The cochlear microphonic potential does not reflect the passive basilar membrane traveling wave.

OBJECTIVE: Understanding the cochlear microphonic potential (CM) can contribute to its clinical usefulness, e.g. in auditory neuropathy where the CM is present, while auditory evoked neural potentials are absent. The space-time pattern of the basilar membrane traveling wave in the cochlea is thought to be responsible for generation of the CM and its pattern along the cochlea. This relationship was studied in two experiments. EXPERIMENT I: METHODS: The threshold of the CM was measured in animals before and after drilling a hole in the wall of the inner ear vestibule. Such a hole likely reduces the magnitude of the basilar membrane traveling wave. RESULTS: The hole did not cause a change in CM threshold. CONCLUSION: This is evidence that the passive basilar membrane traveling wave described by von Bekesy in cadavers in response to high intensity stimulation may not be the trigger for cochlear activation and CM generation at low intensities. EXPERIMENT II: METHODS: A saline filled tube provided fluid coupling between the cochlea of one animal and that of a second through the perforated round windows of their cochleae. RESULTS: In response to sound stimulation of animal 1, CM (and ABR) could be recorded in animal 2, even when animal 1 was no longer living. CONCLUSION: It is highly unlikely that a basilar membrane traveling wave could have been induced in cochlea 2 in these conditions. SIGNIFICANCE: It is therefore suggested that at low sound intensities, the initial event activating the cochlea in general and the CM in particular is the fluid pressures (condensations/rarefactions) induced in the cochlear fluids by sound-induced stapes footplate vibrations.

Image guided navigation system-a new technology for complex endoscopic endonasal surgery.

PURPOSE: Endoscopic endonasal surgery (EES) has become the standard practice in sinonasal and anterior skull base surgery. The purpose of this manuscript is to describe experience using a new technology-the image guided navigation system (IGNS)-in complex cases undergoing EES. The advantages and disadvantages of computer aided surgery are discussed. PATIENTS AND METHODS: A total of 165 endoscopic endonasal procedures were performed between April 2001 and January 2003. IGNS was used in 34 patients in whom it was assumed that the ability to identify surgical sites accurately could be compromised by previous surgery, massive recurrent polyposis, or abnormal anatomy, or when biopsies had to be taken from specific anatomic locations (for example, clivus, wall of sphenoid sinus, orbital apex). The precision of the navigation system, total operating room time, surgeon's satisfaction and confidence, and intraoperative and postoperative complications were recorded. RESULTS: In 33 out of 34 patients the surgical procedure was uneventful. One patient with an atelectatic maxillary sinus developed a minor complication of preseptal orbital haematoma. In 94% the IGNS provided accurate anatomical localisation with less than 2 mm localisation error (1.1-2.0 mm, mean 1.6 mm). In all cases the surgical team felt that the system increased the intraoperative safety factor for the patient. The overall operating room time at the end of the study was 15 minutes longer than when regular EES was used. CONCLUSIONS: IGNS enables a new level of efficiency and safety in EES. Nevertheless, it is not advised for surgeons who are not familiar with regular EES. For the experienced endoscopist, however, IGNS is a valuable new tool in complex procedures.

The pathway enabling external sounds to reach and excite the fetal inner ear.

The human fetus in utero is able to respond to sounds in the amniotic fluid enveloping the fetus after about 20 weeks gestation. The pathway by which sound reaches and activates the fetal inner ear is not entirely known. It has been suggested that in this total fluid environment, the tympanic membrane and the round window membrane become 'transparent' to the sound field, enabling the sounds to reach the inner ear directly through the tympanic membrane and the round window membrane. It is also possible that sounds reach the inner ear by means of tympanic membrane--ossicular chain--stapes footplate conduction (as in normal air conduction). There is also evidence that sounds reach the fetal inner ear by bone conduction. Several animal and human models of the fetus in utero were studied here in order to investigate the pathway enabling sounds to reach and activate the fetal inner ear. This included studying the auditory responses to sound stimuli of animals and humans under water. It was clearly shown in all the models that the dominant mechanism was bone conduction, with little if any contribution from the external and middle ears. Based on earlier experiments on the mechanism and pathway of bone conduction, the results of this study lead to the suggestion that the skull bone vibrations induced by the sound field in the amniotic fluid enveloping the fetus probably give rise to a sound field within the fetal cranial cavity (brain and CSF) which reaches the fetal inner ear through fluid communication channels connecting the cranial cavity and the inner ear.

