vessels in each cochlear turn was counted.

Data were analyzed from October 1 to December 15, 2014. Unless otherwise indicated, results were presented as mean (SD). Statistical evaluation was performed with the nonparametric Mann-Whitney test. The level of significance was set at P < .05. Correlations were calculated with the Spearman rank correlation coefficient.

Eleven patients with presbycusis (7 men and 4 women; age range, 67-88 years; mean [SD] age,78 [7] years) and 15 age-matched controls (7 men and 8 women; age range, 67-94 years; mean [SD] age, 79 [8] years) were included in the analysis. Clinical records were positive for atherosclerosis in 10 of the 11 case patients with presbycusis and in 14 of the 15 controls.

Vessel walls of the spiral modiolar artery were thicker in patients with presbycusis than in controls (Figure 1A). Vessel wall thicknesses of the spiral modiolar artery are shown in Figure 1B. The mean vessel wall thickness was 6.73 (2.39) μm in the presbycusis group compared with 5.55 (0.86) μm in the control group. A statistically significant difference in vessel wall thickness was observed between the 2 groups (P = .02).

Overall, the presbycusis group had significantly greater thickening of the capillaries and vessel walls in the turns of the cochlea compared with the control group (Figure 2). Mean vessel wall thickness of the lower basal turn was 1.57 (0.21) μm in the presbycusis group compared with 1.39 (0.15) μm in the control group (P = .005). Mean vessel wall thickness of the upper basal turn was 1.62 (0.28) μm in the presbycusis group compared with 1.40 (0.13) μm in the control group (P < .001). Mean vessel wall thickness in the lower middle turn was 1.68 (0.22) μm in the presbycusis group compared with 1.39 (0.20) μm in the control group (P < .001); in the upper middle turn, 1.74 (0.39) μm in the presbycusis group compared with 1.40 (0.19) μm in the control group (P = .01); and in the apical turn, 1.70 (0.36) μm in the presbycusis group and 1.47 (0.21) μm in the control group (P = .04).

We found a significant loss of stria vascularis area in the turns of the cochlea in the presbycusis group compared with the control group (Figure 3). The mean area in the lower basal turn was 6614 (1599) μm² in the presbycusis group compared with 8790 (1893) μm² in the control group (P = .002); in the upper basal turn, 6387 (2211) μm² in the presbycusis group compared with 9105 (2700) μm² in the control group (P < .001); in the lower middle turn, 5140 (1471) μm² in the presbycusis group compared with 7269 (2181) μm² in the control group (P = .003); in the upper middle turn, 5583 (1743) μm² in the presbycusis group compared with 7206 (2258) μm² in the control group (P = .02); and in the apical turn, 4286 (1604) μm² in the presbycusis group compared with 6535 (2455) μm² in the control group (P < .001) (Figure 4).

We found a significant loss of vessel area in the stria vascularis in the presbycusis group compared with the control group in the lower basal turn of the cochlea (74.65 [127.64] vs 124.92 [89.04] μm²; P = .01). No significant difference was found in the other turns. The mean areas of capillaries in each turn were 73.90 (107.40) μm² in the presbycusis group and 95.33 (90.46) μm² in the control group for the upper basal turn, 65.62 (84.06) μm² in the presbycusis group and 82.65 (105.25) μm² in the control group for the lower middle turn, 90.42 μm² (119.23) in the presbycusis group and 110.97 (110.38) μm² in the control group for the upper middle turn, and 66.59 (66.33) μm² in the presbycusis group and 103.62 (76.00) μm² in the control group for the apical turn (Figure 5A).

The mean number of vessels in the presbycusis group was significantly smaller than that of the control group in the lower basal (1.00 [0.78] vs 1.94 [0.93]; P = .008) and lower middle (0.81 [0.69] vs 1.43 [1.05]; P = .04) turns of the cochlea. No significant difference was found in the other turns. The mean number of vessels was 0.89 (0.88) in the presbycusis group and 1.39 (1.07) in the control group for the upper basal turn, 0.82 (0.72) in the presbycusis group and 1.35 (0.79) in the control group for the upper middle turn, and 0.88 (0.57) in the presbycusis group and 1.31 (0.71) in the control group for the apical turn (Figure 5B). Interobserver and intraobserver reliability on randomly selected cases showed no significant difference.

Thickening of capillary basal membrane has been reported to occur in several organs with aging.^15-17 Thickening of the vessel walls of the inner ear in models of aged animals¹¹ has been reported previously. In the present study, we showed a significant increase in thickness of the walls of the spiral modiolar arteries and the capillaries of the stria vascularis in patients with presbycusis.

