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.

The Thickness of the facial Nerve Sheath Consistently Varies by Region in Its Intra-Tympanic Course on Cadaveric Study.

OBJECTIVES: Iatrogenic removal of intra-temporal disease processes, such as cholesteatoma and keratosis obturans, can be challenging when the facial nerve (FN) is involved. Despite this concern about possible FN injury during these procedures, our clinical observation has been that the diseased growth can be cleaned quite easily from the vertical FN epineurium. Therefore, we designed a cadaveric protocol to measure thickness of the FN sheath (epineurium) in horizontal, second genu and vertical FN segments and to correlate these measurements with surgical management of FN disorders. METHODS: Fifty non-fixated (wet) cadaveric temporal bones were dissected over 1 year's time. The intra-temporal FN sheath epineurium was harvested from the mid-horizontal, second genu, and mid-vertical segments. Using a digital micrometric technique, the thickness of each sample was measured. Data analysis was performed using student's two-tailed, dependent t-test. RESULTS: Epineurial nerve sheath thickness was the least in the horizontal segment (mean 0.9 mm, range 0.040-0.140 mm), greater at the second genu (mean 0.19 mm, range 0.010-0.280 mm), and greatest in the vertical segment (mean 0.29 mm, range 0.170-0.570 mm). These differences were statistically significant. CONCLUSION: In cases of cholesteatoma and keratosis obturans involving the vertical FN, the disease process can be separated from the FN sheath because of the sheath thickness in this region. Disease in the horizontal segment involves a thinner sheath and separating the disease process from the nerve is more difficult in this area.

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.

A randomized controlled trial evaluating the hemodynamic impact of ultrasound-guided great auricular nerve block in middle ear microsurgery.

BACKGROUND: The peri-operative effectiveness of ultrasound-guided great auricular nerve block (GANB) in patients, especially in adult patients undergoing middle ear microsurgery remains unclear. We hypothesized that ultrasound-guided GANB would decrease the hemodynamic responsiveness to incision and opioid consumption in middle ear microsurgery as well as the post-operative analgesia requirement. METHODS: Sixty patients undergoing middle ear microsurgery were randomized into two equal groups to receive either a GANB with 2 ml of 0.25% ropivacaine under ultrasound guidance (GANB group) or to receive a blank control intervention (without any performed injection) before general anesthesia inductions. The primary outcomes were hemodynamic changes of MAP (mean artery pressure) and HR (heart rate) to skin incision. The secondary endpoints were to determine the consumptions of propofol and remifentanil during the operation and the incidence of remedial analgesia 48 h post-operation to maintain VAS ≤ 3. RESULTS: The MAP post incision in GANB group was significantly lower than that in control group (GANB group 93.83 ± 11.72 mmHg vs. control group 100.87 ± 12.65 mmHg, P = 0.029). The increases for MAP and HR post incision were also lower in GANB group (∆MAP GANB group 11.90 ± 8.32 mmHg vs. control group 19.83 ± 10.37 mmHg, P = 0.002; ∆HR GANB group 3.67 ± 5.30 beat min- 1 vs. control group 8.23 ± 8.56 beat min- 1, P = 0.016). Remifentanil consumption was significantly decreased in GANB group (GANB group 401.55 ± 100.51 µg h- 1 vs. control group 697.34 ± 215.45 µg h- 1, P = 0.000). The incidence of remedial analgesia post-operation in GANB group (5/30) was significantly lower than that in control group (20/30, P = 0.000). CONCLUSION: Ultrasound-guided GANB decreases the hemodynamic responsiveness to incision and remifentanil consumption in middle ear microsurgery as well as the post-operative analgesia requirement. TRIAL REGISTRATION: This trial was retrospectively registered at http://www.chictr.org.cn with the registration number of ChiCTR1800014333 on 6 January, 2018.

Associations between speech recognition at high levels, the middle ear muscle reflex and noise exposure in individuals with normal audiograms.

