Stapedius Research Articles

Bibliometric Analysis of Publications on Stapedius Muscle

Objective: The clinical importance of the stapedius muscle has been particularly emphasized in several publications. The purpose of this study is to bibliometrically analyze all publications on the stapedius muscle and to determine research trends related to this muscle. Methods: The publications related to the stapedius muscle were identified by the Web of Science database. A total of 548 publications were discovered throughout the literature review. Bibliometric techniques were employed to analyze the identified publications (VOSviewer Version 1.6.13). Results: The first studies were conducted in the 1980s. The highest number of publications related to the stapedius muscle was in 2020 (22 studies), while the lowest was in 1985 (2 studies). Most of the publications (90.11%) were written in English. The USA was the most prolific nation, with John J. Guinan having written the most articles on the stapedius muscle. Harvard University was also the most prolific institution. Conclusion: The findings demonstrated the researchers' interest in the stapedius muscle and offered quantifiable information regarding the muscle's position within the scientific domain. Recent years have seen an increase in studies on this topic. To the best of our knowledge, it can be said that this study is the first bibliometric analysis on the stapedius muscle.

Computed tomographyScan Size Analysis of stapedius and tensor tympani muscles in middle ear myoclonic tinnitus.

To analyze the sizes of the stapedius and tensor tympani (TT) muscles using a temporal bone CT (TBCT) scan in patients with middle ear myoclonic tinnitus (MEMT) and investigate their value for the diagnosis of this rare cause of tinnitus. Medical records and TBCT of patients with MEMT or vascular tinnitus (VT) at Seoul St. Mary's Hospital from January 2012 to December 2022 were reviewed. The stapedius and TT muscles were analyzed. Thirty-eight patients with unilateral MEMT and 39 patients with VT were included. More males were in the MEMT group compared to the VT group (MEMT: n = 24, VT: n = 8, p = .001). The mean age of the MEMT group was younger compared to the VT group (MEMT: 35 ± 12 years, VT: 44 ± 14.3 years, p = .005). The mean BMI for the MEMT group was less than the VT group (MEMT: 22.3 ± 2.5, VT: 24.8 ± 4.36, p = .010). The mean length and width of the stapedius in the MEMT group were larger than those of the VT group (Length MEMT: 1.47 ± 0.60 mm, VT: 0.98 ± 0.24 mm, p = .001; Width MEMT: 0.89 ± 0.32 mm, VT: 0.72 ± 0.19 mm, p = .009). The mean length and width of the TT in the MEMT group were larger than that of the VT group (Length MEMT: 3.10 ± 0.50 mm, VT: 2.27 ± 0.42, p = .001; Width MEMT: 2.02 ± 0.36, VT: 1.75 ± 0.26 p = .001). The mean length and width of the stapedius and TT muscles measured in the MEMT group were longer and wider than the VT group. This suggests the use TBCT scan as a diagnostic tool for MEMT. Further studies with a larger study group to validate the results of this study are recommended.Level of Evidence: 4.

Unique fiber phenotype composition and metabolic properties of the stapedius and tensor tympani muscles in the human middle ear.

The middle ear muscles have vital roles, yet their precise function in hearing and protection remains unclear. To better understand the function of these muscles in humans, the morphology, fiber composition, and metabolic properties of nine tensor tympani and eight stapedius muscles were analyzed with immunohistochemical, enzyme-histochemical, biochemical, and morphometric techniques. Human orofacial, jaw, extraocular, and limb muscles were used as references. The immunohistochemical analysis showed that the stapedius and tensor tympani muscles were markedly dominated by fibers expressing fast contracting myosin heavy chain MyHC-2A and MyHC-2X (79 ± 6% vs. 86 ± 9%, respectively, p=0.04). In fact, the middle ear muscles had one of the highest proportions of MyHC-2 fibers ever reported for human muscles. Interestingly, the biochemical analysis revealed a MyHC isoform of unknown identity in both the stapedius and tensor tympani muscles. Muscle fibers containing two or more MyHC isoforms were relatively frequently observed in both muscles. A proportion of these hybrid fibers expressed a developmental MyHC isoform that is normally absent in adult human limb muscles. The middle ear muscles differed from orofacial, jaw, and limb muscles by having significantly smaller fibers (220 vs. 360 μm2 , respectively) and significantly higher variability in fiber size, capillarization per fiber area, mitochondrial oxidative activity, and density of nerve fascicles. Muscle spindles were observed in the tensor tympani muscle but not in the stapedius muscle. We conclude that the middle ear muscles have a highly specialized muscle morphology, fiber composition, and metabolic properties that generally showed more similarities to orofacial than jaw and limb muscles. Although the muscle fiber characteristics in the tensor tympani and stapedius muscles suggest a capacity for fast, fine-tuned, and sustainable contractions, their difference in proprioceptive control reflects different functions in hearing and protection of the inner ear.

