Anatomic features of the fetal round and oval windows, and their relations with the tympanic nerve.

OBJECTIVE: The study aimed to examine morphometric properties of the round window (RW) and oval window (OW) and to show their relation with the tympanic nerve (the Jacobson's nerve, JN) in human fetuses from the otologic surgeon's perspective. METHODS: Thirty temporal bones of 15 fetal cadavers (8 males, 7 females) aged with 24.40 ± 3.71 weeks were included in the study. The height, width and surface area of the RW and OW and also distance from the JN to the OW and RW were measured. RESULTS: The height, width and surface area of the RW in this work were measured as 1.48 ± 0.25 mm, 1.57 ± 0.37 mm, and 2.05 ± 0.69 mm2, respectively. The RW was detected as round-shaped (8 cases, 26.7%), oval-shaped (15 cases, 50%), and dome-shaped (7 cases, 23.3%). The height, width and surface area of the OW were measured as 1.42 ± 0.26 mm, 2.90 ± 0.44 mm, and 3.63 ± 0.74 mm2, respectively. The OW was observed as oval-shaped (15 cases, 50%), kidney-shaped (10 cases, 33.3%), D-shaped (4 cases, 13.3%), and trapezoid-shaped (1 case, 3.3%). The JN was found 1.21 ± 0.60 and 1.18 ± 0.54 mm away from the RW and OW, respectively. CONCLUSION: This study containing morphological data about the shapes, diameters and area of the RW and OW may be useful to predict surgical difficulty, and to select implants of suitable size preoperatively for the windows. Knowing the relationship between the JN and the windows can be helpful to avoid iatrogenic injuries of the nerve.

Cortical representation of tympanic membrane movements due to pressure variation: an fMRI study.

Middle ear sensory information has never been localized in the homunculus of the somatosensory cortex (S1). We investigated the somatosensory representation of the middle ear in 15 normal hearing subjects. We applied small air pressure variations to the tympanic membrane while performing a 3T-fMRI study. Unilateral stimulations of the right ear triggered bilateral activations in the caudal part of the postcentral gyrus in Brodmann area 43 (BA 43) and in the auditory associative areas 42 (BA 42) and 22 (BA 22). BA 43 has been found to be involved in activities accompanying oral intake and could be more largely involved in pressure activities in the oropharynx area. The tympanic membrane is indirectly related to the pharynx area through the action of tensor tympani, which is a Eustachian tube muscle. The Eustachian tube muscles have a role in pressure equalization in the middle ear and also have a role in the pharyngeal phase of swallowing. Activation of BA 42 and BA 22 could reflect activations associated with the bilateral acoustic reflex triggered prior to self-vocalization to adjust air pressure in the oropharynx during speech. We propose that BA 43, 42, and 22 are the cortical areas associated with middle ear function. We did not find representation of tympanic membrane movements due to pressure in S1, but its representation in the postcentral gyrus in BA 43 seems to suggest that at least part of this area conveys pure somatosensory information.

The paratympanic organ: a barometer and altimeter in the middle ear of birds?

A century has passed since the discovery of the paratympanic organ (PTO), a mechanoreceptive sense organ in the middle ear of birds and other tetrapods. This luminal organ contains a sensory epithelium with typical mechanosensory hair cells and may function as a barometer and altimeter. The organ is arguably the most neglected sense organ in living tetrapods. The PTO is believed to be homologous to a lateral line sense organ, the spiracular sense organ of nonteleostean fishes. Our review summarizes the current state of knowledge of the PTO and draws attention to the astounding lack of information about the unique and largely unexplored sensory modality of barometric perception.

The tympanic segment of the facial nerve: anatomical study.