It has been hypothesized that noise-induced cochlear synaptopathy in humans may result in functional deficits such as a weakened middle ear muscle reflex (MEMR) and degraded speech perception in complex environments. Although relationships between noise-induced synaptic loss and the MEMR have been demonstrated in animals, effects of noise exposure on the MEMR have not been observed in humans. The hypothesized relationship between noise exposure and speech perception has also been difficult to demonstrate conclusively. Given that the MEMR is engaged at high sound levels, relationships between speech recognition in complex listening environments and noise exposure might be more evident at high speech presentation levels. In this exploratory study with 41 audiometrically normal listeners, a combination of behavioral and physiologic measures thought to be sensitive to synaptopathy were used to determine potential links with speech recognition at high presentation levels. We found decreasing speech recognition as a function of presentation level (from 74 to 104 dBA), which was associated with reduced MEMR magnitude. We also found that reduced MEMR magnitude was associated with higher estimated lifetime noise exposure. Together, these results suggest that the MEMR may be sensitive to noise-induced synaptopathy in humans, and this may underlie functional speech recognition deficits at high sound levels.

A Rare Case of Bifurcated Chorda Tympani.

Preservation of the chorda tympani is important in middle ear surgery to prevent dysgeusia postoperatively. However, determining the exact course of the chorda tympani before surgery is not always possible, especially in cases with accompanying malformations. In this report, we presented an extremely rare case of bifurcation of the chorda tympani in a 15-year-old male patient. We performed tympanoplasty for a middle ear malformation with conductive hearing loss. During the operation, we noticed and carefully preserved the bifurcated chorda tympani. The patient did not develop dysgeusia postoperatively. Appropriate handling and understanding of the anomalous chorda tympani preserved the patient's sense of taste and hence quality of life.

Is there a relationship between mastoid pneumatisation and facial canal dimensions?

OBJECTIVE: To evaluate mastoid pneumatisation and facial canal dimensions. METHOD: In this retrospective study, 169 multidetector computed tomography scans of temporal bone were reviewed. Facial canal dimensions were evaluated at the labyrinthine, tympanic and mastoid segments using axial and coronal multidetector computed tomography scans of temporal bone. Mastoid pneumatisation and facial canal dehiscence were evaluated. Facial canal dehiscence was measured if it was found to be present. RESULTS: This study showed that facial canal dimensions decreased in pneumatised mastoids. Facial canal dimensions in females were smaller than in males. Facial canal dehiscence was detected in 5.9 per cent and 6.5 per cent of the patients on the right and left sides, respectively. No correlations were found between facial canal dehiscence and mastoid pneumatisation. The length of dehiscence was 1.92 ± 0.44 mm (range, 0.86-2.51 mm) on the left side. In older subjects, left facial canal dehiscence was detected more, and the length of the dehiscence increased. CONCLUSION: This study concluded that during surgery, facial canal dehiscence should be kept in mind in order to avoid complications.

Assessment of the efferent auditory system in children with suspected auditory processing disorder: the Middle ear muscle reflex and contralateral inhibition of OAEs.

OBJECTIVE: To determine whether children aged 7 to 12 years with listening difficulties show objective evidence for efferent auditory function based on measurements of medial olivo-cochlear and middle ear muscle reflexes. DESIGN: Click-evoked otoacoustic emissions recorded with and without contralateral broadband noise and ipsilateral and contralateral tonal (1000, 2000 Hz) middle ear muscle reflex thresholds were examined. STUDY SAMPLE: 29 children diagnosed with suspected auditory processing disorder (APD) and a control group of 34 typically developing children participated in this study. RESULTS: Children with suspected APD had poorer performance on auditory processing tests than the control group. Middle ear muscle reflex thresholds were significantly higher at 2000 Hz in the suspected APD group for contralateral stimulation. MOC inhibition effects did not differ between APD and control groups. CONCLUSIONS: This research supports earlier studies showing altered acoustic reflexes in children with APD. No group differences were found for the MOC reflex measures, consistent with some earlier studies in children with APD.

