Human Temporal Bone Study Research Articles

Blockage of longitudinal flow in Meniere's disease: A human temporal bone study

Conclusion: Blockage of the endolymphatic duct is a significant finding in Meniere's disease. The position of the utriculo-endolymphatic valve (UEV) and blockage of the ductus reuniens in the temporal bones were not found to be directly indicative of Meniere's disease. Objective: Comparison of blockage of the longitudinal flow of endolymph between ears affected by Meniere's disease and normal ears. Methods: We examined 21 temporal bones from 13 subjects who had Meniere's disease and 21 normal temporal bones from 12 controls. Results: The endolymphatic duct was blocked in five (23%) ears affected by Meniere's disease (p = 0.016). The utricular duct was blocked in 16 (76%) ears affected by Meniere's disease and 11 (52%) normal ears (p = 0.112). The saccular duct was blocked in 6 (28%) of ears affected by Meniere's disease and 16 (76%) normal ears (p = 0.001). The ductus reuniens was blocked in 10 (47%) ears affected by Meniere's disease and 10 (47%) normal ears (p = 1.000).

Round Window Insertion of Precurved Perimodiolar Electrode Arrays

The goal of this human temporal bone study was to assess the safety and efficacy of round window insertion of the Cochlear Contour Advance electrode and identify any anatomic obstacles that may affect its insertion. Minimizing intracochlear trauma during electrode insertion reduces the risk of losing residual hearing. The Contour Advance electrode is designed for insertion via an anteroinferior cochleostomy, in which drilling causes a degree of inner ear trauma. If consistently successful round window insertions are possible with this electrode, it would allow for better perimodiolar positioning in the basal turn and greater likelihood of hearing preservation. A total of 16 human temporal bone round window insertions with the Contour Advance electrode were performed at the University of Melbourne and Southwestern Medical Center, Dallas. Surgeons' observations, fluoroscopy, histology and anatomic dissections were analyzed. Successful full insertions of the electrode with minimal resistance and good perimodiolar placement were achieved in less that 50% of cases in the Melbourne series and in two-thirds of cases in the Dallas series. A common finding by both centers was obstruction of electrode entry at the anteroinferior margin of the round window, which prevented optimal scala tympani positioning and often resulted in intracochlear trauma. The anteroinferior region of the round window bony margin influences the trajectory of insertion of the relatively large Contour Advance electrode as well as physically obstructing and distorting the array. A pure round window insertion is not predictable and reliable enough to be a recommended approach for this electrode.

CO2 laser fiber soft cochleostomy: Development of a technique using human temporal bones and a guinea pig model

A novel approach for creating a soft cochleostomy has been described using a handheld CO(2) laser hollow waveguide from termed in the following the handheld CO(2) laser fiber. The effects on cochlear function have been studied in an animal model and were compared to the effects of the micro drill. Combined human temporal bone and experimental animal study. Four human temporal bones were used to describe the technique to create a cochleostomy using the handheld CO(2) laser fiber. A cochleostomy was made by thinning the cochlear wall with a motorized drill and by creating an opening with the CO(2) laser fiber. Eighteen guinea pigs were used to investigate the effects of the CO(2) laser and the drill on cochlear function. An electrode was placed in the round window niche to measure compound action potentials (CAPs). Baseline cochlear function was determined by recording CAP thresholds evoked by acoustic tone pips and was re-assessed during and after a cochleostomy was made. The protocol was repeated using a diamond-burr drill technique. The handheld CO(2) laser fiber is an ideal tool to create cochleostomies under 1 mm in diameter. In the guinea pig animal model, CAP thresholds showed little change after creating the cochleostomy at 4 W laser power setting and revealed focal threshold elevations averaging 32 dB at higher laser power settings. The human temporal bone study introduces a novel surgical approach for soft cochleostomies that uses both the drill and the CO(2) laser fiber. Threshold elevations, which were observed after making the cochleostomy with the laser, compared favorably to the diamond burr technique.

