Validation of the radiological detection of the chorda-facial angle: impact on the round window accessibility during pediatric cochlear implantation.

OBJECTIVES: The facial recess, an essential landmark for the posterior tympanotomy approach, is limited by the facial nerve and the chorda tympani, with a complicated relationship. This study tried to find the most appropriate radiological method to evaluate the chorda-facial angle (CFA). We also checked the effect of this angle on the round window accessibility during cochlear implantation. METHODS: It was a retrospective study that included cochlear implant surgeries of 237 pediatric patients, from September 2016 to April 2021. Two physicians evaluated the CFA in the para-sagittal cut of the preoperative HRCT. The round window accessibility was assessed in the unedited surgery videos. RESULTS: The CFA ranged from 21° to 35° with a mean of 27.14 ± 3.5°. It was detected in all cases with a high agreement between the two CT reviewers' measurements. The CFA differed significantly between the accessible group and the group with difficult accessibility (p value < 0.001). Spearman's correlation coefficient revealed a strong correlation between the CFA and the intraoperative round accessibility. 25.5° was the best cutoff point; below this angle, difficult accessibility into the RW was expected, with high sensitivity, specificity, and accuracy CONCLUSIONS: Our study on a relatively large number of cases provided a precise, valid, reliable, and applicable method to evaluate the CFA in the HRCT scan. We found a significant-close relation between the CFA and the round window accessibility; the difficulty increased with a need for posterior tympanotomy modification when the angle decreased. KEY POINTS: • Radiological detection of the chorda-facial angle was always problematic, without a previous straightforward method in the literature. • We used the para-sagittal cut of the high-resolution CT scans to evaluate the CFA. This cut was beneficial to seeing the chorda tympani nerve in every examined case. There was a high agreement between the two CT reviewers' measurements. • Preoperative evaluation of the CFA in the HRCT accurately predicted the round window accessibility. Patients with CFA less than 25.5° were expected to have difficult accessibility into the round window during cochlear implantation.

Assessment of jugular bulb variability based on 3D surface models: quantitative measurements and surgical implications.

PURPOSE: High-riding jugular bulbs (JBs) among other anatomical variations can limit surgical access during lateral skull base surgery or middle ear surgery and must be carefully assessed preoperatively. We reconstruct 3D surface models to evaluate recent JB classification systems and assess the variability in the JB and surrounding structures. METHODS: 3D surface models were reconstructed from 46 temporal bones from computed tomography scans. Two independent raters visually assessed the height of the JB in the 3D models. Distances between the round window and the JB dome were measured to evaluate the spacing of this area. Additional distances between landmarks on surrounding structures were measured and statistically analyzed to describe the anatomical variability between and within subjects. RESULTS: The visual classification revealed that 30% of the specimens had no JB, 63% a low JB, and 7% a high-riding JB. The measured mean distance from the round window to the jugular bulb ranges between 3.22 ± 0.97 mm and 10.34 ± 1.41 mm. The distance measurement (error rate 5%) was more accurate than the visual classification (error rate 15%). The variability of the JB was higher than for the surrounding structures. No systematic laterality was found for any structure. CONCLUSION: Qualitative analysis in 3D models can contribute to a better spatial orientation in the lateral skull base and, thereby, have important implications during planning of middle ear and lateral skull base surgery.

Radiological and surgical aspects of round window visibility during cochlear implantation: a retrospective analysis.

PURPOSE: The round window approach has become the most preferred option for cochlear implant (CI) insertion, however, sometimes it may not be possible due to the (in)visibility of the round window membrane (RWM). We addressed the prevalence, consequences and indicators of difficult detection of the RWM in cochlear implant surgery. METHODS: This study retrospectively analysed the operative reports and preoperative high resolution axial-computed tomography (CT) scans of a consecutive cohort of patients who underwent a CI insertion. The main outcomes were surgical outcomes of the RW approach, and assessment of radiological markers. RESULTS: The operative reports showed that RWM insertion was feasible in 151 out of 153 patients. In 18% of the patients the RWM was difficult to visualize. All these patients had at least one intraoperative event. The chorda tympani nerve (CTN) or posterior canal wall was affected in 8% of the 153 patients and the fallopian canal in 6%. These patients had a facial-chorda tympani nerve distance on the CT scan that was considerably smaller than normal patients (1.5 mm vs 2.3 mm). In addition, a prediction line towards the anterolateral side of the RWM was found to be more prevalent in these patients' CT scans (sensitivity 81%, specificity 63%). CONCLUSION: The RW approach is feasible in almost all patients undergoing CI surgery. Difficult visualisation of the RWM seems to lead to at least one intraoperative event. Radiological measures showed that these patients had a smaller facial recess and a more anteriorly placed facial nerve, which can be used to better plan a safe insertion approach.