Vestibular end-organ impairment in an animal model of type 2 diabetes mellitus.

OBJECTIVES/HYPOTHESIS: To define and assess the functional impairment of the vestibular part of the inner ear in a diabetic state, using a direct and objective test for evaluating the vestibular end-organ and an animal model for diet-induced type 2 diabetes mellitus. STUDY DESIGN: Prospective controlled animal study. METHODS: Two groups of sand rats (Psammomys obesus) were maintained on two different diets. The experimental group received a specially designed high-energy diet known to induce a diabetic state, and the control group a low-energy diet maintaining these animals in a normal metabolic state. After 1 month of documented hyperglycemia in the experimental group, recordings of vestibular evoked potentials (VsEPs) and recordings of auditory brainstem response (ABR) were conducted in all animals. The latency and the amplitude of the first wave of both responses, shown to reflect end-organ activity, were compared between the two groups. RESULTS: The mean latency of the first wave of the VsEPs was significantly (P = .002) prolonged and the amplitude was significantly (P = .005) decreased in the diabetic group in comparison to the control group. The latency of the first wave of ABR was significantly (P = .02) prolonged, the amplitude was not significantly decreased, and threshold was significantly elevated (P = .01) in the diabetic group. CONCLUSION: For the first time, using an objective assessment test, functional impairment of the vestibular part of the inner ear has been demonstrated in the diabetic metabolic state. Despite this being an animal study, these findings would seem to indicate that the vestibular-end-organ should be added to the long list of organs and tissues adversely affected by diabetes.

Use of evoked potentials to objectively differentiate between selective vulnerability of cochlear and vestibular end organ function.

Auditory nerve brainstem evoked responses (ABR) have been used for several decades to investigate cochlear function. Recently techniques have been developed to elicit similar recordings from the vestibular end organs - short latency vestibular evoked potentials (VsEPs). Both ABR and VsEP reflect appropriate end organ function and may therefore be used to investigate the vulnerability of these end organs to various experimental insults, such as noise exposure and ototoxic drugs.

The effect of clonidine premedication on hemodynamic responses to microlaryngoscopy and rigid bronchoscopy.

The usual hemodynamic response to laryngoscopy and bronchoscopy is an increase in heart rate and arterial blood pressure. Previous work has reported that 10%-18% of the patients develop ischemic ST segment changes during the procedure. Therefore, we performed a prospective, randomized, double-blinded study in 36 patients scheduled for elective microlaryngeal and bronchoscopic surgical procedures to evaluate the effects of 300-microg oral clonidine premedication (n = 18) or placebo (n = 18) on the hemodynamic alterations and the incidence of perioperative myocardial ischemic episodes. Myocardial ischemia was assessed by using continuous electrocardiographic monitoring, beginning 30 min before, and lasting until 24 h after the operation. During the procedure, patients receiving placebo exhibited a significant increase (mean +/- SD) in arterial blood pressure (the systolic increasing from 137+/-11 to 166+/-17 mm Hg, the diastolic increasing from 80+/-11 to 97+/-14 mm Hg) and heart rate (increasing from 79+/-15 to 97+/-12 bpm) compared with the baseline and with the clonidine group. A dose of 300-microg clonidine blunted the hemodynamic response to endoscopy. Ventricular arrhythmias were more frequent in patients who were not premedicated with clonidine. Two patients in the control group, but none in the clonidine group, had evidence of myocardial ischemia. These data should encourage routine premedication with clonidine in patients undergoing microlaryngoscopic and bronchoscopic procedures.

Artifactual thickening of the sinus walls on computed tomography: a phantom model and clinical study.

