A Biochemical Analysis of the Stapes

BACKGROUND Otosclerosis is a primary disease of the bony labyrinth. In the course of otosclerosis, abnormal resorption and recalcification of the endochondral layer of the temporal bone is observed. The otosclerotic process most commonly develops in the anterior part of the oval window. MATERIAL AND METHODS We analyzed stapes superstructures from 4 patients undergoing surgery for otosclerosis. The first step involved tissue assessment under a scanning electron microscope. The resulting images were analyzed in terms of morphological changes. The stapes superstructure was then divided into small "ossicles", including fragments from the closest vicinity of the stapes footplate and a fragment of the head of the stapes. This material was examined using a scanning electron microscope with a unit for chemical analysis in microareas. RESULTS Chemical analysis confirms the appearance of considerable quantities of the following elements: carbon, oxygen, potassium, and calcium, and the appearance of small quantities of sodium and magnesium. Based on a detailed analysis of the chemical composition, these fragments could represent a calcium phosphate compound from the following system: CaO-P₂O₅-H₂O. Fragments of the superstructure from the region closest to the base of the stapes demonstrated a considerably larger presence of carbon, oxygen, and nitrogen, which most likely suggests an increased metabolic process in this region. CONCLUSIONS Our analysis revealed an increased metabolic activity in the closest vicinity of the otosclerotic focus, the fissula ante fenestram. The increased metabolism correlated with the bone tissue changes seen on scanning electron microscopy.

Microcomputed tomography of the stapes: Wide-ranging dimensions

Although human stapes are known to have varied dimensions and the footplate is considered to be oval (fitting as it does into the oval window), few studies of high-resolution imaging of these structures have been performed. No study appears to have addressed the bilateral symmetry of stapes dimensions or to have determined if an association exists between the size of the stapes and the size of mastoid pneumatization; a small mastoid pneumatization is an indicator of childhood otitis media. We obtained 41 ear-normal cadaver crania specimens for study in our temporal bone laboratory and isolated 10 for further analysis: the 5 with the largest areas of mastoid pneumatization and the 5 with the smallest. Microcomputed tomography of tissue blocks was performed on the in situ stapes. Using ImageJ software, we created a three-dimensional model of each stapes. The mean height of these stapes was 3.43 mm (range: 3.20 to 3.80), the mean length of the footplates was 2.71 mm (range: 2.52 to 2.97), and the mean width of the footplates was 1.23 mm (range: 1.12 to 1.46). Qualitatively, the footplate was shaped like a human footprint in moist sand, as Eysell described in 1870. The dimensions of the stapes were found to be bilaterally symmetrical in general, but there was no correlation between these dimensions and the size of mastoid pneumatization. The distribution of footplate widths may be bimodal, which is consistent with the observation of Sim et al that men have wider footplates than do women.

Technical note for post-auricular route surgery in Mongolian gerbil

The Mongolian gerbil (Meriones unguiculatus) is commonly used in hearing research because the hearing frequency spectrum of the gerbil is rather similar to that of the human being. However, a precise description of the surgical post-auricular route has not been reported. The aim of this technical note is to provide details on the procedure and the surgical anatomy of the post-auricular route in the Mongolian gerbil. Surgery was performed under general anesthesia on eight (2 males and 6 females) adult Mongolian gerbils. All steps of the post-auricular route were detailed. This surgery provided an access to the following structures: the semi-circular posterior and lateral canals, the external auditory meatus, the tympanic membrane, the round window, the stapes, the stapedial artery and the reliefs of the cochlea. No anatomic variation was noticed among the 8 animals. This post-auricular route in the Mongolian gerbil defines a brief and simple surgery, overall standardized as a consequence of the absence of common anatomic variation, with painless and uncomplicated post-operative stage.

The Stapes of Gomphodont Cynodonts: Insights into the Middle Ear Structure of Non-Mammaliaform Cynodonts

The stapes is known in several non-mammaliaform cynodonts, although it has only been cursorily studied. Here we thoroughly analyze the stapedial anatomy of several basal cynodonts in a phylogenetic framework. Our study shows that the stapedial anatomy is more variable than previously thought. The morphological variation of the stapes led to the recognition of 11 phylogenetic characters that were included in a total evidence data matrix centered in the analysis of gomphodont cynodonts. Stapes morphology does not provide evidence to suggest a direct connection between the stapes and a postquadrate tympanic membrane (if present) and the hypothesis of a dorsal process as the site of attachment of a small ligament or the stapedial muscle is supported. The re-evaluation of the theories concerning the position of the tympanic membrane in non-mammaliaform cynodonts allowed us to conclude that the hypothetical postquadrate tympanic membrane associated with the squamosal sulcus is at best relictual and most likely non-functional (not connected with the stapes). The sound waves were most likely transmitted to the stapes from a postdentary tympanic membrane through the quadrate. Our analysis results in a better understanding of the auditory system in basal cynodonts and its evolution, highlighting the variability of the stapedial anatomy.

Middle-ear velocity transfer function, cochlear input immittance, and middle-ear efficiency in chinchilla

The transfer function H(V) between stapes velocity V(S) and sound pressure near the tympanic membrane P(TM) is a descriptor of sound transmission through the middle ear (ME). The ME power transmission efficiency (MEE), the ratio of sound power entering the cochlea to power entering the middle ear, was computed from H(V) measured in seven chinchilla ears and previously reported measurements of ME input admittance Y(TM) and ME pressure gain G(MEP) [Ravicz and Rosowski, J. Acoust. Soc. Am. 132, 2437-2454 (2012); J. Acoust. Soc. Am. 133, 2208-2223 (2013)] in the same ears. The ME was open, and a pressure sensor was inserted into the cochlear vestibule for most measurements. The cochlear input admittance Y(C) computed from H(V) and G(MEP) is controlled by a combination of mass and resistance and is consistent with a minimum-phase system up to 27 kHz. The real part Re{Y(C)}, which relates cochlear sound power to inner-ear sound pressure, decreased gradually with frequency up to 25 kHz and more rapidly above that. MEE was about 0.5 between 0.1 and 8 kHz, higher than previous estimates in this species, and decreased sharply at higher frequencies.

[Anatomical measurements and clinical applications through facial recess approach]

OBJECTIVE

To provide the anatomic data for the correlated otologic microsurgery by the microdissection of temporal bone through facial recess approach.

METHOD

Sixteen human temporal bones of eight adult cadaveric heads were dissected under surgical microscope through facial recess approach, and the relative anatomic structures were observed and measured, such as the bony entrance of facial recess approach, facial nerve, stapes, round window, round window niche, pyramidal eminence, cochleariform process, etc. The data were analyzed statistically.

