A Methodology for Visualising Growth and Development of the Human Temporal Bone.

This chapter presents a methodological framework which could be used to produce accurate anatomical 3D models and animations of the developing skull, with a focus on the temporal bone. Initial modelling is based on information from core texts and visual references, before optimising these models for use in interactive real-time applications. A series of 3D modelling and animation workflows typically used in computer games and animation industry were tested and compared. Workflows most suitable for the production of a 3D visualisation of the developing temporal bone were documented in detail and used to produce the final 3D models. 3D models of the developing temporal bone were then implemented in an interactive mobile application, which allowed users to explore the 3D models on their Android mobile device and use augmented reality to enhance real-world information. Results of tests conducted in this research suggest that 3D modelling workflows which mimic the processes occurring during development of the temporal bone are most suitable for producing realistic 3D models. Animation workflows tested in this research have all shown potential to produce morphing animations of the developing temporal bone. The significant time required to create deformation setups and animations themselves however suggests that using scripting to automate these workflows would increase their usability in projects with a limited timeframe.

Patterns of pneumatization of the tympanic plate.

OBJECTIVE: This study aimed to investigate the prevalence of tympanic plate (TP) pneumatisation as well as the various potential patterns. METHODS: A retrospective study involving the archived Cone-Beam Computed Tomography (CBCT) files of 70 patients was performed to investigate anatomical variations of TP pneumatisation. RESULTS: Forty-eight TPs were found to be non-pneumatised, while 92 were found to contain at least peritubal air cells. Twenty patients (28.5%) did not present any variety of TP pneumatisation, while 36 patients (51.4%) exhibited a symmetrical pattern of pneumatisation. CONCLUSION: Aside from those patients who lacked TP pneumatisation, the peritubal pneumatisation pattern was found to be the most common. Further, bilateral symmetry was found to occur in more than half of all cases. CBCT is a powerful diagnostic tool, although appropriate knowledge of the anatomical possibilities remains mandatory for adequate surgical planning.

Morphometric properties of the facial canal in children: A retrospective computed tomography study.

PURPOSE: The main objective of the study was to examine the morphometric development of the facial canal in temporal bones aged from one to 18 years for pediatric otosurgeons and neurosurgeons. METHODS: The study was performed on 41 patients including cochlear implantation cases (20 females and 21 males) with a mean age of 6.44 ±â€¯5.79 years. All the measurements belonging to the facial canal including the length, width and angles of its segments were performed using the data of computed tomography assessment. RESULTS: The numerical data of the facial canal segments were not different in terms of sexes or sides, statistically (p > 0.05). The width of the labyrinthine segment (p = 0.145), the length of the tympanic segment (p = 0.555), the first (p = 0.067) and second (p = 0.060) genu angles seemed to reach adult size at two years of age. In addition, the length of the labyrinthine segment (p = 0.064) and the width of the mastoid segment (p = 0.264) seemed to attain adult size at four years, while the width of the meatal foramen (p = 0.264) seemed to arrive adult size at seven years. However, the length of the mastoid segment and the width of the tympanic segment were developing independently of increasing age between 1 and 18 years. CONCLUSION: Our data suggested that, contrary to the general acceptance in the literature, the dimension of the facial canal segments show remarkable changes during the transition from intrauterine life to adult life. The regression equations representing the facial canal growth dynamic in children may be useful for otosurgeons to estimate the size of its segments and to prevent iatrogenic injury during early childhood surgeries such as cochlear implantation.

Growth pattern of temporal bone pneumatization: a computed tomography study with consecutive age groups.

PURPOSE: To investigate the growth pattern of temporal bone pneumatization (TBP) in consecutive age groups from birth to 18 years old using 3D air-density reconstruction of high-resolution CT (HRCT). METHODS: A total of 570 patients under 18 years old who performed temporal bone HRCT and with no structural abnormalities on both sides were included. Nineteen groups were created to represent consecutive ages, with 15 males and 15 females in each group. Volume rendering of air density was performed using a segmentation threshold of - 200 HU to obtain TBP volume of each side. The differences in TBP between the sides, sexes, and ages were statistically analyzed. RESULTS: The mean volume of TBP was measured as 1.17 ± 0.44 ml in patients less than 1 year old and 6.81 ± 1.93 ml as adult size. High consistencies of TBP volume between different sides or sexes were found in most of age groups. Significant differences were shown between sides only in 9- and 11-year-old female groups (p9 = 0.031, p11 = 0.016) while between sexes only in 6- and 16-year-old groups (p6 = 0.001, p16 = 0.043), although the volume was larger in all the male groups older than 6 years. The curve drawn by the mean volume in consecutive age groups showed that TBP continued to grow linearly in both males and females until they reached 14 years old. The corresponding linear regression equations were as follows: ym = 1.553 + 0.370x, (x ≤ 14 years, R2 = 0.596); yf = 1.561 + 0.304x, (x ≤ 14 years, R2 = 0.565). CONCLUSION: The TBP volume shows a linear growth pattern from birth until reaching adult size after 14 years old.