Stapedius muscle: Don't mistake it for a branch of the facial nerve in images

ObjectiveThe relationship between the stapedius muscle and the vertical part of the facial nerve is important for surgery. The study aims to understand the spatial relationship between the stapedius muscle and the vertical part of the facial nerve in ultra-high-resolution computed tomography (U-HRCT) images. MethodsA total of 105 ears from the heads of 54 human cadavers were analyzed using U-HRCT. The location and direction of the stapedius muscle were evaluated with the facial nerve as the reference. The integrity of the bony septum between the two structures and the distance between the transverse sections were examined. Paired Student's t-test and the nonparametric Wilcoxon test were applied. ResultsThe lower end of the stapedius muscle emerged at the upper (45 ears), middle (40 ears), or lower (20 ears) level of the facial nerve and was positioned medial (32 ears), medial posterior (61 ears), posterior (11 ears), or lateral posterior (1 ear) to the facial nerve. The bony septum was not continuous in 99 ears. The distance between the midpoints of the two structures was 1.75 mm (IQR=1.55-2.16 mm). ConclusionThe spatial relationship between the stapedius muscle and the facial nerve was varied. They were close to each other and in most cases the bony septum was not intact. Preoperative familiarity with the relationship between the two structures is helpful for avoiding unwanted injury to the facial nerve in surgery.

Human middle-ear muscle pulls change tympanic-membrane shape and low-frequency middle-ear transmission magnitudes and delays

The three-bone flexible ossicular chain in mammals may allow independent alterations of middle-ear (ME) sound transmission via its two attached muscles, for both acoustic and non-acoustic stimuli. The tensor tympani (TT) muscle, which has its insertion on the malleus neck, is thought to increase tension of the tympanic membrane (TM). The stapedius (St) muscle, which has its insertion on the stapes posterior crus, is known to stiffen the stapes annular ligament. We produced ME changes in human cadaveric temporal bones by statically pulling on the TT and St muscles. The 3D static TM shape and sound-induced umbo motions from 20 Hz to 10 kHz were measured with optical coherence tomography (OCT); stapes motion was measured using laser-Doppler vibrometry (LDV). TT pulls made the TM shape more conical and moved the umbo medially, while St pulls moved the umbo laterally. In response to sound below about 1 kHz, stapes-velocity magnitudes generally decreased by about 10 dB due to TT pulls and 5 dB due to St pulls. In the 250 to 500 Hz region, the group delay calculated from stapes-velocity phase showed a decrease in transmission delay of about 150 µs by TT pulls and 60 µs by St pulls. Our interpretation of these results is that ME-muscle activity may provide a way of mechanically changing interaural time- and level-difference cues. These effects could help the brain align head-centered auditory and ocular-centered visual representations of the environment.

Absent stapedius muscle, tendon and pyramid – An anomaly revisited

Congenital absence of stapedius is an exquisite entity, with an incidence of 0.5% and very few cases reported in live patients. We herein report a case of a middle-aged female presented with bilateral ear discharge and decreased hearing for more than a year, which, on examination, showed a large central perforation bilaterally, and an audiogram preoperatively revealed an average hearing loss of 45 dB and air-bone gap of 35dB bilaterally. Right endoscopic type I tympanoplasty was done, which unveiled absent stapedius muscle, tendon, and pyramid on the right side. The absent stapedius should circumspect the operating surgeon to look for other associated anomalies such as tympanosclerosis, fixed footplate and aberrant course of the facial nerve.