RESULT

The width of the bony entrance of facial recess approach was (2.94 +/- 0.32) mm, the height was (8.83 +/- 0.84) mm, the depth was (3.51 +/- 0.17) mm. The distances from stapes to tympanic segment of facial nerve, mastoid segment of facial nerve, round window, cochleariform process and anterior ligament of malleus were (1.38 +/- 0.21) mm, (6.94 +/- 0.47) mm, (3.60 +/- 0.55)mm, (2.23 +/- 0.33)mm, (4.93 +/- 0.61) mm, respectively. The distances from pyramidal eminence to tympanic segment of facial nerve, mastoid segment of facial nerve, round window, round window niche and cochleariform process were (1.05 +/- 0.09) mm, (5.63 +/- 0.41) mm, (3.01 +/- 0.34) mm, (3.29 +/- 0.44) mm, (4.13 +/- 0.51) mm, respectively. The distances from round window to cochleariform process and tympanic segment of facial nerve were (5.11 +/- 0.61) mm and (3.97 +/- 0.61) mm. The distances from round window niche to tympanic segment of facial nerve and mastoid segment of facial nerve were (4.13 +/- 0.38) mm and (7.28 +/- 0.29) mm.

CONCLUSION

The facial recess approach played an important role in modern otologic microsurgery. The position of anatomical structure was constant relatively, including short crus of incus, stapes, pyramidal eminence and cochleariform process, etc. These could be used as reference marks for otologic microsurgery.

Characterization of stapes anatomy: investigation of human and guinea pig

The accuracy of any stapes model relies on the accuracy of the anatomical information upon which it is based. In many previous models and measurements of the stapes, the shape of the stapes has been considered as symmetric with respect to the long and short axes of the footplate. Therefore, the reference frame has been built based upon this assumption. This study aimed to provide detailed anatomical information on the dimensions of the stapes, including its asymmetries. High-resolution microcomputed tomography data from 53 human stapes and 11 guinea pig stapes were collected, and their anatomical features were analyzed. Global dimensions of the stapes, such as the size of the footplate, height, and volume, were compared between human and guinea pig specimens, and asymmetric features of the stapes were quantitatively examined. Further, dependence of the stapes dimensions on demographic characteristics of the subjects was explored. The height of the stapes relative to the footplate size in the human stapes was found to be larger than the corresponding value in guinea pig. The stapes showed asymmetry of the footplate with respect to the long axis and offset of the stapes head from the centroid of the medial surface of the footplate for both humans and guinea pigs. The medial surface of the footplate was curved, and the longitudinal arches of the medial surface along the long axis of the footplate were shaped differently between humans and guinea pigs. The dimension of the footplate was gender-dependent, with the size greater in men than in women.

Influence of the middle ear anatomy on the performance of a membrane sensor in the incudostapedial joint gap

There is a great demand for implantable microphones for future generations of implantable hearing aids, especially Cochlea Implants. An implantable middle ear microphone based on a piezoelectric membrane sensor for insertion into the incudostapedial gap is investigated. The sensor is designed to measure the sound-induced forces acting on the center of the membrane. The sensor mechanically couples to the adjacent ossicles via two contact areas, the sensor membrane and the sensor housing. The sensing element is a piezoelectric single crystal bonded on a titanium membrane. The sensor allows a minimally invasive and reversible implantation without removal of ossicles and without additional sensor fixation in the tympanic cavity. This study investigates the implantable microphone sensor and its implantation concept. It intends to quantify the influence of the sensor's insertion position on the achievable microphone sensitivity. The investigation considers anatomical and pathological variations of the middle ear geometry and its space limitations. Temporal bone experiments on a laboratory model show that anatomical and pathological variations of the middle ear geometry can prevent the sensor from being placed optimally within the incudostapedial joint. Beyond scattering of transfer functions due to anatomic variations of individual middle ears there is the impact of variations in the sensor position within the ossicular chain that has a considerable effect on the transfer characteristics of the middle ear microphone. The centering of the sensor between incus and stapes, the direction of insertion (membrane to stapes or to incus) and the effect of additional contact points with surrounding anatomic structures affect the signal yield of the implanted sensor. The presence of additional contact points has a considerably impact on the sensitivity, yet the microphone sensitivity is quite robust against small changes in the positioning of the incus on the sensor. Signal losses can be avoided by adjusting the position of the sensor within the joint. The findings allow the development of an improved surgical insertion technique to ensure maximally achievable signal yield of the membrane sensor in the ISJ and provides valuable knowledge for a future design considerations including sensor miniaturization and geometry. Measurements of the implanted sensor in temporal bone specimens showed a microphone sensitivity in the order of 1 mV/Pa. This article is part of a special issue entitled "MEMRO 2012".

Titanium ball joint total ossicular replacement prosthesis--experimental evaluation and midterm clinical results

During reconstruction of the ossicular chain, there is a need to address the forces and loads caused by the ambient atmospheric pressure variations and the resulting tympanic membrane movements. It is understood that when a rigid middle ear prosthesis is inserted the malleoincudal joint, a keyfactor in controlling pressure variations in the middle ear space is bypassed. In this paper we describe a modified total titanium ossicular replacement prosthesis with an innovative micro ball joint in the headplate which is designed to compensate for tympanic membrane movements caused by atmospheric pressure variations. The characteristics of this modified prosthesis were examined in temporal bone experiments and compared to the standard titanium total ossicular reconstruction prosthesis. Sound-induced stapes footplate movements were investigated by means of a Laser vibrometer and revealed no significant differences between the two prostheses in vitro. Intraoperatively, the insertion of the modified prosthesis required more delicate handling. The angle between the shaft and the headplate was variable and ranged from 60 to 90° as estimated by the surgeon. Twelve consecutive patients were eligible for clinical evaluation. The pure tone average (PTA) air-bone gap after a mean follow up period of 32 months was 18.8 dB. Furthermore, no extrusion, dislocation or other adverse events were observed. We conclude that the modified total ossicular replacement prosthesis with integrated micro ball joint yields similar volume velocities of the stapes footplate in the laboratory experiments compared to the standard rigid prosthesis. The audiological and morphological results are encouraging and show that the mobile prosthesis headplate adjusting to the level of the tympanic membrane is a further step in the development of a physiological middle ear implant. This article is part of a special issue entitled "MEMRO 2012".

In-plane motions of the stapes in human ears

The piston-like (translation normal to the footplate) and rocking-like (rotation along the long and short axes of the footplate) are generally accepted as motion components of the human stapes. It has been of issue whether in-plane motions, i.e., transversal movements of the footplate in the oval window, are comparable to these motion components. In order to quantify the in-plane motions the motion at nine points on the medial footplate was measured in five temporal bones with the cochlea drained using a three-dimensional (3D) laser Doppler vibrometer. It was found that the stapes shows in-plane movements up to 19.1 ± 8.7% of the piston-like motion. By considering possible methodological errors, i.e., the effects of the applied reflective glass beads and of alignment of the 3D laser Doppler system, such value was reduced to be about 7.4 ± 3.1%. Further, the in-plane motions became minimal (≈ 4.2 ± 1.4% of the piston-like motion) in another plane, which was anatomically within the footplate. That plane was shifted to the lateral direction by 118 μm, which was near the middle of the footplate, and rotated by 4.7° with respect to the medial footplate plane.

