Large vestibular aqueduct syndrome: a human temporal bone study

OBJECTIVES/HYPOTHESIS: Large vestibular aqueduct syndrome (LVAS) is one of the common causes of hearing loss (HL). All prior studies have reported some anomalies associated with LVAS by imaging techniques. This study was undertaken to determine prevalence of LVAS in our temporal bone (TB) collection and its relationship to other systemic or otologic anomalies. STUDY DESIGN: Retrospective, TB histopathologic study. METHODS: Anteroposterior diameters of internal (IA) and external (EA) apertures were measured in 40 normal TBs (40 cases). TBs were considered as large vestibular aqueduct (LVA) if width of apertures was 95% greater than "normals." Systemic and otologic anomalies and histopathology of ears with LVAS were noted. RESULT: Of 1,608 non-"normal" TBs, 63 had LVA. There was negative correlation between IA and EA in 48 TBs with only enlarged IA. Fifteen TBs with enlarged EA always had enlarged IA and were therefore considered as LVAS. The most common pathologic condition was congenital heart anomaly. The most common syndrome or dysplasia was Mondini's. The most common anomalies of external and middle ears were dehiscent facial nerves, low set auricles, and ossicular deformities. Inner ear anomalies included modiolar deficiencies, hair cell loss, interscalar septum defects, and strial atrophy. There was no record of family history of HL, head injury, or craniofacial, branchial, or thyroidal abnormalities. CONCLUSION: Because HL associated with LVAS may be attributed to other ear anomalies, it is important to investigate other inner ear problems and system diagnoses that may indicate a syndrome in patients with radiologically diagnosed LVAS.     

Radiology of the cochlear aqueduct

OBJECTIVES: We sought to determine normative data for the radiologic presentation of the cochlear aqueduct (CA), hypothesizing that increasing the scanner's resolution could enhance detection capability. METHODS: Axial sections of 502 high-resolution computed tomography (CT) images of temporal bones (488 patients) were reviewed. A type 1 CA was visualized on CT scans up to the vestibule, and its portion in the otic capsule segment could be seen as a thin (<1 mm) streak. In type 2, we were able to detect the medial two thirds of the structure, but we failed to see the whole otic capsule portion. In type 3, only the external aperture of the aqueduct and/or the medial third was seen. We defined undetectable CAs as type 4. RESULTS: We obtained CT scans with 0.6-, 1.1-, or 1.3-mm-thick slices through the petrous bones in 9.5%, 58.8%, and 31.7% of cases, respectively. The CA was visible and bilaterally symmetric in 49% of the images, and type 2 was the most commonly detected CA type (36%). The CA was invisible on either side in 21.9% of scans, irrespective of CT resolution, and was asymmetric in 53 of the 502 images. The CA types varied with changes in resolution, although type 3 appeared unchanged independent of alterations in resolution in most cases. CONCLUSIONS: There was no significant difference in CT detection capability between CA types at different resolutions. Computed tomography failed to demonstrate any CAs > or =1 mm in width in the otic capsule segment.     

Fine structure of the human cochlear aqueduct: a light and transmission electron microscopic study of decalcified temporal bones

The morphologic features of the human cochlear aqueduct were examined using both light and electron microscopy. The lumen of the cochlear aqueduct was observed to be filled with dense, irregular connective tissue corresponding to dura mater. At the entrance to the cerebrospinal fluid space, the dense connective tissue in the ductal lumen was covered with a thin layer of a few flattened cells, which was contiguous with the arachnoid membrane of the brain. A simple low cuboidal epithelium also separated the perilymphatic space from the lumen of the duct. Our observations confirm the presence of a barrier membrane at the opening to the perilymphatic space, and suggest that no transport occurs in the human cochlear aqueduct.     

