Pathology of otosclerosis: a review

Automated detection of otosclerosis with interpretable deep learning using temporal bone computed tomography images

Objective

This study aimed to develop an automated detection schema for otosclerosis with interpretable deep learning using temporal bone computed tomography images.

Methods

With approval from the institutional review board, we retrospectively analyzed high-resolution computed tomography scans of the temporal bone of 182 participants with otosclerosis (67 male subjects and 115 female subjects; average age, 36.42 years) and 157 participants without otosclerosis (52 male subjects and 102 female subjects; average age, 30.61 years) using deep learning. Transfer learning with the pretrained VGG19, Mask RCNN, and EfficientNet models was used. In addition, 3 clinical experts compared the system's performance by reading the same computed tomography images for a subset of 35 unseen subjects. An area under the receiver operating characteristic curve and a saliency map were used to further evaluate the diagnostic performance.

Results

In prospective unseen test data, the diagnostic performance of the automatically interpretable otosclerosis detection system at the optimal threshold was 0.97 and 0.98 for sensitivity and specificity, respectively. In comparison with the clinical acumen of otolaryngologists at P < 0.05, the proposed system was not significantly different. Moreover, the area under the receiver operating characteristic curve for the proposed system was 0.99, indicating satisfactory diagnostic accuracy.

Conclusion

Our research develops and evaluates a deep learning system that detects otosclerosis at a level comparable with clinical otolaryngologists. Our system is an effective schema for the differential diagnosis of otosclerosis in computed tomography examinations.

Dynamic Molecular Markers of Otosclerosis in the Human Cochlea

OBJECTIVE

To investigate the role and distribution of various molecular markers using immunohistochemistry and immunofluorescence to further elucidate and understand the pathogenesis of otosclerosis.

METHODS

Archival celloidin formalin-fixed 20-micron thick histologic sections from 7 patients diagnosed with otosclerosis were studied and compared to controls. Sections in the mid-modiolar region were immunoreacted with rabbit polyclonal antibodies against nidogen-1, β2-laminin, collagen-IX, BSP, and monoclonal antibodies against TGF β-1 and ubiquitin. Digital images were acquired using a high-resolution light and laser confocal microscope.

RESULTS

Nidogen-1, BSP, and collagen-IX were expressed in the otospongiotic regions, and to lesser extent, in the otosclerotic regions, the latter previously believed to be inactive. β2-laminin and ubiquitin were uniformly expressed in both otospongiotic and otosclerotic regions. There was a basal level of expression of all of these markers in the normal hearing and sensorineural hearing loss specimens utilized as control. TGF β -1, however, though present in the otosclerosis bones, was absent in the normal hearing and sensorineural hearing loss controls.

CONCLUSIONS

Our results propose that the activity and function of TGF-1 may play a key role in the development and pathogenesis of otosclerosis. Further studies utilizing a higher number of temporal bone specimens will be helpful for future analysis and to help decipher its role as a potential target in therapeutic interventions.

Whether cochlea involvement on CT in otosclerosis patients impacts the effect of stapedotomy

BACKGROUND

The success rate of stapedotomy in otosclerosis patients with cochlea involvement was unknown.

AIMS/OBJECTIVES

To determine the difference of surgical outcomes and symptomatology in otosclerosis patients with or without cochlea involvement on CT.

MATERIAL AND METHODS

79 otosclerosis patients were included and grouped by HRCT, including cochlear-involved otosclerosis (C-group) or non-cochlear-involved otosclerosis (NC-group, control group). Patients were defined as NC-group in the presence of normal or solely fenestral involvement, or C-group if the hypodensities involve other parts of the labyrinthine bone Patients in the control group were collected at a 2:1 ratio to the C-group with similar follow-up times. Detailed complaints and surgical outcomes were compared between these groups.