[Applied anatomy of facial recess and posterior tympanum related to cochlear implantation]

OBJECTIVE

To investigate the related parameters of temporal bone structure in the surgery of cochlear implantation through facial recess approach so as to offer a theoretical reference for the avoidance of facial nerve injury and the accurate localization.

METHOD

In a surgical simulation experiment, twenty human temporal bones were studied. The correlation parameters were measured under surgical microscope.

RESULT

Distance between suprameatal spine and short process of incus was (12.44 +/- 0.51) mm. Width from crotch of chorda tympani nerve to stylomastoid foramen was (2.67 +/- 0.51) mm. Distance between short process of incus and crotch of chorda tympani nerve was (15.22 +/- 0.83) mm. The location of maximal width of the facial recess into short process of incus, crotch of chorda tympani nerve were (6.28 +/- 0.41) mm, (9.81 +/- 0.71) mm, respectively. The maximal width of the facial recess was (2.73 +/- 0.20) mm. The value at level of stapes and round window were (2.48 +/- 0.20 mm) and (2.24 +/- 0.18) mm, respectively. Distance between pyramidalis eminence and anterior round window was (2.22 +/- 0.21) mm. Width from stapes to underneath round window was (2.16 +/- 0.14) mm.

CONCLUSION

These parameters provide a reference value to determine the position of cochlear inserting the electrode array into the scale tympani and opening facial recess firstly to avoid potential damage to facial nerve in surgery.

Detection and identification of CD46 splicing isoforms by nested RT-PCR

CD46 (Membrane Cofactor Protein, MCP) is a transmembrane glycoprotein, which is expressed by all nucleated human cells whose purpose is to protect against autologous complement attack. In addition, CD46 can serve as a receptor for several viruses and bacteria and as a potent regulator of the inflammatory response by affecting T cell differentiation. Multiple isoforms of CD46 exist due to alternative splicing and are coexpressed in human cells in various patterns and expression levels. However, specific diseases have not been associated with isoform coexpression. We applied a nested RT-PCR method to investigate the coexpression pattern of CD46 splicing variants in otosclerotic and normal stapes footplate specimens. Using this method, we detected an altered isoform expression pattern and identified four novel CD46 splicing variants overexpressed in otosclerotic bone. This study is the first comprehensive report to provide evidence for disease associated alternative splicing of CD46.

Microscopic guide to the middle ear anatomy in guinea pigs

OBJECTIVES

To reveal microscopic surgical anatomy of the middle ear in guinea pigs (GPs).

MATERIALS AND METHODS

Twenty ears of GPs were dissected under dissection microscopy via inferior approach. By using digital equipment, the most suitable photograph was taken for each step. Differences and similarities between the ears of GPs and those of human beings are discussed to show the advantages and disadvantages of the GP ear for experimental studies.

RESULTS

Tympanic membrane of the GP merely consists of pars tensa and above this there is a bony segment called as supratympanic crest. There were two spaces called bulla and hypotympanium in the GP,s middle ear. Cochlea, which is normally found in the inner ear in humans, separates these two spaces. Upper part of this space which is called epitympanium is a slit like cavity having a bony complex called malleoincudal complex. Bulla, the largest cavity in the middle ear, is a hemispherical cavity having a smooth surface. It corresponds to hypotympanum and mesotympanum of human middle ear. Cochlea has 3.5 turns from basal turn to apical turn. While the oval window is placed vertically, the round window is placed horizontally. While the stapes is almost identical to that of the humans, there is a bony bridge between the crura of the stapes called crista stapedius. Stapes can not removed unless this bony bridge is taken.

CONCLUSION

The middle ear in GP differs from the human middle ear in many aspects. Researchers who are planning to the study with this animal model should be aware of all these differences.

[Measurement study of MDCT 3D reconstruction and microanatomy related to individual piston shaping on malleostapedotomy]

OBJECTIVE

To study the management of basic parameters related to individual piston shaping on malleostapedotomy by MDST 3D reconstruction and microanatomy and to assess the accuracy of MDST method.

METHOD

Ten Chinese temporal bones without ear diseases were numbered randomly and scanned by GE Light Speed Ultra 64 rows of spiral CT. 3D structure of ossicular chain were reconstructed by MPR and VR methods in AW4. 1 workstation. Then measurements of distances between stapes head to stapes footplate (A line), and manubrium to stapes head (B line), and manubrium to stapes footplate (C line), angle between line A and line B (angle AB) are completed. After that, all samples of temporal bone were undergone canal wall down mastoidectomy under microscope and the relevant measurements were completed.

RESULT

The MPR and VR technique of MDCT reconstructed ossicular chain clearly, and revealed the spatial relationship between every structure stereoscopically. Respectively, lengths of A, B, C line by MDST and microanatomy are (3.42 +/- 0.86) mm and (3.60 +/- 0.94) mm, (3.42 +/- 0.80) mm and (2.96 +/- 0.42) mm, (5.86 +/- 0.60) mm and (6.22 +/- 1.10) mm, while angle AB (141.05 +/- 30.07) degrees and (144.57 +/- 41.86) degrees. There are no statistically significant differences between two groups (P>0.05).

CONCLUSION

The MPR and VR technique of MDCT can clearly reconstructed the 3D shapes of the temporal bone and finish the exactly managements on A, B, C lines and AB angel which is crucial for shaping a individual piston on malleus-to-oval window surgery.

Gerbil middle-ear sound transmission from 100 Hz to 60 kHz

Middle-ear sound transmission was evaluated as the middle-ear transfer admittance H(MY) (the ratio of stapes velocity to ear-canal sound pressure near the umbo) in gerbils during closed-field sound stimulation at frequencies from 0.1 to 60 kHz, a range that spans the gerbil's audiometric range. Similar measurements were performed in two laboratories. The H(MY) magnitude (a) increased with frequency below 1 kHz, (b) remained approximately constant with frequency from 5 to 35 kHz, and (c) decreased substantially from 35 to 50 kHz. The H(MY) phase increased linearly with frequency from 5 to 35 kHz, consistent with a 20-29 micros delay, and flattened at higher frequencies. Measurements from different directions showed that stapes motion is predominantly pistonlike except in a narrow frequency band around 10 kHz. Cochlear input impedance was estimated from H(MY) and previously-measured cochlear sound pressure. Results do not support the idea that the middle ear is a lossless matched transmission line. Results support the ideas that (1) middle-ear transmission is consistent with a mechanical transmission line or multiresonant network between 5 and 35 kHz and decreases at higher frequencies, (2) stapes motion is pistonlike over most of the gerbil auditory range, and (3) middle-ear transmission properties are a determinant of the audiogram.