The role of high-resolution Computer Tomography in prediction of the round window membrane visibility and the feasibility of the round window electrode insertion.

OBJECTIVE: The aim of this work is to assess the role of pre-operative high-resolution computerized tomography (HRCT) in prediction of the round window membrane (RWM) visibility and the feasibility of round window electrode insertion. MATERIALS AND METHODS: Retrospective study on a series of 97 cases of cochlear implant (CI) who were implanted in tertiary referral centers. We reviewed HRCT of all cases, and we implicated two radiological measurements on HRCT which are membrano-facial angle (MFA) and length of the bony overhang of the round window niche (RWN). We reviewed the intra-operative surgical video recordings of all cases for detection of the type of RWM visibility, according to The St Thomas' Hospital classification. RESULTS: The MFA was 21.9 ± 14.5. The length of the bony overhang of the RWN was 2.4 ± 0.33 mm. About 37% of the studied patients needed cochleostomy. The best cut-off of MFA in the prediction of the RW (type 2B and 3) was ≥ 15.1o with sensitivity 100%, and specificity 82%. CONCLUSION: HRCT offers highly reliable and reproducible measurements for the prediction of RWM visibility and, therefore, prediction of the utility of the RW approach for electrode insertion. Membrano-facial angle (MFA) is a new measurement that can be used for this purpose.

Subcochlear canaliculus patterns in the pediatric and adult population: radiological findings and surgical implications.

INTRODUCTION: The pneumatization of the different regions of the temporal bone is strictly related to the age and the degree of development of the mastoid and the middle ear. Petrous apex pneumatization is the last step of the development of the petrous bone system. The subcochlear canaliculus is an anatomical cavity, originating in the space between the fustis and the finiculus, and connecting the round window area to the petrous apex. The aim of the present article is analyzing the trend of development of the subcochlear canaliculus pneumatization, classified through CT scan examination, in different age subgroups. MATERIALS AND METHODS: We conducted a retrospective review of patients who underwent temporal bone CT scans between 2014 and 2019. Pediatric and adult patients were included and divided into different age subgroups. The subcochlear canaliculus was examined through coronal view scans at the level of the round window niche and classified into 3 different groups (A, B and C) according to the degree of pneumatization. RESULTS: A total of 270 Petrous bone CT scans was analyzed. The percentage of type A subcochlear canaliculus was significantly higher in the pediatric population if compared to the adult population (p = 0.001326). As far as type B subcochlear canaliculus is concerned, the difference between children and adults was not statistically significant (p = 0.2378). On the other hand, type C subcochlear canaliculus was predominant in the adult population (p = 0.000256). CONCLUSIONS: There is a constant increase in pneumatization of the subcochlear canaliculus from 0 to 19 years and then a progressive decrease. This discovery has relevant surgical implications and has to be borne in mind in particular for cholesteatoma surgery and cochlear implantation surgery in the age groups in which the subcochlear canaliculus is highly pneumatized.

[Laser Doppler vibrometric measurements on human temporal bones]. / Laser-Doppler-vibrometrische Messungen an humanen Felsenbeinen.

Laser Doppler vibrometric (LDV) measurements on human temporal bones represent the standard method for predicting the performance of active middle ear implants (AMEI) and are used as preclinical tests in the development, approval process, and indication expansion of AMEI. The quality of the coupling of the floating mass transducer to the mobile structures of the middle ear is decisive for the performance of the implant and patients' hearing perception. The cochlea can be stimulated via the oval window (forward stimulation) or the round window (reverse stimulation). For forward stimulation, the ASTM standard F2504-05 defines a method to ensure physiologically normal properties of the temporal bones used in the experiments. For reverse stimulation, which depends even more critically on the quality of the temporal bone, a comparable standard method is lacking. Appropriate preparation and storage of the human petrous bone as well as suitable LDV test setups with respect to calibration and reproducibility of measuring positions and angles provide results that allow a comparison of different types of coupling and also correlate well with clinical data.

[A case of obliteration of a round window in otosclerosis]. / Sluchai obliteratsii kruglogo okna pri otoskleroze.

