Stapedial Footplate Research Articles

Diagnosis and Management of Paradoxical Cerebrospinal Rhinnorhea in Mondini's Dysplasia.

To highlight a case of unilateral Mondini's dysplasia and it's potential to manifest as paradoxical cerebrospinal fluid (CSF) rhinorrhoea and recurrent meningitis in an adult. A single case report with presentation and management of a patient with left sided Mondini's Dysplasia who presented with watery nasal discharge in the background of recurrent meningitis. We review the differential diagnoses and the importance of a multi-disciplinary approach to management. Post-auricular approach was taken and the leak was identified at the footplate of Stapes and sealed with fascia lata. The middle ear was obliterated and blind sac closure was done. The patient made a good recovery. The online version contains supplementary material available at 10.1007/s12070-024-04903-5.

Diagnosis and Management of Unexplained Conductive Hearing Loss With Intact Tympanic Membrane: A Systematic Review.

Objective: To analyze the etiology, diagnosis, and treatment of unexplained conductive hearing loss (UCHL) with intact tympanic membrane. Methods: A systematic review was conducted based on the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. A total of 642 articles were retrieved from databases such as PubMed, Embase, Web of Science, and Cochrane. Fifty-four research articles and 21 case reports were screened out according to the inclusion and exclusion criteria for analysis of the etiology of UCHL. Seven research articles with UCHL who underwent exploratory tympanotomy were selected for data extraction and analysis of clinical characteristics. Results: UCHL is a common manifestation of various diseases, including congenital ossicular anomalies (COA), otosclerosis (OTS), congenital middle ear cholesteatoma (CMEC), oval window atresia, superior semicircular-canal dehiscence, congenital stapedial footplate fixation, middle ear osteoma or adenoma, congenital ossification of stapedial tendon, and so on. A total of 522 patients were included in the 7 articles; among whom OTS showed a tendency to increase with age. The main symptoms were hearing loss, followed by tinnitus, dizziness, ear fullness, ear pain, facial paralysis. A total of 87.5% to 93.0% patients with COA manifested as nonprogressive deafness that occurred since childhood, with tinnitus incidence of 15.6% to 30.2%, and 86.4% to 96.4% patients with OTS presented with progressive hearing loss, with tinnitus incidence of 60.1% to 90.9%. The diagnosis positive rate of high-resolution computed tomography (HRCT) was 33.8% to 87.1%, and CMEC was higher than that of COA (83.3%-100% vs 28.6%-64%). All the articles reported good hearing recovery. The most common surgical complications included taste abnormalities, tinnitus, and dizziness. Conclusion: UCHL presents with similar clinical manifestations and poses challenges in preoperative diagnosis. Exploratory tympanotomy is the primary method for diagnosis and treatment, with good prognosis after removing the lesion and reconstructing hearing during the operation. Children can also safely undergo the surgery.

Surgical Considerations in Inner Ear Gene Therapy from Human Temporal Bone Anatomy.

Recently directed methods of inner ear drug delivery underscore the necessity for understanding critical anatomical dimensions. This study examines anatomical measurements of the human middle and inner ear relevant for inner ear drug delivery studied with three different imaging modalities. Post-mortem human temporal bones were analyzed using human temporal bone histopathology (N = 24), micro computerized tomography (μCT; N = 4), and synchrotron radiation phase-contrast imaging (SR-PCI; N = 7). Nine measurements involving the oval and round windows were performed when relevant anatomical structures were visualized for subsequent age-controlled analysis, and comparisons were made between imaging methods. Combined human temporal bone histopathology showed the mean distance to the saccule from the center of the stapes footplate (FP) was 2.07 ± 0.357 mm and the minimum distance was 1.23 mm. The mean distance from the round window membrane (RWM) to the osseous spiral lamina (OSL) was 1.75 ± 0.199 mm and the minimum distance was 1.43 mm. Instruments inserted up to 1 mm past the center of the FP are unlikely to cause saccular damage, provided there are no endolymphatic hydrops. Similarly, instruments inserted up to 1 mm through the RWM in the trajectory toward the OSL are unlikely to cause OSL damage. The combined analyses of inner-ear dimensions of age-controlled groups and imaging modalities demonstrate critical dimensions of importance to consider when inserting delivery vehicles into the human cochlea. N/A Laryngoscope, 134:2879-2888, 2024.