Anatomy and anthropometry of human stapes

Twelve human stapes from temporal bones fixed by formalin were extracted. Different dimensions were measured by an electronic microscope with an accuracy of microm. These dimensions were as follows: (1) maximum diameter of stapes head parallel to the axis of footplate, 1088 microm (range, 857-1277 microm); (2) distance of main nutritional foramen to head surface, 398 microm (range, 250-833 microm); (3) stapes head to shoulders, 757 microm (range, 571-1000 microm), head to foramen, 1047 microm (range, 785-1500 microm), and head to lateral surface of footplate, 2612 microm (range, 1892-3400 microm); (4) anterior crus width at shoulder, 398 microm (range, 333-500 microm); minimum width of anterior crus, 251 microm (range, 214-350 microm); (5) posterior crus width at shoulders, 386 microm (range, 285-600 microm); minimum width of posterior crus, 191 microm (range, 142-300 microm); (6) maximum width of footplate near anterior crus, 371 microm (range, 321-500 microm), maximum width of footplate near the posterior crus, 411 microm (range, 357-611 microm), minimum width of footplate, 228 microm (range, 178-388 microm); (7) maximum width of ossicle, 2298 microm (range, 1928-3050 microm); (8) angle between crura, 19.5 degrees (range, 15-24 degrees ); and (9) diameter of foramen at the end of curve, 1343 microm (range, 1071-1888 microm).

MRI scanners and the stapes prosthesis

OBJECTIVE

Physicians and patients alike have concerns regarding exposing in vivo implanted metal stapes prostheses to magnetic resonance imaging (MRI) scanners. As MRI scanners become more powerful, the possibility for stapes prosthesis displacement due to ferromagnetic forces increases. It is hypothesized that some metal stapes prostheses may be exposed to powerful MRI scanners without leading to potential adversities for patients.

STUDY DESIGN

Literature review, retrospective case review, and physician survey.

SETTINGS

Tertiary care, University Medical Center.

MATERIALS AND METHODS

A review of the medical literature,a retrospective case review, and a clinical survey were performed.

RESULTS

In the history of stapes prostheses, 1 adverse patient outcome was causally substantiated when a defective stapes prosthesis was exposed to an MRI field. Otherwise, a review of the literature on experiments investigating stapes prostheses and MRI fields revealed a lack of any adverse clinical reports. In addition, 2 physician's surveys revealed no other cases of symptoms or damage to the ears of patients with stapes prostheses that had been exposed to an MRI scanner.

CONCLUSION

All patients with a metallic stapes prosthesis may be sent to the MRI scanner, with the exception of 1 specific defective prosthesis type. The exception is a 1987 accidental mismanufacture of several lots of McGee pistons with a magnetic alloy. Patients with these specifically identified lots of McGee pistons should go to a computed tomographic scanner or be reimplanted with another prosthesis if MRI scans are mandatory. It would be advisable for manufacturers to use nonferromagnetic metals such as titanium for production of future stapes prostheses.

CT scans and 3D reconstructions of Florida manatee (Trichechus manatus latirostris) heads and ear bones

The auditory anatomy of the Florida manatee (Trichechus manatus latirostris) was investigated using computerized tomography (CT), three-dimensional reconstructions, and traditional dissection of heads removed during necropsy. The densities (kg/m3) of the soft tissues of the head were measured directly using the displacement method and those of the soft tissues and bone were calculated from CT measurements (Hounsfield units). The manatee's fatty tissue was significantly less dense than the other soft tissues within the head (p<0.05). The squamosal bone was significantly less dense than the other bones of the head (p<0.05). Measurements of the ear bones (tympanic, periotic, malleus, incus, and stapes) collected during dissection revealed that the ossicular chain was overly massive for the mass of the tympanoperiotic complex.

[Three-dimensional morphological measurements of the utricle, saccule and stapes footplate]

OBJECTIVE

To determine the optimal drill area on the footplate with the 3D measurements of the stapes and the vestibular end organs.

METHODS

Four temporal bones were extracted from the fresh cadavers and undecalcified polymer-embedded. After serially sectioning, image processing and the 3D precisely reconstruction, a local Cartesian coordinates was established in which the tympanic surface of the footplate was supposed to be XY plane and the Z coordinate axis passed through the central point of the footplate and was vertical to the XY plane. The configurations of the utricle and saccule were delineated quantitatively, and then any distance between one point on the surface of the footplate and another point on the surface of the utricle or saccule and its orientation can be measured.

RESULTS

There was a "V" shaped cleft between the utricle and the saccule. The angle of the" V" shaped cleft was 50.31 +/- 19.90 (17.00 - 68.00) degrees. The apex of the cleft directed anterosuperiorly and approached the footplate center, while beneath the posteroinferior part of the footplate was an open and deep area. The vertical distance from the center point of the footplate to the vestibular end organs was (2.20 +/- 0.548) mm, the maximum of 3.0 mm and the minimum of 1.6 mm.

CONCLUSIONS

The posterior and inferior quadrant of the footplate may be the optimal drill area for the fenestra.

Promontory Drilling in Stapedectomy

BACKGROUND

Anatomical variants such as an overhanging facial nerve or promontory can impede access to the footplate during stapedectomy. Drilling away bone from the cochlear promontory may be required. In the case of a floating or depressed footplate, it has been recommended that a "pothole" be drilled in the inferior margin of the oval window. There is little published information on the anatomy of the promontory with respect to these maneuvers.

MATERIALS AND METHODS

Twenty temporal bones were studied. A series of measurements was made to assess how much bone may safely be removed without risking damage to the underlying cochlear endosteum and, hence, spiral ligament and stria vascularis.

RESULTS

The bony promontory is thickest posteriorly, and here, the endosteum has least lateral projection. The promontory becomes thinner closer to the oval window. Moving anteriorly, the bone becomes thinner and the underlying endo steum more closely follows the bony contour. The stria vascularis and spiral ligament may be less than 0.2 mm inferior to the inferior margin of the oval window posteriorly. This distance is at least 0.3 mm at the midpoint of the footplate (range, 0.3-0.5 mm).

CONCLUSION

Bone may be removed inferiorly to the posterior one-third of the footplate from lateral to a line that makes an angle of 35 degrees with the superoinferior axis of the footplate. In creating a "pothole" in the case of a floating or depressed footplate, the authors recommend that it be created at the midpoint of the inferior margin of the oval window and should not exceed 0.3 mm in diameter.