RESULTS

Chief complaints were similar in the C-group and NC-group. Although postoperative AC, BC, and ABG decreased significantly in both groups, the success rate was significantly higher in C-group regarding the postoperative ABG ≤10 dB. Furthermore, diffuse lesions may indicate a more severe disease and a poorer prognosis.

CONCLUSIONS AND SIGNIFICANCE

Stapedotomy was effective for clinical otosclerosis. The surgical outcome was inferior favorable for cochlea involvement patients, especially for cases with widely involvement. There was no difference in chief complaints among patients with different CT degree of otosclerosis.

Utility of deep learning for the diagnosis of otosclerosis on temporal bone CT

OBJECTIVE

Diagnosis of otosclerosis on temporal bone CT images is often difficult because the imaging findings are frequently subtle. Our aim was to assess the utility of deep learning analysis in diagnosing otosclerosis on temporal bone CT images.

METHODS

A total of 198 temporal bone CT images were divided into the training set (n = 140) and the test set (n = 58). The final diagnosis (otosclerosis-positive or otosclerosis-negative) was determined by an experienced senior radiologist who carefully reviewed all 198 temporal bone CT images while correlating with clinical and intraoperative findings. In deep learning analysis, a rectangular target region that includes the area of the fissula ante fenestram was extracted and fed into the deep learning training sessions to create a diagnostic model. Transfer learning was used with the deep learning model architectures of AlexNet, VGGNet, GoogLeNet, and ResNet. The test data set was subsequently analyzed using these models and by another radiologist with 3 years of experience in neuroradiology following completion of a neuroradiology fellowship. The performance of the radiologist and the deep learning models was determined using the senior radiologist's diagnosis as the gold standard.

RESULTS

The diagnostic accuracies were 0.89, 0.72, 0.81, 0.86, and 0.86 for the subspecialty trained radiologist, AlexNet, VGGNet, GoogLeNet, and ResNet, respectively. The performances of VGGNet, GoogLeNet, and ResNet were not significantly different compared to the radiologist. In addition, GoogLeNet and ResNet demonstrated non-inferiority compared to the radiologist.

CONCLUSIONS

Deep learning technique may be a useful supportive tool in diagnosing otosclerosis on temporal bone CT.

KEY POINTS

• Deep learning can be a helpful tool for the diagnosis of otosclerosis on temporal bone CT. • Deep learning analyses with GoogLeNet and ResNet demonstrate non-inferiority when compared to the subspecialty trained radiologist. • Deep learning may be particularly useful in medical institutions without experienced radiologists.

The role of imaging in the diagnosis and management of otosclerosis

OBJECTIVE

To examine the evidence for the role of radiologic imaging in the diagnosis and management of otosclerosis.

DATA SOURCES

A review of contemporary (1990 to present) English medical literature via MedLine using the terms imaging, otosclerosis, otospongiosis, stapes surgery, computed tomography, magnetic resonance, CT, and MRI was performed.

STUDY SELECTION

Abstracts were reviewed independently by 2 authors and relevant articles were then evaluated. Exclusion criteria included editorials, non-English language, comments, and letters.

DATA EXTRACTION

Level of evidence was assigned in accordance with the Oxford Centre for Evidence-based Medicine guidance (Levels I-V).

RESULTS

Thirty-seven articles met the inclusion criteria, of which, 11 were of Level III, 22 of Level IV, and 4 of level V evidence. High-resolution computed tomography (CT) of the temporal bones is the imaging technique of choice in the diagnosis of otosclerosis with newer multidetector scanners demonstrating a sensitivity and specificity in excess of 90%. There is Level III evidence that CT densitometry and extent of disease on CT correlates with hearing thresholds. Extensive and multifocal disease on CT has a poorer prognosis (Level III/IV). The potential use of CT in staging classifications, surgical planning, predicting surgical outcomes and risk of complications has also been described and evaluated.

CONCLUSION

This systematic review indicates that imaging has a useful role in both the diagnosis and management of otosclerosis, supported principally by Level III/IV evidence.

