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PubMed1998

Perilymphatic pressure dynamics following posture change in patients with Menière's disease and in normal hearing subjects.

The hydrostatic pressure of the inner ear depends on the cerebrospinal fluid pressure through the cochlear aqueduct. The time-course of inner ear pressure change following rapid change in cerebrospinal fluid pressure is related to the aqueduct patency. In this study the patency of the cochlear aqueduct in 27 patients with Menière's disease (28 affected ears, 16 non-affected ears) and in 12 normal hearing subjects (18 control ears) was assessed non-invasively by means of the MMS-10 Tympanic Displacement Analyser. Following a rapid change in body position, changes in intracranial cerebrospinal fluid pressure were found to influence perilymphatic pressure within 1 min. No significant differences were found among affected ears, non-affected ears and control ears.

Adult↗

PubMed2002

The petromastoid canal on computed tomography.

The objective was to assess visibility and anatomy of the petromastoid canal in high-resolution CT. Computed tomography images of 188 patients were reviewed for delineation of the petromastoid canal. This bony canal connects the mastoid antrum with the cranial cavity and houses the subarcuate artery and vein. The diameter, obtained in the middle portion of the canal, was compared with the diameter of the vestibular and cochlear aqueduct in all patients, and absolute values measured in 20 cases. Collimation was 1 mm in 164 and 2 mm in 24 examinations. Additionally, temporal bone of a cadaver was imaged and microdissected. The petromastoid canal was identified bilaterally in all 164 scans that were obtained with a slice thickness of 1 mm. In 5 of the 24 patients imaged with a collimation of 2 mm, the canal was not visible, most probably due to partial-volume effects. The petromastoid canal had the same diameter as the cochlear aqueduct in 42/44 (right/left), exceeded it in 66/61 and was smaller in 75/78 cases. In comparison to the vestibular aqueduct it had an equal diameter in 38/41 (right/left), exceeded it in 63/61, and was rated as smaller in 82/81 temporal bones. Diameters for the canals were: petromastoid canal 0.51+/-0.04 mm; cochlear aqueduct 0.57+/-0.03; and vestibular aqueduct 0.63+/-0.06 mm. Microdissection of the specimen revealed the entire course of the canal and demonstrated a similar appearance of the structure as in the images. The petromastoid canal can easily be identified on high-resolution, thin-slice CT images. Knowledge of the anatomy of this bony canal prevents misinterpretation as pathological structure, such as fracture line, which might occur if this structure is not known.

Adult↗

PubMed1991

Hearing loss and pneumococcal meningitis: an animal model.

Clinical studies of predisposing factors in the development of hearing loss secondary to bacterial meningitis have produced conflicting results. An animal model of meningogenic labyrinthitis was developed for more precise study of these parameters. Rabbits were inoculated intrathecally with 10(5) pneumococci to induce meningitis. Hearing thresholds were measured using auditory-evoked responses to 1 kHz, 10 kHz, and click stimuli before infection and every 12 hours thereafter. Profound deafness occurred in all subjects at an average of 48 hours following infection. The incidence and severity of hearing loss was strongly correlated with the duration of meningitis. Temporal bone histology revealed acute inflammation of all perilymphatic spaces including the cochlear aqueduct. This model demonstrated that the risk and severity of hearing loss increase with the duration of meningitis and suggested that the cochlear aqueduct is an anatomic pathway for the extension of infection from the cerebrospinal fluid to the cochlea. The implications for therapy in humans is discussed.

Acoustic Stimulation↗

PubMed1997

Preoperative temporal bone computed tomography scan and its use in evaluating the pediatric cochlear implant candidate.

Preoperative computed tomography (CT) scan evaluation of the temporal bones in cochlear implant candidates plays a crucial role in determining candidacy and the side of implantation. The CT scans allow the surgeon to carefully review the anatomy of the inner ear and mastoid cavity in order to predict any potential difficulties or complications that may be encountered during the implant insertion. We retrospectively reviewed 50 preoperative CT scans of the temporal bone in children who have been successfully implanted. In these scans, we assessed the degree of mastoid pneumatization, cochlear anatomy and patency, size of the vestibular aqueduct, cochlear aqueduct, and internal auditory canal. We analyzed our findings and measurements and compared our results with the degree of difficulty noted in the insertion of the implant, the number of electrodes inserted in each case, and the overall complication rate. From this radiographic review, we have created a checklist for cochlear implant surgeons in order to highlight key features that need to be recognized in the temporal bone scan in preoperative evaluation of cochlear implant candidates.