Morphometric study of stapes and its variation in Eastern Indian population

: For audiological prosthesis surgery morphometry of stapes is of utmost importance. Previous studies were mainly based on foreign and northern Indian population. Hence the present study.: To measure the morphometric parameters of stapes and compare the same with the previous studies.: This cross sectional observational study, performed on the ear ossicle, stapes obtained from 26 cadaveric heads. A total of (26 x 2) = 52 sets of stapes were taken out for the study. Measurements of various parameters of the ossicles were done with micrometer. Comparison among them with respect to sex, laterality and race were made. Age variation was not considered as the ossicles reach their full size at birth. Statistically significant difference in the total height of stapes was observed between male and female ossicles, but no such disparity was found between ossicles of the two sides. Height of stapes in males (mean: 3.35mm) was found to be significantly higher (p value: 0.00001) as compared to females (mean:3.18mm) in this present study. In surgeries for otosclerosis, the stapes superstructure is removed and replaced by a prosthetic ‘piston’, the selection of which is determined by the distance between the lenticular process of incus and the footplate of stapes, which in turn corresponds to the height of stapes superstructure. This measurement is vital for a properly fit piston and thus to the outcome of the surgery in terms of hearing improvement and lack of complications like expulsion of the piston, intractable vertigo, etc. When the mean values found in this study were compared with those of previous foreign and Indian studies, some of the values were found to be similar. : The height of stapes was shorter in our study as compared to studies based on North Indian population. These differences might point towards geographic or ethnic variations in the stapes which might call for further research work into this topic.

Audiological phenotyping evaluation in KBG syndrome: Description of a multicenter review.

Our objective was to reinforce clinical knowledge of hearing impairment in KBG syndrome. KBG syndrome is a rare genetic disorder due to monoallelic pathogenic variations of ANKRD11.The typical phenotype includes facial dysmorphism, costal and spinal malformation and developmental delay. Hearing loss in KBG patients has been reported for many years, but no study has evaluated audiological phenotyping from a clinical and an anatomical point of view. This French multicenter study included 32 KBG patients with retrospective collection of data on audiological features, ear imaging and genetic investigations. We identified a typical audiological profil in KBG syndrome: conductive (71%), bilateral (81%), mild to moderate (84%) and stable (69%) hearing loss, with some audiological heterogeneity. Among patients with an abnormality on CT imaging (55%), ossicular chain impairment (67%), fixation of the stapes footplate (33%) and inner-ear malformations (33%) were the most common abnormalities. We recommend a complete audiological and radiological evaluation and an ENT-follow up in all patients presenting with KBG Syndrome. Imaging evaluation is necessary to determine the nature of lesions in the middle and inner ear.

High-resolution computerized tomography for ossicular replacement prostheses

IntroductionTo study the accuracy of high-resolution computed tomography (HRCT) for assessing the ossicular structures in cadaveric temporal bone by the distance between temporal bone elements is of great interest. ObjectivesTo record the distances between the malleal neck and both the stapedial head and footplate by HRCT. Further, after partially opening the temporal bone toward the ossicular structure, to record the actual distances between those structures during surgical dissection. Material and methodsThis study compared actual and HRCT measurements of cadaveric temporal bone. We studied, measured, and recorded distances within and between various structural elements. All data are reported as means and were analyzed to prove the accuracy of HRCT to assess ossicular structure from the temporal bone. ResultsThis study included the temporal bones of 10 male and 10 female cadavers (mean age, 70.4 years). By surgical dissection, the distances between the malleal neck and the stapedial head and footplate were 3.40 and 5.30 mm, respectively (measured from the bone); by HRCT, the corresponding values were 3.35 and 5.29 mm. The intraclass correlation coefficients for assessing ossicular structure in contrast to the actual measurements were 0.901 (malleal neck to stapedial head) and 0.923 (malleal neck to stapedial footplate) (p < 0.05). There were no differences between the actual malleal neck to stapedial head (p = 0.793) or footplate (p = 0.242) measurements. ConclusionHRCT produced statistically comparable, reliable, and accurate measurements compared with actual measurements in cadaveric temporal bone.

