Evaluation of the ear ossicles with photon-counting detector CT.

Recently, computed tomography with photon-counting detector (PCD-CT) has been developed to enable high-resolution imaging at a lower radiation dose. PCD-CT employs a photon-counting detector that can measure the number of incident X-ray photons and their energy. The newly released PCD-CT (NAEOTOM Alpha, Siemens Healthineers, Forchheim, Germany) has been in clinical use at our institution since December 2022. The PCD-CT offers several advantages over current state-of-the-art energy-integrating detector CT (EID-CT). The PCD-CT does not require septa to create a detector channel, while EID-CT does. Therefore, downsizing the anode to achieve higher resolution does not affect the dose efficiency of the PCD-CT. CT is an indispensable modality for evaluating ear ossicles. The ear ossicles and joints are clearly depicted by PCD-CT. In particular, the anterior and posterior legs of the stapes, which are sometimes unclear on conventional CT scans, can be clearly visualized. We present cases of congenital anomalies of the ossicular chain, ossicular chain dislocation, tympanosclerosis, and cholesteatoma in which PCD-CT was useful. This short article reports the usefulness of PCD-CT in the 3D visualization of the ear ossicles.

Handheld laser-fiber vibrometry probe for assessing auditory ossicles displacement.

SIGNIFICANCE: Measurements of auditory ossicles displacement are commonly carried out by means of laser-Doppler vibrometry (LDV), which is considered to be a gold standard. The limitation of the LDV method, especially for in vivo measurements, is the necessity to expose an object in a straight line to a laser beam operating from a distance. An alternative to this approach is the use of a handheld laser-fiber vibrometry probe (HLFVP) with a curved tip. AIM: We evaluate the feasibility of an HLFVP with a curved tip for measuring sound-induced displacement of the auditory ossicles. APPROACH: A handheld vibrometer probe guiding the laser beam with a fiber-optic cable was used for displacement measurements of the incus body and the posterior crus of the stapes. Tonal stimuli at frequencies of 0.5, 1, 2, and 4 kHz were presented by means of an insert earphone positioned in the outer ear canal. The probe was fixed at the measurement site using a tripod or hand-held by one of the two surgeons. RESULTS: The measurements were carried out on six fresh temporal bones. Multivariate analysis of variance showed statistically significant differences for stimulus frequency (F3,143 = 29.37, p < 0.001, and η2 = 0.35), bone (F5,143 = 4.61, p = 0.001, and η2 = 0.01), and measurement site (F1,143 = 4.74, p = 0.03, and η2 = 0.02) in the absence of statistically significant differences for the probe fixation method (F2,143 = 0.15, p = 0.862, and η2 = 0.001). Standard deviations of the means were 6.9, 2.6, 1.9, and 0.6 nm / Pa for frequency, bone, site, and fixation, respectively. Ear transfer functions were found to be consistent with literature data. CONCLUSIONS: The feasibility of applying HLFVP to measure the displacement of auditory ossicles has been confirmed. HLFVP offers the possibility of carrying out measurements at various angles; however, this needs to be standardized taking into account anatomical limitations and surgical convenience.

[Endoscopically guided reconstruction of the ossicular chain-an introduction]. / Endoskopisch geführte Eingriffe an der Ossikelkette ­ ein Einblick.

The term "endoscopic ossiculoplasty" refers to surgical methods with the intention to reconstruct the ossicular chain using endoscopic vision. Apart from malformations and injuries, inflammatory processes cause the majority of indications for ossicular reconstruction. This article offers a commented overview of current literature and preliminary personal experience.

Micro-CT of the human ossicular chain: Statistical shape modeling and implications for otologic surgery.