R447 – Temporal Bone Histopathology in Acute Lymphocytic Leukemia

Problem There are reports of hearing loss, tinnitus, and/or vertigo in patients with leukemia. However, there is no human temporal bone study of a large number of cases specific to acute lymphocytic leukemia. We studied the correlation between clinical otologic complaints and temporal bone histopathology in patients with this disease. Methods Clinical otologic complaints and histologic findings were evaluated in 13 patients (25 temporal bones) with acute lymphocytic leukemia. Results Nine patients had a history of clinical otologic complaints including: hearing loss in 5 patients; otalgia in 3; otorrhea in 3; and dizziness in 2. Hemorrhage was seen most commonly in the middle ear in 10 patients, but was also evident in the cochlea in 5 and the vestibular labyrinth in 2. Leukemic infiltration was observed in the petrous apex in 12 patients, in the middle ear in 6, the cochlea in 5, the vestibular labyrinth in 2 and the internal auditory canal in 3. Inflammatory cell infiltration was also seen in the cochlear labyrinth in 4 patient, the vestibular labyrinth in 5 and the modiolus in 1. Otitis media with hyperplasia of subepithelial fibrous tissue was seen in 10 patients. Three patients had granulation tissue extending into the middle ear or mastoid. Conclusion Ear involvement is a common finding in patients with acute lymphocytic leukemia. Significance With prolonged survival due to new chemotherapeutics, the diagnosis and treatment of non-hematopoietic system complications such as ear problems due to acute lymphocytic leukemia have become more important. Support International Hearing Foundation, Hubbard Foundation, Starkey Foundation.

Effect of absence of malleus on ossiculoplasty in human temporal bones

We evaluated the effect of malleus presence or absence on middle ear sound transmission after middle ear reconstruction in a temporal bone model. Human cadaveric temporal bone study. The velocity of the stapes footplate was measured using a laser Doppler vibrometer. After baseline measurements in eight intact temporal bones, reconstructed middle ear transmission with and without the malleus was analyzed. Furthermore, to assess the influence of interposed cartilage, cartilage pieces of three different diameters were inserted and the three test conditions compared. Reconstruction without a malleus tended to be slightly worse at 0.6 to 3.0 kHz. However, these differences were not statistically significant. In the cartilage experiments, the large-diameter cartilage was the worst at 0.25 kHz and 0.5 kHz but was better than the medium-diameter cartilages at 3.0 kHz and 4.0 kHz (P < 0.05). Absence of the malleus impaired middle ear sound transmission slightly in the mid frequencies compared to reconstruction with the malleus present; the differences were not statistically significant.

Human Temporal Bone Consortium for Research Resource Enhancement

Knowledge of the pathologic basis of disease is central to the study of medicine. Otology is unique because the inner ear is inaccessible during life so that conventional techniques of pathologic studies such as biopsy and surgical excision are not feasible. Hence, insight into the pathologic basis of ear disease within the 3-dimensional framework of the inner ear and its surroundings can be obtained only by postmortem study of temporal bones and by developing better animal models. Improved understanding of the pathology and pathogenesis of auditory and vestibular system disorders will lead to more rational diagnosis and management of these disorders. The procurement, processing, and study of human temporal bones are time consuming and costly and is a research endeavor performed in the few existing temporal bone laboratories.

Tympanic Membrane Collagen Fibers: A Key to High‐Frequency Sound Conduction

To investigate the significance of tympanic membrane collagen fiber layers in high frequency sound transmission. Human cadaver temporal bone study. Laser Doppler vibrometry was used to measure stapes footplate movement in response to acoustic stimulation. The tympanic membrane was altered by creating a series of slits and applying paper patches to isolate the effects of specifically oriented collagen fibers. Three groups of membrane alterations were evaluated: 1) circumferentially oriented slits involving each quadrant to primarily disrupt radial fibers, made sequentially within superior-anterior, inferior-anterior, inferior-posterior, and superior-posterior quadrants; 2) the same slits made in the reverse order; and 3) radially oriented slits from the umbo to the annulus to primarily disrupt circumferential fibers. For each group, measurements of the middle-ear cavity pressure, ear canal pressure, and stapes velocity were made each time the tympanic membrane was altered. Regardless of the order in which the circumferentially oriented slits were made, there was a consistent decrease in stapes velocity above 4 kHz for the third and fourth cuts compared to the control. The mean decrease in the range of 4 to 12.5 kHz was 11 dB for the third patched slit and 14 dB for the fourth patched slit (P < .01). Radially oriented slits appear to produce smaller effects. Radial collagen fibers in the tympanic membrane play an important role in the conduction of sound above 4 kHz.

