Review of the caroticotympanic nerves: Anatomy, function and pathology

The caroticotympanic nerves provide postganglionic sympathetic fibres to the tympanic plexus. However, there are scant reports in the literature detailing with these nerves in great depth. As the caroticotympanic plexus lies near the often-operated tympanic nerve, it is important for the surgeon to understand the anatomy, pathology and surgical implications of it. Here, we present a review of the available literature regarding the caroticotympanic nerves.

Middle ear myoclonus: Systematic review of results and complications for various treatment approaches

OBJECTIVE

To perform a systematic review of the diagnosis and treatment of patients with pulsatile tinnitus secondary to middle ear myoclonus.

DATABASES REVIEWED

PubMed, EMBASE, and Scopus.

METHODS

A systematic review was performed using standardized methodology. Computerized and manual searches were performed to identify studies of all ages (patients) who had middle ear myoclonus (intervention). All study designs were assessed. Extracted data included demographics, clinical features, duration of followup as well as the diagnosis and reversibility of symptoms with medical or surgical intervention. Studies were included if they included subjects with middle ear myoclonus. Exclusion criteria included letters/commentaries and reviews.

RESULTS

Twenty articles representing 115 subjects with middle ear myoclonus were included. The mean age was 29.7 (range 6-67). The follow-up period ranged from 5 weeks to 36 months. Primary treatment consists of medical therapy utilising anxiolytics, antiepileptics, botulinum toxin and surgical treatment involving division of middle ear muscular tendon(s). In total, 60 patients underwent middle ear muscular tenotomies, with division of both stapedius and tensor tympani tendons being the most prevalent (88%). Limitations in the data arose from study design, related comorbidities such as palatal myoclonus, and concomitant drug administration. No study provided any objective criteria to diagnose this condition or evaluate post-treatment outcome.

CONCLUSION

Middle ear myoclonus is an entity that is poorly assessed in the literature. There is a lack of consensus regarding the criteria and strategies for both diagnosing and treating this condition. Although level of evidence of current studies remains modest, it is felt that a stepwise approach is deemed best, with therapeutic decisions being made on an individual basis, evaluating each patient's specific circumstances and priorities.

Frey's Syndrome

The history of Frey's syndrome is explored together with its physiopathological and anatomical basis. A study of 19 cases of parotidectomy in 15 patients is reviewed and the results of 17 tympanic neurectomies presented.

Micro-CT study of the dehiscences of the tympanic segment of the facial canal

PURPOSE

To depict the anatomy of the tympanic segment of the facial canal using a 3D visualization technique, to detect dehiscences, and to evaluate their frequency, location, shape, and size.

METHODS

Research included 36 human temporal bones (18 infant and 18 adult samples) which were scanned using a Nanotom 180N device. The final resolution of the reconstructed object was 18 µm. Obtained micro-CT data were subsequently processed by the volume rendering software.

RESULTS

The micro-CT study allowed for the 3D visualization of the tympanic segment of the facial canal and detects dehiscences in the studied material in both infants and adults. Most of the dehiscences (66.7 %) involved the inferior wall of the tympanic segment in infants as well as in adults, and were located above and backward to the oval window. The most frequent dehiscence shape was elliptic (66.7 % in infants; 50 % in adults). Furthermore, we observed dehiscences of fusiform and trapezoidal shape in infants. Length of the dehiscences in most cases ranged from 0.5 to 1.4 mm (50 % in infants; 75 % in adults).

CONCLUSIONS

Volumetric reconstructions demonstrated the course of the tympanic segment of the facial canal and its relationship with the tympanic cavity. Knowledge about the size and location of any dehiscence within the tympanic segment of the facial canal is necessary due to the surgical significance of this region. If a dehiscence occurs, there is an increased risk of injury to the facial nerve during the operations or spread of inflammation from the middle ear.

The middle ear muscle reflex in the diagnosis of cochlear neuropathy

Cochlear neuropathy, i.e. the loss of auditory nerve fibers (ANFs) without loss of hair cells, may cause hearing deficits without affecting threshold sensitivity, particularly if the subset of ANFs with high thresholds and low spontaneous rates (SRs) is preferentially lost, as appears to be the case in both aging and noise-damaged cochleas. Because low-SR fibers may also be important drivers of the medial olivocochlear reflex (MOCR) and middle-ear muscle reflex (MEMR), these reflexes might be sensitive metrics of cochlear neuropathy. To test this hypothesis, we measured reflex strength and reflex threshold in mice with noise-induced neuropathy, as documented by confocal analysis of immunostained cochlear whole-mounts. To assay the MOCR, we measured contra-noise modulation of ipsilateral distortion-product otoacoustic emissions (DPOAEs) before and after the administration of curare to block the MEMR or curare + strychnine to also block the MOCR. The modulation of DPOAEs was 1) dominated by the MEMR in anesthetized mice, with a smaller contribution from the MOCR, and 2) significantly attenuated in neuropathic mice, but only when the MEMR was intact. We then measured MEMR growth functions by monitoring contra-noise induced changes in the wideband reflectance of chirps presented to the ipsilateral ear. We found 1) that the changes in wideband reflectance were mediated by the MEMR alone, and 2) that MEMR threshold was elevated and its maximum amplitude was attenuated in neuropathic mice. These data suggest that the MEMR may be valuable in the early detection of cochlear neuropathy.

Adaptation of distortion product otoacoustic emissions predicts susceptibility to acoustic over-exposure in alert rabbits

A noninvasive test was developed in rabbits based on fast adaptation measures for 2f1-f2 distortion-product otoacoustic emissions (DPOAEs). The goal was to evaluate the effective reflex activation, i.e., "functional strength," of both the descending medial olivocochlear efferent reflex (MOC-R) and the middle-ear muscle reflex (MEM-R) through sound activation. Classically, it is assumed that both reflexes contribute toward protecting the inner ear from cochlear damage caused by noise exposure. The DP-gram method described here evaluated the MOC-R effect on DPOAE levels over a two-octave (oct) frequency range. To estimate the related activation of the middle-ear muscles (MEMs), the MEM-R was measured by monitoring the level of the f1-primary tone throughout its duration. Following baseline measures, rabbits were subjected to noise over-exposure. A main finding was that the measured adaptive activity was highly variable between rabbits but less so between the ears of the same animal. Also, together, the MOC-R and MEM-R tests showed that, on average, DPOAE adaptation consisted of a combined contribution from both systems. Despite this shared involvement, the amount of DPOAE adaptation measured for a particular animal's ear predicted that ear's subsequent susceptibility to the noise over-exposure for alert but not for deeply anesthetized rabbits.