Acoustic reflexes are common but not pervasive: evidence using a diagnostic middle ear analyser.

OBJECTIVE: The objective of this study is to determine whether acoustic reflexes are pervasive (i.e. known with 95% confidence to be observed in at least 95% of people) by examining the frequency of occurrence using a friction-fit diagnostic middle ear analyser. DESIGN: Adult participants with very good hearing sensitivity underwent audiometric and middle ear testing. Acoustic reflexes were tested ipsilaterally and contralaterally in both ears across a range of elicitor frequencies. Reflex elicitors were 700 ms tones presented at maximum level of 100 dB HL. Two automated methods were used to detect the presence of an acoustic reflex. STUDY SAMPLE: A group of 285 adult volunteers with normal hearing. RESULTS: There were no conditions in which the proportion of participants exhibiting acoustic reflexes was high enough to be deemed pervasive. Ipsilateral reflexes were more likely to be observed than contralateral reflexes and reflexes were more common at 0.5 and 1 kHz elicitor frequencies as compared with 2 and 4 kHz elicitor frequencies. CONCLUSIONS: Acoustic reflexes are common among individuals with good hearing. However, acoustic reflexes are not pervasive and should not be included in damage risk criteria and health hazard assessments for impulsive noise.

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.

Laser tympanic neurectomy for post-cochlear implant pain: A new technique.

OBJECTIVES: To present the case histories and management by LASER tympanic neurectomy of two patients who presented with pain as their only symptom after cochlear implantation, avoiding the need for device removal. CLINICAL PRESENTATION: Two of our patients presented with otalgia, which appeared 6 months after cochlear implantation and resulted in their refusing to use the device. The pain was not controlled by repeated remapping or medical management. Neither patient showed evidence of infection or inflammation around their device. X-rays showed that there were no extracochlear electrodes or evidence of extrusion. One patient had current leakage from two electrodes, which were switched off, but the pain persisted. INTERVENTION: Both patients received an intratympanic injection of 1 ml of 0.5% Bupivacaine to anaesthetize the tympanic plexus in the middle ear and were then observed for a day, found to have relief of their pain and were able to use the implant with audiological benefit for this short time, until the effect of the anaesthetic had worn off. Therefore we planned and performed a tympanic neurectomy on both patients using CO2 laser. CONCLUSION: Tympanic neurectomy removed the pain in two cochlear implant patients who presented with pain which was present only when the implant was switched on.

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.

[Global and Spatial Gustatory Function after Proven Unilateral Transsection of the Chorda Tympani]. / Globales und regionales Schmeckvermögen nach einseitiger Durchtrennung der Chorda tympani.

BACKGROUND: A transection of the chorda tympani results in loss of spatial gustatory function on the ipsilateral tongue. Most patients do not notice anymore this alteration. The cause is unclear. Do adjacent gustatory areas become more sensitive or is the gustatory perception rather independent of the size of stimulated area? METHODS: 51 patients with proven unilateral transection of the chorda tympani and 51 healthy subjects were tested for gustatory recognition thresholds. The methods used were the "three-drops-choice-technique" by Henkin to evaluate the whole mouth taste (global taste examination) and the "spatial taste test" to evaluate the local gustatory function on 4 areas of the tongue. The taste solutions were sweet, sour, salty and bitter with increasing concentrations. RESULTS: The global gustatory function of the patients and of the control group did not differ in either the 4 taste qualities but the composite score was increased within the group of patients. Most patients did not realize that. The spatial taste examination showed reduction of taste perception on 3 of the 4 gustatory areas of the tongue in the patients. The decreased gustatory function on the area of the transected chorda remained unchanged over time. The taste attenuation on the ipsilateral back area and the contralateral front area improved over time. CONCLUSION: Transection of chorda tympani also leads to an attenuation of spatial gustatory function in adjacent areas. Therefore, adjacent areas cannot be taken as reference. Instead, taste function has to be compared to the results of healthy probands.