Human Temporal Bone Consortium for Research Resource Enhancement

Knowledge of the pathologic basis of disease is central to the study of medicine. Otology is unique because the inner ear is inaccessible during life, so that conventional techniques of pathologic studies such as biopsy and surgical excision are not feasible. Hence, insight into the pathologic basis of ear disease within the three-dimensional framework of the inner ear and its surroundings can be obtained only by postmortem study of temporal bones and by developing better animal models. Improved understanding of the pathology and pathogenesis of auditory and vestibular system disorders will lead to more rational diagnosis and management of these disorders. The procurement, processing, and study of human temporal bones are time consuming and costly and is a research endeavor performed in the few existing temporal bone laboratories.

Bacterial meningitic deafness: historical development of epidemiology and cellular pathology

Meningitis resulting in labyrinthitis and its associated hearing loss was first described by several authors during 1864 and 1865 but it was not integrated into the otological cannon until H. Knapp's publications of 1871. These reports were incorporated by St John Rossa in his textbook of 1873. Politzer, in 1882, included a fuller description of the clinical symptoms. Analysis of records of the etiologies of students in 90 schools for the deaf in North America from 1817 to 1893 showed that before the mid-1870s meningitis was rarely identified as an etiology (<1%) but by the 1880s it accounted for 10–20% of all etiologies, with male preponderance. Cellular pathology of meningitic labyrinthitis from the 1860s to the 1990s examined the ways in which bacteria invaded the inner ear. Human temporal bone studies were a major source of understanding of the pathological processes. Honda, in 1927, injected guinea pigs intracranially with live bacteria, and observed the effects on the membranous labyrinth. In 1988 Lebel's observation of the effectiveness of dexamethasone in preventing much deafness from meningitis stimulated the examination of the labyrinthine immune response. Immunological mechanisms can account for some of the variable morbidity of unilateral, progressive, less-than-severe deafness.

The Effect of Organ of Corti Loss on Ganglion Cell Survival in Humans

Severe spiral ganglion cell loss does not necessarily follow loss of hair cells or supporting cells in humans. Despite some publications to the contrary, statements that loss of hair cells and/or supporting cells of the organ of Corti results in a severe loss of spiral ganglion cells in humans still appear in the literature, especially in respect to cochlear implants. This assumption is apparently based on studies in animals or cell culture and not from studies of human temporal bones. Morphological analysis of archival temporal bones with microscopic and statistical analysis of ganglion cell, hair cell, and supporting cell populations was performed in 33 ears with total hearing losses of varying causes and durations of deafness. None of the ears had remaining hair cells. Six ears had had cochlear implants. Ganglion cell counts ranging from 2,889 to 34,299 and the corresponding percentage of remaining ganglion cells based on age-normative data were not significantly related to the duration of hearing loss (r = -0.13 and 0.02, respectively, p > 0.05) or to remaining supporting cell populations (r's from 0.15 to 0.27, p > 0.05). More than half of ears (51.5%) had ganglion cell counts within two standard deviations of age-normative means. Mean ganglion cell counts and percentage of remaining ganglion cells of ears with surviving peripheral processes (dendrites) did not differ significantly from those of ears with no peripheral processes. The loss of hair and supporting cells in the organ of Corti in humans does not necessarily result in as significant a loss of spiral ganglion cells as has been reported animals. In fact, our results suggest that ganglion cell loss may be a primary concomitant loss due to the disease process.

Association Between Cupular Deposits and Otosclerosis

To evaluate whether otosclerosis is an underlying mechanism for the production of cupular deposits and to study the association between cupular deposits and dysequilibrium in otosclerosis. Retrospective human temporal bone (TB) study. The incidence of cupular deposits in these 70 TBs was analyzed. Correlations between cupular deposits and vestibular symptoms, endosteal involvement of the otosclerotic focus, stapedial fixation, and clinical history of stapes surgery were evaluated. Otolaryngology laboratory in a tertiary academic medical center. The study material consisted of 35 human TBs with otosclerosis and 35 age-matched controls. Morphometric evaluations of the incidence of cupular deposits, endosteal involvement of the otosclerotic focus, and stapedial fixation were made by light microscopy. Clinical records were reviewed retrospectively for clinical history of stapes surgery and prevalence of vestibular symptoms. The incidence of cupular deposits was compared between the otosclerotic and control groups. Correlations between cupular deposits and vestibular symptoms, endosteal involvement of the otosclerotic focus, stapedial fixation, and clinical history of stapes surgery were evaluated in the subjects with otosclerosis. The incidence of cupular deposits in TBs with otosclerosis was significantly higher than in those without whereas there was no correlation between the incidence of the deposits and dysequilibrium in cases of otosclerosis. An increase in deposits did not correlate with stapedial fixation, stapes surgery, or endosteal involvement. Our results suggest otosclerosis as an underlying mechanism for the production of cupular deposits; however, we did not find an association between these deposits and vestibular symptoms.