Anatomy of small canals around the jugular foramen: Special reference to Jacobson's and Arnold's nerves.

The jugular foramen harbors anatomically complex bony, venous and neural structures. It is closely associated with small canals including the mastoid, tympanic, and cochlear canaliculi, and the stylomastoid foramen. The minute intraosseous branches of Arnold's and Jacobson's nerves (<1 mm in length) remain difficult to study with current imaging techniques, and cadaveric dissection is the most reliable approach. Our aim was to examine the variations of Jacobson's and Arnold's canaliculi and nerves and to provide detailed cadaveric graphics. To reveal the anatomical structures of small canals around the jugular foramen, 25 sides of dry skulls and 14 sides of cadaveric heads were examined. Intraosseous branches varied more in Arnold's nerve than Jacobson's nerve. In our cadaveric dissection, all specimens formed a single canal for Jacobson's nerve connecting the jugular foramen to the tympanic cavity. The intraosseous course of Arnold's nerve varied in its communication with the facial nerve. A descending branch crossing the facial nerve was identified in five of 14 sides, an ascending branch in 13. In two specimens, an ascending branch clearly reached the base of the stapedius muscle. Classical anatomical studies of cadavers remain a supplementary tool for analyzing these tiny structures. The present study confirms Gray's findings of 1913. Variations of these nerves could be even more complex than previously reported. Our study provides additional information regarding the anatomy of Jacobson's and Arnold's nerves.

Accessing the stapedius muscle via novel surgical retrofacial approach during cochlear implantation surgery: Intraoperative results on feasibility and safety.

Human stapedius muscle (SM) can be directly and safely accessed via retrofacial approach, opening new approaches to directly measure the electrically evoked stapedius reflex threshold (eSRT). The measurement of the SM activity via direct surgical access represents a potential tool for objective eSRT fitting of cochlear implants (CI), increasing the benefit experienced by the CI users and leading to new perspectives in the development of smart implantable neurostimulators. 3D middle-ear reconstructions created after manual segmentation and related SM accessibility metrics were evaluated before the CI surgery for 16 candidates with assessed stapedius reflex. Retrofacial approach to access the SM was performed after facial recess exposure. In cases of poor exposition of SM, the access was performed anteriorly to the FN via drilling of the pyramidal eminence (PE). The total access rate of the SM via both the retrofacial and anterior approach of the FN was 100%. In 81.2% of cases (13/16), the retrofacial approach allowed to access the SM on previously categorized well exposed (8/8), partially exposed (4/5), and wholly concealed (1/3) SM with respect to FN. Following intraoperative evaluation in the remaining 18.8% (3/16), the SM was accessed anteriorly via drilling of the PE. Exposure of SM with respect to the FN and the sigmoid sinus's prominence was a predictor for the suitable surgical approach. The retrofacial approach offers feasible and reproducible access to the SM belly, opening direct access to electromyographic sensing of the eSRT. Surgical planner tools can quantitatively assist pre-surgical assessment.

Temporary and Permanent Auditory Effects Associated with Occupational Coexposure to Low Levels of Noise and Solvents.

This study aimed to assess temporary and permanent auditory effects associated with occupational coexposure to low levels of noise and solvents. Cross-sectional study with 25 printing industry workers simultaneously exposed to low noise (<80 dBA TWA) and low levels of solvents. The control group consisted of 29 industry workers without the selected exposures. Participants answered a questionnaire and underwent auditory tests. Auditory fatigue was measured by comparing the acoustic reflex threshold before and after the workday. Workers coexposed to solvents and noise showed significantly worse results in auditory tests in comparison with the participants in the control group. Auditory brainstem response results showed differences in III–V interpeak intervals (p = 0.046 in right ear; p = 0.039 in left ear). Mean dichotic digits scores (exposed = 89.5 ± 13.33; controls = 96.40 ± 4.46) were only different in the left ear (p = 0.054). The comparison of pre and postacoustic reflex testing indicated mean differences (p = 0.032) between the exposed (4.58 ± 6.8) and controls (0 ± 4.62) groups. This study provides evidence of a possible temporary effect (hearing fatigue) at the level of the acoustic reflex of the stapedius muscle. The permanent effects were identified mainly at the level of the high brainstem and in the auditory ability of binaural integration.