Adolescent↗

PubMedDate not supplied

Transmission of square wave pressure pulses through the perilymphatic fluid in cats.

The inner ear hydrodynamics have been studied in a series of experiments on cats. A detailed analysis has been made of the perilymphatic pressure response to square wave pressure pulses applied to the ear canal and middle ear. It was found that the initial pressure response was followed by a rebound pressure response of the opposite phase. It was also found that in most cases each phase of the pressure response could be expressed in terms of two time constants. When the cochlear aqueduct was patent, the perilymphatic pressure response showed almost equal positive and negative pressure changes. However, when the cochlear aqueduct was surgically blocked, the perilymphatic pressure response consisted almost exclusively of the first phase of the response, while the rebound phase disappeared almost completely. The possibility of influencing the inner ear fluid balance in Meniere's disease by external pressure changes is discussed in the light of the present experimental results.

Animals↗

PubMed1997

Pressure gradients affecting the labyrinth during hypobaric pressure. Experimental study.

Hypobaric effects on the perilymph pressure were investigated in 18 cats. The perilymph, tympanic cavity, cerebrospinal fluid, and systemic and ambient pressure changes were continuously recorded relative to the atmospheric pressure. The pressure equilibration of the eustachian tube and the cochlear aqueduct was studied, as well as the effects of blocking these channels. During ascent, the physiologic opening of the eustachian tube reduced the pressure gradients across the tympanic membrane. The patent cochlear aqueduct equilibrated perilymph pressure to cerebrospinal fluid compartment levels with a considerable pressure gradient across the oval and round windows. With the aqueduct blocked, the pressure decrease within the labyrinth and tympanic cavities was limited, resulting in large pressure gradients toward the chamber and the cerebrospinal fluid compartments, respectively. We conclude that closed cavities with limited pressure release capacities are the cause of the pressure gradients. The strain exerted by these pressure gradients is potentially harmful to the ear.

Animals↗

PubMed1998

[An experimental study of tumor cell infiltration into temporal bones--route into the inner ear from the arachnoid space].

In humans, metastatic tumors which invaded the temporal bones have been studied in regard to the relationship between histopathologic findings and clinical symptoms. On the other hand, there is no experimental study using an animal model for tumor infiltration into the temporal bone. This study was designed to establish such an animal model and examine the temporal bones histopathologically. Rat thymic lymphoma cell (FTL-A2) were inoculated into the cisterna magna of Wistar rats. The animals were decapitated under deep anesthesia with pentobarbital sodium from the 1st to 8th day after inoculation. Their heads were fixed with Heiden-hain SuSa solution, decalcified, dehydrated, embedded in celloidin, and sectioned horizontally at a thickness of 25 microns. These were stained with hematoxylin and eosin, and histologically examined by light microscopy. Inoculated tumor cells showed active viability in the arachnoid space at a rate of 98%. Two major routes of tumor cell infiltration into the inner ear were found: the cochlear aqueduct and the internal auditory canal. At the early stage after the inoculation, tumor cells infiltrated the scala tympani through the cochlear aqueduct. Invading the fiber of the cochlear nerve, tumor cells infiltrated Rosenthal's canal via the tractus spiralis foraminosus, and passed through Rosenthal's canal and the osseous spiral lamina into the scala tymani. However, tumor cells did not infiltrate the organ of Corti through the habenula perporata. Tractus spiralis foraminosus and habenula perforata functioned as a barrier against tumor infiltration. In a few cases, tumor cells infiltrated over the macula cribrosa into the subepithelial space of the utricule and saccule. The macula cribrosa functioned as a barrier.

Acoustic Maculae↗

PubMed1989

[Congenital perilymphatic fistula in children].

We report twenty case of perilymphatic fistulae in children. A fistula was discovered in every case where the cochlear aqueduct is larger than normal on high resolution CT scan of the temporal bone. The surgical treatment of these fistulae allowed only a significant improvement of hearing in the cases were an asymmetry or a dilatation of the cochlear aqueducts and a fluctuating deafness coexisted. Unfortunately these improvements do not look permanent.

Adolescent↗

PubMedDate not supplied

Lymphocytic streaming as an indicator of inner ear compartmentalization.