Aging of the medial olivocochlear reflex and associations with speech perception

The medial olivocochlear reflex (MOCR) modulates cochlear amplifier gain and is thought to facilitate the detection of signals in noise. High-resolution distortion product otoacoustic emissions (DPOAEs) were recorded in teens, young, middle-aged, and elderly adults at moderate levels using primary tones swept from 0.5 to 4 kHz with and without a contralateral acoustic stimulus (CAS) to elicit medial efferent activation. Aging effects on magnitude and phase of the 2f1-f2 DPOAE and on its components were examined, as was the link between speech-in-noise performance and MOCR strength. Results revealed a mild aging effect on the MOCR through middle age for frequencies below 1.5 kHz. Additionally, positive correlations were observed between strength of the MOCR and performance on select measures of speech perception parsed into features. The elderly group showed unexpected results including relatively large effects of CAS on DPOAE, and CAS-induced increases in DPOAE fine structure as well as increases in the amplitude and phase accumulation of DPOAE reflection components. Contamination of MOCR estimates by middle ear muscle contractions cannot be ruled out in the oldest subjects. The findings reiterate that DPOAE components should be unmixed when measuring medial efferent effects to better consider and understand these potential confounds.

Intratemporal course of the facial nerve: morphological, topographic and morphometric features

The purpose of this study is to present some morphological and morphometric aspects of the facial nerve and especially of the tympanic and mastoid segments of this nerve. The authors follow up a mesoscopic study concerning the tract (length, angulation, width) of these segments and the anatomic relations with the important structures of the middle ear. At the same time, some anatomical variations which involve the canal of the facial nerve (dehiscences, tract deviation or other anatomical deviations) are presented. To evaluate the risk of the facial nerve injury during operations for chronic otitis media with or without cholesteatoma, stapedectomy in otosclerosis, exploratory tympanotomy, tympanoplasty, canaloplasty, osteomas surgery or other otologic surgery that involve facial nerve area. The intricate course of the facial nerve through the temporal bone is of vital concern to all otologic surgeons, since it often traverses the surgical field. Therefore, authors will review the course of the facial canal through the petrosal portion of the temporal bone from the internal auditory meatus to the stylomastoid foramen, paying particular attention to its relations to adjacent structures.

Changes of oral trigeminal sensitivity in patients after middle ear surgery

OBJECTIVES

The specific aim of this study was to re-investigate the effect of chorda tympani damage on both trigeminal sensitivity and taste ability.

STUDY DESIGN

Prospective study.

METHODS

Capsaicin-impregnated filter paper strips (5 concentrations, 0.0001-1%) were used to measure trigeminal thresholds. The strips were placed on the anterior tongue for 10 seconds. Thresholds were estimated in two ways: 1) thresholds related to sensory perception and 2) intensity-related thresholds. The test was applied to 29 patients who underwent middle ear surgery (mean age, 49 yr; 16 females, 13 males). Results were compared with those of 63 healthy subjects (mean age, 40 yr; 36 females, 29 males). In addition to trigeminal thresholds, measures of gustatory function were also obtained using both the validated "taste strips" test kit and electrogustometry.

RESULTS

For lateralized testing with capsaicin, significant differences were found between preoperative and postoperative thresholds and between the operated and nonoperated side, with thresholds being higher postoperatively on the operated side. The sensation-related thresholds from the operated tongue side exhibited a correlation with the corresponding postoperative electrogustometric thresholds. A higher degree of chorda manipulation was associated with higher postoperative capsaicin thresholds at the operated tongue side.

CONCLUSION

Pain-related sensitivity of the tongue decreases after middle ear surgery, indicating that chorda tympani function also influences intraoral trigeminal sensitivity.

The significance of assessing the perineural vascular plexus for locating the facial nerve in microsurgery of the ear

CONCLUSIONS

The perineural vascular plexus is a reliable indicator for the detection of the horizontal segment of the facial nerve in surgery for otologists and neurologists.

OBJECTIVE

To evaluate the validity and reliability of the perineural vascular plexus for locating the facial nerve in microsurgery of the ear to avoid iatrogenic facial paralysis.

PATIENTS AND METHODS

Our study group comprised 311 patients who underwent tympanoplasty or facial nerve decompression from July 2002 to July 2005. The validity of using the perineural vascular plexus to locate the facial nerve was observed and assessed.

RESULTS

The perineural vascular plexus was well differentiated on the horizontal mesotympanic segment of the nerve in 95.8% of patients. The 95% confidence interval was 93.6-98.0%.

Primary middle ear schwannoma

Schwannomas of the middle ear may originate from the nerves of the middle ear cavity or by extensions from neighboring structures. We present a case of a 51-year-old female patient with primary middle ear schwannoma believed to arise from Jacobson's nerve. The tumor was easily divided from the facial nerve and the chorda tympani nerve. Erosion of the promontory was noted, and the jugular foramen and posterior wall of the ear canal were preserved without destruction. The mass was successfully removed by a canal down mastoidectomy procedure, while preserving the hearing and facial nerve functions of the patient. To our knowledge, this is only the second reported case of a patient with Jacobson's nerve schwannoma.

Feeling of ear fullness in acute sensorineural hearing loss

CONCLUSIONS

This study revealed two characteristic findings of the feeling of ear fullness (FEF) in acute sensorineural hearing loss (ASNHL). First, that the appearance of FEF was not associated with the auditory function on audiograms; and second, that the disappearance of FEF is clearly associated with the hearing prognosis.

OBJECTIVE

FEF appears frequently in patients with ASNHL. However, there are few reports on this symptom and its mechanism has yet to be clarified. So we tried to investigate the character of FEF in ASNHL.