Sinus tympani revisited for planning retrofacial approach—radiologic study in pneumatized temporal bones and its surgical implications

Background and purposeRetrofacial approach (RFA) is an access route to sinus tympani (ST) and it is used in cholesteatoma surgery, especially when type C ST is encountered. It may also be used to gain an access to stapedius muscle to assess the evoked stapedius reflex threshold. The primary object of this study was to evaluate the morphology of sinus tympani and its relationship to facial nerve (FN) and posterior semicircular canal (PSC) in context of planning retrofacial approach in pneumatized temporal bones.MethodsCBCT of 130 adults were reviewed. The type of sinus tympani was assessed according to Marchioni's classification. Width of entrance to sinus tympani (STW), depth of ST (STD), distance between the posterior semicircular canal and facial nerve (F-PSC), distance between the latter plane to the floor of ST at the right angle (P-ST) were measured at level of round window (RW) and pyramidal ridge (PR).ResultsAll of the bones were well-aerated and classified in Dexian Tan pneumatization group 3 or 4. Type B of ST is dominant (70.8%) in adult population with no history of inflammatory otologic diseases, followed by type C (22.7%) and then type A (6.5%). The depth of ST (STD) presented significant deviations (ANOVA, p < 0.05) among all three types. STW reaches greater values on the level of PR. F-PSC does not correlate with type of ST. In over 75% of examined type C sinus tympani the distance P-ST was less than 1 mm.ConclusionsThe qualitative classification of the sinus tympani into types A, B and C, introduced by Marchioni is justified by statistically significant differences of depth between individual types of tympanic sinuses. The STW distance reaches greater values inferiorly—it may suggest that RFA should be performed in infero-superior manner rather than opposite direction. Preoperative assessment of temporal bones CT scans gives very important information about size of sinus tympani and distance between FN and PSC.

Middle ear myoclonus

Myoclonus is an involuntary, sudden jerking of a muscle or group of muscles. Middle ear myoclonus (MEM) is an idiopathic clinical entity attributed to causing abnormal repetitive contractions of the tensor tympani and/or stapedius muscles. MEM is an uncommon disorder produced by repetitive contractions of the middle ear muscles. In MEM, the objective tinnitus is produced by synchronous repetitive contraction of the tensor tympani and/or stapedius muscle. The exact etiology of MEM remains unclear. The diagnosis of MEM is often based on the history of rhythmic and involuntary clicking or buzzing tinnitus which is invariably unilateral. The important differential diagnosis of the MEM is palatal myoclonus while other local otological diseases must be excluded with careful clinical examination. Transcanal microscopic/endoscopic middle ear exploration with the injection of botulinum toxin into the tensor tympani and stapedius muscles is helpful to relieve the symptoms of MEM. This approach is both helpful as a diagnostic and therapeutic tool that allows temporary paralysis of the middle ear muscles before providing definitive surgical treatment. The surgical section of the middle ear muscles through tympanotomy is an excellent treatment option for MEM. There are not adequate research articles available concerning MEM and mainly case reports and few case series are available during the literature search. Proper methods for diagnosis and treatment of MEM are helpful to early resolution of the symptoms and enhance the quality of life. Here, this review article is attempting to discuss the etiopathology, clinical manifestations, diagnosis, and medical and surgical treatment of MEM. Literature search for MEM was done from the database of PubMed, MEDLINE, Scopus, and Google Scholar search with the use of the words MEM, middle ear muscles contractions, symptoms of MEM, diagnosis of MEM, and treatment of MEM.