There is a conroversy in the literature about the length of the proximal tympanic segment of the facial nerve (PTSFN). The objective of the current study is to measure the length of the tympanic segment of the facial nerve (TSFN) and of its proximal (PTSFN) and distal (DTSFN) segments, in normal human temporal bones. Moreover, we will explore if these lengths are correlated. If a form of a functional relationship can be established, it could offer insights in partially predicting or estimating the length of the TSFN as well as of its proximal and distal portions. Direct measurements were obtained in 40 normal human temporal bones, which were examined by surgical dissection. Relationships between these measurements were established using Pearson's correlation method (two-tailed). The length of the TSFN was on average 10.97 mm. The length of the PTSFN was on average 5.25 mm and of the DTSFN was 5.72 mm. No significant statistical differences according to gender or side (right or left) were detected. It was determined that the length of the TSFN was in linear correlation with positive direction with its proximal (PTSFN) and distal (DTSFN) segments. Also the PTSFN length was in linear correlation with positive direction with the DTSFN length. The length of the PTSFN comprises about one-half of the TSFN length. The existence of a definite correlation between the lengths of the TSFN, PTSFN, and DTSFN implies the existence of a form of functional interrelationship. This could facilitate prediction and identification of the TSFN and PTSFN lengths from the easily identifiable DTSFN length during surgery.

Tympanic-mastoid and parotid schwannomas of the facial nerve: clinical presentation related to the anatomic site of origin.

Objective: To describe the clinical presentation of the facial nerve schwannomas according to the anatomical site of origin. Method: A retrospective study in which the clinical presentation, diagnostic protocol and treatment of facial nerve tumors in adults was evaluated. Results: We found 6 cases, 4 cases of tympanic-mastoid location at the spectrum of its possible clinical presentation: from symptomatic cases with facial paralysis, to an asymptomatic case in the tympanic portion found as intraoperative finding; and also found two cases located at the parotid gland, one with complete facial paralysis and one without facial palsy. Conclusions: For the diagnosis of intratemporal and parotid schwannomas of the facial nerve, a high clinical suspicion is required given its heterogeneous presentation; its clinical course depends on the segment of origin and expansion: more frequently asymptomatic at the tympanic horizontal portion and symptomatic at the mastoid vertical portion. These tumors must be assessed with imaging studies, incisional biopsy is not recommended. The treatment is surgical resection in symptomatic patients with facial paralysis greater than grade III of House-Brackmann, with immediate reconstruction of the nerve.

Objetivo: Describir la presentación clínica de los schwannomas del nervio facial de acuerdo con el sitio anatómico de origen. Método: Se realizó un estudio retrospectivo en el que se evaluó la presentación clínica, el protocolo diagnóstico y el tratamiento de tumores del nervio facial en adultos. Resultados: Se encontraron seis casos, cuatro de ellos de localización tímpano-mastoidea en los extremos de su posible presentación clínica: desde casos sintomáticos con parálisis facial, hasta un caso asintomático de la porción timpánica encontrado como hallazgo transoperatorio; y se encontraron dos casos de localización parotídea, uno con parálisis facial completa y otro sin parálisis facial. Conclusiones: Para el diagnóstico de tumores intratemporales y parotídeos del nervio facial se requiere una elevada sospecha clínica dado lo heterogéneo de su presentación; su curso clínico depende del segmento de origen y de su extensión: más frecuentemente son asintomáticos los de la porción timpánica y son sintomáticos los de la porción mastoidea. Estos tumores deben evaluarse con estudios de imagen; no se recomienda realizar biopsia incisional. El tratamiento es la resección quirúrgica en los casos sintomáticos con parálisis facial de grado IV o mayor de House-Brackmann, con reconstrucción inmediata del nervio.

Chronic Conductive Hearing Loss Leads to Cochlear Degeneration.

Synapses between cochlear nerve terminals and hair cells are the most vulnerable elements in the inner ear in both noise-induced and age-related hearing loss, and this neuropathy is exacerbated in the absence of efferent feedback from the olivocochlear bundle. If age-related loss is dominated by a lifetime of exposure to environmental sounds, reduction of acoustic drive to the inner ear might improve cochlear preservation throughout life. To test this, we removed the tympanic membrane unilaterally in one group of young adult mice, removed the olivocochlear bundle in another group and compared their cochlear function and innervation to age-matched controls one year later. Results showed that tympanic membrane removal, and the associated threshold elevation, was counterproductive: cochlear efferent innervation was dramatically reduced, especially the lateral olivocochlear terminals to the inner hair cell area, and there was a corresponding reduction in the number of cochlear nerve synapses. This loss led to a decrease in the amplitude of the suprathreshold cochlear neural responses. Similar results were seen in two cases with conductive hearing loss due to chronic otitis media. Outer hair cell death was increased only in ears lacking medial olivocochlear innervation following olivocochlear bundle cuts. Results suggest the novel ideas that 1) the olivocochlear efferent pathway has a dramatic use-dependent plasticity even in the adult ear and 2) a component of the lingering auditory processing disorder seen in humans after persistent middle-ear infections is cochlear in origin.