PATIENTS AND METHODS

In this study, observations were made during the period from the first medical examination to 2 months after obtaining a steady audiogram on 227 ears from unilateral ASNHL cases, and the relationship between FEF and the audiograms was analyzed.

RESULTS

The FEF prevalence at the first medical examination was about 80% for any audiogram shape or hearing threshold. Moreover, the better the hearing prognosis, the higher the improvement rate of FEF.

Emergence of Hearing in the Chicken Embryo

It is commonly held that hearing generally begins on incubation day 12 (E12) in the chicken embryo ( Gallus domesticus). However, little is known about the response properties of cochlear ganglion neurons for ages younger than E18. We studied ganglion neurons innervating the basilar papilla of embryos (E12–E18) and hatchlings (P13–P15). We asked first, when do primary afferent neurons begin to encode sounds? Second, when do afferents evidence frequency selectivity? Third, what range of characteristic frequencies (CFs) is represented in the late embryo? Finally, how does sound transfer from air to the cochlea affect responses in the embryo and hatchling? Responses to airborne sound were compared with responses to direct columella footplate stimulation of the cochlea. Cochlear ganglion neurons exhibited a profound insensitivity to sound from E12 to E16 (stages 39–42). Responses to sound and frequency selectivity emerged at about E15. Frequency selectivity matured rapidly from E16 to E18 (stages 42 and 44) to reflect a mature range of CFs (170–4,478 Hz) and response sensitivity to footplate stimulation. Limited high-frequency sound transfer from air to the cochlea restricted the response to airborne sound in the late embryo. Two periods of ontogeny are proposed. First is a prehearing period (roughly E12–E16) of endogenous cochlear signaling that provides neurotrophic support and guides normal developmental refinements in central binaural processing pathways followed by a period (roughly E16–E19) wherein the cochlea begins to detect and encode sound.

The effect of monaural middle ear destruction on response properties of neurons in the auditory midbrain of juvenile and adult mice

This article reviews our studies of the effect of monaural middle ear destruction on midbrain auditory response properties of the laboratory mouse, Mus musculus. Monaural middle ear destruction was performed on juvenile and adult mice and the auditory sensitivity of neurons in the midbrain inferior colliculus (IC) ipsilateral and contralateral to the intact ear was examined 4 weeks later. When stimulated with sound pulses, IC neurons of the control mice typically had lower minimum threshold, larger dynamic range, and sharper frequency tuning curve than IC neurons of the experimental juvenile and adult mice. In the experimental mice, neurons in the ipsilateral IC had significantly longer latency, higher minimum threshold, and smaller dynamic range than neurons in the contralateral IC. When determined at two sound directions (ipsilateral 40 degrees and contralateral 40 degrees to the recording site), IC neurons of the control mice had higher minimum threshold, sharper frequency tuning curve but smaller dynamic range at I-40 degrees than at C-40 degrees . However, these direction-dependent response properties were not observed for IC neurons of the experimental juvenile and adult mice. Clear tonotopic organization was only observed in the IC of the control mice and experimental adult mice but not in the IC of experimental juvenile mice. These different response properties are discussed in relation to the effect of monaural middle ear destruction.

Central auditory pathways mediating the rat middle ear muscle reflexes

The middle ear muscle (MEM) reflexes function to protect the inner ear from intense acoustic stimuli and to reduce acoustic masking. Sound presented to the same side or to the opposite side activates the MEM reflex on both sides. The ascending limbs of these pathways must be the auditory nerve fibers originating in the cochlea and terminating in the cochlear nucleus, the first relay station for all ascending auditory information. The descending limbs project from the motoneurons in the brainstem to the MEMs on both sides, causing their contraction. Although the ascending and descending pathways are well described, the cochlear nucleus interneurons that mediate these reflex pathways have not been identified. In order to localize the MEM reflex interneurons, we developed a physiologically based reflex assay in the rat that can be used to determine the integrity of the reflex pathways after experimental manipulations. This assay monitored the change in tone levels and distortion product otoacoustic emissions within the ear canal in one ear during the presentation of a reflex-eliciting sound stimulus in the contralateral ear. Preliminary findings using surgical transection and focal lesioning of the auditory brainstem to interrupt the MEM reflexes suggest that MEM reflex interneurons are located in the ventral cochlear nucleus.

Objective Assessment of the Perineural Vascular Plexus as a Landmark for the Horizontal Part of the Facial Nerve in Middle Ear and Mastoid Surgery

OBJECTIVE

To objectively evaluate the usefulness and the reliability of the perineural vascular plexus as a landmark for identification of the facial nerve in surgery for chronic squamous otitis media.

STUDY DESIGN

Prospective case series.

SETTING

Tertiary otologic center.

PATIENTS

Seventy consecutive patients requiring surgery for cholesteatomatous otitis media.

INTERVENTION

Use of a semiquantitative grading system intraoperatively to assess the utility and ease of using the perineural facial plexus as the pointer to the facial nerve.

MAIN OUTCOME MEASURES

Description of the perineural vascular plexus and assessment of the reproducibility of the grading system.

RESULTS

In 82.5% of patients, the plexus was used as the sole pointer to the level of the facial nerve, with other landmarks being used in the remaining 17.5%. A very prominent vessel was used to identify the nerve in 82.5%, therefore being classified as Grade 1. Multiple small vessels were seen in 15.8% (Grade 2), and in 1.5% the vessel plexus was thin and difficult to identify. The average measure intraclass correlation was 0.75 (95% confidence interval, 0.57-0.85), indicating excellent reproducibility of the system.

CONCLUSION

We believe that the perineural vascular plexus is a dependable and reliable landmark for the level of the facial nerve in surgery for chronic otitis media.