Despite a great deal of anatomic and physiologic data in animals, controversy still exists over whether or not the perilymphatic space in man is directly connected to the intracranial space via a patent cochlear aqueduct or other fluid channel. Human physiologic data are limited, indirect, and conflicting. Anatomic and pathologic data have heretofore been inadequate for answering the question convincingly. The temporal bones of a 19-year-old woman with central nervous system lymphoblastic leukemia are discussed. The passive-appearing movement of lymphoblasts between cerebrospinal fluid and perilymphatic spaces suggests both a functionally patent cochlear aqueduct and alternate pathways.

Adult↗

PubMed1992

Three-dimensional computer-aided reconstruction and measurement of the temporal bone for singular neurectomy.

A computer reconstruction method was used to study five normal temporal bones for the three-dimensional anatomy necessary for singular neurectomy. The length of the singular canal was 4.9 +/- 0.6 mm. The distal portion of the singular canal courses at a sharp angle (48.2 degrees) to the direction of the transmeatal surgical approach for this operation. The reconstructions indicated that the singular canal can be exposed by introducing a drill through the external auditory meatus at a point 0.71 mm posteroinferior to the posteromedial margin of the round window on the saucerized medial wall of the round window niche. The distance from this site to the distal end-portion of the singular canal averaged 1.47 mm. The point on the drilling course (from the drilling site to the singular canal) closest to the vestibular end of the hook portion of the cochlea was 0.48-1.00 mm from the drilling site. The reconstructions also indicated that the dissection should proceed superomedially, if necessary, after a 1-mm-deep straight dissection along the transmeatal approach. The ampulla of the posterior semicircular canal, cochlear aqueduct and inferior cochlear vein were all found to lie within 2 mm of the drilling point.

Adolescent↗

PubMed1991

The site of the lesion causing hearing loss in bacterial meningitis: a study of experimental streptococcal meningitis in guinea-pigs.

The pathological basis of hearing loss in bacterial meningitis was investigated using an animal model of Streptococcus suis meningitis. Forty guinea-pigs were infected after their hearing had been assessed by brain stem auditory evoked potentials. In 17 animals, it was possible to repeat the procedure at the onset of meningitis; this included one animal with subclinical disease. Fifteen animals showed evidence of hearing loss, which on subsequent histological examination was found to be associated invariably with suppurative labyrinthitis. The remaining two animals without hearing loss had normal cochleas. It is suggested that cochlear sepsis rather than eighth cranial nerve involvement by meningeal sepsis is primarily responsible for hearing loss in bacterial meningitis, and that bacteria enter the cochlea via the cochlear aqueduct and not the internal auditory canal. The tissue within the lumen of the cochlear aqueduct may act as a barrier against invasion by micro-organisms, and haemolytic streptococci could cause lysis of this barrier by the exotoxins they produce.

Animals↗

PubMed2003

Anatomic landmarks of the glossopharyngeal nerve: a microsurgical anatomic study.

OBJECTIVE: Compared with other lower cranial nerves, the glossopharyngeal nerve (GPhN) is well hidden within the jugular foramen, at the infratemporal fossa, and in the deep layers of the neck. This study aims to disclose the course of the GPhN and point out landmarks to aid in its exposure. METHODS: The GPhN was studied in 10 cadaveric heads (20 sides) injected with colored latex for microsurgical dissection. The specimens were dissected under the surgical microscope. RESULTS: The GPhN can be divided into three portions: cisternal, jugular foramen, and extracranial. The rootlets of the GPhN emerge from the postolivary sulcus and course ventral to the flocculus and choroid plexus of the lateral recess of the fourth ventricle. The nerve then enters the jugular foramen through the uppermost porus (pars nervosa) and is separated from the vagus and accessory nerves by a fibrous crest. The cochlear aqueduct opens to the roof of this porus. On four sides in the cadaver specimens (20%), the GPhN traversed a separate bony canal within the jugular foramen; no separate canal was found in the other cadavers. In all specimens, the Jacobson's (tympanic) nerve emerged from the inferior ganglion of the GPhN, and the Arnold's (auricular branch of the vagus) nerve also consisted of branches from the GPhN. The GPhN exits from the jugular foramen posteromedial to the styloid process and the styloid muscles. The last four cranial nerves and the internal jugular vein pass through a narrow space between the transverse process of the atlas (C1) and the styloid process. The styloid muscles are a pyramid shape, the tip of which is formed by the attachment of the styloid muscles to the styloid process. The GPhN crosses to the anterior side of the stylopharyngeus muscle at the junction of the stylopharyngeus, middle constrictor, and hyoglossal muscles, which are at the base of the pyramid. The middle constrictor muscle forms a wall between the GPhN and the hypoglossal nerve in this region. Then, the GPhN gives off a lingual branch and deepens to innervate the pharyngeal mucosa. CONCLUSION: Two landmarks help to identify the GPhN in the subarachnoid space: the choroid plexus of the lateral recess of the fourth ventricle and the dural entrance porus of the jugular foramen. The opening of the cochlear aqueduct, the mastoid canaliculus, and the inferior tympanic canaliculus are three landmarks of the GPhN within the jugular foramen. Finally, the base of the styloid process, the base of the styloid pyramid, and the transverse process of the atlas serve as three landmarks of the GPhN at the extracranial region in the infratemporal fossa.