Maturation of bone-conduction transcranial and forehead attenuation using a measure of sound pressure in the ear canal.

OBJECTIVE: Although it is understood that bone-conduction (BC) hearing is different between infants and adults, few studies have attempted to explain why these differences exist. The main objective in this study was to better understand how properties of the developing skull contribute to the maturation of BC sensitivity through an indirect measurement of BC attenuation across the skull. DESIGN: Estimation of transcranial and forehead attenuation of pure-tone BC stimuli was conducted using sound pressure in the ear canal for a transducer placed on the skull ipsi- and contralateral to the probe ear and at the forehead. STUDY SAMPLE: Seventy-six individuals participated in the study, including 59 infants and children (1 month-7 years) and 17 adults. RESULTS: BC attenuation was greatest for young infants, and decreased throughout maturation. Attenuation from the forehead to the ipsilateral temporal bone was also greater compared to the transcranial measures for infants and children older than 10 months. CONCLUSIONS: These results provide evidence that physical maturation of the skull contributes to infant-adult differences in BC attenuation. Clinicians may consider these results, in combination with previous studies using physiological measures, when fitting infants and young children with bone-anchored hearing systems.

COUP-TFII is required for morphogenesis of the neural crest-derived tympanic ring.

Chicken Ovalbumin Upstream Promoter-Transcription Factor II (COUP-TFII) plays pivotal roles in cell growth, cell differentiation, and cell fate determination. Although genome-wide studies have identified COUP-TFII binding on gene sets mainly involved in neural crest cell (NCC) development and craniofacial morphogenesis, the direct functional connection between COUP-TFII and NCCs in vivo has not been well characterized. In this study, we show that COUP-TFII is expressed in the subpopulation of NCCs and its derivatives, and targeted ablation of COUP-TFII in mouse NCCs results in markedly shortened and bifurcated tympanic rings, which in turn disturb the caudal direction of external acoustic meatus invagination. However, formation of the manubrium of the malleus (MM) in Wnt1-Cre/+;COUP-TFII flox/flox mice is not perturbed, suggesting that the rostral half of the tympanic ring is sufficient to support proper MM development. Interestingly, we found that loss of COUP-TFII up-regulates Sox9 in the tympanic ring primordium and affects the distribution of preosteoblasts before mesenchymal condensation. Together, our results demonstrate that COUP-TFII plays an essential role in regulating the patterning of the NCC-derived tympanic ring.

Bone Density Development of the Temporal Bone Assessed by Computed Tomography.

HYPOTHESIS: The temporal bone shows regional differences in bone development. BACKGROUND: The spreading pattern of acute mastoiditis shows age-related differences. In infants, it spreads laterally and causes retroauricular swelling, whereas in older children, it tends to spread medially and causes intracranial complications. We hypothesized that bone maturation may influence the spreading pattern of acute mastoiditis. METHODS: Eighty participants with normal hearing, aged 3 months to 42 years, participated in this study. Computed tomography (CT) values (Hounsfield unit [HU]) in various regions of the temporal bone, such as the otic capsule (OC), lateral surface of the mastoid cavity (LS), posterior cranial fossa (PCF), and middle cranial fossa (MCF), were measured as markers of bone density. Bone density development curves, wherein CT values were plotted against age, were created for each region. The age at which the CT value exceeded 1000 HU, which is used as an indicator of bone maturation, was calculated from the development curves and compared between the regions. RESULTS: The OC showed mature bone at birth, whereas the LS, PCF, and MCF showed rapid maturation in early childhood. However, there were significant regional differences in the ages of maturation: 1.7, 3.9, and 10.8 years for the LS, PCF, and MCF, respectively. CONCLUSION: To our knowledge, this is the first report to show regional differences in the maturation of temporal bone, which could partly account for the differences in the spreading pattern of acute mastoiditis in individuals of different ages.

A Three-Dimensional Geometric-Morphometric Study to Quantify Temporal Bone Growth and its Consequences for the Success of Implanting Bone Anchored Hearing Devices.