Fallopian canal dehiscences: a survey of clinical and anatomical findings

This survey investigates fallopian canal dehiscences in order to assess the risk of encountering an unprotected facial nerve during routine ear surgery. In a prospective non-randomized study, the intraoperative appearance of the facial canal in 357 routine ear operations was compared with 300 temporal bone specimens from 150 autopsies. Intraoperatively, a dehiscence was detected in 6.4% (23/357) of the operations, most frequently at the oval niche region (16/23 cases). The incidence increased with the number of operations (P<0.0002). Cholesteatoma surgery had the highest relative risk (RR 4.6) of exposing an unprotected facial nerve. Postoperatively, no persistent facial paralysis was observed. In four of five cases with a transient facial palsy due to local anesthetics, a bony dehiscence could be found. The anatomical study revealed fallopian canal dehiscences in 29.3% (44/150) of the autopsies. One-third (15/44) of the individuals affected displayed bilateral findings, thus resulting in 19.7% (59/300) of temporal bones affected. A total of 17/59 bones showed microdehiscences, and most (55/59) were located at the oval niche. The actual prevalence of fallopian canal dehiscences is significantly higher than intraoperative findings suggest. The oval niche is the most affected region. High-resolution computed tomography is of diagnostic value only in selected cases. Facial paralysis following local anesthesia is the most significant clinical sign. Vigilance in acute facial palsy after local anesthetics and in cholesteatoma surgery and adequate intraoperative exposure help to prevent iatrogenic injury of the uncovered nerve. In unclear cases, nerve monitoring can facilitate a safe outcome.

Hearing in hooktip moths (Drepanidae: Lepidoptera)

This study presents anatomical and physiological evidence for a sense of hearing in hooktip moths (Drepanoidea). Two example species, Drepana arcuata and Watsonalla uncinula, were examined. The abdominal ears of drepanids are structurally unique compared to those of other Lepidoptera and other insects, by having an internal tympanal membrane, and auditory sensilla embedded within the membrane. The tympanum is formed by two thin tracheal walls that stretch across a teardrop-shaped opening between dorsal and ventral air chambers in the first abdominal segment. There are four sensory organs (scolopidia) embedded separately between the tympanal membrane layers: two larger lateral scolopidia within the tympanal area, and two smaller scolopidia at the medial margin of the tympanal frame. Sound is thought to reach the tympanal membrane through two external membranes that connect indirectly to the dorsal chamber. The ear is tuned to ultrasonic frequencies between 30 and 65 kHz, with a best threshold of around 52 dB SPL at 40 kHz, and no apparent difference between genders. Thus, drepanid hearing resembles that of other moths, indicating that the main function is bat detection. Two sensory cells are excited by sound stimuli. Those two cells differ in threshold by approximately 19 dB. The morphology of the ear suggests that the two larger scolopidia function as auditory sensilla; the two smaller scolopidia, located near the tympanal frame, were not excited by sound. We present a biophysical model to explain the possible functional organization of this unique tympanal ear.

Vestibular nerve section in a child with intractable Menière's disease

Clinical presentation of Menière's disease in children is not as typical as in adults. The triad of vertigo, tinnitus and deafness are not usually elicited, diagnosis often being made after years of follow up and batteries of investigation. A case of Menière's disease in a 3-year-old boy is presented. The diagnosis was only obvious at the age of 8 when the triad of vertigo, deafness and tinnitus were present. His disease progressed despite a trial of intratympanic gentamicin injections and endolymphatic sac decompression. Vestibular nerve section was subsequently performed for his intractable disease. Following the procedure he was asymptomatic and able to attend school.

Jacobson's nerve schwannoma: a rare middle ear mass

The case of a 55-year-old woman with a middle ear mass is presented. The preoperative diagnostic workup, including an audiogram and imaging studies, and the histopathologic findings of the tumor are reviewed. The tumor, a schwannoma, arose from Jacobson's nerve in the middle ear. The surgical anatomy of Jacobson's nerve and the surgical approach to this tumor and to other tumors of the middle ear space are discussed. Tumors of the tympanic cavity are rare, with the exception of cholesteatoma; otherwise, the most common among them are paraganglioma and facial nerve neuroma. This report represents the first documented case of a schannoma arising from Jacobson's nerve in the tympanic cavity.

Structure of the middle ear and auditory tube in the house musk shrew, Suncus murinus

Anatomical features of the middle ear and auditory tube (AT) in the house musk shrew, Suncus murinus, were examined by dissection and light microscopy. The tensor veli palatini (TVP) and tensor tympani (TT) have no connections with the wall or cartilage of the AT although they are connected by the intermediate tendon. None of the levator veli palatini (LVP) muscle bundles are attached to the AT. The salpingopharyngeus (SA) alone has its origin on the caudal edge of the tubal cartilage. The origin extends to the pharyngeal two thirds of the cartilage. The SA originates perpendicular to the AT and runs caudomedialward. Some SA muscle bundles intermingle with those of the palatopharyngeus to end on the dorsal wall of the pharynx. The observations provide no evidence that the TVP, LVP and TT have any role in AT function. The only muscle affecting the AT function in S. murinus is the SA, and it would be the AT dilator.

Jacobson's nerve schwannoma presenting as middle ear mass

Schwannoma is one of the common benign middle ear space tumors. Middle ear space schwannomas may originate from the nerves of the tympanic cavity or by extensions from outside the middle ear space. In the English-language literature, the facial nerve and chorda tympani nerve, but not yet the tympanic branch of glossopharyngeal nerve (Jacobson's nerve), have been reported as the origins of intrinsic middle ear space schwannomas. We present the clinical and radiologic features of a middle-space schwannoma originating from Jacobson's nerve, and suggest that such a tumor be included in the differential diagnosis of middle ear tumors.

Main trajectories of nerves that traverse and surround the tympanic cavity in the rat

To guide surgery of nerves that traverse and surround the tympanic cavity in the rat, anatomical illustrations are required that are topographically correct. In this study, maps of this area are presented, extending from the superior cervical ganglion to the otic ganglion. They were derived from observations that were made during dissections using a ventral approach. Major blood vessels, bones, transected muscles of the tongue and neck and supra and infrahyoid muscles serve as landmarks in the illustrations. The course of the mandibular, facial, glossopharyngeal, vagus, accessory and hypoglossal nerves with their branches, and components of the sympathetic system, are shown and discussed with reference to data available in the literature. Discrepancies in this literature can be clarified and new data are presented on the trajectories of several nerves. The course of the tympanic nerve was established. This nerve originates from the glossopharyngeal nerve, enters the tympanic cavity, crosses the promontory, passes the tensor tympani muscle dorsally, and continues its route intracranially to the otic ganglion as the lesser petrosal nerve after intersecting with the greater petrosal nerve. Auricular branches of the glossopharyngeal and of the vagus nerve were noted. We also observed a pterygopalatine branch of the internal carotid nerve, that penetrates the tympanic cavity and courses across the promontory.