3D Finite Element Model of Human Ear with 3-Chamber Spiral Cochlea for Blast Wave Transmission from the Ear Canal to Cochlea

Blast-induced auditory trauma is a common injury in military service members and veterans that leads to hearing loss. While the inner ear response to blast exposure is difficult to characterize experimentally, computational models have advanced to predict blast wave transmission from the ear canal to the cochlea; however, published models have either straight or spiral cochlea with fluid-filled two chambers. In this paper, we report the recently developed 3D finite element (FE) model of the human ear mimicking the anatomical structure of the 3-chambered cochlea. The model consists of the ear canal, middle ear, and two and a half turns of the cochlea with three chambers separated by the Reissner's membrane (RM) and the basilar membrane (BM). The blast overpressure measured from human temporal bone experiments was applied at the ear canal entrance and the Fluent/Mechanical coupled fluid-structure interaction analysis was conducted in ANSYS software. The FE model-derived results include the pressure in the canal near the tympanic membrane (TM) and the intracochlear pressure at scala vestibuli, the TM displacement, and the stapes footplate (SFP) displacement, which were compared with experimentally measured data in human temporal bones. The validated model was used to predict the biomechanical response of the ear to blast overpressure: distributions of the maximum strain and stress within the TM, the BM displacement variation from the base to apex, and the energy flux or total energy entering the cochlea. The comparison of intracochlear pressure and BM displacement with those from the FE model of 2-chambered cochlea indicated that the 3-chamber cochlea model with the RM and scala media chamber improved our understanding of cochlea mechanics. This most comprehensive FE model of the human ear has shown its capability to predict the middle ear and cochlea responses to blast overpressure which will advance our understanding of auditory blast injury.

Characterization of middle ear soft tissue damping and its role in sound transmission

Damping plays an important role in the middle ear (ME) sound transmission system. However, how to mechanically characterize the damping of ME soft tissues and the role of damping in ME sound transmission have not yet reached a consensus. In this paper, a finite element (FE) model of the partial external and ME of the human ear, considering both Rayleigh damping and viscoelastic damping for different soft tissues, is developed to quantitatively investigate the damping in soft tissues effects on the wide-frequency response of the ME sound transmission system. The model-derived results can capture the high-frequency (above 2kHz) fluctuations and obtain the 0.9kHz resonant frequency (RF) of the stapes velocity transfer function (SVTF) response. The results show that the damping of pars tensa (PT), stapedial annular ligament (SAL) and incudostapedial joints (ISJ) can help smooth the broadband response of the umbo and stapes footplate (SFP). It is found that, between 1 and 8kHz, the damping of the PT increases the magnitude and phase delay of the SVTF above 2kHz while the damping of the ISJ can avoid excessive phase delay of the SVTF, which is important in maintaining the synchronization in high-frequency vibration but has not been revealed before. Below 1kHz, the damping of the SAL plays a more important role, and it can decrease the magnitude but increases the phase delay of the SVTF. This study has implications for a better understanding of the mechanism of ME sound transmission.

Juvenile otosclerosis and congenital stapes footplate fixation. A systematic review and meta-analysis of surgical outcomes and management.

Juvenile Otosclerosis (JO) and Congenital Stapes Footplate Fixation (CSFF) are rare ossicular chain disorders seen in the paediatric population and present with conductive hearing loss. Ongoing controversy exists regarding the role of surgical intervention in JO and CSFF given the poorer hearing outcomes and complications when compared with surgical intervention for adult otosclerosis. The objective of this study is to assess the published data on the surgical outcomes of JO and CSFF in order to guide clinicians and counsel patients on the various medical options for these disease entities. A systematic review of MEDLINE, EMBASE and Cochrane was performed with inclusion criteria of children with JO or CSFF and hearing outcomes following stapes surgery. Studies identified by the search were reviewed and assessed by two independent reviewers in line with the PRISMA guidelines. 464 articles were initially reviewed and 28 articles met inclusion in the systematic review and meta-analysis. A total of 810 ears (473 and 337 cases of JO and CSFF respectively) underwent stapes surgery. Average age at time of surgery for JO and CSFF was 14.3 and 10.2 years old respectively. The mean pre-operative Air-Bone-Gap (ABG) for JO and CSFF was 31.8±5.2dB and 39.4±10dB respectively. Following stapes surgery, the mean post-operative ABG for JO and CSFF was 9.6±6dB and 19.2±12.5dB respectively. Surgical success rate (defined as ABG <10dB) was 81% for JO and 41% for CSFF. Mean ABG gain for JO and CSFF was 24.8dB (95% CI: 18.6-33.1) and 22.6dB (95% CI: 18.4-27.8) respectively. The reported number of dead ears was 4/473 (0.8%) for JO and 2/337 (0.6%) for CSFF. 23 cases (2.8%) reported sensorineural hearing loss (SNHL) >10dB. CSFF was associated with poorer hearing outcomes compared to JO, however both entities showed similar improvement in ABG post operatively. Counselling patients and their families on the surgical success rates and complications of JO or CSFF is an important part of the decision making process when deciding between a surgical option or conservative measures such as hearing aids.