The article presents a brief review of the literature on the anatomy and physiology of the round window (RW) niche, the causes of occlusion, the diagnosis of this pathology, the features of auditory disorders and tactics when it is detected in patients with otosclerosis (OS). A clinical case of diagnosis and effective surgical treatment for obliteration of RW in a patient with advanced OS, which occurred in 2019 in 0.7% of cases, is described. Removal of RW niche obliteration was carried out with a curette and microcresis by smoothing the canopy over RW until partial visualization of the secondary membrane. It was this stage of the operation that made it possible to restore the normal hydrodynamics of the inner ear fluids and contributed to a functional result. Thus, the diagnosis of RW obliteration in patients with OS is difficult, but possible when using computed tomography of the temporal bones and assessing the mobility of the RW membrane or analyzing changes in hearing at the end of the operation, if it is performed under local anesthesia. The simultaneous performance of stapedoplasty and the removal of bone obliteration of RW makes it possible to safely achieve functional rehabilitation in patients with OS.

Anatomical landmarks for cochlear implantation in ossified cochleas.

PURPOSE: In this study, we aimed to introduce the facial nerve as a new anatomical landmark which can be used in ossified cochleas during cochlear implantation. We also set out to define a safe line to preserve the internal auditory canal (IAC) while drilling the basal turn of the cochlea. METHODS: Thirty patients who had temporal computed tomography (CT) were studied. The distances from the facial nerve and the round window to the IAC, carotid artery, and jugular bulb were measured in the reformatted CT images. We have created a line in the direction of the stapedial tendon from the round window to the IAC and called it ROWIAC (Round window-IAC) line. We have investigated whether this line intersects the IAC and measured the distances from this line to the IAC. RESULTS: Fifty-four temporal CT scans were included to the study. The mean distances from the facial nerve to the IAC, carotid artery, and jugular bulb were 8.8 ± 0.9, 15.0 ± 2.0, and 12.2 ± 2.9 mm, respectively. The mean distances from the round window to these structures were 3.8 ± 0.7, 9.4 ± 2.2, and 8.3 ± 2.9 mm, respectively. ROWIAC line did not intersect the IAC in any of the patients. The mean distance between this line and the IAC was 0.8 ± 0.4 mm. CONCLUSION: We propose that facial nerve and ROWIAC line can be used as potential landmarks during cochlear implantation in ossified cochleas to protect the adjacent neurovascular structures.

CT and MRI for the diagnosis of perilymphatic fistula: a study of 17 surgically confirmed patients.

BACKGROUND: We evaluated the usefulness of CT and MRI for the diagnosis of perilymphatic fistula (PLF) of the round (RW) and/or oval (OW) windows, with surgery as gold standard. METHODS: We retrospectively enrolled 17 patients who presented a surgically confirmed PLF of the round (RW) or oval (OW) windows. All patients were imaged by CT + MRI (T2W SSFP without contrast) prior to surgery (= gold standard). Two radiologists, analyzed the RW and OW on the side of the clinical symptoms and sensitivity (Se) + Specificity (Sp) were calculated. RESULTS: Round window fistula was the most frequent (71%). The best sign of PLF on imaging was a fluid filling of the window niches, which had good Se (83-100% for RW, 66-83% for OW) and Sp (60% for RW, 91-100% for OW). Disorientation of the footplate and pneumolabyrinth were also only observed in 50% of OW PLF. CONCLUSION: The combination of CT and MRI is a reliable tool for a fast and accurate diagnosis of round and oval window perilymphatic fistula, with good sensitivity (> 80%). The most common sign of PLF on imaging is the presence of a fluid-filling in the RW (especially if > 2/3 of the RW niche) or in the OW niches on both CT and MRI. A disorientation of the footplate or the presence of a pneumolabyrinth are clearly in favor of an oval window perilymphatic fistula.

Effects of Various Trajectories on Tissue Preservation in Cochlear Implant Surgery: A Micro-Computed Tomography and Synchrotron Radiation Phase-Contrast Imaging Study.