[Adrenergic innervation of the middle and internal ear in man]

Adrenergic nervous structures (ANS) in morphofunctional formations of human middle and internal ear were studied on the autopsy material obtained from 5 victims of accidents free of any ear disease. The samples were treated histochemically with glyoxylic acid. Non-varicose dilated sympathetic nerve fibers (single and in bundles, non-myelinized, intensively luminescent, twisted and direct) were detected in vertical nerve sections, in spiral and vestibular ganglia, in chorda tympani. A thick net of adrenergic nerve fibers (ANF) was noted around the labyrinthine artery. ANF were absent long along the walls of the utriculus and semicircular canals, in the modiolus vessels, spiral ligament, vascular stripe. ANF were most numerous on the osseous spiral lamina. Near the Corti's organ ANF are thicker and often varicose. On the vertical sections of m. stapedius ANF with varicose parts locate in the connective tissue perimysial layers and in the endomysium directly between the muscular cells. At the site of muscle transition into the tendon and in tendon as such no ANF were found. Two sets of ANF were noted in the middle ear mucosa: perivascular and unrelated to blood vessels.

Somatic (craniocervical) tinnitus and the dorsal cochlear nucleus hypothesis

PURPOSE

Of all nonauditory sensory systems, only the somatosensory system seems to be related to tinnitus (eg, temporomandibular joint syndrome and whiplash). The purpose of this study is to describe the distinguishing characteristics of tinnitus associated with somatic events and to use these characteristics to develop a neurological model of somatic tinnitus.

MATERIALS AND METHODS

Case series.

RESULTS

Some patients with tinnitus, but no other hearing complaints, share several clinical features including (1) an associated somatic disorder of the head or upper neck, (2) localization of the tinnitus to the ear ipsilateral to the somatic disorder, (3) no vestibular complaints, and (4) no abnormalities on neurological examination. Pure tone and speech audiometry of the 2 ears is always symmetric and usually within normal limits. Based on these clinical features, it is proposed that somatic (craniocervical) tinnitus, like otic tinnitus, is caused by disinhibition of the ipsilateral dorsal cochlear nucleus. Nerve fibers whose cell bodies lie in the ipsilateral medullary somatosensory nuclei mediate this effect. These neurons receive inputs from nearby spinal trigeminal tract, fasciculus cuneatus, and facial, vagal, and glossopharyngeal nerve fibers innervating the middle and external ear.

CONCLUSIONS

Somatic (craniocervical) modulation of the dorsal cochlear nucleus may account for many previously poorly understood aspects of tinnitus and suggests novel tinnitus treatments.

Axonal degeneration with tympanal nerve of Schistocerca gregaria

This study describes time course and ultrastructural changes during axonal degeneration of different neurones within the tympanal nerve of the locust Schistocerca gregaria. The tympanal nerve innervates the tergit and pleurit of the first abdominal segment and contains the axons of both sensory and motor neurones. The majority of axons (approx. 97%) belong to several types of sensory neurones: mechano- and chemosensitive hair sensilla, multipolar neurones, campaniform sensilla and sensory cells of a scolopidial organ, the auditory organ. Axons of campaniform sensilla, of auditory sensory cells and of motor neurones are wrapped by glial cell processes. In contrast, the very small and numerous axons (diameter <1 microm) of multipolar neurones and hair sensilla are not separated individually by glia sheets. Distal parts of sensory and motor axons show different reactions to axotomy: 1 week after separation from their somata, distal parts of motor axons are invaded by glial cell processes. This results in fascicles of small axon bundles. In contrast, distal parts of most sensory axons degenerate rapidly after being lesioned. The time to onset of degeneration depends on distance from the lesion site and on the type of sensory neurone. In axons of auditory sensory neurones, ultrastructural signs of degeneration can be found as soon as 2 days after lesion. After complete lysis of distal parts of axons, glial cell processes invade the space formerly occupied by sensory axons. The rapid degeneration of distal auditory axon parts allows it to be excluded that they provide a structure that leads regenerating axons to their targets. Proximal parts of severed axons do not degenerate.

The presence of ganglion cells in the human middle ear: a histological survey

A histological survey of 871 previously sectioned temporal bones from the Ear Pathology Research Laboratory (EPRL) of the University of Toronto was undertaken to determine the presence of ganglion cell and ganglion cell rests within the human middle ear. The presence of ganglion cells within the middle ear was a common finding noted in 52.3% of temporal bones surveyed. So-called 'ectopic' ganglion cells were identified most often in the greater superficial petrosal nerve (38.7%), the lesser superficial petrosal nerve (12.4%) and on the promontory (11.4%). They were also identified in the main trunk of the intratemporal facial nerve, but in smaller numbers (3%), and for the first time in the tensor tympani muscle. Their consistent presence implies that they should not be considered an abnormal anatomic variant, and further questions accepted conventional anatomic descriptions of middle ear innervation.

Temporal bone fractures

High-resolution technique is essential to the evolution of temporal bone fractures. Axial and coronal scan planes are optimal but may not be possible in acutely traumatized patients. A knowledge of normal temporal bone anatomy is important and can be obtained from standard texts, so it will not be considered in detail in this article. Classically, petrous temporal bone fractures have been classified as longitudinal, transverse, or mixed. Recent publications have emphasized the importance of describing fractures in terms of planes rather than lines. According to this concept, most temporal bone fractures are actually oblique, and true longitudinal fractures are rare. Petrous temporal bone fractures may be associated with cranial nerve or vascular injuries when the fracture extends to the skull base. This is particularly true of the oblique fracture, which characteristically extends anteromedially to the skull base through weak places in that area, thus avoiding the compact bone of the otic capsule surrounding the labyrinth. The most common associated injury is to the facial nerve in its geniculate or proximal tympanic segment. Transverse fractures frequently involve the labyrinth. A careful search for various types of ossicular dislocation should be performed in association with temporal bone fractures, because this may result in conductive hearing loss. The site of cerebrospinal fluid otorhinorrhea resulting from temporal bone fractures can usually be defined on plain high-resolution temporal bone images, but intrathecal contrast may be helpful. Temporal bone fractures caused by gunshot wounds are frequently complex and may be limited by metallic streak artifacts. Pediatric patients have different proportions of facial nerve injury and types of hearing loss as compared with adults.