Real-time measurement of stapes motion and intracochlear pressure during blast exposure

Blast-induced auditory injury is primarily caused by exposure to an overwhelming amount of energy transmitted into the external auditory canal, the middle ear, and then the cochlea. Quantification of this energy requires real-time measurement of stapes footplate (SFP) motion and intracochlear pressure in the scala vestibuli (Psv). To date, SFP and Psv have not been measured simultaneously during blast exposure, but a dual-laser experimental approach for detecting the movement of the SFP was reported by Jiang et al. (2021). In this study, we have incorporated the measurement of Psv with SFP motion and developed a novel approach to quantitatively measure the energy flux entering the cochlea during blast exposure.Five fresh human cadaveric temporal bones (TBs) were used in this study. A mastoidectomy and facial recess approach were performed to identify the SFP, followed by a cochleostomy into the scala vestibuli (SV). The TB was mounted to the “head block”, a fixture to simulate a real human skull, with two pressure sensors – one inserted into the SV (Psv) and another in the ear canal near the tympanic membrane (P1). The TB was exposed to the blast overpressure (P0) around 4 psi or 28 kPa. Two laser Doppler vibrometers (LDVs) were used to measure the movements of the SFP and TB (as a reference). The LDVs, P1, and Psv signals were triggered by P0 and recorded simultaneously.The results include peak values for Psv of 100.8 ± 51.6 kPa (mean ± SD) and for SFP displacement of 72.6 ± 56.4 μm, which are consistent with published experimental results and finite element modeling data. Most of the P0 input energy flux into the cochlea occurred within 2 ms and resulted in 10–70 μJ total energy entering the cochlea. Although the middle ear pressure gain was close to that measured under acoustic stimulus conditions, the nonlinear behavior of the middle ear was observed from the elevated cochlear input impedance.For the first time, SFP movement and intracochlear pressure Psv have been successfully measured simultaneously during blast exposure. This study provides a new methodology and experimental data for determining the energy flux entering the cochlea during a blast, which serves as an injury index for quantifying blast-induced auditory damage.

Intratympanic Substance Distribution After Injection of Liquid and Thermosensitive Drug Carriers: An Endoscopic Study.

In the treatment of inner ear conditions, intratympanic injection emerges as an important drug delivery method. Novel compounds designed for intratympanic injection are routinely loaded in viscous drug carriers. To date, it is unclear if they can freely distribute in the middle ear. The aims of this study were to investigate the middle ear distribution of different drug carriers during intratympanic injection and to determine an optimal injection method for thermosensitive hydrogels. Twenty-one human temporal bones were intratympanically injected with fluid drug carriers or poloxamer-407 hydrogels at different tympanic membrane injection sites (inferior, anterior-superior) using different needle types (Whitacre, Quincke). Fluid distribution was evaluated via an endoscopic view. Injection volume, duration, backflow, and overall safety were analyzed. Liquid drug carriers distribute effortlessly in the middle ear, whereas an additional ventilation hole is advantageous when applying thermosensitive hydrogels. The round window is coated with required volumes between 150 and 200 μl, irrespective of the injection position. Required volumes to also coat the stapedial footplate ranged from 310 to 440 μl. Use of the Whitacre-type needle reduced backflow to the ear canal and enabled longer tympanic membrane visibility when no additional ventilation hole was placed. Intratympanic injection is a safe and reliable method for the application of thermosensitive hydrogels. The round window niche is readily filled regardless of the injected formulation and injection position. Although fluid drug carriers distribute effortlessly in the middle ear, the placement of an additional ventilation hole might facilitate the application of viscous hydrogels.