The ossicular chain is a middle ear structure consisting of the small incus, malleus and stapes bones, which transmit tympanic membrane vibrations caused by sound to the inner ear. Despite being shown to be highly variable in shape, there are very few morphological studies of the ossicles. The objective of this study was to use a large sample of cadaveric ossicles to create a set of three-dimensional models and study their statistical variance. Thirty-three cadaveric temporal bone samples were scanned using micro-computed tomography (µCT) and segmented. Statistical shape models (SSMs) were then made for each ossicle to demonstrate the divergence of morphological features. Results revealed that ossicles were most likely to vary in overall size, but that more specific feature variability was found at the manubrium of the malleus, the long process and lenticular process of the incus, and the crura and footplate of the stapes. By analyzing samples as whole ossicular chains, it was revealed that when fixed at the malleus, changes along the chain resulted in a wide variety of final stapes positions. This is the first known study to create high-quality, three-dimensional SSMs of the human ossicles. This information can be used to guide otological surgical training and planning, inform ossicular prosthesis development, and assist with other ossicular studies and applications by improving automated segmentation algorithms. All models have been made publicly available.

Precision Medicine in Ossiculoplasty.

INTRODUCTION: Long term results of ossiculoplasty surgery are considered poor with displacement and extrusion amongst the common reasons for failure. Application of 3Dimensional (3D) printing may help overcome some of these barriers, however digital methods to attain accurate 3D morphological studies of ossicular anatomy are lacking, exacerbated by the limitation of resolution of clinical imaging. METHODS: 20 human cadaveric temporal bones were assessed using micro computed tomography (CT) imaging to demonstrate the lowest resolution required for accurate 3D reconstruction. The bones were then scanned using conebeam CT (125 µm) and helical CT (0.6 mm). 3D reconstruction using clinical imaging techniques with microCT imaging (40 µm resolution) as a reference was assessed. The incus was chosen as the focus of study. Two different methods of 3D printing techniques were assessed. RESULTS: A minimum resolution of 100 µm was needed for adequate 3D reconstruction of the ossicular chain. Conebeam CT gave the most accurate data on 3D analysis, producing the smallest mean variation in surface topography data relative to microCT (mean difference 0.037 mm, p < 0.001). Though the incus varied in shape in between people, paired matches were identical. Thus, the contralateral side can be used for 3D printing source data if the ipsilateral incus is missing. Laser based 3D printing was superior to extrusion based printing to achieve the resolution demands for 3D printed ossicles. CONCLUSION: Resolution of modern imaging allows 3D reconstructions and 3D printing of human ossicles with good accuracy, though it is important to pay attention to thresholding during this process.

Scanning Electron Microscopy in the Evaluation of Defects to the Ossicular Chain in the Course of Chronic Otitis Media.

OBJECTIVE: Chronic otitis media is a heterogeneous disorder. Chronic suppurative otitis media with cholesteatoma and, to a lesser extent, chronic otitis media with granulation lead to the destruction of bone structures within the middle ear. Bone loss may appear in the prominence of the horizontal semicircular canals and the bony canal of the facial nerve. The inflammatory process may spread to the bony labyrinth of the sigmoidal sinuses and the cranial cavities. MATERIALS AND METHODS: The analysis comprised the examination of fragments of auditory ossicles removed during surgery in 21 patients with various types of chronic inflammation of the middle ear. The purpose of this study was to evaluate the usefulness of scanning electron microscopy in evaluating the erosion of middle ear ossicles in different types of chronic otitis media. Images captured at various magnifications were used for the best possible illustration of the observed lesions in bone tissue. RESULTS: The observed lesions and the degree of bone surface damage were dependent on the type of chronic inflammation of the middle ear. The largest destructive changes in the ossicular chain were observed in chronic otitis media with cholesteatoma; smaller changes were observed in chronic otitis media with granulation. CONCLUSION: In the case of damage to the ossicles inflicted by inflammation, the use of a modeled bone block made of a temporal bone taken from outside the tympanic cavity or a biomaterial prosthesis is a good choice in ossiculoplasty.

Pneumatized middle ear ossicle - A normal variant.