The locations of stapedius and tensor tympani motoneurons in the cat.

The numbers and locations of motoneurons to the stapedius and tensor tympani muscles were determined by retrograde transport of horseradish peroxidase. Stapedius motoneurons lay outside the traditionally recognized facial nucleus, in several distinct locations: (1) in the interface between the facial nucleus and the superior olive; (2) in a thin, scattered lamina of somewhat smaller cells spread dorsal to the facial nucleus; and (3) in a cluster located ventromedial to the rostral third of the facial nucleus. Some cells also lay dorsal to the superior olive or scattered in the reticular formation, just medial to the descending loop of the facial nerve. Tensor tympani motoneurons also lay outside the traditionally recognized trigeminal motor nucleus, in an area just ventral to it. Both motoneuron pools were large, producing innervation ratios that establish stapedius and tensor tympani among the most finely innervated muscles yet studied. The degree of intermingling of large and small cells in these pools may explain, in part, why it has been easier to identify slow muscle fibers physiologically in tensor tympani than in stapedius.

Identification of motoneurons innervating the tensor tympani and tensor veli palatini muscles in the cat.

The somatotopic arrangement of the motoneurons associated with the two non-masticatory muscles innervated by the trigeminal motor nerve, tensor tympani (TT) and tensor veli palatini (TVP), was determined in the cat using retrograde transport of horseradish peroxidase. The motoneurons of the TT are distinct and separate, ventral and ventral-lateral to the rostral two-thirds of the trigeminal motor nucleus. The cells are smaller than those of the motor nucleus and constitute a parvocellular division. Based on functional and morphological criteria, TT motoneurons may be considered as an accessory trigeminal nucleus. The somatotopic arrangement of TVP motoneurons has been described for the first time. These motoneurons are located in the rostral two-thirds of the ventromedial division of the cat trigeminal motor nucleus. The location of motoneurons associated with TT and TVP does not fit the parcellation of the cat trigeminal motor nucleus as described by previous investigators. The motoneurons of these muscles can now be assigned to areas either within (TVP) or adjacent to (TT) the rostral two-thirds of the motor nucleus.

Peptidergic nociceptive axon visualization in whole-mount preparations of cornea and tympanic membrane in rat.

A whole-mount preparation is described for visualizing unmyelinated peptide immunoreactive axons in two specialized tissues, thin enough for tracing axons to their terminal knobs. These tissues, the cornea and the mucosal surface of the tympanic membrane, are known to possess specialized nociceptor innervation and can be used for selecting sensory endings labeled by peroxidase reaction product and embedded in plastic for more detailed analysis. Rat calcitonin gene-related peptide antibody proved a particularly robust primary antibody found in a substantial proportion of sensory unmyelinated axons in a variety of fixation and preparative conditions.

Localization of motoneurons innervating the tensor tympani muscles: an horseradish peroxidase study in the guinea pig and cat.

Motoneurons innervating the tensor tympani muscle were identified in the adult guinea pig and cat by the horseradish peroxidase (HRP) method. After HRP injection into the tensor tympani muscle, HRP-labeled neurons were seen in the regions outside the cytoarchitectonically-defined confines of the trigeminal motor nucleus; in the regions rostral to the rostral pole of the nucleus, as well as in the regions ventral and ventrolateral to the nucleus at the levels of the rostral half (guinea pig) or the rostral two-thirds (cat) of the nucleus. The tensor tympani motoneurons were generally smaller than the masticatory motoneurons.