High-resolution computerized tomography for ossicular replacement prostheses

IntroductionTo study the accuracy of high-resolution computed tomography (HRCT) for assessing the ossicular structures in cadaveric temporal bone by the distance between temporal bone elements is of great interest. ObjectivesTo record the distances between the malleal neck and both the stapedial head and footplate by HRCT. Further, after partially opening the temporal bone toward the ossicular structure, to record the actual distances between those structures during surgical dissection. Material and methodsThis study compared actual and HRCT measurements of cadaveric temporal bone. We studied, measured, and recorded distances within and between various structural elements. All data are reported as means and were analyzed to prove the accuracy of HRCT to assess ossicular structure from the temporal bone. ResultsThis study included the temporal bones of 10 male and 10 female cadavers (mean age, 70.4 years). By surgical dissection, the distances between the malleal neck and the stapedial head and footplate were 3.40 and 5.30 mm, respectively (measured from the bone); by HRCT, the corresponding values were 3.35 and 5.29 mm. The intraclass correlation coefficients for assessing ossicular structure in contrast to the actual measurements were 0.901 (malleal neck to stapedial head) and 0.923 (malleal neck to stapedial footplate) (p < 0.05). There were no differences between the actual malleal neck to stapedial head (p = 0.793) or footplate (p = 0.242) measurements. ConclusionHRCT produced statistically comparable, reliable, and accurate measurements compared with actual measurements in cadaveric temporal bone.

Do CT values change over time and correlate with hearing in the non-surgical ears of otosclerosis patients?

Background High-resolution computed tomography (HRCT) is often used to diagnose otosclerosis. Aims/Objectives To investigate whether CT values change over time and correlate with hearing in the non-surgical ears of otosclerosis patients. Materials and methods 32 patients with bilateral otosclerosis who had undergone unilateral stapedectomy were enrolled in the study. HRCT examination and pure tone audiometry were performed before and after the surgery. CT values of different regions of interest (ROIs) were measured manually and the data were collected for analysis. Results The CT value of anterior to the inner auditory meatus (AIAM) decreased by 88.5 HU (p < .05), and the changes in CT values in other ROIs showed no statistical difference. Regarding hearing, the value of air bone gap (ABG) increased by 3.6 dB (p = .020), and the average hearing deterioration rate of ABG was 3.1 dB/year. The CT value of the mid-point of the stapes footplate (MPSF) showed a certain correlation with the change of ABG (p < .05). Conclusions and significance The CT value of AIAM may change over time. The overall hearing of non-surgical ears in otosclerosis patients shows a deteriorating trend. Moreover, the changes in the CT value of MPSF may be related to the hearing, which needs further research.

Stimulation efficiency of an actuator driven piston at the biological interface to the inner ear

Direct acoustic cochlear stimulation uses piston motion to substitute for stapes footplate (SFP) motion. The ratio of piston to stapes footplate motion amplitude, to generate the same loudness percept, is an indicator of stimulation efficiency. We determined the relationship between piston displacement to perceived loudness, the achieved maximum power output and investigated stapes fixation and obliteration as confounding factors. The electro-mechanical transfer function of the actuator was determined preoperatively on the bench and intraoperatively by laser Doppler vibrometry. Clinically, perceived loudness as a function of actuator input voltage was calculated from bone conduction thresholds and direct thresholds via the implant. The displacement of a 0.4 mm diameter piston required for a perception equivalent to 94 dB SPL at the tympanic membrane compared to normal SFP piston displacement was 27.6–35.9 dB larger, consistent with the hypothesis that the ratio between areas is responsible for stimulation efficiency. Actuator output was 110 ± 10 eq dB SPLFF @1Vrms ≤ 3 kHz and decreased to 100 eq dB SPLFF at 10 kHz. Output was significantly higher for mobile SFPs but independent from obliteration. Our findings from clinical data strongly support the assumption of a geometrical dependency on piston diameter at the biological interface to the cochlea.

Three-Dimensional Finite Element Modeling of Blast Wave Transmission From the External Ear to a Spiral Cochlea.