OBJECTIVE: A computed tomography (CT)-based morphological-investigation to describe temporal bone growth and to devise a predictive test of the likely success of Bonebridge implantation into the growing mastoid region of the temporal bone in young patients. STUDY DESIGN: Retrospective cross-sectional study. SETTING: University Hospital Halle (Saale), Germany. PATIENTS: Two cohorts participated. This first, of patients aged less than 21 years, comprised 42 men, and 33 women patients. The second cohort, for those aged more than or equal to 21 years, comprised 17 men, and 20 women patients. INTERVENTION: One hundred eighty three three-dimensional (3-D) reconstructions of the mastoid portion of the temporal bone without malformations or chronic middle ear disease were created on the base of high resolution computer tomography. The 3-D-reconstructions were analyzed using 13 linear measurements and volumetry. PRIMARY OUTCOME MEASURE: A CT/3-D model derived metric with which to best estimate the likely success of fitting a Bonebridge. RESULTS: Volume increase stagnated at, on average, 15.6 years of age (men), or 17.5 years (women). The most obvious extent of growth was observed in the craniocaudal direction from the middle cranial fossa to the tip of the mastoid process (total height). This growth is highly correlated with the increase of the mastoid volume (r = 0.938) and thus represents the most influential factor on mastoid volume increase. The total height of the mastoid portion can be used to usefully predict the chance of successful Bonebridge implantation.The depth of the mastoid almost doubled its size from birth (8.93 mm) to adulthood (16.34 mm) and also strongly affects the mastoid volume (r = 0.912). That portion between the external auditory canal (EAC) and the sigmoid sinus showed a lower growth capacity. CONCLUSIONS: The highly significant correlations between CT derived linear parameters and Bonebridge fitting (p < 0.001) can be used to estimate the success of Bonebridge implantation. The remarkable inter-individual variation of mastoid shape underlines the necessity of radiological preoperative planning.

The developing temporal bone: computed tomography measurements and assessment of suture closure from birth to 18 years of age.

PURPOSE: To describe the normal CT appearance of the developing temporal bone in children from birth to 18 years of age. METHODS: Two hundred and six temporal bone CTs of children from 0.14 to 18.95 years were retrospectively selected and reviewed. Temporal bones were measured in a standardized slice orientation using the length of the basal turn of the cochlea, the length and width of the petrous bone, the coronal extent, trailing edge and anterior-posterior dimension of the temporal bone and the angle between petrous bone's length and the midsagittal line in the axial plane showing the basal turn of the cochlea in its greatest extent. Two sutures, two synchondroses and three fissures of the temporal bone were evaluated and graded. RESULTS: Chosen measurements and calculations demonstrate an increase of values from 0 to 18 years with the greatest increase occurring during the first 2 years of life. The angle between the basal turn of the cochlea and the midsagittal line shows a large variability. Logarithmic trend lines illustrate larger measurements of males as compared to females. The ratio of the basal turn of the cochlea and the length of the petrous bone is about 1:4.1 (f/m) during the first year of life and about 1:6.1 (f)/1:6.8 (m) from 17 years onwards. Results of suture closure are described using box-and-whisker plots. CONCLUSIONS: The developing temporal bone grows the most during the first 2 years of life. Knowledge of changing proportions and suture closure is essential for evaluation of temporal bone CT of children.

Evaluation of temporal bone pneumatization with growth using 3D reconstructed image of computed tomography.

OBJECTIVE: To evaluate temporal bone pneumatization with growth using 3D reconstructed computed tomography (CT) images. PATIENTS AND METHODS: Eighty-four temporal bones of 42 patients under the age of 16 years who had undergone head and facial bone CT were included in this retrospective study. The bony growth of the temporal bone and the head size were evaluated with horizontal- and vertical-plane CT images. Pneumatization of the temporal bone was investigated with 3D reconstruction software using axial CT images, dividing them as follows: medially, anterosuperiorly, posterolaterally, and inferiorly. Pneumatization of each individual part was compared with that of other parts and was also evaluated according to the aging process. RESULTS: The mean pneumatization was measured as 1696.7mm3 in patients aged under 2 years, 3609.1mm3 in those aged 2-4 years, 5351.1mm3 in those aged 5-7 years, 7295.9mm3 in those aged 8-10 years, 7797.5mm3 in those aged 11-13 years, and 8526.6mm3 in those aged 14-16 years. The degree of temporal bone pneumatization of each part was correlated with that of other parts (p<0.05). The volume of pneumatization increased with growth of the temporal bone and with aging. The degree of pneumatization of specific parts might be related to developmental periods. CONCLUSION: The pneumatization of one part might affect the pneumatization of other nearby parts, or all parts might be affected by the same driving force of pneumatization.