A bifid intra-tympanic facial nerve in association with a normal stapes

A rare facial nerve anomaly was incidentally discovered whilst performing a tympanoplasty and ossicular reconstruction on a patient with an acquired unilateral conductive hearing loss. The nerve was seen to bifurcate and straddle a normal stapes superstructure as it ran posteriorly through the middle ear, a unique and as yet unreported combination. This case highlights the importance of vigilance regarding facial nerve anatomical variations encountered during middle-ear surgery thus avoiding inadvertent damage. The purported embryological mechanism responsible for such anomalies of the intra-tympanic facial nerve is discussed.

Three-dimensional regular arrangement of the annular ligament of the rat stapediovestibular joint

The stapes footplate articulates with the vestibular window through the annular ligament. This articulation is known as the stapediovestibular joint (SVJ). We investigated the ultrastructure of adult rat SVJ and report here on the characteristic ultrastructure of the corresponding annular ligament. Transmission electron microscopy showed that this annular ligament comprises thick ligament fibers consisting of a peripheral mantle of microfibrils and an electron-lucent central amorphous substance that is regularly arranged in a linear fashion, forming laminated structures parallel to the horizontal plane of the SVJ. Scanning electron microscopy revealed that transverse microfibrils cross the thick ligament fibers, showing a lattice-like structure. The annular ligament was vividly stained with elastica van Gieson's stain and the Verhoeff's iron hematoxylin method. Staining of the electron-lucent central amorphous substance of the thick ligament fibers by the tannate-metal salt method revealed an intense electron density. These results indicate that the annular ligament of the SVJ is mainly composed of mature elastic fibers.

Developing a Physical Model of the Human Cochlea Using Microfabrication Methods

Advances in micro-machining technology have provided the opportunity to explore possibilities of creating life-sized physical models of the cochlea. The physical model of the cochlea consists of two fluid-filled channels separated by an elastic partition. The partition is micro-machined from silicon and uses a 36-mm linearly tapered polyimide plate with a width of 100 microm at the basal end and 500 microm at the apex to represent the basilar membrane. Thicknesses from 1 to 5 microm have been fabricated. Discrete aluminum fibers (1.5 microm in width) are machined to create direction-dependent properties. A 0.5 x 0.5 mm opening represents the helicotrema. The fluid channels are machined from plexiglas using conventional machining methods. A magnet-coil system excites the fluid channel. Measurements on a model with thickness 4.75 microm show a velocity gain of 4 and phase of 3.5 pi radians at a location 23 mm from the base. Mathematical modeling using a 3-D formulation confirm the general characteristics of the measured response.

The Ponticulus: An Anatomic Study

HYPOTHESIS

The purpose of this study was to resolve anatomic ambiguities of the ponticulus so the surgeon will be better able to remove disease from the posterior tympanum.

BACKGROUND

The first step in refining an operative approach is to acquire a thorough understanding of the anatomy. A detailed study of one structure of the posterior tympanum, the ponticulus, has not yet been reported.

METHODS

Fifty temporal bone plugs harvested from human cadavers were studied. The presence or absence of the ponticulus, its configuration, and its proximity to other middle ear structures were recorded for each temporal bone.

RESULTS

There was complete formation of the ponticulus in 33 of the 50 specimens. In 7, only a remnant of the ponticulus formed, and it was completely absent in 10 of the 50 specimens. In the 33 specimens in which the ponticulus was present, it measured less than 1 mm in thickness in 22, it was larger than 1 mm in 7, and in 4 specimens it extended down to the floor of the middle ear as a sheet of bone. In 8 specimens, the ponticulus lay just adjacent to the stapes.

CONCLUSION

The ponticulus is present in the majority of ears. It is best defined as a bridge of bone from the pyramidal eminence to the promontory and most commonly occurs as a thin, bony structure. This definitive study of the ponticulus will allow the otologic surgeon to better remove disease from the posterior tympanum.

High-resolution X-ray computed tomographic scanning of the human stapes footplate

OBJECTIVES

The mechanical behaviour of the footplate and its annular ligament depends critically on their shape and orientation in the oval window, but accurate measurements have been difficult to make owing to their small size. Our aims are to visualize the footplate at high resolution and understand its dynamics.

METHODS

The human cadaver stapes footplate was dissected, and very high-resolution x-ray computed tomographic (CT) scans, with voxel sizes from 4 to 8 pm, were performed. Locally developed software was used to reconstruct the images.

RESULTS

The data permit us to explore minor details of shape and orientation. The footplate looks like a footprint, and the annular ligament has variable thickness, with a cleft (groove) in its anterior attachment to the oval window. The CT data also permit us to create a three-dimensional finite-element model that can simulate footplate motion.

CONCLUSIONS

The results obtained lead to further understanding of the mechanical behaviour of the footplate and the annular ligament.

On the coupling between the incus and the stapes in the cat

The connection between the long process and the lenticular process of the incus is extremely fine, so much so that some authors have treated the lenticular process as a separate bone. We review descriptions of the lenticular process that have appeared in the literature, and present some new histological observations. We discuss the dimensions and composition of the lenticular process and of the incudostapedial joint, and present estimates of the material properties for the bone, cartilage, and ligament of which they are composed. We present a preliminary finite-element model which includes the lenticular plate, the bony pedicle connecting the lenticular plate to the long process, the head of the stapes, and the incudostapedial joint. The model has a much simplified geometry. We present simulation results for ranges of values for the material properties. We then present simulation results for this model when it is incorporated into an overall model of the middle ear of the cat. For the geometries and material properties used here, the bony pedicle is found to contribute significant flexibility to the coupling between the incus and the stapes.

Experimental study of an adjustable-length prosthesis in a temporal bone model

CONCLUSIONS

This prosthesis has the advantage of rapid adjustment at the time of insertion in order to achieve optimal tension and, as a result, optimal sound transmission.

OBJECTIVE

To test the acoustic performance of a new, adjustable incus replacement prosthesis in a human temporal bone model.

MATERIAL AND METHODS

Experiments were performed in seven human temporal bones, before and after removal of the incus and insertion of the prosthesis. The input comprised 406 pure tones ranging in frequency between 0.1 and 10 kHz at an intensity of 80 dB SPL at the tympanic membrane. The output measurement was stapes footplate displacement, determined by means of a laser Doppler vibrometer. Three lengths of the prosthesis were investigated: optimal, optimal +0.2 mm and optimal +0.4 mm.

RESULTS

The optimal-length prosthesis produced similar results to those of an intact middle ear. The slightly longer prostheses decreased middle ear sound transmission at all test frequencies, except those near 1.5 kHz.

[Preparation and clinical application of Teflon-wire piston and stapes height measurer]

With Teflon, and a tiny stainless steel needle of a number 7 injector and an acupuncture needle,Teflon-piston and a measurer of the stapes height were prepared respectively of stapedectomy for treatment of otosclerosis. Good clinical results were achieved with these simple and useful devices.