Measuring sinus wall thickness on computed tomography may be important for distinguishing between acute and chronic inflammation of the paranasal sinuses or in cases of a suspected neoplasm. The objective of this study was to investigate the effects of opacified and aerated sinuses on the appearance of sinus wall thickness. A phantom model consisting of a skull half-immersed in water was scanned, and various slice thicknesses and different windows were used. The sinus walls of the water-immersed side appeared to be thicker than those of the aerated side. Bone windows did not completely eliminate this partial volume effect. It was concluded that comparison between a fluid- or tissue-filled sinus and an air-filled counterpart is not accurate enough for evaluating sinus wall thickness. Bone windows do not completely eliminate the artifactual thickening of the bony wall of a filled sinus.

Vestibular and cochlear ototoxicity of topical antiseptics assessed by evoked potentials.

OBJECTIVES/HYPOTHESIS: To evaluate and compare the effect of chlorhexidine gluconate, povidoneiodine, and alcohol-three antiseptics used before ear surgery-on the function of the vestibular and cochlear parts of the sand rat's inner ear. The assessment of damage is based on the recording of vestibular evoked potentials (VsEPs) and auditory brainstem response (ABR). STUDY DESIGN: Prospective controlled animal study. METHODS: Fat sand rats were randomly assigned to five different groups, each receiving topical application of a different agent: saline (control), gentamicin (ototoxic control), chlorhexidine, povidone-iodine, and alcohol. Right-side total labyrinthectomy was performed, and a polyethylene tube was inserted into the left (contralateral) middle ear. After baseline recordings were taken of VsEPs and ABR, each animal received five consecutive daily applications of the specific agent into the left middle ear. Three days after the fifth application, evoked potential recordings (VsEPs and ABRs) were repeated and compared with baseline measurements. RESULTS: Administration of saline affected neither VsEPs nor ABR. In contrast, as expected, neither of these responses could be recorded after gentamicin application. After application of chlorhexidine all waves disappeared in all sand rats. Alcohol caused the waves to disappear in some of the animals only. Povidone-iodine did not affect VsEP recordings and had only a small effect on ABR. CONCLUSIONS: Chlorhexidine and alcohol had a clear toxic effect on the vestibular and cochlear function of the inner ear of the sand rat, whereas povidone-iodine did not. Thus, taking into consideration that this is an animal study, it appears that povidone-iodine might be preferable to the other agents tested in disinfecting ears with a perforated tympanic membrane.

Bone conduction experiments in animals - evidence for a non-osseous mechanism.

Bone conducted stimuli are used to differentiate between conductive and sensori-neural hearing loss. It has been thought that the main route for the transfer of vibratory energy from the point of application of the bone vibrator on the skull to the inner ear is completely osseous. An additional mechanism may play a prominent role. In rats, a bone vibrator was applied to the skull and also directly on the brain, after removing bone (a craniotomy), exposing the brain. Auditory nerve-brainstem evoked response (ABR) could be elicited not only with the vibrator on bone, but also with the vibrator directly on the brain. Similar results were obtained in guinea-pigs and fat sand rats. Noise masked this ABR. Extensive removal of skull bone did not alter the ABR to bone-conducted stimuli delivered to the exposed brain. Experimental elimination of the ossicular chain inertial mechanism and of the occlusion effect did not greatly alter the bone conduction response. A reduction in the fluid volume of the cranial cavity induced threshold elevations of the bone conducted ABR but not of the air conducted ABR. These findings can be interpreted as evidence that the 'classical' bone conduction mechanisms should be modified to include a major pathway for cochlear excitation which is non-osseous: when a bone vibrator is applied to the skull, the bone vibrations may induce audio-frequency sound pressures in the skull contents (brain and cerebro-spinal fluid) which are then communicated by fluid channels to the fluids of the inner ear.

Assessment of vestibular ototoxicity of ear drops by recording of vestibular evoked potentials to acceleration impulses.