Brain Diseases↗

PubMed2002

Temporal bone histopathology related to cochlear implantation in congenital malformation of the bony cochlea.

HYPOTHESIS: Histopathologic findings in temporal bones with congenital malformations of the bony cochlea may provide insight into cochlear implantation planning, surgical approach, and complications. BACKGROUND: Patients with congenitally malformed cochleae account for an increasing percentage of candidates for cochlear implantation. Few studies on the relationship between histopathologic findings of temporal bones with malformation of the bony cochlea and cochlear implantation have been reported. METHODS: We studied 21 temporal bones from 12 cases with congenital malformations of the bony cochlea. Ages ranged from stillborn to 50 years. Length of the cochleae and dimensions of facial recesses were measured with light microscopy. Other malformations associated with a shortened cochlea were determined, emphasizing how they affect cochlear implantation. RESULTS: The average length of the malformed cochlear duct was 22.84 +/- 0.69 mm. Average dimensions of facial recesses were not significantly different between malformed cochleae and the controls. Other malformations included enlarged cochlear aqueduct (43%), abnormal facial nerve course (57%), enlarged vestibular aqueduct (52%), aplasia of the middle ear (19%), malformed ossicles (67%), abnormal oval window (57%), and abnormal round window (29%). CONCLUSION: A shortened cochlear duct may cause an incomplete insertion of the implant electrode. Because dimensions of the facial recesses are similar to normal cases, a facial recess surgical approach is recommended. An enlarged cochlear aqueduct may cause perilymphatic oozing or gushing on fenestration of the cochlea. An anomalous course of the facial nerve is a common finding. Tympanic malformations such as round and oval window deformities and small middle ear cleft should be noted preoperatively to better guide surgery.

Adolescent↗

PubMed1990

Cochlear and cerebrospinal fluid pressure: their inter-relationship and control mechanisms.

The patency of the cochlear aqueduct is a key factor in intra-cochlear hydromechanics. If patent, the cerebrospinal fluid (CSF) provides the reference pressure for the perilymph and also to a large extent the endolymph, since Reissner's membrane can only withstand a relatively small pressure differential. The aqueduct often becomes sealed as a natural process of ageing. In this instance the reference pressure is from a source, its position unknown, within the boundaries of the cochlea itself. Relatively large and rapid changes in the cerebrospinal fluid pressure may result from everyday events such as coughing (ca. 175 mm saline) and sneezing (ca. 250 mm saline). The resistive nature of the cochlear aqueduct and the mechanical compliance of the cochlear windows are probably important factors in limiting the amount of stress, and therefore possible damage, which may occur to the cochlea and cochlear windows for a given pressure change within the CSF system. A narrow aqueduct and compliant cochlear windows reduce the risk of structural damage. In practice, this should mean that the risk of structural damage will be increased by any process which reduces the compliance of one or both of the cochlear windows, for example, extremes of middle ear pressure perhaps brought about by Eustachian tube dysfunction or rapid barometric pressure changes. Techniques are now available which provide non-invasive indirect measures of perilymphatic pressure and CSF-perilymphatic pressure transfer. The tympanic membrane displacement measurement technique has been used to provide reliable measures of perilymphatic pressure and CSF-perilymphatic pressure transfer on an individual subject basis.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1989

Perilymph composition in scala tympani of the cochlea: influence of cerebrospinal fluid.

A commonly used technique to obtain cochlear perilymph for analysis has been the aspiration of samples through the round window membrane. The present study has investigated the influence of the volume withdrawn on sample composition in the guinea pig. Samples of less than 200 nl in volume taken through the round window showed relatively high glycine content, comparable to the level found in samples taken from scala vestibuli. If larger volumes are withdrawn, lower glycine levels are observed. This is consistent with cerebrospinal fluid (having a low glycine content) being drawn into scala tympani through the cochlear aqueduct and contaminating the sample. The existence of a concentration difference for glycine between scala tympani perilymph and cerebrospinal fluid suggests the physiologic communication across the cochlear aqueduct is relatively small in this species. The observation of considerable exchange between cerebrospinal fluid and perilymph, as reported in some studies, is more likely to be an artifact of the experimental procedures, rather than of physiologic significance. Alternative sampling procedures have been evaluated which allow larger volumes of uncontaminated scala tympani perilymph to be collected.