Blast-induced injuries affect the health of veterans, in which the auditory system is often damaged, and blast-induced auditory damage to the cochlea is difficult to quantify. A recent study modeled blast overpressure (BOP) transmission throughout the ear utilizing a straight, two-chambered cochlea, but the spiral cochlea's response to blast exposure has yet to be investigated. In this study, we utilized a human ear finite element (FE) model with a spiraled, two-chambered cochlea to simulate the response of the anatomical structural cochlea to BOP exposure. The FE model included an ear canal, middle ear, and two and half turns of two-chambered cochlea and simulated a BOP from the ear canal entrance to the spiral cochlea in a transient analysis utilizing fluid-structure interfaces. The model's middle ear was validated with experimental pressure measurements from the outer and middle ear of human temporal bones. The results showed high stapes footplate (SFP) displacements up to 28.5 μm resulting in high intracochlear pressures and basilar membrane (BM) displacements up to 43.2 μm from a BOP input of 30.7 kPa. The cochlea's spiral shape caused asymmetric pressure distributions as high as 4 kPa across the cochlea's width and higher BM transverse motion than that observed in a similar straight cochlea model. The developed spiral cochlea model provides an advancement from the straight cochlea model to increase the understanding of cochlear mechanics during blast and progresses toward a model able to predict potential hearing loss after blast.

Value of cone-beam computer tomography in the middle and inner ear observation

Objective:To identified the feasibility and normal range of cone beam computer tomography（CBCT） in the measurement of temporal bone. Methods:15 formalin fixed human cadaver head specimens were scanned by CBCT, high resolution CT, and Micro CT, respectively. Morphological parameter measurements of the middle and inner ear structures including ossicular chain, cochlea, semicircular canal and facial nerve were performed, and the results measured by the three scanning methods were compared. Results:None of the parameters measured by the three scanning methods were statistically significant except the thickness of stapes footplate（P<0.01） and the diameter of cochlear basal turn（P<0.01）. CBCT was superior in detecting facial nerve bony canal dehiscence. Conclusion:CBCT has the advantages of short scanning time, low radiation dose and high resolution. It can accurately display the morphological characteristics of the temporal bone structures, and is a reliable evaluation method for otological surgery.

Radiological Features and Pathognomonic Sign of Stapes Footplate Fistula in Inner Ear Malformations.

Objective:Some inner ear malformations may cause recurrent meningitis, which may be fatal. The etiology is usually a stapes footplate fistula which enables microorganisms to pass into the inner ear containing cerebrospinal fluid (CSF), causing repeated attacks of meningitis. Radiological signs of the fistula are not obvious and are not reported in detail in the literature. The aim of the study is to investigate the radiological features of stapes footplate fistula in inner ear malformations.Methods:Radiological findings were analyzed for seventeen patients with inner ear malformations (IEMs) operated on because of recurrent meningitis. Using this information, images of 1,010 patients with IEMs were retrospectively reviewed to investigate the radiological findings of stapes footplate fistula and their relationship to IEMs. They were classified according to the Sennaroglu classification system, and according to different stages of stapes footplate fistula.Results:In the case of a stapes footplate cyst, computerized tomography shows an opacity at the oval window. On magnetic resonance imaging, a fluid filled cystic structure continuous with and having similar signal characteristics to the CSF in the inner ear is a pathognomonic finding of a stapes footplate cyst. It is most commonly found in common cavity anomaly (18.2%); the second most frequent finding is incomplete partition type I (15%). And it can even be seen in cases of cochlear aplasia where only the vestibule is present.Conclusion:If the history reveals recurrent meningitis, particular attention should be given to the oval window area, where an opacity, cyst or a leaking lesion should be looked for on the imaging. It is the responsibility of the otolaryngologist to notice these findings, and to operate on the patient to prevent further attacks of meningitis.

Absent pyramidal eminence and stapedial tendon associated with congenital stapes footplate fixation: Intraoperative and radiographic findings

ObjectiveReport an association between congenital stapes footplate fixation (CSFF) and radiological absence of the pyramidal eminence and stapedial tendon. PatientsChildren and adults with intraoperatively confirmed CSFF and an absent stapedial tendon. InterventionsComputed tomography (CT); exploratory tympanotomy with stapedotomy. Main outcome measuresAbsence of a pyramidal eminence and stapedial tendon aperture identified on preoperative CT that was confirmed intraoperatively. ResultsEight patients with intraoperative confirmation of CSFF and absent stapedial tendon were retrospectively identified. The average preoperative bone conduction and air conduction pure tone averages were 19.6 dB (SD 15.6 dB) and 55.9 dB (SD 23.6 dB), respectively. The average air-bone gap was 36.3 dB (SD 17.9 dB) preoperatively. In the seven patients who underwent preoperative CT, all were consistently identified to have an absent or hypoplastic pyramidal eminence and absent stapedial tendon aperture at the pyramidal eminence. In six cases, the stapedial footplate appeared normal, while in one case the footplate appeared abnormal which correlated with severe facial nerve prolapse observed intraoperatively. All eight cases underwent exploratory tympanotomy and demonstrated intraoperative stapes footplate fixation, absent stapedial tendon and either absent or hypoplastic pyramidal eminence, which correlated with preoperative CT findings. ConclusionsThis study identifies a clinically pragmatic association between an absent pyramidal eminence identified on high-resolution CT and the diagnosis of CSFF. In a condition that otherwise generally lacks distinctive radiological features, the absence of a pyramidal eminence on CT in a patient with nonprogressive, congenital conductive hearing loss may strengthen clinical suspicion for CSFF.