[Validation of therapeutical policy choice in exudative otitis media]

132 patients with diagnosis acute or subacute exudative otitis media were treated conservatively (n = 79) or surgically (n = 53). Conservative treatment was effective in 41% of the cases, surgical treatment produced positive results in 62.3%. The operative treatment combined elements of endoscopic nasal surgery and methods used in tympanoplasty, plastic treatment of the auditory tube, surgery of the internal ear.

Autonomic innervation of the human middle ear: an immunohistochemical study

PURPOSE

Although there have been numerous studies of autonomic innervation of the middle ear mucosa, and the mechanism of effusion into the middle ear cavity in animals, the autonomic innervation of the human middle ear has not received much attention. The purpose of this study is to show the presence of catecholaminergic nerve fibers in the human middle-ear mucus membrane that may play an important role in the pathogenesis of middle-ear effusion.

MATERIALS AND METHODS

A total of 126 celloidin-embedded temporal bone sections from the temporal bone bank at the House Ear Institute were used for immunohistochemical study. A polyclonal antibody to tyrosine hydroxylase enzyme was used to show the presence of catecholaminergic nerve fibers.

RESULTS

Tyrosine hydroxylase immunoreactive nerve fibers containing numerous fine varicosities along their course, characteristic of noradrenergic neurons, were observed throughout the middle-ear mucosa including the promontary, sinus tympani, mesotympanum, and hypotympanum. In addition, these nerve fibers were seen in close promixity to the small-caliber blood vessels. A striking variation in the intensity of staining as well as in the amount of nerve fibers was observed among the temporal bone sections.

CONCLUSION

It is possible that the catecholaminergic nerve fibers, like elsewhere in the body, may exert a direct influence on the middle-ear mucosal blood vessels. We speculate that the effusion into the middle-ear space is an active, rather than a passive process. It is conceivable that cholinergic-sympathetic nerves might exist in the human middle-ear mucus membrane, and that these autonomic nerves, in conjunction with the neuropeptides, may play an active role in the pathogenesis of human middle-ear effusion.

Reversing click polarity may uncover auditory neuropathy in infants

OBJECTIVE

To identify patients with primary auditory neuropathies whose cochlear potentials to a 100 microsec click persist after click cessation and simulate synchronous auditory brain stem responses (ABRs) at high intensities.

DESIGN

ABRs to condensation and rarefaction clicks, as well as Maximum Length Sequence ABRs and one transtympanic electrocochleogram (ECochG), were collected from five infants with absent middle ear muscle reflexes and normal or near normal otoacoustic emissions. These infants failed ALGO screens, which used alternating polarity clicks, and/or failed full ABRs done elsewhere with alternating polarity clicks.

RESULTS

When ABRs were collected in response to a single polarity pulse, they revealed robust and reproducible wave forms over 4 to 6 msec that initially were mistaken for a normal ABR by the referring agents. However, when condensation and rarefaction click data are compared, the waveforms change polarity when the stimulus is inverted. Furthermore, the waveforms fail to shift in latency as the intensity of the stimulation is reduced. Transtympanic ECochG on one of the children revealed the same polarity reversal and fixed latency functions, confirming that they were cochlear rather than neural responses.

CONCLUSIONS

Comparing responses with positive versus negative polarity clicks may help separate ABRs from cochlear potentials and alert clinicians to the possibility of an auditory neuropathy. Therefore, absent or abnormal ABRs in the presence of normal otoacoustic emissions need not always implicate a purely "central disorder," but might be consistent with dysfunction between outer hair cells and primary afferent fibers.

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.

Jean Marquet Award. Regeneration of the neurosensory structures in the mammalian inner ear

Regeneration of the neurosensory structures in the mammalian inner ear. Motivated by the absence of treatment of neurosensory deafness apt to restore auditory function or alter the course of progressive hearing loss, we developed two different experimental strategies to approach these diseases: one is otoprotection, designed to prevent further degradation of auditory function; the other is regeneration which is defined as the replacement of hair cells in the deaf ear and their reconnection to the central nervous system through primary auditory neurons. In this paper, we summarize our data on the regeneration of auditory neurons and hair cells. Neuronal maintenance and regeneration was studied through an initial investigation of growth factors during inner development. Once the effect of various neurotrophic molecules was determined, the factors were tested on mature auditory neurons in vitro and in vivo. The hair cell regeneration was investigated on the basis of a concept derived from comparative physiology and from the study of the development of the inner ear. We showed that in young rats it is possible to induce the regeneration/repair of hair cells in the organ of Corti in cultures using retinoïc acid and transforming growth factor alpha. The clinical prospects of these findings of inner ear regeneration are discussed.

Fine structure of the afferent synapses in the paratympanic organ of the chicken, with special reference to the synaptic bodies

The afferent synapses of the paratympanic organ in the chicken were studied by TEM. These synapses were formed by non-myelinated fibres which reached the basal part of the hair cells. The fibres contained a number of irregular mitochondria and a few pale vesicles. In the hair cells, near the presynaptic membrane, typical synaptic bodies formed by an electron-dense core surrounded by several small pale vesicles were present. The core was connected with the vesicles by numerous thin filaments, and at same time with the presynaptic membrane by some dense projections. Moreover, we have observed that the connections between the core and the adjacent vesicles also consisted of similar structures to the dense projections. We suggest that this device is involved in the movement of the vesicles towards the presynaptic membrane. Our hypothesis is in agreement with that formulated by some authors who believe that the electron-dense core of the synaptic bodies is able to channel the vesicles to the presynaptic membrane (conveyor-belt hypothesis). Moreover, our work showed that the synaptic bodies of the paratympanic organ in the chicken are variable in density and in shape. These morphological aspects might be linked to regression-reconstitution cycles of the SBs and to the functional level of the afferent synapses.