It is important to be familiar with normal anatomic variants in order to not to mistake them for pathology. It is well known that the middle ear ossicles have varying normal morphology on gross anatomy, but can also be malformed in certain congenital syndromes or eroded in the setting of chronic ear infection or cholesteatoma. This case series describes the pneumatized ossicle on imaging, a rare normal anatomic variant.

Isolated Incudostapedial Cholesteatomas: Unique Radiologic and Surgical Features.

OBJECTIVES: Congenital cholesteatomas originate from epithelial tissue present within the middle ear in patients with an intact tympanic membrane, no history of otologic surgery, otorrhea, or tympanic membrane perforation. They are diagnosed by a pearl-like lesion on otoscopy and computed tomography (CT) scan showing an expansile soft-tissue mass. We describe a series of patients with no prior otologic history presenting with progressive unilateral conductive hearing loss and normal otoscopy. The CT scans showed ossicular erosion without obvious soft-tissue mass. Surgery confirmed incudostapedial erosion found to be cholesteatoma. In this study, we characterize the clinical course of patients diagnosed with isolated incudostapedial cholesteatoma (IIC) and review possible pathologic mechanisms. METHODS: Retrospective review of IIC cases treated by the Department of Pediatric Otolaryngology, Rady Children's Hospital, San Diego, 2014 to 2020. Data included patient demographics, clinical features, imaging, surgical findings, and audiologic data. RESULTS: Five patients were diagnosed with IIC (3 [60%] female; mean age at presentation 10.7 years [range 5.5-16.0]). All patients presented with postlingual unilateral conductive hearing loss and normal otoscopy without any past otologic history; delay in diagnosis ranged from 4 months to several years. The CT scans showed ossicular chain erosion with an absent long process of the incus and/or stapes superstructure. All patients underwent middle ear exploration, revealing a thin layer of cholesteatoma in the incudostapedial region, confirmed by histopathology. Mean preoperative speech reception threshold was 55 dB and improved to a mean of 31 dB in the 4 patients who underwent ossicular chain reconstruction. CONCLUSION: Isolated incudostapedial cholesteatoma should be included as a possible etiology in pediatric patients with insidious onset of unilateral conductive hearing loss with normal otoscopy, unremarkable otologic history, and a CT scan showing ossicular abnormality/disruption without notable middle ear mass. These patients should be counseled preoperatively regarding the possibility of cholesteatoma and should undergo middle ear exploration with possible ossiculoplasty.

[Isolated congenital middle ear malformations: comparison of preoperative HRCT and surgical findings].

Objective:To compare preoperative temporal bone HRCT readings to intraoperative findings during exploratory tympanotomy for suspected cases of isolated congenital middle ear malformations（CMEMs） and summarize the malformations that can be diagnosed with HRCT. Method:A retrospective study was conducted. All cases were confirmed as isolated CMEMs during surgery. Detailed clinical records were reviewed, with a focus on imaging and surgical findings. Result:One hundred and fifty-two patients and 168 ears were reviewed. One hundred and seven cases（63.7%） could be identified as isolated CMEMs and at least one as middle ear anomaly using preoperative HRCT. Sixty-one cases（36.3%） were reported to be completely normal and the patients underwent exploratory tympanotomy to determine the final diagnosis. Stapes fixation, either alone or associated with other ossicular chain anomalies, contributed to 51.2% of the cases.The stapes and incudostapedial complex are the most commonly involved structures. Conclusion:HRCT provides helpful preoperative clinical information in CMEM.Most cases of aplasia or dysplasia of the ossicular chain, e.g., aplasia/dysplasia of the long process of the incus, aplasia of the stapes'superstructure, and atresia of the oval window were easily identified in preoperative HRCT. However, fixation of the ossicular chain can be elusive in HRCT, and exploratory tympanotomy is needed for a definitive diagnosis.

Auditory ossicles in ScanningElectron Microscopy.