Presbycusis: A Human Temporal Bone Study of Individuals With Downward Sloping Audiometric Patterns of Hearing Loss and Review of the Literature

The purpose of this retrospective case review was to identify patterns of cochlear element degeneration in individuals with presbycusis exhibiting downward sloping audiometric patterns of hearing loss and to correlate these findings with those reported in the literature to clarify conflicting concepts regarding the association between hearing loss and morphologic abnormalities. Archival human temporal bones from individuals with presbycusis were selected on the basis of strict audiometric criteria for downward-sloping audiometric thresholds. Twenty-one temporal bones that met these criteria were identified and compared with 10 temporal bones from individuals with normal hearing. The stria vascularis volumes, spiral ganglion cell populations, inner hair cells, and outer hair cells were quantitatively evaluated. The relationship between the severity of hearing loss and the degeneration of cochlear elements was analyzed using univariate linear regression models. Outer hair cell loss and ganglion cell loss was observed in all individuals with presbycusis. Inner hair cell loss was observed in 18 of the 21 individuals with presbycusis and stria vascularis loss was observed in 10 of the 21 individuals with presbycusis. The extent of degeneration of all four of the cochlear elements evaluated was highly associated with the severity of hearing loss based on audiometric thresholds at 8,000 Hz and the pure-tone average at 500, 1,000, and 2,000 Hz. The extent of ganglion cell degeneration was associated with the slope of the audiogram. Individuals with downward-sloping audiometric patterns of presbycusis exhibit degeneration of the stria vascularis, spiral ganglion cells, inner hair cells, and outer hair cells that is associated with the severity of hearing loss. This association has not been previously reported in studies that did not use quantitative methodologies for evaluating the cochlear elements and strict audiometric criteria for selecting cases.

Cellular correlates of age-related endocochlear potential reduction in a mouse model

Age-related degeneration of cochlear stria vascularis and resulting reduction in the endocochlear potential (EP) are the hallmark features of strial presbycusis, one of the major forms of presbycusis, or age-related hearing loss (ARHL) (Schuknecht, H.F., 1964. Further observations on the pathology of presbycusis. Archives of Otolaryngology 80, 369–382; Schuknecht, H.F., 1993. Pathology of the Ear. Lea and Febiger, Philadelphia; Schuknecht, H.F., Gacek, M.R., 1993. Cochlear pathology in presbycusis. Annals of Otology, Rhinology and Laryngology 102, 1–16). It is unclear whether there are multiple forms of strial ARHL having different sequences of degenerative events and different risk factors. Human temporal bone studies suggest that the initial pathology usually affects strial marginal cells, then spreads to other strial cell types. While inheritance studies support a moderate genetic influence, no contributing genes have been identified. Establishment of mouse models of strial ARHL may promote the identification of underlying genes and gene/environment interactions. We have found that BALB/cJ mice show significant EP reduction by 19 months of age. The reduction only occurs in a subset of animals. To identify key anatomical correlates of the EP reduction, we compared several cochlear lateral wall metrics in BALBs with those in C57BL/6J (B6) mice, which show little EP reduction for ages up to 26 months. Among the measures obtained, marginal cell density and spiral ligament thickness were the best predictors of both the EP decline in BALBs, and EP stability in B6. Our results indicate that the sequence of strial degeneration in BALBs is like that suggested for humans. Additional strain comparisons we have performed suggest that genes governing strial melanin production do not play a role.

The Expression and Genetic Variations of Heat Shock Protein 70 in Ménière’s Disease