A detailed subgross morphometric study on the auditory ossicles of the New Zealand rabbit

This study was designed to reveal, in detail, the features of the auditory ossicles of the New Zealand rabbit, one of the most frequently used animals in scientific researches. Heads of 10 dead adult New Zealand rabbits of both sexes weighing 2.5 +/- 0.2 kg were used in the study. The auditory ossicles were gently removed from their situs and observed. The auditory ossicles were three small bones: the malleus, the incus and the stapes. The lenticular bone seemed to be the lenticular process, as is in human beings. In general, macroanatomic features of the bones were similar to those reported in the literature. Findings in this study, however, differed greatly, especially in detail. There were statistically significant differences in the morphometric data of the features of the auditory ossicles between the right- and left-hand sides. Data from the right-hand side were significantly higher.

Sex differences in the middle ear of the bullfrog (Rana catesbeiana)

Impedance transformation by the middle ear of terrestrial vertebrates is considered to be a function of the ossicular lever apparatus, which increases force and decreases velocity at the stapes footplate relative to the tympanic membrane, and the ratio of tympanic membrane area to stapes footplate area (the area ratio), which increases pressure at the stapes. A recent vibrometric study has found that the velocity ratio between tympanic membrane and stapes footplate is higher in male bullfrogs (Rana catesbeiana) than in females. Although the tympanic membrane area is known to be larger in male bullfrogs, the area ratio has apparently never been compared between the sexes. The hypothesis that a lower area ratio in males helps to compensate for the higher velocity ratio was investigated by comparing tympanic membrane, stapes footplate and operculum areas in frogs of both sexes. Contrary to expectation, the difference in stapes footplate area between males and females is very small, and area ratios are considerably higher in males. Area ratios increase with increasing body size in both sexes. Operculum area does not differ between the sexes. The apparent difference in impedance transformation between male and female frogs might be necessary due to different inner ear impedances, or might reflect serious inadequacies in the conventional models of middle ear function.

[An anatomical investigation relating to the stapes elevation surgery]

OBJECTIVE

For the purpose of improving patient's hearing in stapes elevation surgery.

METHOD

The anatomical features relating to this operation were observed and measured in 30 ears of fresh cadavers, which included the length of lenticular process, the highness of stapes head and neck, the thickness of lower border of footplate, the angle of incudostapecial joint and the gradients of upper and lower wall of vestibular niche. The relation between two types of the present operation and the investigation were discussed.

RESULT

The two types of present operations were in accord with the physiologicoanatomical features of the stapes and incus.

CONCLUSION

In order to improve the patient's hearing, making use of biobinder for strengthening the incudostapedial connexion as a routine is suggested.

Relationship of the utriculus and sacculus to the stapes footplate: anatomic implications for sound-and/or pressure-induced otolith activation

One hundred thirty human temporal bones that were sectioned in the vertical plane were examined to evaluate the relationship between the stapes footplate and the otolith organs. The shortest distance between the footplate and the utriculus was 0.58+/-0.10 mm in the posterior third of the oval window, 1.04+/-0.20 mm in the middle third, and 1.51+/-0.20 mm in the anterior third. The distance from the sacculus to the footplate was 1.33+/-0.20 mm in the middle third of the oval window and 1.31+/-0.18 mm in the anterior third. Membranous connections extending between the utriculus and the footplate were found in 26% of temporal bones. These membranous connections in coexistence with additional anatomic factors such as stapes hypermobility and/or dehiscence of bone within labyrinthine structures may predispose patients to sound- and/or pressure-induced otolith activation. The findings may have implications for different causes of the Tullio phenomenon.

Comparing in vitro, in situ, and in vivo experimental data in a three-dimensional model of mammalian cochlear mechanics

Normal mammalian hearing is refined by amplification of the motion of the cochlear partition. This partition, comprising the organ of Corti sandwiched between the basilar and tectorial membranes, contains the outer hair cells that are thought to drive this amplification process. Force generation by outer hair cells has been studied extensively in vitro and in situ, but, to understand cochlear amplification fully, it is necessary to characterize the role played by each of the components of the cochlear partition in vivo. Observations of cochlear partition motion in vivo are severely restricted by its inaccessibility and sensitivity to surgical trauma, so, for the present study, a computer model has been used to simulate the operation of the cochlea under different experimental conditions. In this model, which uniquely retains much of the three-dimensional complexity of the real cochlea, the motions of the basilar and tectorial membranes are fundamentally different during in situ- and in vivo-like conditions. Furthermore, enhanced outer hair cell force generation in vitro leads paradoxically to a decrease in the gain of the cochlear amplifier during sound stimulation to the model in vivo. These results suggest that it is not possible to extrapolate directly from experimental observations made in vitro and in situ to the normal operation of the intact organ in vivo.

[The evolution of the lower jaw and the jaw joint, from reptiles to man]

The evolution of the mandible shows two characteristic features: transformation of the angular, articular and square bones in reptiles into the tympanic bone, malleus and incus of the middle ear respectively; and specific volume expansion of the tooth-bearing bone which in mammals comprises the entire mandible. Posture, locomotion and mastication are the basic evolutionary factors which simultaneously provoked 1) a displacement of the temporal regions, 2) a transformation of the face lowering and widening the lower jaw and 3) an elongation of the sutures uniting the different bones in the reptile jaw bone, progressively leading to their separation and transversal orientation. These transformations were accentuated in the biped. Thus in man the temporomandibular joint is in a very lateral and elevated position near the mastoids. The mandibular condyls are elongated transversally with a medial cantilever. The medial part of the meniscus is drawn medially by the lateral pterygoid while the lateral part is drawn laterally by the temporal and masseter fibers. The ramus is oriented vertically and lies close to the cervical spine. The dental arches are displaced posteriorly on the bone and have lost their anterior abutment. The strongest occlusal forces are displaced to the posterior part of the arches and are transmitted vertically to the intra-articular meniscus. All these phenomena are termed extreme adaptations and the temporomandibular joint would (apparently) suffer if the evolution continued. The architectural features of temporomandibular joint overload can be deducted by comparison with the "ideal" architectural conditions for the craniofacial equilibrium.

Surgical Anatomy of the Rat Middle Ear

This study was designed to aid experimental otologic studies of the rat middle ear. The topographic anatomy of the albino rat middle ear is described. A set of microphotographs with matching illustrations presents the structural details at several surgical exposures. Anatomic differences between the rat, guinea pig, and cat are noted.