The radiological diagnosis of fenestral otosclerosis: the utility of histogram analysis using multidetector row CT

Bone density measurements using high-resolution CT have been reported to be useful to diagnose fenestral otosclerosis. However, small region of interest (ROI) chosen by less-experienced radiologists may result in false-negative findings. Semi-automatic analysis such as CT histogram analysis may offer improved assessment. The aim of this study was to evaluate the utility of CT histogram analysis in diagnosing fenestral otosclerosis. Temporal bone CT of consecutive patients with otosclerosis and normal controls was retrospectively analyzed. The control group consisted of the normal-hearing contralateral ears of patients with otitis media, cholesteatoma, trauma, facial nerve palsy, or tinnitus. All CT images were obtained using a 64-detector-row CT scanner with 0.5-mm collimation. AROI encompassing 10 × 10 pixels was placed in the bony labyrinth located anterior to the oval window. The mean CT value, variance and entropy were compared between otosclerosis patients and normal controls using Student's t test. The number of pixels below mean minus SD in the control (%Lowcont) and total subjects (%Lowtotal) were also compared. In addition, the area under the receiver operating characteristic curves (AUC) value for the discrimination between otosclerosis patients and normal controls was calculated. 51 temporal bones of 38 patients with otosclerosis and 30 temporal bones of 30 control subjects were included. The mean CT value was significantly lower in otosclerosis cases than in normal controls (p < 0.01). In addition, variance, entropy, %Lowcont and %Lowtotal were significantly higher in otosclerosis cases than in normal controls (p < 0.01, respectively). The AUC values for the mean CT value, %Lowcont and %Lowtotal were 0.751, 0.760 and 0.765, respectively. In conclusion, our results demonstrated that histogram analysis of CT image may be of clinical value in diagnosing otosclerosis.

Otosclerosis of the incus

OBJECTIVE

To report a case of a patient with otosclerosis of the incus.

PATIENTS

A 61-year-old woman with a progressive hearing loss on her left ear and a computed tomographic scan of the temporal bone revealing an expansible lesion of the incus.

INTERVENTIONS

The ossicle was removed by using a transtympanomastoid approach; the ossicular chain was reconstructed using a titanium partial ossicular replacement prosthesis.

MAIN OUTCOME MEASURE

The diagnosis of the disease was obtained by means of histopathologic examination of the specimen.

RESULTS

The patient obtained a good postoperative hearing result. The histopathologic examination of the specimen documented an otosclerosis of the incus.

CONCLUSION

Otosclerotic involvement of the middle ear ossicles, apart from footplate, was very rarely mentioned. Most subjects were incidentally diagnosed postmortem by means of examination of specimens from temporal bone collections. The diagnosis and treatment of a patient with otosclerosis of the incus is exceptional; however, otosclerosis should be considered in the differential diagnosis of expansible lesions of the ossicles.

Relationship between CT densitometry with a slice thickness of 0.5 mm and audiometry in otosclerosis

The appropriate cutoff Hounsfield unit (HU) value for the diagnosis of otosclerosis was determined and the correlation between the bone conduction threshold and the findings of computed tomography (CT) densitometry investigated. CT images, 0.5-mm thick, were evaluated in 24 ears with otosclerosis and 19 control ears. Eight regions of interest were set around the otic capsule. The mean HU values in the area anterior to the oval window (A-OW) and anterior to the internal auditory canal (A-IAC) were significantly lower in otosclerosis than in controls. Based on receiver operating characteristic (ROC) analysis, the cutoff HU value in A-OW was determined to be 2,187.3 HU. The mean HU value in retrofenestral otosclerosis was significantly lower in the area A-OW, A-IAC and around the cochlea than in controls. Based on ROC analysis, the cutoff HU value in the latter was determined to be 2,045 HU. A statistically significant correlation was found between the density of the area A-OW and the hearing level at 500 and 1,000 Hz, and between the density of the area around the cochlea and the hearing level at most frequencies. These results suggest the semi-automated diagnosis of otosclerosis may be possible.