Evidence of a medial olivocochlear involvement in contralateral suppression of otoacoustic emissions in humans

Otoacoustic emissions (OAEs) evoked by click stimuli were recorded in both ears of 20 normal human subjects, in the presence and absence of a contralateral masking broad band noise. No difference in the amplitude of OAE suppression was noted between the first tested ear and the second one. In addition, 20 pathological subjects were tested according to the same protocol. Ten of them belonged to a group of patients whose vestibular nerve was sectioned on one side to relieve incapacitating vertigo and thus represented a group in whom olivocochlear efferents were severed. A great reduction of suppression observed in the operated ear suggested that olivocochlear efferent fibers are necessary to obtain a full suppressive effect. Three of the pathological subjects were patients who had undergone a decompression of the facial nerve which necessitated the same surgical approach as vestibular neurotomy, but without any section of vestibular fibers. This surgical control group demonstrated that the surgical act by itself cannot explain the difference observed in the neurotomized group. Finally, seven of the pathological subjects were patients with Bell's palsy, which paralyses the facial nerve and abolishes the stapedial reflex. No suppression difference was observed between healthy ears and ears without stapedial reflex. Therefore, it appeared that the stapedial reflex was not involved in the contralateral suppression of EOAEs. However, as the tensor tympani muscle remained functional in these patients, its involvement in the suppressive effect cannot be excluded.

Tympanic neurectomy in the management of parotid sialectasis

The term sialectasis refers to dilation of the salivary ducts. Parotid sialectasis presents itself as recurrent painful swellings during mastication and/or swallowing. Our results with 10 cases treated by tympanic neurectomy over a period of nine years, from 1983 to 1992, were encouraging as seven cases had improvement of their symptoms. Anatomy of the tympanic plexus and surgical procedure are discussed as well as a review of the literature. We recommend extensive interruption of the secreto-motor nerve fibers by thoroughly drilling into the hypotympanum and below the basal turn of the cochlea. We also recommend that this be carried out by an experienced otologist to avoid possible complications.

The clinical significance of the communicating branches of the somatic sensory supply of the middle and external ear

The sensory supply of the middle and external ear is complicated by multiple neural communications. The anatomy of these communications and their clinical significance will be described in this paper.

A mechanism for sympathectomy-induced bone resorption in the middle ear

BACKGROUND

Recent investigations have demonstrated a link between sympathectomy and osteoclast-mediated bone resorption. The exact nature of this link, however, is unknown. We hypothesize that substance P, a potent vasoconstrictive neuropeptide found in peripheral sensory fibers, including those innervating bone, is the mediator of this phenomenon. To test this theory, the effects of substance P on in vitro calcium release from cultured neonatal mouse calvaria were assessed. In addition, an in vivo study was conducted whereby gerbils were injected with capsaicin to eliminate substance P-containing fibers before sympathectomy with 6-hydroxydopamine. If the effects of 6-hydroxydopamine were eliminated by prior administration of capsaicin, the role of sensory nerves in sympathectomy-induced resorption would be strongly implicated.

IN VITRO STUDY

Substance P at 10(-8) mol/L was incubated with eight newborn Swiss-Webster mouse hemicalvarial explants and compared with explants incubated in control media alone. The neonatal mice were euthanized at day 3, and their hemicalvaria were preincubated in 2 ml of stock media without treatment for 24 hours at 36.5 degrees C as a stabilization period. After the stabilization period, the stock media were replaced with 2 ml of fresh control media or media containing substance P at 10(-8) mol/L. A similar experiment was performed with the addition of indomethacin at 5 x 10(-7). The explants were then incubated for 72 hours with gassing every 12 hours with a mixture of O2, N2, and CO2. At the end of the 72-hour period, the media were analyzed for calcium content by atomic absorption spectrophotometry and compared by one-way analysis of variance with Bonferroni-corrected post hoc tests.

IN VIVO STUDY

Forty-eight Mongolian gerbils were placed into four groups: group 1 received intraperitoneal injections of 6-hydroxydopamine at 75 micrograms/gm body weight on days 1, 2, 6, 7, and 8; group 2 received identical injections of hydroxydopamine, but 12 hours after receiving subdermal injections of capsaicin at 50 micrograms/gm body weight; group 3 received only subdermal injections of capsaicin; and group 4 received only saline injections to serve as controls. Seven days after treatment, the animals were euthanized, and the ventral wall of each animal's right bulla was resected and quantified for osteoclast number and surface with a computer-based histomorphometry system. Analysis was then made by one-way analysis of variance with Bonferroni-corrected post hoc tests.

RESULTS

The results of the in vitro study revealed that substance P at 10(-8) mol/L (11.05 +/- 3.37 micrograms/ml) induced significant calcium release from cultured neonatal mouse calvaria when compared with control bone incubated in base media alone (0.92 +/- 2.85 micrograms/ml, p < 0.01). The process was completely inhibited by 5.0 x 10(-7) indomethacin. The results of the in vivo study showed 6-hydroxydopamine treatment significantly increased both the osteoclast number (NOc/TL = 3.14 +/- 1.33/mm) and the osteoclast surface (OcS/BS = 16.04% +/- 6.95%) of bone when compared with bone from saline-treated controls (NOc/TL = 1.77 +/- 0.79/mm, p < 0.01; OcS/BS = 8.88% +/- 4.15%, p < 0.01). These 6-hydroxydopamine-induced increases were eliminated, however, in animals pretreated with capsaicin before sympathectomy (NOc/TL = 1.86 +/- 0.68/mm, p > 0.05; OcS/BS = 9.92 +/- 3.73, p > 0.05), whereas treatment with capsaicin alone had no effect when compared with bone from saline-treated controls (NOc/TL = 2.02 +/- 0.50/mm, p > 0.05; OcS/BS = 10.28% +/- 2.62%, p > 0.05). Substance P has thus been shown to induce calcium release from membranous bone in vitro, whereas capsaicin, a substance P-specific sensory neurolytic chemical, eliminates the in vivo osteoclast-inductive effects of 6-hydroxydopamine when given 12 hours before treatment. The results indicate that substance P is capable of inducing resorption and that substance P-containing sensory ne