OBJECTIVES: The purpose of this study was to evaluate the three-dimensional (3D) anatomy and potential damage to the hook region of the human cochlea following various trajectories at cochlear implantation (CI). The goal was to determine which of the approaches can avoid lesions to the soft tissues, including the basilar membrane and its suspension to the lateral wall. Currently, there is increased emphasis on conservation of inner ear structures, even in nonhearing preservation CI surgery. DESIGN: Micro-computed tomography and various CI approaches were made in an archival collection of macerated and freshly fixed human temporal bones. Furthermore, synchrotron radiation phase-contrast imaging was used to reproduce the soft tissues. The 3D anatomy was investigated using bony and soft tissue algorithms, and influences on inner ear structures were examined. RESULTS: Micro-computed tomography with 3D rendering demonstrated the topography of the round window (RW) and osseous spiral laminae, while synchrotron imaging allowed reproduction of soft tissues such as the basilar membrane and its suspension around the RW membrane. Anterior cochleostomies and anteroinferior cochleostomies invariably damaged the intracochlear soft tissues while inferior cochleostomies sporadically left inner ear structures unaffected. CONCLUSIONS: Results suggest that cochleostomy approaches often traumatize the soft tissues at the hook region at CI surgery. For optimal structural preservation, the RW approach is, therefore, recommended.

Extension patterns of vestibular schwannomas towards the middle ear: three new cases and review of the literature.

OBJECTIVE: Middle ear extension of vestibular schwannomas is not a common occurrence, and only a few cases have been described so far in past publications. We report three new cases of vestibular schwannomas extending to the middle ear and reviewed the literature to specify the patterns of such an extension. MATERIALS AND METHODS: We analysed databases of previously published articles to search for additional cases of middle ear extension of vestibular schwannomas and compared them to the cases we have documented. Extension patterns of the tumours were analysed, especially focusing on the extension through the round and oval windows. RESULTS AND CONCLUSION: Middle ear vestibular schwannomas are uncommon tumours and only 13 cases have been published so far. The vestibular schwannoma (internal auditory canal or intralabyrinthine) has to invade the labyrinth first (complete invasion in 88% of the cases, n = 14), before reaching the middle ear. In the majority of cases (69%, n = 11/16), internal auditory canal vestibular schwannomas or intralabyrinthine schwannomas extended in the middle ear though the round window.

Anatomic variations of the round window niche: radiological study and related endoscopic anatomy.

PURPOSE: In the last decades, literature has shown an increasing interest in round windows (RW) anatomy due to its pivotal role in deafness surgery. The high variability of this anatomical region, with particular regard to the round windows niche (RWN), has been studied by several authors through different methods of investigation. The aim of the present research was to radiologically examine the morphological variability of the RWN and to link the imaging findings to the endoscopic view. METHODS: High-resolution CT scans of 300 temporal bones without neuro-otological pathologies were retrospectively reviewed by 2 neuroradiologist and 1 ENT surgeon who independently evaluated the RWN morphological variations. To link the radiological to the endoscopic data, 45 cadaveric human temporal bones were submitted to a radiological evaluation and to an otoendoscopy conducted through a posterior tympanotomy approach. RESULTS: Three variants of the RWN were detected on coronal CT scan reconstructions: 155 "cylindrical-type", 97 "j-type" and 48 "truncated cone-type". For each radiological type the endoscopic findings showed a specific endoscopic position of the RW chamber, which results in different degrees of RW membrane visibility when analysed through a posterior tympanotomy approach. CONCLUSIONS: To the best of our knowledge, this is the first description of the above-mentioned RWN radiological variations supported by endoscopic data. This study suggests an additional anatomical evaluation that could be useful to predict the RW membrane visibility through a posterior tympanotomy approach. Further studies are required to support the clinical implications of our observations.

Endoscopic optical coherence tomography enables morphological and subnanometer vibratory imaging of the porcine cochlea through the round window.

A highly phase stable hand-held (HH) endoscopic system has been developed for optical coherence tomography and vibrometry. Designed to transit the ear canal to the middle ear space and peer through the round window (RW), it is capable of imaging the vibratory function of the cochlear soft tissues with subnanometer scale sensitivity. A side-looking, 9 cm long rigid endoscope with a distal diameter of 1.2 mm, was able to fit within the RW niche and provide imaging access. The phase stability was achieved in part by fully integrating a Michelson interferometer into the HH device. Ex vivo imaging of a domestic pig demonstrated the system's ability for functional vibratory imaging of the cochlea via the RW.

Measuring cochlear duct length in Asian population: worth giving a thought!