Identification of motoneurons innervating the tensor tympani muscle in the rabbit: a retrograde horseradish peroxidase study.

After injecting horseradish peroxidase into the tensor tympani muscle in the rabbit, neuronal cell bodies labeled retrogradely with the enzyme were seen in the ventrolateral regions of the pontine tegmentum. These tensor tympani motoneurons were located in the 'nucleus n' as well as in the rostrodorsal part of the medial 'cell group k' of Meessen and Olszewski [4].

Tensor tympani reflex pathways studied with retrograde horseradish peroxidase and transneuronal viral tracing techniques.

The neural pathway involved in activation of the tensor tympani (TT) muscle was studied in the rat using retrograde HRP and transneuronal viral tracing techniques. The pool of TT motoneurons labeled with HRP was located ipsilaterally under the anterior third of the trigeminal motor nucleus and extended rostrally towards the lateral lemniscus. The origin of the inputs to these motoneurons was then determined using transneuronal viral transport: presumably transneuronally infected neurons appeared bilaterally in the vicinity of the superior olivary complex, mainly in between the two nuclei of the trapezoid body. The present data are consistent with previous conclusions based on lesion experiments that the TT reflex loop is made up of a chain of 4 neurons.

Head-related transfer functions of the barn owl: measurement and neural responses.

Sounds arriving at the eardrum are filtered by the external ear and associated structures in a frequency and direction specific manner. When convolved with the appropriate filters and presented to human listeners through headphones, broadband noises can be precisely localized to the corresponding position outside of the head (reviewed in Blauert, 1997). Such a 'virtual auditory space' can be a potentially powerful tool for neurophysiological and behavioral work in other species as well. We are developing a virtual auditory space for the barn owl, Tyto alba, a highly successful auditory predator that has become a well-established model for hearing research. We recorded catalogues of head-related transfer functions (HRTFs) from the frontal hemisphere of 12 barn owls and compared virtual and free sound fields acoustically and by their evoked neuronal responses. The inner ca. 1 cm of the ear canal was found to contribute little to the directionality of the HRTFs. HRTFs were recorded by inserting probetube microphones to within about 1 or 2 mm of the eardrum. We recorded HRTFs at frequencies between 2 and 11 kHz, which includes the frequencies most useful to the owl for sound localization (3-9 kHz; Konishi, 1973). Spectra of virtual sounds were within +/- 1 dB of amplitude and +/- 10 degrees of phase of the spectra of free field sounds measured near to the eardrum. The spatial pattern of responses obtained from neurons in the inferior colliculus were almost indistinguishable in response to virtual and to free field stimulation.

Effectiveness of the CO2 laser in experimental tympanic neurectomy.

As one of a series of investigations to evaluate the efficacy and safety of CO2 lasers in otologic microsurgery, squirrel monkeys were subjected to tympanic neurectomies by means of vaporizing Jacobson's nerve in the promontory region. Air and bone conduction hearing acuity was measured by computer-averaged pure tone evoked responses and behavioral audiometry before and after laser surgery. A moderate (avoidable) conductive loss was found as a consequence of the surgical approach selected, but no significant sensorineural loss was apparent. Thus, there would appear to be no adverse cochlear side effects as a result of using this instrument in the middle ear. The laser neurectomy procedure, however, was no more effective for the clinical purposes for which it was proposed than those techniques reported by several other investigators.

Overlay versus underlay tympanoplasty. Part I: historical review of the literature.

The history of otology is the history of the successful treatment of infections of the middle ear and the eardrum. Otologists have sought to restore hearing lost to infections of the eardrum since the 1600s. The development of instruments, techniques, and materials to treat infection is fascinating because of the serendipitous nature of the discoveries and the insight of the discoverers. This historical review describes the history of the treatment of infections of the ear and the development of modern techniques of ear surgery. Two contemporary methods of tympanic membrane repair are then described.

Gustatory otalgia and wet ear syndrome: a possible cross-innervation after ear surgery.