To evaluate the histopathologic changes in tympanic membranes (TMs) with ventilation tubes (VTs).In this retrospective human temporal bone study our overall study group included 4 subgroups of TMs from deceased donors as follows: 24 with a history of VT insertion for chronic otitis media with effusion (COME-VT); 5 with a history of VT insertion for Meniere’s disease (MD-VT); 33 without a history of VT insertion for chronic otitis media with effusion (COME); and 14 without a history of VT insertion for Meniere’s disease (MD). We classified the extent of migration of the outer keratinized squamous epithelium onto the inner surface of TM perforations and noted the presence and location of tympanosclerosis, of atrophy, of perforation, and/or of cholesteatoma formation.Tympanosclerosis occurred in 14/24 TMs in the COME-VT subgroup; 2/5, MD-VT; 7/33, COME; and 0/14, MD. The VT insertion site was mostly in the anteroinferior (63%) quadrant of the TM; tympanosclerosis occurred more frequently in the posteroinferior (42%) and posterosuperior (33%) quadrants. We found no significant correlation between the location of tympanosclerosis and the VT insertion site (P > 0.05). Atrophy occurred in 7/24 TMs in the COME-VT subgroup; 3/5, MD-VT; 8/33, COME; and 2/14, MD. We found no significant correlation between the location of atrophy and the VT insertion site; however, atrophy was located mostly in the anteroinferior quadrant (one of the most common VT insertion sites) of the TM. Regarding the ingrowth of keratinized epithelium, the mucocutanous junction was detected at any point at the inner surface of the TM in 50% of the specimens. We observed intratympanic cholesteatoma formation in 2/24 TMs in the COME-VT subgroup.TM changes due to VT insertion are more common than previously realized. Meticulous otomicroscopic evaluation of the TM is necessary during tympanomastoidectomies in order to prevent the intratympanic inclusion pearls and squamous epithelial ingrowth to prevent any further cholesteatoma formation.

Predicting Basal Cochlear Length for Electric-Acoustic Stimulation

To assess the feasibility and accuracy of predicting electrode insertion depth necessary in cochlear implantations for electric-acoustic stimulation by means of preoperative high-resolution computed tomography (HRCT). Human temporal bone study with evaluation of cochlear dimensions. Tertiary care medical center. Eight fresh human temporal bones were scanned, and basal cochlear structures were reconstructed and measured. Standard cochlear implantations with a free-fitting array were performed, and the bones then underwent histologic analysis using a technique that allows sectioning of undecalcified bones. After embedding, all bones underwent conventional radiologic analysis with further insertion measurements. Preimplantation HRCT data were compared with radiologic and histologic data. Preimplantation HRCT-based measurements correlated very well with postimplantation radiologic data. A mean failure of 0.3 mm was found. Mean values for the first 360 degrees ranged from 18.8 to 22.0 mm. Preimplantation HRCT-based prediction of cochlear implant insertion depths is both feasible and accurate. It is especially useful when aiming for hearing preservation, where insertion depths of 360 degrees are necessary.

Optical coherence tomography: Temporal bone applications

Problem: To evaluate the potential efficacy of fiberoptic optical coherence tomography (OCT) to provide real-time anatomic detail of the inner ear to aid in diagnosis and surgery. Methods: The study was designed as a human temporal bone and animal study. Results: Optical coherence tomography is an imaging technique that uses infrared light to produce an image. Novel technology has allowed this imaging technique to be delivered via a 250-micron diameter fiberoptic cable, making it a perfect tool for transtympanic applications. Transympanic imaging of the temporal bone of a mouse showed that this technology is capable of 15-micron resolution, allowing real-time rendering of structures such as Reissner’s membrane and the organ of Corti. Human temporal bone studies demonstrated that the device could be used to help visualize the scala tympani when performing a cochleostomy. Additionally the device could be used to perform endoscopic assessment of the inner ear. Conclusion: OCT is a new imaging technique with many potential uses in the ear. Significance: Potential uses for this new technology include assessment for endolymphatic hydrops and inner ear disease and improvement of cochlear implant placement. Support: None reported.

The image-guided approach to the antrum for cochlear implantation

Problem: To evaluate whether image guidance could be used to aid in developing an approach for minimally invasive cochlear implantation. Methods: This was a human temporal bone study. Results: Image guidance systems were used to plan a surgical trajectory from the surface of the temporal bone to the antrum. Using real-time image guidance and image-guided drills a 4-mm tunnel was created just posterior to the external auditory canal, reaching into the antrum. Using a soft silastic guide, cochlear implant electrodes were guided into the middle ear and implanted via a transtympanic approach. Including set-up time, the procedure was feasible in an average of 20 minutes. Subsequently the temporal bones were examined for signs of injury to the tegmen and semicircular canals. No evidence of damage to any structures was noted. Conclusion: The use of image guidance may allow a novel and minimally invasive approach to cochlear implantation in selected patients. Significance: The adoption of minimally invasive techniques could potentially significantly decrease OR time. Support: None reported.