On the role played by ontogenetic remodeling and functional transformation in the evolution of terrestrial hearing

Using examples from the octavolateral system, evidence is reviewed suggesting a relationship between regressive events, such as loss of one function, or loss of one sensory subsystem, and progressive evolutionary changes in topologically associated systems. While none of the neuronal examples in the evolutionary reorganization of the otic region are as clear-cut as the initial example of non-neuronal reorganization on which the correlation of regressive with progressive changes is based (the functional transformation of the hyomandibular bone into the stapes), the general principle that a chance correlation of two insignificant events may lead to a novel function may be valid for more aspects of the evolution of the ear, in particular the auditory system, than is currently appreciated. It is suggested that regressive events may not only be an evolutionary dead end but that they may provide, through the relaxation of constraints imposed on the respective structure, a source for innovations. However, transformations of functionally uncoupled structures into a novel adaptive function will occur only when topologically adjacent structures require these transformations to improve their own function.

The vestibular nerve: its course to the anterior and lateral ampullae

The course of the ampullary nerve to the anterior and lateral ampullae was studied using 25 human temporal bones. Sudan Black B staining was applied to decalcified temporal bones in order to stain nerve fibers. After removing the external and middle ear, each temporal bone was divided into four blocks by three parallel planes, making an angle of 45 degrees to the long axis of the stapes footplate or a line along the stapedial tendon. Two planes were in contact with the anterior and posterior margin of the oval window, respectively. The third plane passed through the capitulum of the stapes. Distances from the upper margin of the oval window, to the distal and proximal part of the ampullary nerve, to the facial nerve, and to the utricular macula were measured in the third plane. The thickness of the thinnest part of the wall of the facial canal facing the stapes was also measured. A new surgical approach to the ampullary nerve is discussed.

[A comparison of the morphology of mammalian and bird ear ossicles and reflections on the asymmetrical form of the human stapes arch]

BACKGROUND

The human middle ear presents some anatomical detail which can not be explained exclusively by sound transmission (joints, muscles). These details can be interpreted as an adaptation to environmental atmospheric pressure loads. In order to further investigate the influence of these non-acoustic loads on the geometry of the middle ear structures, the ossicles of animals from different environments were examined.

METHODS

In the first half of our century, the zoologist C. F. Werner collected the ossicles of 175 species, mostly mammals and birds. This collection was now cataloged and analysed with light and x-ray microscopy.

RESULTS AND DISCUSSION

The diversity in size and design of the ossicles seems to be influenced not only by the acoustic environment of the animal--the ossicles of mammals living in the desert are relatively large, reflecting the better sensitivity of their middle ear for the far traveling low frequencies--but especially the bony structure of the ossicles can be related to the static loads of the environment of the animal. Ossicles of aquatic mammals are more solid and denser than in terrestrial forms. The bony structure aligns to the static load. This structural principle forms the basis of the skeleton and muscles and can also be found in the human stapes: the asymmetry of the stapedial arch can be explained as adaptation of the bony structure to the pull of the stapedius muscle.

CONCLUSIONS

The anatomical structure of the ossicles of human and animal origin is not only influenced by its function as sound transmitter, but it is also shaped by nonacoustic forces and static loads of the environment.

Measurements of the stapes superstructure

Ten human stapes from fresh temporal bones were measured to obtain relevant distances of the stapes superstructure. The dimensions of the parts of the superstructure are as follows: 1) stapes head 1.14 mm (range, 0.91 to 1.49) in diameter parallel to the axis of the footplate and 0.83 mm (range, 0.65 to 1.08) perpendicular to it; 2) stapes head to shoulders 0.93 mm (range, 0.81 to 1.07), head to foramen 1.26 mm (range, 1.15 to 1.39), and head to lateral surface of stapes footplate 3.19 mm (range, 2.91 to 3.45); 3) neck width parallel to the axis of the footplate 1.18 mm (range, 0.88 to 1.47) and 0.64 mm (range, 0.48 to 0.88) perpendicular to it; 4) anterior crus 0.58 mm wide (range, 0.41 to 0.74) at the shoulder of the arch and 0.51 mm (range, 0.39 to 0.65) closer to the stapes footplate; 5) posterior crus 0.65 mm wide (range, 0.46 to 0.77) at the shoulder of the arch and 0.55 mm (range, 0.38 to 0.75) closer to the stapes footplate; and 6) maximum width of entire superstructure near footplate 2.48 mm (range, 2.06 to 2.98).

Measurement of cochlear basilar membrane traveling wave velocity by derived ABR

Auditory brainstem response (ABR) can be used to measure the basilar membrane traveling wave velocity (TWV). Traveling wave velocity was calculated from the latency difference between wave V of different derived ABR and the cochlear location distance between the appropriate derived band center frequency. The latency of wave V of derived ABR produced by 6 noise-masked ABR using high pass filtered noise and the location of the corresponding cochlear partition (distance from the stapes foot-plate) were measured, and five traveling wave velocities were estimated based on this parameter. Ten subjects with normal hearing, 7 patients with Meniere's disease, and 8 patients with sensorineural hearing loss were used in this study. The traveling wave velocity in the sensorineural hearing loss group was within normal limits at all frequencies, whereas the traveling wave velocity at 8 kHz in the Meniere group greatly exceeded that of the normal and sensorineural hearing loss group.

Homologies in the fossil record: the middle ear as a test case

This paper examines the middle ear of fossil living animals in terms of the homologies which have been drawn between its parts in different vertebrate groups. Seven homologies are considered: 1, the middle ear cavity/spiracular pouch; 2, the stapes/hyomandibula; 3, the stapedial/hyomandibular processes; 4 the tympanic membrane; 5, the otic notch; 6, the fenestra ovalis; 7, and the stapedial/hyomandibular foramen. The reasons leading to assessments of homology are reviewed. Homologies 1 and 2, based largely on embryological evidence, are fairly robust, though there are arguments about the details. Homologies 3, 4 and 5 stem from ideas about early tetrapod evolution, and were influenced by contingent factors including the order and time of discovery of early fossil taxa, and perceptions of their phylogeny which resulted from this. They were also influenced by ideas of the evolution of terrestriality among tetrapods. Most of the conceptions have been overturned in recent years by new fossil discoveries and new ways of looking at old data. Homology 6 has been little considered. One possible hypothesis, placed in a strictly 'archetypal' theoretical framework has been ignored but deserves consideration on other grounds. Homology 7 depends on how tetrapods are characterised, not a question which has posed difficulties until recently, but which is likely to with the discovery of intermediate fossil forms.

Ossification patterns of the tympanic facial canal in the human fetus and neonate

Dehiscences in the bony facial canal are comparatively common in the human adult. The highest incidence occurs in the tympanic segment of the facial nerve near the region of the oval window. Thirty-three fetal temporal bones, ranging from 16 to 40 weeks' gestation, and four from 1, 2, 4 and 12 weeks' postpartum neonates, were studied to evaluate the normal patterns of ossification of the fallopian canal of the tympanic facial nerve segment in the human. The tympanic facial nerve segment elongates three-fold during this period (from 1 mm to 3 mm). The ossification starts at 21 weeks' gestation anteriorly from apical otic ossification centers and at 26 weeks from canalicular ossification centers near the stapedius muscle. The ossification proceeds in an anterior-to-posterior direction as two periosteal shelves of bone surround the facial nerve. The superior periosteal bony ledge contributes 75% of the circumference of the fallopian canal. The anterior ossification center forms over 83% of the fallopian canal length. The two centers fuse post partum near the region of the oval window. The anatomic location of the facial nerve, nerve branching, and neural vasculature precede ossification. In 80% of the paired temporal bones, this ossification pattern appears to be symmetrical. The patterns and incidence of bony dehiscences within the tympanic fallopian canal segment can be explained by these observations. This study demonstrates that fallopian canal dehiscences are not congenital anomalies, but variations of normal developmental anatomic processes.