The effects of contralateral noise on masked compound action potential in humans

The effects of contralateral noise on the masked compound action potential (CAP) were examined in human subjects. Small but significant enhancements of masked CAP amplitude (anti-masking effects) were observed in some patients with facial palsy, as well as in some subjects with healthy ears when noise was added to the contralateral ear. There were no significant differences in fractional changes of CAP by the addition of contralateral noise between subjects with healthy ears and patients with facial palsy in which acoustic reflexes of middle ear muscles (MEMs) had disappeared or were impaired. It is suggested that the anti-masking effects seen in the present study were possibly caused via the olivocochlear (OC) efferent system.

Characterization of auditory afferents in the tiger beetle, Cicindela marutha Dow

We have identified a nerve carrying auditory afferents and characterized their physiological responses in the tiger beetle, Cicindela marutha. 1. The tympana are located at the lateral margins of the first abdominal tergum. The nerve carrying the tympanal afferents is a branch of the dorsal root from the first abdominal ganglion. 2. Both male and female auditory afferent responses are sharply tuned to 30 kHz with sensitivities of 50-55 dB SPL. 3. The auditory afferents show little adaptation and accurately code the temporal characteristics of the stimulus with the limit of a resolution of 6-10 ms. 4. The difference in threshold between contralateral and ipsilateral afferents for lateral stimuli is greatest at 30 kHz and is at least 10-15 dB. 5. Ablation studies indicate that the floppy membrane in the anterolateral corner of the tympanum is crucial for transduction while the medial portion of the tympanum is less important. 6. The tiger beetle and acridid (locust and grasshopper) ears have evolved independently from homologous peripheral structures. The neural precursor of the tympanal organs in both animals is likely the pleural chordotonal organ of the first abdominal segment.

Postnatal developmental changes in facial nerve morphology. Computer-aided 3-D reconstruction and measurement

Accurate measurements of the lengths and angles of the facial nerve were obtained in eight normal human temporal bones of varying ages from 7 days to 76 years. Measurements were made on serial histological sections, using computer-aided three-dimensional (3-D) reconstruction. The most noteworthy of the findings demonstrated that both the mastoid portion of the facial nerve and the segment of the facial nerve between the second genu and the divergence of the chorda tympani nerve lengthened with age. The mastoid segment lengthened more significantly than the latter, indicating the facial canal grows more than the facial nerve in its mastoid portion. This difference in growth rates results in the site of the chorda tympani nerve divergence shifting with age relative to the stylomastoid foramen.

Parotid fistulae treated by tympanic neurectomy

OBJECTIVE

To study the feasibility of tympanic neurectomy in the treatment of parotid fistulae.

DESIGN

Five patients with parotid fistulae were treated by tympanic neurectomy at the ENT Department, General Hospital, Kandy.

RESULTS

Four were completely and one was partially cured.

Prevalence of facial canal dehiscence and of persistent stapedial artery in the human middle ear: a report of 1000 temporal bones

A total of 1000 temporal bones were used to study the prevalence of facial canal dehiscence and of persistent stapedial artery in detail. Of the temporal bones studied, 560 (56%) contained at least one facial canal dehiscence. There was a 76.3% prevalence of bilaterality of this canal wall gap. The most common site of dehiscence was the oval window area. The concept of microdehiscence of the facial canal is introduced. One third of the temporal bones observed had a microdehiscence of the facial canal, usually located at the oval window area (74.9%) and found bilaterally 40% of the time. The authors found a 0.48% prevalence (5 out of 1045) of persistent stapedial artery. This is the first histological study of temporal bones to report a prevalence of this vascular anomaly.

Facial nerve enhancement in Gd-MRI in patients with Bell's palsy

The diagnostic value of a contrast enhanced MRI in patients with Bell's palsy was investigated. It was a characteristic finding that the internal acoustic meatal segment of the facial nerve was enhanced only on the affected side. The signal intensity ratio of the geniculate ganglion and the tympanic segment was significantly higher on the affected side than on the normal side. The severity of the facial palsy and the results of physiological examinations showed no relation to the results of MRI scans. Gd enhanced MRI thus appears to provide some useful findings for estimating the affected region of Bell's palsy, whereas it is not considered to be valuable in the diagnosis of severity.

Functional morphology of the paratympanic organ in the middle ear of birds

The paratympanic organ (PTO) is a small sense organ in the middle ear of birds. This luminal organ contains mechanoreceptors (hair cells) with afferent and efferent innervation and may function as a baroreceptor. The hypothesis that elastic ligaments of the middle ear may be involved in the transduction of barometric pressure was tested. Two elastic ligaments are shown to attach to the PTO. The columellar-squamosal ('Platner's') ligament inserts at its caudal pole; the superior portion of the superior drum-tubal ligament attaches at the rostral tip of the organ. To determine if pressure to the tympanic membrane and tension of ligaments may cause lumen changes in the PTO, the length of elastic ligaments, and the length, volume and configuration of the PTO were measured in normal animals and in animals following application of positive or negative pressure to the tympanic membrane. The rostral pole of the PTO changes its shape differentially as a function of the tension of the superior drum-tubal ligament, resulting in volume shifts of about 10% of the total volume in the PTO. With negative pressure, volume moves from the rostral pole to the caudal half of the PTO; with positive pressure, volume shifts rostrally. Displacement of fluid in the lumen of the PTO thus may stimulate the paratympanic hair cells. Tracing of efferent projections to the PTO with the fluorescent compound DiI reveals a cluster of about 40 labeled neurons at the caudal pole of the ventral facial motor nucleus adjacent to the superior olive. These findings support the notion that the PTO may be part of a neural circuit that controls the position of the tympanic membrane and may mediate barometric perception in birds.