Laser-Modified Surface Enhances Osseointegration and Biomechanical Anchorage of Commercially Pure Titanium Implants for Bone-Anchored Hearing Systems.

Osseointegrated implants inserted in the temporal bone are a vital component of bone-anchored hearing systems (BAHS). Despite low implant failure levels, early loading protocols and simplified procedures necessitate the application of implants which promote bone formation, bone bonding and biomechanical stability. Here, screw-shaped, commercially pure titanium implants were selectively laser ablated within the thread valley using an Nd:YAG laser to produce a microtopography with a superimposed nanotexture and a thickened surface oxide layer. State-of-the-art machined implants served as controls. After eight weeks' implantation in rabbit tibiae, resonance frequency analysis (RFA) values increased from insertion to retrieval for both implant types, while removal torque (RTQ) measurements showed 153% higher biomechanical anchorage of the laser-modified implants. Comparably high bone area (BA) and bone-implant contact (BIC) were recorded for both implant types but with distinctly different failure patterns following biomechanical testing. Fracture lines appeared within the bone ~30-50 µm from the laser-modified surface, while separation occurred at the bone-implant interface for the machined surface. Strong correlations were found between RTQ and BIC and between RFA at retrieval and BA. In the endosteal threads, where all the bone had formed de novo, the extracellular matrix composition, the mineralised bone area and osteocyte densities were comparable for the two types of implant. Using resin cast etching, osteocyte canaliculi were observed directly approaching the laser-modified implant surface. Transmission electron microscopy showed canaliculi in close proximity to the laser-modified surface, in addition to a highly ordered arrangement of collagen fibrils aligned parallel to the implant surface contour. It is concluded that the physico-chemical surface properties of laser-modified surfaces (thicker oxide, micro- and nanoscale texture) promote bone bonding which may be of benefit in situations where large demands are imposed on biomechanically stable interfaces, such as in early loading and in compromised conditions.

Fracturas de temporal graves en niños: presentación, complicaciones y secuelas observadas en los últimos 11 años / Severe temporal bone fractures in children: Clinical presentation, complications and sequelae observed in the last 11 years

OBJETIVO: Analizar las características de presentación, complicaciones y secuelas, de las fracturas de temporal ingresadas en UCIP.MATERIAL Y MÉTODOS: Análisis descriptivo retrospectivo de las historias clínicas y TC craneal. RESULTADOS: Veintisiete pacientes ingresados en UCIP presentaron fractura del temporal: 13 (48%) sin afectación de peñasco (grupo 1) y 14 (52%) con afectación de peñasco (grupo 2). El grupo 2 presentó mayor estancia en la UCIP: 4,5 días (RI: 2,75-22,25) vs. 2 (RI: 1-3) (p = 0,018), mayor frecuencia de secuelas (p = 0,04) y presencia de fístula del LCR (p < 0,02). Los scores de PRIMS III e índice de traumatismo pediátrico no mostraron diferencias significativas. El 31% presentó hipoacusia, 2 pacientes fallecieron y 4 (15%) presentaron secuelas permanentes. CONCLUSIONES: Las fracturas temporales pueden ser graves, especialmente si incluyen al peñasco, bien por las lesiones asociadas, que marcan el riesgo vital, como por las secuelas (déficit auditivo o fístula LCR). Los autores indican el seguimiento de estos pacientes a largo plazo por Otorrinolaringología

OBJECTIVES: To evaluate the clinical presentation, complications and sequelae in patients with temporal bone fracture in the last 11 years. MATERIAL AND METHODS: A total of 27 patient medical records were retrospectively analysed. RESULTS: Of the 27 patients who were admitted for temporal bone fracture from 2001 to 2012, 13 (48%) had no petrous involvement (Group 1), and 14 (52%) with petrous involvement (Group 2). Patients in Group 2 had a longer P-ICU stay: median 4.5 days (RI: 2.75-22.25 d) vs 2 (RI: 1-3 d) (P=.018); more days on mechanical ventilation support: median 3 days (RI: 1.50-17 d) vs 1 (RI: 1-1.25 d). This group also had a higher frequency in sequelae (P=.04 OR = 1.4 (95% CI: 1.05-1.95)) and a higher incidence in cerebrospinal fluid (CSF) fistula (P<.02; OR 2.33; 95% CI (1.27-4.27)). Severity scores (PRIMS III and PTI) showed no significant differences. Some degree of hearing loss was observed in 31% of the patients. Traffic accident was the main cause of trauma (33%), followed by falls (27%). There were 2 deaths and 4 (15%) had permanent sequelae. CONCLUSIONS: Isolated temporal bone fractures usually have a good outcome in children, but in some cases they can be fatal or have permanent sequelae. Long term follow up is recommendedby authors

The effects of denervation and formoterol administration on facial growth.