HYPOTHESIS: The chorda tympani and Arnold's nerves have close approximation to each other and their cross-innervation is possible after ear surgery. STUDY DESIGN: A retrospective study was performed with a temporal bone pathology case and two clinical cases as representatives of such a possibility. Patients had severe otalgia and wet ear during gustatory stimulation. METHODS: A temporal bone pathology case was studied under a light microscope. Earache and/or wet ear were provoked during gustatory stimulation. Wet ear was tested with iodine-starch reaction after the subject tasted lemon juice. RESULTS: The temporal bone specimen has clusters of regenerated fibers in the tympanic cavity in the area of the chorda tympani and Arnold's nerves, suggesting a possibility of mixing. There are regenerated fibers in the iter chordae anterius, showing successful bridging of the chorda tympani nerves across a long gap. Detachment of the skin over the operated mastoid bowl obscured signs in one clinical case. Another clinical case of gustatory wet ear showed objective evidence of cross-innervation with iodine-starch reaction. CONCLUSION: The detachment procedure and iodine-starch reaction were the proofs that the signs were related to regenerated fibers. This is the first report of gustatory otalgia and wet ear after ear surgery.

Cholinergic innervation of the guinea pig tympanic membrane.

While cholinergic nerve fibers of the parasympathetic system have been demonstrated in the middle ear mucosa, such innervation of the tympanic membrane has never been shown. Such fibers may prove important since the tympanic membrane may be one of the initial sites of effusion production, and since parasympathetic innervation is thought to be involved with middle ear effusion. To demonstrate cholinergic innervation, we have used modified direct thiocholine histochemical staining. Anesthetized Hartley guinea pigs were killed, and the tympanic bullae were removed intact, fixed in 4% paraformaldehyde, and then stained whole. Following staining, the tympanic membrane was dissected from each bulla and whole-mounted for light microscopy. Numerous acetylcholinesterase-positive fibers were observed on the tympanic membrane. Some fibers appeared to be vessel associated, although the majority did not. This suggests that these fibers may act on the mucosa or vasculature of the tympanic membrane and contribute to the pathogenesis of middle ear effusion.

Electrophysiological and HRP studies of the direct afferent inputs from the cochlear nuclei to the tensor tympani muscle motoneurons in the cat.

The direct fiber connections from the cochlear nuclei to the tensor tympani muscle (TTM) motoneurons were investigated by means of electrophysiological and horseradish peroxidase (HRP) methods, using cats. When HRP was injected into motoneuron region of the TTM, HRP-labelled cells were found bilaterally in the dorsal cochlear nucleus (DCN) and ventral cochlear nucleus (VCN). When the electrical stimulus was applied to the cochlear nucleus, the TTM motoneurons fired spikes monosynaptically with s short latency. These histological and electrophysiological results indicate the existence of direct fiber connections from the bilateral cochlear nuclei to the TTM motoneurons.

Autonomic innervation of the tympanic membrane. An immunocytochemical and histofluorescence study.

The innervation of the tympanic membrane of the rat was investigated with respect to noradrenergic and peptide-containing nerve fibres. In sections, most of the nerves in both the flaccida portion and the tensa portion seemed to be of the small, unmyelinated types, though a few larger myelinated nerves were also found. Noradrenergic fibres, exhibiting specific catecholamine fluorescence (CA), were detected along the blood vessels in the pars flaccida and along the vascular network of the annulus fibrosus. In the pars flaccida, fibres exhibiting SP-like, VIP-like- and enkephalin-like immunoreactivity were noted. None of these peptides could be detected in the pars tensa. The exclusive localization of the oedema-provoking peptides, SP and VIP, to the pars flaccida may be of importance with regard to establishing pars flaccida as the initial site of effusion production in experimental secretory otitis media.

Anatomy and orientation of the human external ear.

A knowledge of the external ear and tympanic membrane is essential to practicing audiologists. This article provides an introduction to the anatomy of this area including dimensions, orientation, vasculature, innervation, and relations to other structures. Traditional diagrams are often inadequate in describing these structures. For example, typical frontal and sagittal views of the external auditory meatus do not adequately describe its anteroposterior course. Axial (transverse) views provide easier visualization of these areas. A nomenclature is also provided for areas and angles of the external auditory meatus.