The Element of Paaw in Marsupials and the Ear Region of Philander opossum (Linnaeus, 1758) (Didelphimorphia, Didelphidae)

A small piece of cartilage or bone, the element of Paaw, occurs in the tendon of the stapedius muscle in some extant marsupial and placental mammals. It has been nearly a century since the last comprehensive treatment of the distribution of the element of Paaw in mammals. The current report updates knowledge on this structure by synthesizing the subsequent literature and providing new observations of extant marsupials from the collections of the Section of Mammals, Carnegie Museum of Natural History, and two online resources for CT scanned data: DigiMorph.org and MorphoSource.org. We found an element of Paaw in some representatives of all seven extant marsupial orders: Didelphimorphia, Microbiotheria, Notoryctemorphia, Peramelemorphia, Paucituberculata, Dasyuromorphia, and Diprotodontia. In the first four orders, the element is substantial, longer than the long axis of the fenestra vestiuli (oval window), which holds the stapedial footplate; it is smaller than the long axis of the fenestra vestibuli in Paucituberculata and we do not have measures to report for the last two orders. In most marsupials examined, the element of Paaw contacts the petrosal behind the oval window, suggesting it functions as a sesamoid bone, increasing the lever arm of the stapedius muscle. Although there is some variability in the presence of the bone both between and within individual museum specimens, we interpret this as the result of preparation techniques rather than true variation.To place the element of Paaw in its anatomical context, we describe in detail the ear region and middle-ear auditory apparatus of the gray four-eyed opossum, Philander opossum (Linnaeus, 1758), a didelphid from Central and South America, based on a CT scanned specimen from Carnegie Museum of Natural History. It has an ossified element of Paaw with a volume greater than the stapes. Comparisons are made with petrosals of Didelphis marsupialisLinnaeus, 1758, and Monodelphis domestica (Wagner, 1842), also based on CT scanned specimens.

The stapes of stem and extinct Marsupialia: implications for the ancestral condition

ABSTRACT This paper describes, for the first time, the stapedes of several non-marsupial species of the metatherian clade Sparassodonta (Sipalocyon gracilis, Arctodictis sinclairi, and Borhyaena tuberata) which were fortuitously encountered during routine microtomography. To augment our comparative set we also scanned and reconstructed single examples of the stapedes of the fossil taxa Sparassocynus bahiai and Thylophorops cf. T. chapalmalensis (Didelphimorphia), Argyrolagus scagliai (?Paucituberculata), as well as single examples drawn from extant members of Caenolestidae (Caenolestes sp.) and Microbiotheriidae (Dromiciops gliroides). The sparassodont, didelphid, and microbiotherian samples exhibit a common bauplan (stapes triangular, with intracrural foramen), whereas the paucituberculatan samples differ in possessing columelliform, imperforate stapes as also previously reported for various australidelphians. The stapedial footplate is rounded in sparassodonts (stapedial ratio, ∼1.6), in both of the fossil didelphimorphians (∼1.7), and in the fossil ?paucituberculatan (∼1.5). According to our optimization of our results of mammalian phylogeny, and in contrast to some other reconstructions, a triangular stapes with intracrural foramen and rounded footplate is likely the ancestral condition for Marsupialia. No particular function can be correlated with possession of the intracrural foramen as opposed to an imperforate stapes, apart from accommodation of the proximal stapedial artery (as seen also in many eutherians). The frequent presence of the intracrural foramen in members of both infraclasses suggests that the ontogenies of the second arch’s blood supply (stapedial artery) and its main skeletal element (stapes) have remained strongly integrated throughout therian evolution, even in cases in which the proximal part of the vessel involutes.