OBJECTIVE: To identify and demonstrate possible alterations of skeletal structures which might follow either unilateral surgical denervation of the masseter muscle, unilateral intramuscular injection of formoterol directly into the masseter muscle, or intramuscular formoterol injection after surgical denervation. MATERIALS AND METHODS: Male Sprague Dawley rats (N = 16; four weeks of age) were prepared as four groups: 1. surgical sham + saline injection into the masseter muscle (sham); 2. surgical denervation of the masseter muscle only (den.); 3. surgical denervation of the masseter muscle plus intramuscular formoterol injection into the affected muscle (den.+form.); 4. intramuscular formoterol injection into the masseter muscle only (form.). The specimens were submitted for CT examination, the skulls and hemimandibles were photographed and measurements of craniofacial bones were made. RESULTS: In this relatively small sample, comparisons between non-experimental and experimental sides revealed differences, both within the groups and for the same measurements between groups, with the den. and den.+form. groups showing the most change. Relative increases in the gonial angle shown in these groups occurred bilaterally, with the change on the experimental side always greater in magnitude than the change on the contralateral side. CONCLUSIONS: Surgical denervation of the masseter muscle leads to an alteration in the size and shape of the skeletal structures close to the zygoma and the mandible. The intramuscular injection of formoterol into denervated masseter muscle seems to limit this skeletal alteration after surgical denervation.

A complete skull from Dmanisi, Georgia, and the evolutionary biology of early Homo.

The site of Dmanisi, Georgia, has yielded an impressive sample of hominid cranial and postcranial remains, documenting the presence of Homo outside Africa around 1.8 million years ago. Here we report on a new cranium from Dmanisi (D4500) that, together with its mandible (D2600), represents the world's first completely preserved adult hominid skull from the early Pleistocene. D4500/D2600 combines a small braincase (546 cubic centimeters) with a large prognathic face and exhibits close morphological affinities with the earliest known Homo fossils from Africa. The Dmanisi sample, which now comprises five crania, provides direct evidence for wide morphological variation within and among early Homo paleodemes. This implies the existence of a single evolving lineage of early Homo, with phylogeographic continuity across continents.

[Peculiarities of the development of antrum in the prematurely born infants].

The objective of the present study was to elucidate specific surgical anatomical features of the antrum in the children prematurely born at different gestational age. A total of 70 temporal bones from 35 newborn infants were available for the examination. The study revealed clinical and anatomical peculiarities in the antrum structure of the children prematurely born at different gestation age.

[Clinical and anatomical features of the middle ear in the premature infants at different gestational time].

The objective of the present study was to analyse anatomical features of the middle ear in the premature infants of different gestational age. Materials from 100 still-born and live-born babies (200 temporal bones) were available for the investigation. The study has revealed a number of distinctive clinical and morphological peculiarities in the structure of tympanic membranes in both the prematurely born infants depending on the gestational age and in the full-term babies. The fluid from the tympanic cavity was found to contain human beta-chorionic gonadotropin.

[Specific surgical features of the tympanic cavity in the children under the age of 3 years].

UNLABELLED: The objective of the present study was to obtain new data of practical significance from the comparative analysis of the anatomical structure of the tympanic cavity in newborn infants and young children. MATERIALS AND METHODS: A total of 23 and 24 temporal bone macropreparations obtained from the newborn infants and young children (between 1 to 3 years of age) respectively were available for the examination that included sequential dissection, measurement, and macrophotographing of the specimens. RESULTS: The study has revealed a number of distinctive features of the anatomical structure of the tympanic cavity in newborn infants and young children.

Comparison of treatments with the Forsus fatigue resistant device in relation to skeletal maturity: a cephalometric and magnetic resonance imaging study.