Contraction of the stapedius and tensor tympani muscles explored by tympanometry and pressure measurement in the external auditory canal

It has been suggested that tensor tympani muscle (TTM) contraction may be involved in the development of ear-related pathologies such as tinnitus, hyperacusis and otalgia, called the tonic tensor tympani syndrome (TTTS). However, as there is no precise measure of TTM function under normal and pathological states, its involvement remains speculative. When the TTM or the stapedius muscle (SM) contracts, they both generate an increase of middle ear stiffness that can be measured through middle ear admittance. However, this technique cannot differentiate the contraction between the two muscles. On the other hand, the air pressure measured in a sealed external auditory canal can provide a measure of the eardrum displacement that may be able to differentiate SM from TTM contraction. TTM is attached to the malleus, and its contraction causes a retraction of the eardrum inside the middle ear cavity, while SM can have a small but reversed effect on TTM displacement. To investigate this issue, we compared the middle ear admittance and air pressure in a sealed external ear canal upon auditory stimulation (sMEMC) and voluntary middle ear muscle contraction (vMEMC). In addition, we assessed the perceptual effect of vMEMC, including pitch and loudness matching of the fluttering noise produced by vMEMC and the threshold shifts, were measured. Out of the 14 ears tested, sMEMC was associated with a decrease of admittance in 93% (mean peak average: -0.06 ml, SD:0.04) and an increase of air pressure in 29% of ears (mean peak average: 8.1 Pa, SD:5.1). No decrease in air pressure was found upon sMEMC. For vMEMC (n = 8 ears), decreases were found for both admittance and air pressure in 100% and 88%, with a mean peak average of -0.38 ml, SD: 0.54 and -149 Pa, SD:156, for admittance and pressure respectively. These results suggest that SM and TTM are involved in sMEMC and vMEMC, respectively. In addition, vMEMC was associated with perceptual effects including a low-frequency sound, pitch-matched at ∼30 Hz (>15 dB SL), and a low-frequency hearing loss of at least 10 dB between 20 and 200 Hz. In conclusion, admittance and air pressure recordings provide useful and complementary information on middle ear muscle contraction and can be used to explore the middle ear function.

Absent Stapedius Muscle and other Rare Congenital Ossicular Anomalies

Conductive hearing loss due to ossicular anomalies is generally associated with external auditory canal dysplasia. Congenital ossicular anomalies in isolation are rare and often have a delayed diagnosis, particularly if unilateral. In such cases, the predominant symptom is conductive hearing loss and otosclerosis is usually the major differential diagnosis. We present a series of three cases of congenital ossicular chain anomaly. These patients were initially diagnosed as a case of otosclerosis. However, the diagnosis was revised based on intraoperative findings and managed accordingly.

Microscopic Surgical Anatomy of the Stapedius Muscle in Fresh Cadaveric Temporal Bone

Introduction: Stapedius muscle is the smallest bone in the human body and it has an important role for preventing loud noise exposing to the inner ear. This stapedius muscle has also a very significant role during stapes surgery for otosclerosis. Materials and Methods: We studied the microscopic anatomy of the 36-stapedius muscle at our temporal bone dissection laboratory during the period of March 2019 to April 2021. All the 36 fresh temporal bones were dissected with the help of the microdrill, burr, and Zeiss microscope. Details of the stapedius muscle anatomy such as origin, extension, and attachment were studied. Results: The length of the stapedius muscle was ranging from 8 to 11 mm. The tendon of the stapedius muscle was ranging from 1.5 to 2.5 mm. The classical shape of the stapedius muscle was sickle shape. The bulky bell of the stapedius muscle was from 1.5 to 3.5 mm. Discussion and Conclusion: Clear anatomical knowledge of the stapedius muscle is needed for the postgraduates and during learning period of the otologist. If anatomical knowledge is not clear, it may lead to confusion between the stapedius muscle and facial nerve. Awareness regarding microscopic anatomic is required for avoiding the confusion between the facial nerve and stapedius muscle or during the facial nerve grafting.

The Potential Significance of Reversed Stapes Reflex in Clinical Practice in Idiopathic Intracranial Hypertension.