Endolymphatic duct violation during retrosigmoid dissection of the internal auditory canal: a human temporal bone radiographic study

OBJECTIVE/HYPOTHESIS: Successful hearing preservation after acoustic neuroma resection is sometimes complicated by delayed hearing deterioration. The goal of this study was to investigate the hypothesis that internal auditory canal (IAC) drilling during retrosigmoid acoustic neuroma removal may result in endolymphatic duct (ELD) injury, a potential cause of delayed hearing loss (HL) after hearing preservation surgery. STUDY DESIGN: Temporal bone anatomic and radiographic study and literature review. METHODS: Twenty-one human temporal bones were analyzed with high-resolution multislice computed tomography (HRMCT) and subjected to standard retrosigmoid IAC dissection with labyrinthine preservation and follow-up HRMCT for analyses of the ELD. A MEDLINE search was performed of studies documenting long-term hearing preservation outcomes after retrosigmoid dissection. RESULTS: Five of 21 (24%) bones were found to have violation of the ELD despite preservation of labyrinthine structures and the endolymphatic sac. These results correlate with the mean incidence of long-term hearing decline (26.6%). Reviews of human and animal studies indicate that injury to the ELD may create endolymphatic hydrops. CONCLUSIONS: The ELD is vulnerable to injury during IAC dissection even if labyrinthine structures at the lateral aspect of the IAC are preserved. These findings may be helpful in explaining and potentially preventing some cases of long-term hearing deterioration that may be a result of endolymphatic hydrops after ELD injury during acoustic tumor removal. Careful preoperative review of imaging studies using HRMCT may prove useful before retrosigmoid dissection.     

Histopathology of temporal bone fractures: Implications for cochlear implantation

Temporal bone fractures often cause loss of audiovestibular function. Those patients with bilateral profound sensorineural hearing losses secondary to temporal bone fractures become candidates for cochlear implantation. The authors present the histopathology of five temporal bone fractures in three patients, evaluating specifically the traumatic effects on the neural elements of the inner ear. Transverse fractures of the temporal bone result in severe loss of hair cells, ganglion cells, and other supporting cells in the inner ear. Occasionally labyrinthitis ossificans may occur as a consequence of trauma or infection. While longitudinal fractures do not violate the otic capsule, these same neural elements may be damaged by concussion.     

Endolymphatic duct status during middle fossa dissection of the internal auditory canal: a human temporal bone radiographic study

OBJECTIVE: Successful hearing preservation after acoustic neuroma resection is sometimes complicated by delayed hearing deterioration. The middle fossa approach appears to offer superior long-term hearing results when compared to the retrosigmoid surgical approach. The goal of this study is to investigate the hypothesis that internal auditory canal (IAC) drilling during middle fossa acoustic neuroma removal is associated with a lower incidence of endolymphatic duct (ELD) injury, a potential cause of delayed hearing loss (HL) known to accompany retrosigmoid hearing preservation dissection techniques. STUDY DESIGN: A human temporal bone anatomic and radiographic study complemented with a literature review. METHODS: Twenty human temporal bones were analyzed with high-resolution multislice computed tomography (HRMCT) and subjected to standard extended middle fossa IAC dissection with labyrinthine preservation and follow-up HRMCT for analyses of the ELD. RESULTS: Zero of 20 (0%) temporal bones were found to have violation of the ELD with preservation of the labyrinthine structures and the endolymphatic sac. Reviews of human and animal studies indicate that injury to the ELD may create endolymphatic hydrops, a known cause of hearing deterioration. CONCLUSION: The ELD is not vulnerable to injury during IAC dissection using the middle fossa approach. A previous radiographic study has shown that the ELD is violated in 24% of temporal bones during retrosigmoid dissection of the IAC. These findings support and may help explain other outcome studies that show that long-term hearing results are superior with the use of the middle fossa approach when compared to results following retrosigmoid dissection.     

Ultrastructure of the guinea pig cochlear aqueduct. An electron microscopic study of decalcified temporal bones

The ultrastructure of the guinea pig cochlear aqueduct was examined using semi-thin and thin sections. The lumen of the cochlear aqueduct was occupied by a sparse meshwork of fibroblasts and delicate connective tissue trabeculae. The periotic tissue lining the bony wall of the aqueduct was composed of multiple layers of both elongated cells and densely arranged laminae of collagen fibrils. These structures were identical to those of the dura mater and the arachnoid. The opening to the perilymphatic space of the scala tympani also contained connective tissue trabeculae, but the arrangement of fibroblasts was more compact here than in the main part of the duct. These structural features suggest that fluid can move freely through cochlear aqueduct, and that the effects of sudden pressure changes in the CSF may be protected against by the densely and perpendicularly arranged fibroblast at the opening to the perilymphatic space.     