INTRODUCTION: The anatomy of the cochlea forms the basis for a successful cochlear implantation. Cochlear duct length (CDL) is defined as the length of the scala media as measured from the middle of the round window to helicotrema. Preoperative measurement of CDL is particularly important when precise intracochlear electrode array placement is desired. It can be done both histologically and radiologically. Preoperative high-resolution computed tomography (HRCT) scan which forms an integral part of cochlear implant workup is a useful tool to calculate CDL using 3D reconstructions. METHOD: This study was done in SMS Medical College and Hospital, Jaipur, India, which is a tertiary care hospital and referral centre for cochlear implants. HRCT temporal bones of all children less than 6 years of age, with congenital bilateral severe-to-profound SNHL who were being worked up for cochlear implant were studied and analysed. 124 patients (56 females and 68 males) with hearing loss were evaluated for cochlear implantation. HRCT temporal bone of these patients was analysed and a variable A was measured which is defined as the linear measurement from the round window to the farthest point on the opposite wall of the cochlea on a reformatted CT scan slice. RESULTS: Mean of distance A for right ear of these patients was 8.10 mm (range 7.7-9.2 mm). Mean for the same in left ear of these patients was 8.14 mm (range 7.7-9.0 mm), giving an overall average of 8.12 mm. Using the formula, CDL = 4.16A-3.98, we calculated the length of cochlear duct. Mean cochlear duct length was 29.8 mm with a range from 28 to 34.3 mm. CONCLUSION: To the best of our knowledge, this is the first large sample study of cochlear length in population of this part of the world. A smaller cochlear length in this part of the world as compared to the Caucasian cochlear duct is a significant finding in understanding of the cochlear anatomy and physiology. It would also have great implications on the insertion depth in cochlear implantation.

Radiological parameters related to success of the round window approach in cochlear implantation: A retrospective study.

OBJECTIVES: To evaluate the radiologic parameters related to success of round window (RW) approach for cochlear implantation (CI). DESIGN: A retrospective cohort study. SETTING: Academic-tertiary centre. PARTICIPANTS: Eighty-four consecutive patients without inner ear anomaly who underwent CI with the intent of the RW approach were included. The RW approach was performed through the facial recess after posterior tympanotomy (RW group). When the RW approach was not possible despite maximum effort to expose the RW, promontory cochleostomy (PC) was performed (PC group). MAIN OUTCOME MEASURES: The following radiologic parameters were compared between the two groups: (a) Width of the facial recess, (b) oblique distance between the cochlear basal turn (CBT) and facial nerve (FN), (c) anteroposterior distance between the posterior margin of the RW and FN and (d) angle between the EAC and CBT. RESULTS: Seventy patients (83.3%) were implanted using the RW approach, and 14 patients (16.7%) underwent the PC approach for CI. The anteroposterior distance between the posterior margin of the RW and FN and the angle between the EAC and CBT in the RW group were significantly longer and wider than those in the PC group (P < 0.001 and P = 0.001, respectively). Multivariate analysis revealed that these two parameters were independent parameters for success of the RW approach. CONCLUSIONS: The distance between the posterior margin of the RW and FN and the angle between the EAC and CBT are associated with success of RW approach. Therefore, preoperative radiologic analysis of the two parameters might help CI surgeons to select RW approach.

Spatial orientation of the adult cochlea: rotation, tilt, and angle theta 3.

OBJECTIVE: Quantitative description in adult crania of (1) angular orientation of the basal turn of the cochlea relative to the sagittal (termed "rotation") and Frankfort horizontal (termed "tilt") planes, and angle theta 3 [angular relationship of the line defined by the cochlea's spiral center and cochlear (round) window, to the cochlear window]; (2) orientation of the cochlea relative to the plane defined by the horizontal and vertical portions of the facial nerve; (3) orientation of the basal turn of the cochlea relative to the plane of the posterior semicircular canal; and (4) the association of these orientations with the extent of mastoid pneumatization. METHODS: Postmortem material analysis. From 41 bequeathed anatomical ear-normal cadaveric cranial, high-resolution CT scans were performed of the five crania with the largest and the five with the smallest mastoids. Eleven points in three-dimensional Cartesian space were appointed and studied with the software program FIJI. RESULTS: The median angle values (and ranges) for right ears were: "rotation" 52° (range 47-61); and, "tilt" 84° (79-89). The planes of the cochlear basal turn and facial nerve approximated superimposition: median 15° (2-19). Angle theta 3 for right ears was median 40° (28-44). Bilateral symmetry was found for the relationships between the planes. However, no association of any planar relationship with mastoid pneumatization was suggested. CONCLUSION: Considering the range of angles found in clinically normal adult specimens, spatial orientation of the cochlea may explain some of the difficulties in implantation.