Increased Activity of the Diastrophic Dysplasia Sulfate Transporter in Otosclerosis and Its Inhibition by Sodium Fluoride

HYPOTHESIS

This study investigates the function of the diastrophic dysplasia sulfate transporter (DTDST) in otosclerotic bone and the effect on it of sodium fluoride (NaF).

BACKGROUND

Otosclerosis is a localized bone dystrophy with increased bone turnover. DTDST is implicated in the regulation of the bone turnover.

MATERIALS AND METHODS

Primary cultures of cells were obtained from the stapes and external auditory canal (EAC) of 26 patients with otosclerosis and from nine control patients. Sulfate uptake was quantified under basal conditions and with NaF. The NaF signaling pathways were investigated using forskolin and verapamil.

RESULTS

The relative initial rates of sulfate uptake and the apparent Vmax values were: otosclerotic stapes > EAC > control stapes = control EAC. The sulfate uptake by the otosclerotic stapes was correlated with the loss of sensorineural hearing. The amounts of DTDST mRNA (RNase protection assay) in the four subgroups did not differ. NaF (10(-6)M, 1 hr) inhibited sulfate uptake by the otosclerotic stapes and EAC cells but not by control samples.

CONCLUSION

The authors believe that whether the increased DTDST activity is a cause or an effect of otosclerosis, it appears to be a specific target for NaF treatment.

Histologic changes on stapedial footplate in otosclerosis. Correlations between histologic activity and clinical findings

OBJECTIVE

To quantify the relationship between the stage of histologic changes of the stapedial footplate in otosclerosis and the magnitude of preoperative hearing loss, tinnitus, vestibular disorder, and postoperative improvement of hearing.

STUDY DESIGN

Retrospective case review.

SETTING

Tertiary referral center.

PATIENTS

The study included 97 patients (ears) (69 female and 28 male patients), with conductive or mixed hearing loss who were operated on for otosclerosis. The criterion for including a patient in the study was otosclerosis established by tympanoscopy and confirmed by histologic examination of a piece of the stapedial footplate.

MAIN OUTCOME MEASURES

By the histologic features of the stapedial footplate fragments, the stage of the otosclerotic lesion was classified as spongiotic, fibrotic, or sclerotic. The patients were carefully matched for sex, age, duration of hearing impairment, presence of tinnitus, and vestibular symptoms. Preoperative and postoperative air-conduction and bone-conduction thresholds were calculated as an average of four frequencies (0.5, 1, 2, and 4 kHz). Analysis was subsequently carried out on the preoperative and postoperative air-bone gap and bone-conduction threshold improvement.

RESULTS

With regard to the histologic stage of otosclerotic lesions, tinnitus and vestibular disorders were present more frequently in patients with the sclerotic type of lesion. The type of otosclerotic lesion had no significant influence on the mean preoperative air-conduction threshold, bone-conduction threshold, and air-bone gap or on postoperative air-conduction threshold and bone-conduction threshold, but the postoperative air-bone gap was higher in patients with the fibrotic type of otosclerotic lesion and was highest in patients with the spongiotic type of otosclerotic lesion (p < 0.01).

CONCLUSIONS

Tinnitus, vestibular disorders, and better postoperative closure of the air-bone gap are present more frequently in patients with a sclerotic type of otosclerotic lesion on the stapedial footplate.

Middle ear dynamic characteristics in patients with otosclerosis

OBJECTIVE

To investigate the middle ear dynamic characteristics in patients with otosclerosis using the sweep frequency impedance meter (SFI test) and conventional tympanometry, and also to evaluate the diagnostic efficiency of the SFI test for otosclerosis.