INTRODUCTION: The aim of this study was to compare the dentoskeletal changes and alterations of mandibular condyle-disc-fossa relationships in subjects at the peak and the end of the pubertal growth period treated with the Forsus fatigue resistant device (3M Unitek, Monrovia, Calif). METHODS: The sample consisted of 29 subjects with Class II Division 1 malocclusions who were classified according to their hand-wrist radiographs. Fifteen patients were at or just before the peak phase of pubertal growth (peak pubertal group). Fourteen patients were near the end of the pubertal growth period (late pubertal group). The study was conducted by using lateral cephalometric radiographs and magnetic resonance images obtained at the beginning and at the end of the application of the Forsus fatigue resistant device. The treatment period was 9 months. RESULTS: The Wilcoxon signed rank test was used to evaluate differences within groups. The changes observed in both groups were compared by using the Mann-Whitney U test. There were statistically significant group differences in mandibular length and ramus length, with significant increases of these parameters in the peak pubertal group (P <0.05). No significant differences were observed between the groups concerning dental parameters (P >0.05), with the exception of mandibular molar vertical movements, which were significantly greater in the peak pubertal group (P <0.05). Analysis of the magnetic resonance images showed no positional changes of the mandibular condyle in relation to the glenoid fossa in either group (P >0.05). Although the articular disc was positioned more anteriorly in the peak pubertal group compared with its pretreatment position (P <0.05), the position of the disc was still within the physiologic range. No significant intergroup difference was observed for disc-condyle relationship (P >0.05). CONCLUSIONS: The Forsus fatigue resistant device did not appear to cause significant increases in mandibular dimensions in subjects in late puberty. According to the magnetic resonance image findings, Forsus treatment is not a risk factor for the development of temporomandibular dysfunction in subjects with no signs and clinical symptoms of dysfunction.

Imaging of osseointegrated implants in the temporal bone by accuitomo 3-dimensional cone beam computed tomography.

OBJECTIVE: Follow-ups of osseointegrated implants in the temporal bone have been limited to clinical stability and resonance frequency measurements. Standard computed tomographic scanning is restricted because of the high radiation doses to the brain and the presence of disturbing metal artifacts. The present study was undertaken to evaluate the use of cone beam computed tomography preoperatively and postoperatively. STUDY DESIGN: Prospective investigation of patients intended for implant surgery and patients participating in a follow-up protocol. SETTING: Tertiary referral center. PATIENTS AND METHODS: Patients with osseointegrated implants and patients intended for implants in the temporal bone for bone-anchored epistheses and bone conduction hearing devices were investigated by a 3-D Accuitomo cone beam computed tomography machine. Images in sagittal, coronal, and axial planes were obtained and analyzed in a personal computer. Preoperative and postoperative views were analyzed regarding implant integration, bone resorption, anatomic landmarks, and implant failure. RESULTS: Eighteen patients were included in the study. With the used technique, it was easy to detect air cells, the sigmoid sinus, and posterior fossa and to recommend an ideal implant installation site. Bone resorption, bone overgrowth, and implant connex to air cells and dura were easy to detect. CONCLUSION: Accuitomo cone beam tomography showed to be a reliable method for investigating osseointegrated implants in the temporal bone.

Posterior semicircular canal dehiscence: a histopathologic human temporal bone study.

BACKGROUND: Posterior semicircular canal dehiscence has been shown to cause ear symptoms. OBJECTIVE: To evaluate the incidence of dehiscence of the posterior semicircular canal, thin bone overlying the posterior semicircular canal, and the normal development of the distance between the posterior semicircular canal and posterior cranial fossa. METHODS: The shortest distance between the posterior semicircular canal and posterior cranial fossa was measured in 1,051 adult human temporal bones (557 cases), and temporal bones with a distance less than 0.1 mm were evaluated. The shortest distance also was measured in 4 fetal temporal bones (2 cases) and 110 temporal bones from children. RESULTS: Of the 1,051 temporal bones, 23 temporal bones (2.2%) had a distance less than 0.1 mm between the posterior semicircular canal and posterior cranial fossa. Two temporal bones (0.2%) had posterior semicircular canal dehiscence, and 2 temporal bones had microfractures in the thin bone; however, related clinical symptoms were not confirmed. In children, the distance between the posterior semicircular canal and the posterior cranial fossa increased with age (rho = 0.68, p < 0.01). CONCLUSION: The histopathologic incidence of posterior semicircular canal dehiscence was lower than the previous radiographic reports. The dehiscence of the posterior semicircular canal may be due to a developmental anomaly. In our study, none of the cases with a distance less than 0.1 mm had apparent symptoms related to canal dehiscence syndrome. Other factors, in addition to thinning of the bone, may be required to cause the clinical manifestations.