Animals↗

PubMed1998

Longitudinal endolymph movements induced by perilymphatic injections.

Endolymph movements and endocochlear potential (EP) changes were measured during disturbances of perilymphatic pressure. induced by injecting artificial perilymph into scala tympani (ST) or scala vestibuli (SV) of the guinea pig cochlea. Injections were performed either with or without an outlet made in the opposite perilymphatic scala. Injections into ST without an outlet induced large pressure changes but virtually no endolymph movement or EP change. Injection at the same rate into ST with an outlet in SV produced smaller pressure changes which were accompanied by a basally-directed displacement of endolymph and significant EP changes. The magnitude of endolymph displacements and EP changes varied as a function of injection rate. Injections into SV, either with or without an outlet in ST, produced apically-directed endolymph displacement and EP changes. For the SV injections without an outlet, the cochlear aqueduct and round window are likely to provide an outlet and compliance, permitting flow along the perilymphatic scalae to occur even when no ST outlet was provided. We conclude that endolymph movements are not dependent on the absolute pressure of the perilymph, but instead occur when small, sustained pressure gradients are present across the cochlear partition, corresponding to times when perilymph flow is induced. This study demonstrates that in the normal. sealed cochlea, endolymph and EP are insensitive to fluid injections into ST, but are sensitive to fluid injections into SV. Endolymph movements are therefore unlikely to be generated by cerebrospinal fluid pressure fluctuations (such as those produced by respiration, posture changes, coughing, sneezing, etc) which are transmitted to ST by the cochlear aqueduct.

Animals↗

PubMed2003

In vivo observation of dynamic perilymph formation using 4.7 T MRI with gadolinium as a tracer.

OBJECTIVE: To investigate the pharmacokinetics of gadolinium in the perilymphatic fluid spaces of the cochlea in vivo using high-resolution MRI to obtain information concerning perilymph formation. MATERIAL AND METHODS: A Bruker Biospec Avance 47/40 experimental MRI system with a magnetic field strength of 4.7 T was used. Anesthetized pigmented guinea pigs were injected with the contrast agent Gd-diethylenetriaminepentaacetic acid-bismethylamide and placed in the magnet. The signal intensity of Gd in the tissues was used as a biomarker for dynamic changes in the perilymphatic fluid. RESULTS: The most rapid uptake of Gd in the perilymphatic fluid spaces occurred in the lower part of the modiolus, followed by the second turn of the scala tympani. Within the scala tympani, the distribution of Gd in the basal turn was significantly lower than that in the other turns. Destruction of the cochlear aqueduct was followed by an increase in Gd uptake in the perilymph instead of a reduction. CONCLUSIONS: These findings offer further evidence that the pervasive perilymphatic fluid derives from the cochlear blood supply via the cochlear glomeruli, which are in close proximity to the scala tympani within the modiolus, and the capillary in the spiral ligament. Cerebrospinal fluid communicates with perilymph via the cochlear aqueduct but is not the main source of perilymph. These findings are of relevance to the treatment of inner ear diseases, as well as to our understanding of the flow and source of perilymphatic fluid.

Animals↗

PubMedDate not supplied

[Congenital malformation of the inner ear and repeated meningitis. Anatomo-clinical considerations illustrated by a case].

The atuhors analyze the case of a three-year-old child suffering from an abnormal condition of the left internal ear, revealed by copious discharge of cerebro-spinal fluid at the onset of 5 attacks of meningitis. A direct approach to the plate and the bony and aponeurotic contents of the oval fossa made it possible to seal this off and this was checked surgically eighteen months later. On this occasion a general survey was carried out into the usual circumstances in which such a discovery is made, pathological concepts and treatment for these accidents. It would appear that unusual permeability may be found either in the internal auditory meatus or in the cochlear aqueduct. Therapeutic procedure depends on circumstances. Blocking the oval fossa is not always effective and should be reserved for cases in which abnormalities impair function. Choice between blocking the internal auditory meatus and eradication of the cochlear aqueduct depends to some extent on the information supplied by tomography, but more on the pathogenetic conclusions reached.

Cerebrospinal Fluid Otorrhea↗