Preoperative evaluation of cochlear implantation through the round window membrane in the facial recess using high-resolution computed tomography.

PURPOSE: We evaluated the risk of cochlear implantation through the round window membrane in the facial recess through a preoperative analysis of the angle between the facial nerve-round window and the cranial midline using high-resolution temporal bone CT. METHODS: Temporal bone CT films of 176 patients with profound sensorineural hearing loss at our hospital from 2013 to 2015 were reviewed. The preoperative temporal bone CT scans of the patients were retrospectively analysed. The vertical distance (d value) from the leading edge of the facial nerve to the posterior wall of the external auditory canal and the angle (α value) between the line from the leading edge of the facial nerve to the midpoint of the round window membrane and the median sagittal line on the round window membrane plane were measured. Based on intraoperative observation, the round window membrane was divided into complete round window membrane exposure (group A), partial exposure (group B), and unexposed (group C) groups, and statistical analysis was performed. RESULTS: The α value could be effectively measured for all 176 patients (62.60 ± 7.12), and the d value could be effectively measured for 95 cases (5.53 ± 1.00). An analysis of the correlation between the α and d values of these 95 cases found a negative correlation. Of the 176 cases, one-way analysis of variance (ANOVA) showed that the differences among the groups were significant [P = 0.000 (< 0.05)]. CONCLUSION: The angle (α value) between the line connecting the leading edge of the facial nerve to the midpoint of the round window and the median sagittal line measured in preoperative CT scans was associated with the difficulty of intraoperatively exposing the round window membrane. When the α value was larger than a certain degree, the difficulty of exposing the round window membrane was increased. In such cases, the surgeon should fully expose the round window membrane during surgery, which could result decrease the likelihood of complications.

The Crista Fenestra and Its Impact on the Surgical Approach to the Scala Tympani during Cochlear Implantation.

OBJECTIVE: The aim of this work was to describe the dimensions of the crista fenestra and determine its presence by means of high-resolution computed tomography (CT) for the purpose of cochlear implantation via the round window approach. METHODS: A series of 10 adult human temporal bones underwent high-resolution CT scanning and were further dissected for microscopic study of the round window niche. RESULTS: In all of the specimens, the round window membrane was fully visualized after the complete removal of bony overhangs. The crista fenestra was identified as a sharp bony crest located in the anterior and inferior borders of the niche; its area ranged from 0.28 to 0.80 mm2 (mean 0.51 ± 0.18). The proportion of the area occupied by the crista fenestra in the whole circumference of the round window ranged from 23 to 50% (mean 36%). We found a moderate positive correlation between the area of the niche and the dimensions of the crista fenestra (Spearman rho: 0.491). In every case, high-resolution CT scanning was unable to determine the presence of the crista fenestra. CONCLUSION: The crista fenestra occupies a variable but expressive area within the bony round window niche. Narrower round window niches tended to house smaller crests. The presence of the crista fenestra is an important obstacle to adequate access to the scala tympani. Nevertheless, a high-resolution CT scan provides no additional preoperative information with regard to its presence for the purpose of surgical access to the scala tympani via the round window niche.

[The fistula of the round window of the cochlea]. / Fistula okna ulitki.

This article presents the data on the frequency, diagnostics, and variants of the surgical treatment of the fistula of the round window of the cochlea. A case of this pathology is reported with the special emphasis placed on the approaches to the diagnostics and surgical management of this condition.

The endoscopic study of human middle ear mucociliary transport.

The mucociliary clearance (MCC) is an important defence mechanism of the middle ear. The mucociliary transport (MCT) is a part of MCC. We measured the duration of MCT and visualised its routes in middle ears of 31 patients (mean age 45 years; range 7-61 years; SD 11.6) with intact tympanic membrane, with ventilated middle ears and without a history of prolonged otitis media. The transition time of indigo carmine dye from the promontory mucosa to the middle ear orifice of the Eustachian tube (ET) was observed with a rigid 30°, 1.7-mm-diameter tympanoscope. The dye took an average of 7 min (range 4.5-15 min; SD 3.4; median 4.5) to reach the ET orifice in 25 (81 %) patients. Three main ciliary pathways were detected: (1) below and parallel to the tensor tympani muscle; (2) downwards, anterior to the round window, and then ascending to the ET; and (3) straight across the promontory.