<b>Introduction: </b>Knowledge about the physiology of a healthy middle ear is essential for understanding the activity and mechanics of the ear as well as the basics of ossiculoplasty. Trauma of the epithelial lining of the tympanic cavity as well as the ossicular chain may be the result of chronic inflammation and surgery. Depending on the observed changes of the middle ear lining, there are several types of distinguished chronic inflammatory changes: simple, with cholesteatoma, with the formation of inflammatory granulation tissue, in course of specific diseases. <br><b>Purpose: </b>The aim of the article is presentation of the microstructure and vasculature of the ossicular chain in the Scanning Electron Microscope. Particular attention is drawn to the anatomical aspects of the structure and connections of auditory ossicles as vital elements for reconstruction of the conduction system of the middle ear. <br><b>Material and method: </b>The analysis covered auditory ossicles standardly removed in accordance with the methodology of the investigated surgical procedures. The preparations were evaluated in a scanning electron microscope. <br><b>Results: </b>The exposure of bone surface promotes deep erosion. The advanced process of destruction of bone surface in the case of chronic otitis media correlates with a significant degree of damage to both the lining covering the auditory ossicles and that surrounding articular surfaces. <br><b>Conclusions: </b>(1) The ossicles in the image of the Scanning Electron Microscope are covered with lining. It passes from the surface of the ossicles to the vascular bundles, forming vascular sheaths; (2) Damage to lining continuity on the surface of the auditory ossicles promotes the rapid destruction of bone tissue in the inflammatory process; (3) The dimensions of the individual ossicles are respectively: malleus - 8.36 +/- 0.01, incus - 8.14 +/- 0.0, stapes - 3.23 +/- 0.01 mm. Behavior of the anatomical length of ossicular chain during tympanoplasty appears to be essential to maintaining adequate vibration amplitude of the conductive system of the middle ear.

Virtual Quality Control in Middle Ear Surgery: Is Image-guided Tympanoscopy a Valuable Tool for Depicting Borderline Situations?

HYPOTHESIS: Before modern imaging was introduced, revision surgery was the only way to evaluate possible reasons for inadequate improvement in hearing after ossicular replacement during reconstructive middle ear surgery. BACKGROUND: The aim of this study was to evaluate freely navigable virtual tympanoscopy using different computed tomographic modalities. We compared cone-beam computed tomography (CBCT), flat panel computed tomography (FPCT), and conventional computed tomography in helical mode (CTH), volume mode (CTV), and ultra high resolution mode (CTD). METHODS: Four temporal bone specimens were reconstructed with partial or total ossicular replacement prostheses. The best functional results for prosthetic coupling were achieved under the control of laser Doppler vibrometry (LDV). Afterward, a progressive step-by-step decoupling of the prostheses was carried out. Different prosthesis positions were evaluated by LDV as well as different computed tomographic modalities with 3D reconstruction of each dataset. RESULTS: Anatomical structures were better depicted and the best position and coupling of inserted prostheses were achieved using CBCT. All imaging techniques could be used to control the position of middle ear prostheses, but CBCT provided the highest resolution and the best image quality in both 2D and 3D reformations and in 3D-animated video representation. CONCLUSION: Compared with several other imaging modalities, CBCT was best at depicting miscellaneous coupling problems. Noninvasive detection of coupling problems caused by minimal loss of contact between prostheses and middle ear ossicles will influence the clinical outcome. This early detection will help to determine whether revision surgery is needed.

Concurrent Occurrence of Congenital Ossicular Anomaly and Localized Cholesteatoma: Series of 10 Cases.