Background:Stapes reflex test is a method of evaluating the involuntary muscle contraction of the stapedius muscle in response to a high-intensity sound stimulus. The formation of this reflex involves the intact function of the 7th nerve, brain stem, 8th nerve, and middle ear. Due to ease of administration and information yielded, the stapedial reflex is considered one of the most powerful differential diagnostic audiological procedures. Numerous studies have remarked on the fluid communication between the intracochlear and intracranial spaces through the cochlear aqueduct. Currently, the potential significance of a noninvasive audiological technique in the discrimination of raised intracranial pressure constitutes a crucial topic of interest.Methods:We have performed the pre-LP and post-LP detailed otorhinolaryngological investigations, including the detailed inspection, audiometric testing, tympanometry, and stapedial reflex in a total of four consecutive patients with IIH.Results:We found that the stapedial reflex was bilateral absent initially in two of the patients. However, the second stapedial reflex investigations after LP showed reversal of the reflex responses in both of the patients.Conclusions:We suggest some hypotheses and propose some clinical applications. Future studies focusing on the potential utility of this reflex in the monitorization of IIH may provide crucial perspectives.

Congenital Absence of Stapedius Muscle and Tendon: Case Report with Review of Literature

Absence of stapedius muscle and its tendon is an extremely rare congenital anomaly, with only nine indexed reports in live patients. It presents with non progressive, occasionally bilateral conductive deafness, although this cannot be confirmed from Pure Tone Audiometry (PTA) and High Resolution Computed Tomography (HRCT). This makes it one of the least probable differential diagnosis of conductive deafness with unremarkable tympanic membrane. The definitive diagnosis is made only at time of surgery. The condition often co-exists with other genetic/acquired disorders of the middle/inner ear (otosclerosis, tympanosclerosis, etc.,). In absence of standardised, evidence based management protocol, diagnosis and appropriate treatment become challenging, and are predominantly situational. Its occurrence follows complex embryologic sequences where the internal portion of the interhyale- the mesenchymal condensation separating the cranial mesenchyme of the second pharyngeal arch (stapedial anlage) from Reichert’s cartilage- remains either absent or undergoes regression. Here, authors presents a case of 19-year-old female with congenital absence of stapedius muscle and tendon. She presented with congenital, bilateral, non progressive, moderate conductive hearing loss, and was diagnosed with this condition at surgery. There was co-existent tympanosclerosis in the middle ear that resulted in ossicular chain fixation and absence of round window reflex. The tympanosclerotic plaques were meticulously removed, ossicular chain mobility was restored, and a type II ossiculoplasty was done, along with reconstruction of the posterosuperior bony canal wall with cartilage perichondrium complex. Apart from the clinical presentation and its management, the present report also emphasises the plausible theories on relevant embryology explaining such an unusual event.

Accessing the Stapedius Muscle Via Novel Surgical Retrofacial Approach: A Cadaveric Feasibility Study.

Despite the complete embodiment of the stapedius muscle (SM) into the pyramidal eminence, it is possible to safely gain access to the SM belly via a retrofacial approach. This presents a novel approach to directly measure the electrically evoked stapedius reflex threshold (eSRT). Objective fitting of maximum comfortable loudness levels for cochlear implant users can improve the benefit introduced by the device. Sensing SM activity via direct surgical access represents a potential tool for objective eSRT fitting. Eighteen human temporal bones (TBs) were used. Micro-computed tomography was performed for six TBs. Standard computed tomography for six TBs. Manual 3D-segmentation of the relevant middle and inner ear anatomy was performed on 12 TBs. Mastoidectomy and posterior tympanotomy allowed the access to middle ear of all 18 the TBs. Once identified the mastoidal segment of the facial nerve (FN), the retrofacial access to the SM was drilled. The total access rate was 72.2%. Only in the first three cases the posterior semi-circular canal was hit. The SM access was identified posterior to the FN at a 4 ± 0.78 mm distance from the stapes' head, almost halfway to the chorda tympani's branching point along the FN direction. The drilling depth to access the SM posterior to the external surface of FN on average was 2 ± 0.30 mm. The exposure took on average of 5 to 8 minutes. The retrofacial approach seems to offer a feasible and reproducible access to the SM belly opening an avenue to electromyographic sensing of eSRT.