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.

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.

First bite syndrome: our experience of laser tympanic plexus ablation.

INTRODUCTION: First bite syndrome is a condition characterised by severe facial pain brought on by the first bite of each meal. This can severely affect the patient's ability to eat. METHODS: We present a 70-year-old woman for whom we performed a laser ablation of the left ear tympanic plexus, as treatment of first bite syndrome. A permeatal approach was used to raise a tympanomeatal flap. The tympanic plexus was identified on the promontory and a 4 mm2 area of the plexus was ablated using CO2 laser. The flap was repositioned and a dressing was placed with topical antibiotics. RESULTS: At two-month follow up, there was full resolution of the patient's symptoms. DISCUSSION: First bite syndrome carries a high morbidity; treatment options are variable, and often unsuccessful. We describe the first documented case of laser tympanic plexus ablation, with a very effective initial response. This procedure represents a useful therapeutic option for first bite syndrome.

Measurement and analysis of facial nerve on fully displayed multislice computed tomographic multiplanar reconstruction image.

The objectives of this study were to measure the length of horizontal segment of facial nerve (HFN), the length of vertical segment of facial nerve (VFN), and the angle between these 2 segments on a fully displayed multislice computed tomographic multiplanar reconstruction (MPR) images of HFN and VFN and to analyze the data with respects to side, sex, and age. Parameters of 234 patients (468 observations, 118 men and 116 women, aged 4-70 years) with intact temporal bone were measured on multislice computed tomographic multiplanar reconstruction images. The data gained were analyzed by statistical method. The left and right lengths of VFN were significantly different (P < 0.05). And the length of HFN, the length of VFN, and the angle between males and females were significantly different (P < 0.05). We divided the data into 3 groups to study correlations between measurements and age. In underaged group, there was a strong positive correlation between the length of VFN and age; the value of Pearson correlation was 0.645. And there was a weak correlation between the angle and the age; the value of Pearson correlation was 0.270. In older-aged group, there was a moderate negative correlation between the length of VFN and age; the value of Pearson correlation was -0.408. Our results are of high potential to expand the visual field to facial nerve and may provide more detailed information to surgeries of facial nerve, middle ear, and temporal bone.

Chorda tympani nerve, may it have a role in stabilizing middle ear pressure?

The chorda tympani (ChT) is a mixed nerve, branch of the facial nerve, crossing the middle ear and containing the preganglionic parasympathetic axons that innervate the sublingual and submandibular glands. The maintenance of a correct middle ear pressure (MEP) is essential for normal ear functions; its regulation has a sophisticated neural control mainly provided by middle ear receptors (tympanic plexus, TP) and Eustachian tube (ET). The information provided by chemoreceptors and baroreceptors of the TP is transmitted to the nuclei of the solitary tract (NST) and then a neural circuit promotes the activation of ET muscles. We hypothesize that the information provided by the TP may modulate submandibular and sublingual glands activity through a neural pathway involving the NST, the superior salivatory nucleus (SSN) and finally the ChT. According to our hypothesis, sudden perturbations of the MEP may stimulate saliva production with consequent swallowing, opening of the Eustachian tube and endotympanic pressure rebalancing.

Key methods of identifying the horizontal facial nerve during difficult middle-ear surgery.

BACKGROUND: The key to avoiding damage to the horizontal facial nerve in middle-ear surgery is to formally identify the nerve in the early stages of the procedure. METHODS: In the non-infected ear this can be achieved relatively easily by identifying the oval window niche. However, in the infected ear with cholesteatoma, the safest landmark to use is the processus cochleariformis, which can be identified by three different methods. CONCLUSION: In an infected ear that is full of granulation tissue and/or cholesteatoma, the horizontal facial nerve can be reliably identified by locating the processus cochleariformis using the three methods described. This avoids damage to the nerve and important structures around it.

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.