OBJECTIVE: The objective of this study is to describe the clinical features, managements and outcomes of a rare coexistence of congenital ossicular anomaly and localized cholesteatoma. A literature review on these cases and each congenital disorder is also presented. METHODS: A retrospective chart review was performed on patients diagnosed with congenital ossicular anomaly with concurrent localized cholesteatoma from 2008 to 2017. Clinical data of these patients were collected. RESULTS: A total of 10 patients were identified. All patients presented with unilateral hearing loss. Pure-tone audiometry showed conductive hearing loss in all affected ears with an average air conduction (AC) threshold of 59 dB. High-resolution computed tomography scans of the temporal bone diagnosed ossicular anomaly for 90% (9/10); however, only 50% (5/10) had a diagnosis of localized cholesteatoma. A transcanal exploratory tympanotomy under the microscope was performed to discover whether the localized tiny-sized cholesteatoma around the ossicular chain did not have direct contact with the ossicular chain, which could be diagnosed as congenital cholesteatoma. We removed the localized cholesteatoma and reconstructed the ossicular chain in each patient. All localized cholesteatomas were found in the posterior-superior quadrant of the middle ear. Ossicular chain anomalies were associated with the incus and/or the stapes in all cases. Hearing improvement was achieved in each of the 6 patients who were followed up postoperatively, with an average AC threshold of 35 dB. The clinical features of congenital ossicular anomaly with concurrent congenital cholesteatoma were compared with those of each congenital disorder. The pathogenesis of each condition was also discussed. CONCLUSIONS: Congenital ossicular anomaly with concurrent congenital cholesteatoma is rare. It shares similar clinical features with congenital ossicular anomaly occurring alone, therefore awareness should be raised for a possible concurrent congenital cholesteatoma which was easy to miss in the diagnosis (50%) by the radiologist. A patient's hearing level can be improved by removal of the cholesteatoma and reconstruction of the ossicular chain. Localized cholesteatoma does not usually show residuals or recurrence.

Synchrotron radiation imaging revealing the sub-micron structure of the auditory ossicles.

PURPOSE: Synchrotron-based X-ray Phase Contrast Imaging (SR X-PCI) allows, thanks to a highly coherent and powerful X-ray beam, the imaging of surface and cross-sectional tissue properties with high absorption-contrast. The objective of this study is to investigate the sub-micron structure of the ossicular chain. The understanding of its morphological properties at sub-micron scale will help to refine the understanding of its structural properties. The investigation of intact, non-decalcified and unstained ossicular bones allows to study the spatial relationship between surface properties, internal structure and tomographical slides. MAIN RESULTS: The tomography datasets with a pixel size of 0.65 µm were reconstructed and 3D volume rendering models of all specimens were analyzed. Based on surface models, the surfaces of the articulations, the insertion of the tensor tympani and stapedial muscle tendons and the nutritional foramina, where the vessels penetrate the ossicles, were visualized. Moreover, a branched network of inner channels could be represented and its connection to the nutritional foramen was demonstrated. Looking at the tomographic structure of the three ossicles a mineralization pattern for every auditory bone was described, indicating a considerable variation throughout the bones. CONCLUSIONS: This study investigates the submicron-structure of the auditory ossicles at a pixel size of 0.65 µm, which is to the best of our knowledge the highest resolution reported in the investigation of the human auditory system so far. The provided data helps in the further understanding of the anatomical conformation of the ossicular chain.

The Antrum-Malleus-Tegmen Score: A Pilot Study Assessing Preoperative Radiographic Predictors for Transcanal Endoscopic Cholesteatoma Dissection.