Radiographic classification of the vestibular and cochlear aqueducts: the paired correlation between normal and abnormal vestibular aqueduct and cochlear aqueduct anatomy

Multidirectional tomography (MDT) can be useful in determining the caliber, shape, and course of the vestibular aqueduct (VA) and cochlear aqueduct (CA). Clinical decisions have been based on the findings from MDT. Unfortunately, the clinical utility of these observations has been confusing and controversial because similar MDT techniques were not used. This study will address some of the difficult questions and clinical controversies derived from MDT observations. This new perspective has evolved with the use of high resolution computed tomography (HRCT). An analysis of 750 petrous bones for the occurrence of the various types of VAs and CAs using Gado's classification, further vestibular aqueduct and a variation of Gado's classification for the cochlear classification is reported. The distribution of the possible paired types of VA and CA are evaluated. MDT results indicate that the paired analysis in patients with inner ear dysfunction is not useful, cost effective, diagnostic, or of prognostic value. MDT can provide clinically valid observations of periaqueductal and perilabyrinthine pneumatization which is helpful in anticipating the size and position of the endolymphatic sac at the time of surgery for those few patients who may benefit from endolymphatic system surgery. However, when a comparison is made between MDT and CT of 60 ears in those same patients, the clinical limitations of MDT for inner ear diagnosis and prognosis became apparent. The future for HRCT scanning with reformatting holds potential for clinically meaningful visualization of inner and middle ear structures previously expected from MDT imaging.     

Histopathology of the temporal bone following multichannel cochlear implantation.

The temporal bone histopathologic findings of a patient having received a Nucleus 22-channel cochlear implant (Cochlear Corp, Englewood, Colo) following bilateral transverse otic capsule fractures is presented. The case was complicated by perilymph fistulas, labyrinthitis, meningitis, and death due to drowning. The left cochlea revealed complete labyrinthitis ossificans; the implanted right cochlea demonstrated new bone formation in the basal turn of the scala tympani, degeneration of the organ of Corti, but normal ganglion cell counts. Results of psychophysical and speech perception 4 months after implantation are presented.     

Bilateral cochlear implantation in a patient with bilateral temporal bone fractures

With the emphasis on bilateral hearing nowadays, bilateral cochlear implantation has been tried out for bilateral aural rehabilitation. Bilateral sensorineural hearing loss caused by head trauma can get help from cochlear implantation. We present the case of a 44-year-old man with bilateral otic capsule violating temporal bone fractures due to head trauma. The patient demonstrated much improved audiometric and psychoacoustic performance after bilateral cochlear implantation. We believe bilateral cochlear implantation in such patient can be a very effective tool for rehabilitation.     

Sculpting the temporal bone: an easy reversible cochlear implant electro-array stabilization technique

European Archives of Oto-Rhino-Laryngology - Since the beginning of cochlear implant (CI) surgery, several techniques to fixate the electrode array at the cochleostomy and stabilize it have been...     

Application of UNETR for automatic cochlear segmentation in temporal bone CTs

ObjectiveTo investigate the feasibility of a deep learning method based on a UNETR model for fully automatic segmentation of the cochlea in temporal bone CT images.MethodsThe normal temporal bone CTs of 77 patients were used in 3D U-Net and UNETR model automatic cochlear segmentation. Tests were performed on two types of CT datasets and cochlear deformity datasets.ResultsThrough training the UNETR model, when batch_size=1, the Dice coefficient of the normal cochlear test set was 0.92, which was higher than that of the 3D U-Net model; on the GE 256 CT, SE-DS CT and Cochlear Deformity CT dataset tests, the Dice coefficients were 0.91, 0.93, 0 93, respectively.ConclusionAccording to the anatomical characteristics of the temporal bone, the use of the UNETR model can achieve fully automatic segmentation of the cochlea and obtain an accuracy close to manual segmentation. This method is feasible and has high accuracy.     

A temporal bone preparation for the study of cochlear micromechanics at the cellular level

An in vitro preparation of the guinea pig temporal bone was developed for studying the micromechanical behaviour of the cochlea. The preparation consists of the cochlea opened at the apex, allowing observation of cellular structures within the cochlear partition with an optical sectioning microscope and measurements of cellular vibration with laser interferometry. The middle ear ossicles and the tympanic membrane are left intact as well as the bony part of the external auditory canal, which is used for delivering a sound stimulus to the cochlea.