DESIGN

The study was designed to collect a total of 25 (36 ears) consecutive patients with otosclerosis. All subjects followed a clinical protocol, which consisted of a hearing problem questionnaire, otoscopic examination, and audiometric measurements. These included pure tone audiometry, conventional tympanometry, and SFI test.

RESULTS

In the SFI test, the middle ear dynamic characteristics were measured in terms of the resonance frequency and middle ear mobility. Three distinct categories of middle ear dynamic characteristics were found in patients with otosclerosis, i.e., high stiffness, normal stiffness, and low stiffness middle ear status. On comparison of the results of SFI with conventional tympanometry, a significantly higher percentage of abnormal stiffness was found when using the SFI test than that when using conventional tympanometry.

CONCLUSIONS

The present findings confirm the advantage of the SFI test over conventional tympanometry in detecting middle ear status and mechanics in patients with otosclerosis. Moreover, different middle ear dynamic characteristics in patients with otosclerosis are most likely to be related to the different stages of the pathological changes.

Glycosaminoglycan metabolism and cytokine release in normal and otosclerotic human bone cells interleukin-1 treated

Glycosaminoglycans (GAGs), normal components of the extracellular matrix (ECM), and the glycosidases, that degrade them, play a key role in the bone remodelling process. The effects of interleukin-1 alpha (IL-1 alpha) on GAG metabolism in normal and otosclerotic human bone cells as well as its capacity to modulate IL-1 alpha, IL-1 beta and IL-6 secretion in both populations was analyzed. The amount of radiolabeled GAGs was lower in otosclerotic than in normal bone cells. IL-1 alpha reduced newly synthesized cellular and extracellular GAGs in normal cells, but only those of the cellular compartment in otosclerotic bone cells. It depressed heparan sulphate (HS) more in normal cells and chondroitin sulphate (CS) more in otosclerotic bone cells. The HA/total sulphated GAG ratio was shifted in favour of the latter in otosclerotic cells, whereas the opposite effect was seen after IL-1 alpha treatment. There was little difference in the beta-D-glucuronidase levels of the normal and pathological cells, while beta-N-acetyl-D-glucosaminidase was significantly increased in otosclerotic bone cells. As the activity of neither enzyme was modified by treatment with IL-1 alpha, the cytokine seems to exert its influences on GAG synthesis rather than on the degradation process. IL-1 alpha, IL-1 beta and IL-6 secretion was markedly higher in otosclerotic cells. IL-1 alpha modulated the secretion of each interleukin differently, thus resulting in a cytokine cascade that may act in autocrine/paracrine manner on target cells. The authors suggest that changes in the cytokine network may have a specific, yet still unknown, role during normal and pathological osteogenesis.

Risedronate activity in the fetal and neonatal mouse

Otosclerosis, chronic otitis media with and without cholesteatoma, and Paget's disease of bone are just a few of the many diseases of the ear that exhibit abnormalities of bone modeling and remodeling. These diseases result in chronic infection, vestibular dysfunction, and hearing loss. Bisphosphonates are a promising new class of drugs potentially useful in the treatment of these disorders. Currently used in diseases with high rates of bone turnover (Paget's disease of bone, hypercalcemia of malignancy, and osteoporosis), they have been found to be strong inhibitors of bone resorption. A third generation bisphosphonate, 2-(3-pyrindyl)-hydroxyethylidene bisphosphonate (risedronate) is being investigated for toxicity, increased efficacy, and oral administration. In this study the in vitro and in vivo anti-resorptive activity of risedronate was quantified by measuring calcium release in a neonatal mouse calvarial culture system. This model was used to test direct in vitro effects, in vivo exposure in neonatal mice, and the possible effects of in utero and lacteal exposure. Calcium release activated by parathyroid hormone (PTH) was significantly inhibited when risedronate was only present in the pre-incubation media. When risedronate was administered subcutaneously to neonatal mice it resulted in a significant decrease in PTH-activated calcium release in explanted calvaria in vitro. Transplacental and lactational transfer of biologically effective risedronate was not demonstrated in this study; however, a paradoxic increase in PTH-stimulated calcium release in vitro from calvaria theoretically exposed transplacentally and lacteally was noted. This effect was unexplained by the data.