OBJECTIVE: Identify features on computed tomography (CT) that predict mastoidectomy conversion (MC) during transcanal endoscopic ear surgery (TEES). STUDY DESIGN: Retrospective case-control. SETTING: University otology practice. PATIENTS: Consecutive patients with cholesteatoma. INTERVENTION: TEES cholesteatoma dissection versus those requiring MC. MAIN OUTCOME MEASURES: Antrum opacification, depth of scutum involvement, and erosion of the mastoid trabeculae, ossicular chain, and tegmen were evaluated. Univariable and multivariable regression analysis was performed. The Antrum-Malleus-Tegmen (AMT) score was created using receiver operating characteristic curves to assess feasibility of performing TEES for cholesteatoma dissection. RESULTS: There were 39 TEES and 19 MC cases. Groups had similar age (median 28.5 yr), gender, laterality, and revision surgery status. Median surgical time for MC cases was longer than TEES (231 min vs. 171 min, p < 0.001). Radiographic predictors of MC by multivariable regression included antrum opacification (p = 0.036), malleus erosion (p = 0.044), and tegmen erosion (p = 0.023). The AMT score predicted the feasibility of TEES without MC with a sensitivity of 90% and specificity of 75% when ≥2 of the following conditions were met on preoperative CT: intact tegmen, intact malleus, and absence of antrum opacification. CONCLUSIONS: An aerated antrum, intact malleus, and intact tegmen suggest that TEES cholesteatoma dissection without the need for mastoidectomy is highly likely. A score of ≥2 on the AMT score predicts this with a positive predictive value of 88% and negative predictive value of 78%.

Conductive hearing loss with a "dry middle ear cleft"-A comprehensive pictorial review with CT.

Conductive hearing loss (CHL) commonly results from middle ear fluid and inflammation (otitis media). Less commonly in patients with CHL, the middle ear cleft is well aerated or 'dry' with absence of soft tissue or fluid clinically and on imaging. There are numerous causes for this but they can be clinically challenging to diagnose. This pictorial review aims to illustrate and discuss the CT features of both common and less common causes of CHL in patients with a "dry middle ear cavity".

Reporting and Description for Congenital Middle Ear Malformations to Facilitate Surgical Management.

INTRODUCTION: The aim of this work was to report and describe the different types of congenital middle ear malformations in order to guide surgical treatment approaches and improve outcomes for affected patients. METHODS: The authors reviewed patients with congenital middle ear malformations who received surgical treatment between September 2010 and March 2017. Patient characteristics, middle ear deformities, and surgical procedures were documented. RESULTS: In this retrospective study, 35 patients were reviewed. A description of middle ear malformation was proposed that considers ear embryogenesis and focuses on stapes deformity, with the main purpose of facilitating surgical approach selection to reconstruct the ossicular chain. Patients were classified into 3 categories: type I (19 cases), mobile stapes footplate, which included type Ia with normal stapes suprastructure and type Ib with abnormal stapes suprastructure; type II (4 cases), fixed stapes footplate, which included type IIa with normal ossicular chain and type IIb with abnormal ossicular chain; and type III (12 cases), oval window bony atresia or aplasia, with or without round window atresia. Types II and III could have concomitant aberrant facial nerve. Different surgical approaches are described. CONCLUSIONS: The authors describe the different types of congenital middle ear malformations. This category description considers ear embryogenesis and is focused on stapes deformity. It may provide better understanding of disease development and guide modern hearing reconstructive surgery.

Special Anatomic Considerations in Otosclerosis Surgery.

The anatomy of the vestibular organs together with considerations of the middle and inner ear anatomy relevant to stapes surgery is discussed. An archival collection of macerated and freshly frozen human temporal bones underwent micro-computed tomography (CT) with subsequent volume-rendering. Three-dimensional (3D) reconstructions and the topographic anatomy of the oval window were considered. Micro-CT and 3D rendering revealed the relationship between the otolith organs and the oval window. Anatomic variations were extensive and included the distance between the footplate and the reconstructed macula margins. A "no-go" zone is suggested for the surgeon to avoid injury during stapes surgery.

Experimental Simulation of Clinical Borderline Situations in Temporal Bone Specimens After Ossiculoplasty.