Analysis of tympanic sinus shape for purposes of intraoperative hearing monitoring: a microCT study

PurposeSinus tympani is the space in the retrotympanum, with variable morphology. Computed tomography is a common tool to investigate sinus tympani anatomy. During cochlear implantation or tympanoplasty, electrocochleography can be used for hearing monitoring. In such a surgical strategy the electrode is placed in the round window’s region throughout posterior tympanotomy. Common accessible needle-shaped electrodes using is difficult in achieving intraoperative stabilization. The aim of the study is to assess the dimensions and shape of sinus tympani, basing on the micro computed tomography scans for purposes of establishing the possible new electrocochleography electrode shape.Materials and methodsSixteen fresh frozen cadaveric temporal bones were dissected. MicroCT measurements included the depth and the width of sinus tympani, width of facial canal with stapedius muscle chamber. Obtained data were analyzed statistically with the use of RStudio 1.3.959 software.ResultsThe highest average width of sinus tympani amounted for 2.68 mm, depth measured at the round window plane for 3.19 mm. Width of facial canal with stapedius muscle chamber highest average values at the round window plane- 3.32 mm. The lowest average minimum and maximum values were calculated at the 1 mm above the round window plane. The highest average posterior tympanotomy width was 2.91 mm.ConclusionsThe shape of the tympanic sinus is like a trough with the narrowest and deepest dimensions in the middle part. The ST shape and dimensions should be taken into account in constructing the ECochG electrode, designed for optimal placement through posterior tympanotomy approach.

Intraoperative recordings of electromyogenic responses from the human stapedius muscle

Following surgical implantation of a cochlear implant, the external processor must be programmed individually, which is typically achieved by behavioral measurements, with the user indicating the perceived loudness between the threshold and the maximum comfort levels (MCLs). However, the stapedius reflex measurement could be used instead, as the basis for programming the fitting maps. The electrically evoked stapedius reflex threshold is known to have a high correlation with the MCLs and thus is used as an objective tool to determine the MCL, especially in children and non-cooperative patients. Previous studies demonstrated that the electromyogenic (EMG) activity of the stapedius muscle could be measured to determine stapedius reflex responses. The objective of this study was to demonstrate that intraoperative EMG recordings from the stapedius muscle could be performed with an EMG recording electrode designed for chronical implantation.Ten adult subjects with single sided deafness (SSD) participated in this study. The study was split up into a pre-, intra- and postoperative phase. In the preoperative phase the subjects were screened for the presence of the acoustic stapedius reflex by using a standard tympanometer in the ear to be implanted, while the contralateral ear was stimulated acoustically. During the intraoperative phase an EMG recording electrode was placed in the stapedius muscle and EMG responses were recorded during acoustical and electrical stimulation. The surgical procedure consisted of two interconnected procedures: A classical surgical approach for cochlear implantation with two additional surgical steps, and the temporary placement of an EMG recording electrode in the stapedius muscle made through an opening in the pyramidal eminence, allowing EMG recordings. The postoperative phase was used to evaluate the preservation of the stapedius reflex postoperatively at 1- and 6-months with contralateral acoustic and ipsilateral electrical stimulation.The EMG recording electrode could successfully be placed in the stapedius muscle in all subjects and was able to reliably record EMG signals from the stapedius muscle elicited by acoustic and electrical stimulation. Overall, EMG recordings were obtained intraoperatively in all subjects tested (8 out of 8 subjects). Contralateral acoustic stapedius reflexes were obtained in 6 out of 8 subjects and ipsilateral electrical stapedius reflex in 7 out of 8 subjects. In the postoperative phase, the preservation of the postoperative reflex was observed in 6 out of 10 subjects 1-month after surgery and in 8 out of 10 subjects 6-months after surgery.The study showed that intraoperative EMG recordings from the stapedius muscle can be performed with an EMG recording electrode designed for chronical implantation. The minimally invasive procedure is promising; in particular with regard to the future perspective of measurements in the long-term with an integrated closed-loop self-fitting system.

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.