Composition of the otosclerotic stapes: electron microprobe analyses

For the first time, otosclerotic stapes have been distinguished from unafflicted controls at a high level of significance by using a spectrum of elements measured by energy-dispersive spectrometer-electron probe microanalyses (EDS/EPMA). Discriminant analyses of the maximum concentration of 13 elements measured at several sites within each of 32 stapes differentiated otosclerotic from unafflicted individuals well above the 95% confidence level. Eight of the 9 control (unafflicted) and 21 of the 23 afflicted stapes were correctly classified. In descending order of contribution to the discriminant function, the elements are Zn > Cr > K > Ca > Si > Mn > Na > Al > Mg > P > Fe > S > Ti. Zinc and chromium account for much of the difference, but discriminant analyses excluding them still distinguish the two groups at the 95% confidence level. These results are consistent with previous reports of high levels of alkaline phosphatase, a zinc-containing enzyme, in afflicted stapes. But the broad spectrum of elements capable of distinguishing otosclerotic stapes warrants study of additional zinc-containing and other metal-containing or metal-activated moieties.

Distribution of bone remodeling units in the otic capsule of the rabbit. A semiquantitative morphometric study

Distribution of bone remodeling units (BRU) in relation to the perilymphatic space was studied in undecalcified temporal bones from adult rabbits labeled in vivo with bone-seeking fluorochromes. Based on recordings of focal bone formation, relative densities of BRUs inside concentric tissue zones around the inner ear spaces were estimated. Zonal densities of BRUs were found to decline towards the perilymphatic space, lending further support to the existence of a local inner ear mechanism in control of capsular bone tissue dynamics. The possible nature of this mechanism is considered briefly with special reference to inner ear electromechanic activity.

Ibuprofen inhibits localized bone resorption in the middle ear

Localized osteoclastic bone resorption plays a significant role in the pathogenesis of several diseases of the middle ear as well as orthodontic tooth movement and long bone remodeling. The mechanisms of control of localized bone loss and systemic bone resorption may be different but both may be mediated by a final common pathway which includes prostaglandins. Prostaglandins seem to have a predominantly stimulatory effect on bone resorption, although the exact mechanism is poorly understood. Ibuprofen, a nonsteroidal antiinflammatory drug, is known to inhibit the synthesis of prostaglandins. It is likely that ibuprofen, through its inhibition of prostaglandin synthesis, would decrease the localized osteoclastic bone resorption in a previously described animal model system. Mongolian gerbils were divided into three groups: low dose ibuprofen (10 mg/kg per day), high dose ibuprofen (30 mg/kg per day), and a control group. Following surgical implantation of catheters to the right bullae of each gerbil, pressure was applied for 8 days, stimulating osteoclastic bone resorption. After killing the animals and histomorphometric analysis of the bullae from each, comparisons were made between each group using osteoclast surface (percentage of bone area covered by osteoclasts), osteoclast number (number of osteoclasts/mm bone length), and osteoclast profile area (in microns2). Significantly lower osteoclast surface (Oc.S/BS) was found in pressurized bullae from both treatment groups when compared with pressurized bullae from controls (P less than 0.05) and significantly lower osteoclast number (N.Oc/T.L) in pressurized bullae from both treatment groups when compared with pressurized bullae from controls (P less than 0.05). These differences were found to be dose-dependent.(ABSTRACT TRUNCATED AT 250 WORDS)