OBJECTIVES: One reason for insufficient hearing improvement with a distinct air-bone gap after ossiculoplasty with implantation of partial or total ossicular replacement prostheses can be the dislocation or minimal shifting of the prosthesis. The aim of this study was the simulation of common clinical borderline situations with minimal shifting of the prosthesis in temporal bone specimens after ossiculoplasty. It was furthermore the goal to identify these specific situations through imaging by cone beam computed tomography (cbCT) and direct visual inspection using the operation microscope. Additionally, the functional status was evaluated using laser-Doppler vibrometry (LDV). DESIGN: We used a total of four temporal bone specimens for this study. A reconstruction with a partial ossicular replacement prostheses was performed in three specimens and with a total ossicular replacement prostheses in one specimen, with good initial acoustic properties. Subsequently, one specific type of prosthesis failure was simulated in each specimen, respectively, by minimally shifting, tilting, or bending the prostheses from their initial positions. These changes were introduced step-by-step until a borderline situation just short of complete acoustic decoupling was reached. Each step was examined using both LDV and cbCT and observed through the operation microscope. RESULTS: LDV was able to quantify the mechanic function of the ossicular chain after most of the manipulation steps by demonstrating the effect of any shifting of the prosthesis on the middle ear transfer function. However, in some situations, the middle ear transfer function was better with a visually more advanced failure of the prosthesis. In addition, cbCT showed most of the steps with excellent resolution and was able to delineate changes in soft tissue (e.g., cartilage covering). CONCLUSION: cbCT seems to be a promising imaging technique for middle ear problems. As cbCT and LDV exhibited slightly different advantages and disadvantages regarding the demonstration of borderline situations, the combination of both techniques allowed for a more precise evaluation of middle ear reconstructions. Knowledge of the specific characteristics of these methods and their possible combination might help otologists and otosurgeons to refine indications for revision surgery and improve their personal patient counseling.

Anatomical measurement of the ossicles in patients with congenital aural atresia and stenosis.

OBJECTIVES: Our aims were to measure and compare anatomical parameters of the ossicles in normal, congenital aural stenosis (CAS), and congenital aural atresia (CAA) ears. METHODS: This retrospective study was performed using three-dimensional reconstructed images derived from computed tomography scans of 20 normal subjects, 20 CAS patients, and 20 CAA patients. RESULTS: The lengths of the malleus handle and long process of the incus were greater in normal ears than in CAS and CAA ears (all P < 0.05). The angles of the incudostapedial joint and between the short and long processes of the incus were smaller in normal ears than in CAS and CAA ears (all P < 0.05). There were no significant differences in the positions of the malleus head and incudomalleolar joint, the size of the malleus head, the length of the short process of the incus, or the angle of the incudomalleolar joint (P > 0.05). CONCLUSIONS: Anatomical parameters of the lower part, but not of the upper part, of the ossicular chain in CAS and CAA ears differed from those in normal ears. Different branchial arch origins of the upper and lower parts of the ossicular chain may explain these findings. Dysplasia of the second arch, which develops into the lower part of the ossicular chain, may contribute to ossicular malformation in CAA and CAS. Accurate radiographic measurement of malformed ossicles may be useful for reconstructive surgery of CAA and CAS using the patient's native ossicular chain and for choosing an appropriate place for active middle ear implants.

Atlas-Based Segmentation of Temporal Bone Anatomy.

PURPOSE: To develop a time-efficient automated segmentation approach that could identify critical structures in the temporal bone for visual enhancement and use in surgical simulation software. METHODS: An atlas-based segmentation approach was developed to segment the cochlea, ossicles, semicircular canals (SCCs), and facial nerve in normal temporal bone CT images. This approach was tested in images of 26 cadaver bones (13 left, 13 right). The results of the automated segmentation were compared to manual segmentation visually and using DICE metric, average Hausdorff distance, and volume similarity. RESULTS: The DICE metrics were greater than 0.8 for the cochlea, malleus, incus, and the SCCs combined. It was slightly lower for the facial nerve. The average Hausdorff distance was less than one voxel for all structures, and the volume similarity was 0.86 or greater for all structures except the stapes. CONCLUSIONS: The atlas-based approach with rigid body registration of the otic capsule was successful in segmenting critical structures of temporal bone anatomy for use in surgical simulation software.