Three-dimensional surgical anatomy for stapes surgery computer-aided reconstruction and measurement

To define anatomical relationships relevant to stapes surgery, computer-aided three-dimensional reconstruction and measurement were performed on nine normal temporal bones. The mean distance from the inferior portion of the long process of the incus to the center of the oval window was 3.80 mm. The shortest distance from the center of the oval window to the utricular macula, saccular membrane, and macula averaged 1.37, 1.60, and 2.13 mm. Surgery directed posteromedial-superior from the oval window was found to be most dangerous because it would come so close to the utricular macula; a posteromedial-inferior approach was found to be safest. The distance from the inferior margin of the oval window inferiorly to the cochlear duct in the hook portion ranged between 0.58 and 1.29 mm, suggesting that when a drill hole is made on the inferior margin of the oval window to lift up a depressed stapes footplate, the hole should not be greater than 0.5 mm in diameter.

Functional structure of human auditory ossicles

In a series of 52 auditory ossicles, their structure and functional significance were studied, with special reference to the patterns of force transmission. The significance of the different degrees of cavitation in the ossicles as well as their eventual pathological significance are also discussed.

Utricle, saccule, and cochlear duct in relation to stapedotomy. A histologic human temporal bone study

This study was performed to determine the area in which and the circumstances under which stapedotomy can be relatively safely performed. Measurements were made from central areas of the medial surface of the stapedial footplate to the utricle, the saccule, and the cochlear duct in 10 normal and 11 otosclerotic temporal bones. The mean distances to the utricle ranged from 1.9 to 2.4 mm, and those to the saccule from 1.7 to 2.1 mm. The minimal distance to the utricle was measured from the posterior (0.58 mm) and superior (0.62 mm) borders of the stapedial footplate. The minimal distances to the saccule were from the anterior (0.76, 0.86, and 1.00 mm) border of the stapedial footplate. All other measurements were of more than 1 mm. The shortest distance between the cochlear duct and the inferior border of the footplate was 0.2 mm. Statistical analysis has shown no significant differences for the mean values obtained in normal and otosclerotic temporal bones. Fathoming of the vestibule below the central and inferior thirds of the footplate surface has shown that there is no likely danger to the vestibular end organs or cochlear duct if manipulations are carried out no deeper than 1 mm below the surface. The safest place for a stapedotomy opening is in the central and inferior-central thirds of the footplate. A stapedotomy piston of 0.4 mm in diameter can be introduced relatively safely to a depth of 0.5 mm in the vestibule over the entire surface of the stapedial footplate.

Ossicular geometry and the choice of technique for ossiculoplasty

The dimensions of the space between the handle of the malleus and the plane of the head of the stapes have been investigated in 31 preserved temporal bones and 20 patients with defects of the incus. The width (A) and depth (B) were measured directly and other dimensions were then calculated. In the preserved temporal bones A varied between 0.5 and 3 mm (mean 2.0 mm), while for the patients the range was 1.5-3.8 mm (mean 2.2 mm). The dimension B varied between 1 and 2.5 mm (mean 1.7 mm) in the temporal bones and between 0 and 2 mm in the patients (mean 0.9 mm). This difference is statistically significant (P less than 0.0001). The angle at which a graft placed directly between the stapes head and malleus handle would lie relative to the long axis of the stapes varied between 14 degrees and 71 degrees in the temporal bones (mean 49 degrees) and between 0 degrees and 79 degrees in the patients (mean 63 degrees). This difference is also statistically significant (P less than 0.001). These differences may be due to chronic Eustachian tube dysfunction or to a tendency of the malleus to become displaced medially when it is not supported by the incus/stapes complex. These findings have significant implications for the mechanical properties of different methods of ossiculoplasty, and the relative position of the malleus and stapes should be taken into account when choosing the technique to be used in an individual case.

Neuromagnetic evidence of functional organization of the auditory cortex in humans

The influence of two physical stimulus parameters (frequency and intensity) and of one sensation parameter (pitch) on the auditory evoked magnetic field (AEF) was quantified by approximating the measured magnetic field distribution by that of an equivalent current dipole (ECD) embedded in a homogeneous semi-infinite volume conductor. The main results are as follows: The depth of the ECD increases with increasing frequency, but decreases with increasing intensity. In the case of a complex tone with missing fundamental it is the virtual pitch that determines the ECD location and not the spectral contents of the stimulus.

Postnatal development of the middle ear: areal ratios in kittens

Developmental changes in tympanic membrane to stapedial footplate areal ratios were investigated in kittens from birth through the twentieth postnatal day. Measurements from 45 kittens (85 temporal bones) were obtained from the pars tensa region of the tympanic membrane and the stapedial footplate region bounded by the annular ligament using standard macrophotographic and computer digitization techniques. Tympanic membrane and stapedial footplate areas were approximately 70% and 80%, respectively, of their adult size at birth and relevant areas increased exponentially during early postnatal life. Adultlike dimensions were achieved by the end of the first postnatal week. Tympanic membrane:stapedial footplate areal ratios increased from approximately 25:1 to 30:1 during the first postnatal week, before the developmental period during which adultlike auditory thresholds and response amplitudes are acquired. Thus, the areal ratio influences on impedance-matching characteristics of the middle ear do not appear to significantly affect the postnatal development of auditory function in cats.

Discovery of the earliest-known tetrapod stapes

The evolution of the middle ear is central to the discussion of how the first tetrapods adapted to life on land as well as their phylogeny. Here I report the discovery of the stapes of Acanthostega gunnari, from the Upper Devonian of east Greenland. This is the earliest tetrapod stapes so far described, and it throws new light on both these aspects of early tetrapod biology. It has been assumed that the common inheritance of all early tetrapods was a light, rod-like stapes associated with a temporal notch in the otic region that was thought to have supported a tympanum, or eardrum. The stapes would have conducted vibrations from the tympanum to the otic capsule. By contrast, the stapes of Acanthostega was stout with a broad distal ramus associated with the temporal notch. I suggest that the temporal notch of Acanthostega and other early tetrapods supported a spiracular opening rather than a tympanum, and that the stapes controlled palatal and spiracular movements in ventilation.