Otic capsule bony lesions in the Palmerston North autoimmune mouse

Otosclerosis is an otic capsule disorder of unknown etiology. While autoimmunity has been proposed as part of the etiopathogenesis of otosclerosis, no spontaneous autoimmune disease animal model has been identified. In the Palmerston North mouse, a model for systemic lupus erythematosus, sclerotic lesions consistently develop within the modiolus that are correlated with systemic autoimmune disease symptoms. No lesions were seen in 2-month-old mice, which is before autoimmune disease onset at 4 months. Lesions were first seen in mice at 6 to 8 months of age and increased in size and frequency thereafter. By 20 months, all ears examined had the otic capsule lesions, which were primarily perivascular in location and composed of both noncellular and cellular elements. The noncellular material was globular to fibrillar in arrangement and stained positively for calcium. The associated cells appeared to be metabolically active fibroblasts. It is proposed that the Palmerston North mouse may serve as a model to further investigate the role of autoimmunity in otosclerosis and other forms of otic capsule osteogenesis.

Inhibition of osteoclast recruitment at a local site by 1-hydroxyethylidene-1,1-bisphosphonate (HEBP)

We hypothesized that bisphosphates, a class of antiosteolytic drugs that affect bone cells, may block localized bone modeling in the middle ear. Prior studies have shown that transmitted pressure in the middle ear leads to osteoclastic bone resorption. Catheters were surgically implanted into the middle ear cavity (bulla) of 31 Mongolian gerbils. The animals were then divided into two groups, one subset receiving a bisphosphonate, and the other receiving no drug. Positive air pressure was applied to one middle ear, and the other side served as a control. At the end of the experimental period, tissue specimens were obtained, and histomorphometric evaluation of the ventral bullae was performed. Significant differences in osteoclast surface, osteoclast number, and mean individual osteoclast profile area led us to conclude that administration of the bisphosphonate used at the dose studied inhibits localized recruitment and activation of osteoclasts.

Osteoclasts in chronic otitis media, cholesteatoma, and otosclerosis

Bone resorption and remodeling are characteristic of chronic otitis media with and without cholesteatoma and otosclerosis. The consequences of this remodeling process may be hearing loss, repeated infection, vestibular disturbance, or intracranial complications. Evidence of osteoclastic bone resorption was found in surgical specimens of 11 of 24 cases of cholesteatoma, two of three cases of chronic otitis media, and three of ten cases of otosclerotic stapes; all three spongiotic lesions had osteoclasts. With careful serial sectioning these cells are almost always multinucleate and have the typical appearance of osteoclasts with ruffled borders. Some specimens had evidence of bone erosion in the absence of osteoclasts; this finding represents an inactive phase of the remodeling process. Since the osteoclast plays an important role in the resorption and remodeling of bone in these middle ear diseases, the source, physiology, and local control of these cells are of prime importance in investigating the pathophysiology of these diseases. At the present time, the local control of activation and recruitment of osteoclasts, as well as their chemotactic responses, is poorly understood.

New concepts in bone remodeling: an expanding role for the osteoblast

Until recently, the prevailing view regarding the function of osteoblasts and osteoclasts was to attribute bone formation to the former and bone resorption to the latter. While the capacity of the osteoclast to degrade bone matrix remains unquestioned, there is now provocative evidence indicating that the osteoblast plays a critical role in regulating osteoclast resorptive activity as well as in contributing directly to matrix dissolution. The first of these points follows from observations indicating that the osteoblast (but not the osteoclast) 1) exhibits receptors and/or responses to resorption-promoting agents (including parathyroid hormone and vitamin D), and 2) releases agents capable of stimulating bone resorption. The second point is derived from studies demonstrating that the osteoblast produces neutral collagenase (an enzyme specialized to degrade type I collagen, the principal organic constituent of bone matrix) and an inhibitor capable of blocking collagenase activity. The synthesis of both of these proteins is, in part, regulated by parathyroid hormone and other resorption-stimulating agents and appears to involve control at the transcriptional, translational, and secretory levels. Thus, in both physiologic bone remodeling and modeling, as well as the altered bone turnover associated with some disease states, it is the osteoblast rather than the osteoclast that may hold the key to understanding the mechanism of tissue form and function.