The cochlea is supplied by the spiral modiolar artery and the cochlear branch of the vestibulocochlear artery, which are the terminal branches of the inner ear artery.¹⁸ Circulatory disturbance induced by microvascular problems may be a main factor underlying sensorineural hearing loss in patients with presbycusis because it occurs, for example, in individuals with diabetes mellitus.^19-21 Our findings revealed that the cochlear microcirculation is affected in patients with presbycusis.

The blood-labyrinth barrier is thought to be an important homeostatic mechanism that protects the delicate ionic balance within the labyrinth. Like other barrier systems (the blood-brain barrier, blood–cerebrospinal fluid barrier, and blood–aqueous humor barrier), tight junctions within capillaries of the stria vascularis form the morphologic site of the blood-labyrinth barrier and prevent the passage of substances from blood into the fluid of the inner ear.²² Thickened vessel walls in patients with presbycusis may compromise the function of this barrier.

Atherosclerosis is one of the main causes of age-related hearing loss. A previous study showed that elderly people with arteriosclerosis have worse hearing than people of the same age without arteriosclerosis.²³ The mean number of spiral ganglion cells in the cochlea with generalized arteriosclerosis was significantly less than that in healthy controls in the basal turn.²⁴ In a mouse model of arteriosclerosis, the cochlea had degeneration and the spiral modiolar artery had a thickened intima.²⁵

However, endothelial impairment from atherosclerosis does not fully explain the development of angiopathy in patients with presbycusis. We checked the medical and autopsy records for atherosclerosis. Most of our case patients with presbycusis and most of the controls had atherosclerosis; therefore, we suggest that arteriosclerosis alone is not the cause of thickening.

The present study showed that the number of vessels in the stria vascularis of case patients with presbycusis was significantly decreased compared with those of control. Although we do not know the reason for the decrease in the number of vessels and atrophy of the stria vascularis, an association between these 2 findings with presbycusis may exist.

Our present findings demonstrate that the area of the stria vascularis in patients with presbycusis was significantly decreased compared with that in controls. Schuknecht and Gacek²⁶described degeneration of the stria vascularis as the most common morphologic characteristic of age-related hearing loss, based on their observations of human temporal bones. Recent morphometric analysis of human temporal bones also supported this hypothesis.⁵

The stria vascularis is essential for generating positive endocochlear potential, which is necessary for auditory hair cell function.^27,28 Strial atrophy causes degeneration of hair cells by alteration of endolymph composition.⁷

We found a significant loss of area in the capillaries of the stria vascularis in the presbycusis group compared with the control group in the lower basal turn of the cochlea. The narrowing of the vessel lumen area may cause failure of blood flow. The disorder of blood flow may be the cause of the atrophy.

The thickness of the cochlear vessel wall and capillaries in the stria vascularis were increased in case patients with presbycusis. The present study also showed that atrophy of the stria vascularis, which decreased the area of the vessels, and the smaller number of vessels in the stria vascularis are more common in case patients with presbycusis than in controls. Further studies with a larger patient population are necessary to confirm these results. Based on the findings of our study, we can speculate that deficiency in the circulation and perfusion of the cochlea might be one of the factors leading to hearing impairment with aging.

Corresponding Author: Sebahattin Cureoglu, MD, Department of Otolaryngology, University of Minnesota, 2001 Sixth St SE, Mail LRB 210, MMC2873, Minneapolis, MN 55455 (cureo003@umn.edu).

Submitted for Publication: May 26, 2015; final revision received September 10, 2015; accepted November 3, 2015.

Published Online: January 7, 2016. doi:10.1001/jamaoto.2015.3163.

Author Contributions: Dr Kurata had full access to all the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.

Study concept and design: All authors.

Acquisition, analysis, or interpretation of data: Kurata, Cureoglu.

Drafting of the manuscript: Kurata.

Critical revision of the manuscript for important intellectual content: All authors.

Statistical analysis: Kurata.

Obtained funding: Kurata.

Administrative, technical, or material support: Kurata, Schachern.

Study supervision: Schachern, Paparella, Cureoglu.

Conflict of Interest Disclosures: None reported.

Funding/Support: This study was supported by grant U24 DC011968 from the National Institute on Deafness and Other Communication Disorders, National Institutes of Health; by the International Hearing Foundation; by 5M Lions International; and by the Starkey Foundation.

Role of the Funder/Sponsor: The funding sources had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; and decision to submit the manuscript for publication.

Additional Contributions: Monika Schachern, BS, and Tamika Kennedy, BS (Department of Otolaryngology, University of Minnesota, Minneapolis), provided technical support. Both were compensated for this role.