Cellular changes of Reissner's membrane in Meniere's disease: human temporal bone study

Objective To study the cellular characteristics of Reissner's membrane (RM) in temporal bones (TBs) from patients with endolymphatic hydrops with symptoms of Meniere's disease (EH/+MD) and TBs with endolymphatic hydrops without symptoms of Meniere's disease (EH/−MD) in an effort to understand the role of endolymphatic hydrops in MD symptoms. Study design Comparative study of human TB histopathology. Methods and materials Epithelial and mesothelial cellularity of RM from control TBs, TBs from patients with EH/+MD, and TBs from patients with EH/−MD were compared. The cellularity of epithelial and mesothelial cell nuclei (defined as number of cells/100 μm width of RM) were counted along the width of RM. The width of RM was measured from the vestibular crest of the spiral ligament to the limbus spiralis. Results The cellular densities of epithelial cells in the basal and middle turns of RM were significantly higher in the EH/+MD and EH/−MD groups compared with “controls.” There was no difference in epithelial cellularity between EH/+MD and EH/−MD. There was a decrease in the number of mesothelial cells of RM in the basal turn in EH/+MD and EH/−MD groups (statistically significant only in EH/+MD group) when compared with controls. The number of mesothelial cells of RM in the middle turn in EH/+MD and EH/−MD groups were significantly decreased compared with normals. Discussion Similar findings in cellularity of RM in temporal bones with EH/+MD and EH/−MD suggest that pathophysiologic mechanisms other than hydrops may be responsible for symptoms in Meniere's disease.

Presbycusis: a human temporal bone study of individuals with flat audiometric patterns of hearing loss using a new method to quantify stria vascularis volume.

The purpose of this study was to determine the prevalence of stria vascularis atrophy in individuals with presbycusis and flat audiometric patterns of hearing loss. Individuals with presbycusis have historically been categorized by the shape of their audiograms, and flat audiometric thresholds have been reported to be associated with atrophy of the stria vascularis. Stria vascularis volume was not measured in these studies. Retrospective case review. Archival human temporal bones from individuals with presbycusis were selected on the basis of strict audiometric criteria for flat audiometric thresholds. Six temporal bones that met these criteria were identified and compared with 10 temporal bones in individuals with normal hearing. A unique quantitative method was developed to measure the stria vascularis volume in these temporal bones. The hair cell and spiral ganglion cell populations also were quantitatively evaluated. Only one of the six individuals with presbycusis and flat audiometric thresholds had significant atrophy of the stria vascularis. This individual with stria vascularis atrophy also had reduced inner hair cell, outer hair cell, and ganglion cell populations. Three of the individuals with presbycusis had spiral ganglion cell loss, three individuals had inner hair cell loss, and all six individuals had outer hair cell loss. The results of this investigation suggest that individuals with presbycusis and flat audiometric patterns of hearing loss infrequently have stria vascularis atrophy. Outer hair cell loss alone or in combination with inner hair cell or ganglion cell loss may be the cause of flat audiometric thresholds in individuals with presbycusis.

Proximity of carotid canal wall to tympanic membrane: a human temporal bone study.

The objective was to examine the possible risk of injury to the internal carotid artery during procedures in the middle ear, including myringotomy. Histopathological morphometric study of human temporal bones. One hundred forty-two human temporal bone specimens obtained from 92 individuals without any known ear disease were prepared for light microscopic study. Using 83 bones that were available for measurement, the thickness of the carotid canal wall (CCW), which is the medial wall of the bony portion of the eustachian tube, was measured. Using 15 bones selected for three-dimensional measurement, the closest distance from CCW to the anterior tympanic annulus was measured. Using all 142 temporal bone specimens, the CCW was examined to detect the presence of partial dehiscence. In one case, the images of CCW dehiscence and its surrounding structures were reconstructed by a personal computer. The thickness of the CCW was 0.00 to 0.73 mm (average thickness, 0.24 mm [+/-0.12 mm]). The distance from the CCW to the anterior tympanic annulus was 1.8 to 8.1 mm (average distance, 4.9 [+/-1.7 mm]). Dehiscence of CCW was observed in 7 (4.9%) of 142 temporal bone specimens. The reconstructed image showed that the posterior half of the dehiscence of CCW could be seen from the external ear canal. The CCW was found to be extremely thin or even dehiscent in some cases, rendering the internal carotid artery vulnerable during transtympanic procedures. The study's findings emphasized the need for judicious care when operating in the anterior mesotympanum.