INTRODUCTION: The cochlear ototoxicity of several ear drops is well documented in the literature, but very few studies exist on the vestibular ototoxicity of these topical drugs. GOAL OF STUDY: To develop an animal model for the assessment of the vestibular ototoxicity of ear drops. MATERIALS AND METHODS: Two animal groups, consisting of five fat sand rats (FSRs) each, underwent unilateral labyrinthectomy. Normal saline was topically applied into the middle ear cavity of rats in the first group for 7 days (control group). Rats in the second group were treated in the same way by topical gentamicin solution. Cochlear function was assessed by the recording of auditory evoked potential (ABPs) thresholds, and vestibular function was assessed by the recording of vestibular evoked potentials (VsEPs) to angular accelerations. RESULTS: In the control group, except for the amplitude of the first wave, there was no significant difference in the VsEPs recorded before and after topical application. In the gentamicin group, VsEPs could not be recorded after 7 days, and ABPs were recorded in one case only, with a threshold of 100 dB sound pressure level (SPL). CONCLUSION: VsEPs seem to be a reliable measure for evaluating the vestibular ototoxicity of topical ear drops.

Management of congenital laryngeal malformations.

Congenital malformations of the larynx are relatively rare but may be life-threatening. The most common causes include laryngomalacia, vocal cord paralysis, and subglottic stenosis. The last 20 years has seen major advances in the field of surgical correction of such anomalies also serving to reduce the number of tracheotomies in children and the inherent dangers they pose. Success rates for the most popular surgical procedures have been favorable. These include supraglottoplasty for cases of severe laryngomalacia, in which relief of respiratory symptoms has been shown to occur in excess of 80% of cases. Complication rate is low, although postoperative death has been reported. Failure usually occurs in patients with concomitant airway abnormalities including pharyngomalacia. Vocal cord lateralization for vocal cord paralysis with airway compromise is achieved by means of arytenoidopexy or arytenoidectomy, using the lateral approach. Arytenoidectomy also can be performed using laryngofissure or endoscopic laser excision. Subglottic stenosis is the 3rd most common congenital anomaly. Anterior or multiple cricoid splitting with cartilage graft interpositioning is usually performed. The success rates for these procedures has been shown to be approximately 90%.

Surgical anatomy of the ear of the fat sand rat.

OBJECTIVE: This study was conducted to investigate and describe the anatomical details of the ear of the fat sand rat (Psammomys obesus). METHODS: Thirty ears (15 in dry skull and 15 in live animals) were dissected with the aid of an operating microscope and microsurgical techniques. Photographs were taken through an operating microscope. RESULTS: The temporal bone of the fat sand rat consists mainly of an unusually large bulla. Three distinct auditory ossicles were visualized and the manubrium of the malleus is relatively long in relation to the size of the ear. Most parts of the inner ear bulge into the bulla cavity and are easily accessible. The cochlea consists of 3.25 turns. The tympanic membrane, facial nerve, stapedial artery, and eustachian tube are described in detail. The large size of the bulla is probably related to the high sensitivity, particularly at low frequencies of the animals ear. CONCLUSION: The fat sand rat was found to be an excellent experimental animal for the investigation of middle and inner ear physiology.

Computed tomography diagnosis of esophageal bone impaction: a prospective study.

A prospective study was performed on 45 patients for an assessment of the use of computed tomography (CT) in the management of a suspected esophageal fish bone or chicken bone. All patients had negative findings on laryngoscopy; therefore, pharyngeal and hypopharyngeal foreign bodies were excluded from further consideration. The patients underwent radiographic examination with plain films and a cervical CT scan without contrast material. Patients with positive findings were taken to the operating room, where they underwent rigid esophagoscopy under general anesthesia, while those with negative findings remained for observation for 24 hours. Thirty CT scans were positive for an esophageal foreign body, and in all cases but 1, a foreign body was found during the operation. Fourteen of 15 patients with normal CT scan findings managed well with no further intervention. One patient with persistent complaints underwent esophagoscopy, but no foreign body was found. Our conclusion is therefore that CT is a simple and reliable method for diagnosing esophageal bone impaction and may reduce the rate of unnecessary esophagoscopies.

Dermoid cyst of the eustachian tube.

We report a case of dermoid cyst of the Eustachian tube in a 2 1/2 -year-old-girl with CT and MRI imaging. This is the 12th described case of such a pathology. Most of the reviewed previous 11 cases affected females on the left side. The surgical approach and the contribution of CT and MRI are discussed.