Preoperative Imaging Protocol for Cochlear Implant Candidates

Objective —To formulate and test a CT imaging protocol for preoperative scanning of the temporal bone in cochlear implant candidates.

Material and Methods —A human head was scanned in three CT planes: axial, axiopetrosal and semilongitudinal. Multiplanar reformats (MPRs), based on axial slices, were created and compared with the corresponding images obtained by direct scanning in the respective planes. All scans were analyzed on a viewing workstation.

Results —The axial plane image allowed for an overview of the temporal bone. The width of the facial recess and the cochlear nerve canal could be studied on combined axial and axiopetrosal images. Cochlear patency could be evaluated using combined axial and semilongitudinal images. Axiopetrosal and semilongitudinal MPRs were able to replace the images obtained by direct scanning in the respective planes.

Conclusion —The combination of the axial CT plane image and MPRs was found to be sufficient for preoperative analysis of the temporal bone morphology.     

Dimensions of the cochlear nerve canal: a radioanatomic investigation

The purpose of this study was to determine the normal variations of cochlear nerve canal dimensions, which is useful information to have when assessing congenital malformations, i.e. during the preoperative evaluation of cochlear implant candidates. The length and diameter of the cochlear nerve canal were measured in 117 casts from randomly selected temporal bone specimens obtained from the Uppsala Temporal Bone Laboratory. In 16 of the casts the dimensions were correlated with those obtained from CT scans of the same temporal bone. Measurements were also made from CT examinations of the temporal bone of 50 patients referred for evaluation of cholesteatoma or chronic otitis media. The mean length and diameter in the axiopetrosal plane measured in casts were 1.17 and 2.58 mm, respectively. The mean diameter in the axial plane was 2.59 mm. The mean length and diameter determined from CT scans of the specimens were 1.19 and 1.98 mm, respectively. The mean length and diameter determined from CT examinations of patients were 1.08 and 1.91 mm, respectively. In conclusion, the cochlear nerve canal is short, with a circular cross-section. If the diameter of the canal is < 1.4 mm then the possibility of cochlear nerve abnormality should be considered; if it is > 3.0 mm then other anomalies may coexist.     

Dimensions of the Cochlear Nerve Canal: A Radioanatomic Investigation

The purpose of this study was to determine the normal variations of cochlear nerve canal dimensions, which is useful information to have when assessing congenital malformations, i.e. during the preoperative evaluation of cochlear implant candidates. The length and diameter of the cochlear nerve canal were measured in 117 casts from randomly selected temporal bone specimens obtained from the Uppsala Temporal Bone Laboratory. In 16 of the casts the dimensions were correlated with those obtained from CT scans of the same temporal bone. Measurements were also made from CT examinations of the temporal bone of 50 patients referred for evaluation of cholesteatoma or chronic otitis media. The mean length and diameter in the axiopetrosal plane measured in casts were 1.17 and 2.58 mm, respectively. The mean diameter in the axial plane was 2.59 mm. The mean length and diameter determined from CT scans of the specimens were 1.19 and 1.98 mm, respectively. The mean length and diameter determined from CT examinations of patients were 1.08 and 1.91 mm, respectively. In conclusion, the cochlear nerve canal is short, with a circular cross-section. If the diameter of the canal is < 1.4 mm then the possibility of cochlear nerve abnormality should be considered; if it is > 3.0 mm then other anomalies may coexist.     

The predictive value of semilongitudinal and axial computerized tomography planes in assessing cochlear patency in cochlear implant candidates

Introduction. The objective was to establish the predictive value of semilongitudinal and axial computerized tomography (CT) planes in assessing cochlear patency in cochlear implant candidates. Methods. In a retrospective study, preoperative CT scans of 45 patients who received a cochlear implant were independently reviewed by a junior and senior observer. The predicted degree of cochlear patency was compared with the peroperative findings. Results. A decreased cochlear patency was found at surgery in nine patients (20%). The sensitivity of CT was 33% for the junior observer and 11% for the senior observer, whereas specificity was 86% and 89% respectively. Inter‐observer reliability was reflected in a kappa of 0.38. In 14 patients deafened as a result of meningitis (31%), sensitivity for the junior observer amounted to 60% with a specificity of 89%. Statistical analysis revealed that this improvement did not solely depend on a higher prevalence of decreased cochlear patency. Conclusion. The sensitivity of CT scans in the semilongitudinal and axial plane in assessing cochlear patency, in our patient group, is small. In patients deafened as a result of meningitis, sensitivity was found to be increased.     

Semilongitudinal and axial CT planes in assessing cochlear patency in cochlear implant candidates

OBJECTIVE: To investigate how cochlear patency as seen on computed tomography (CT), using axial plus semilongitudinal planes, is correlated with findings at surgery in cochlear implant patients. METHODS: Pre-operative CT scans of 45 patients were reviewed by three, independent observers. They classified the cochlear patency and recorded the location of any suspected decreased patency. The results were compared with the findings noted during surgery. RESULTS: In nine patients a decreased cochlear patency was found at surgery. The sensitivity and specificity of CT assessment were, respectively, 56-33-11% and 100-86-94%. The interobserver reproducibility is reflected in a mean kappa of 0.46. The sensitivity increased when only patients suffering from post-meningitic deafness were considered. CONCLUSION: Our study suggests that CT scans can be useful in assessing cochlear patency, especially in patients with post-meningitic deafness. This good performance might be explained by the combined use of scans in semilongitudinal and axial planes.     

Magnetic resonance imaging versus computed tomography in pre-operative evaluation of cochlear implant candidates with congenital hearing loss

Recent reports indicate that the cochlear nerve may be absent in some cases of congenital sensorineural hearing loss. The aim of this prospective study was to determine the incidence of cochlear nerve anomaly in cochlear implant candidates with congenital hearing loss using magnetic resonance imaging (MRI). Twenty-seven patients with congenital profound bilateral sensorineural hearing loss who were being evaluated for the cochlear implant procedure were studied. These patients had high-resolution computerized tomography (CT), through the petrous bone in axial sections. MRI examinations consisted of T1 and turbo spin echo (TSE) T2-weighted 3 mm axial images, and additional 3D Fourier Transform T2-weighted TSE sequences obtained on three different planes (axial, perpendicular and parallel to the internal auditory canal (IAC) i.e. oblique sagittal and coronal, respectively) for the purpose of cochlear nerve demonstration. Results showed that all of the 14 patients with normal CT of the temporal bone, had four distinct nerves in the distal part of the IAC on TSE-MRI. Thirteen patients demonstrated various bony malformations of the cochleovestibular system on CT. MRI revealed the absence of the cochleovestibular nerve in four patients where the IAC was very narrow or completely absent on CT. One patient with severe Mondini malformation who had an enlarged IAC demonstrated an isolated absent cochlear nerve.     

Use of reconstructed,non-orthogonal plane,high-resolution computed tomography of the temporal bone in the planning of temporal bone surgery

OBJECTIVES: To demonstrate the utility of high-resolution computed tomography (HRCT) reconstructed in non-orthogonal planes in the planning of temporal bone surgery. STUDY DESIGN: Qualitative and quantitative comparison of in vivo anatomic measurements between orthogonal and non-orthogonal plane reformatted HRCT of the temporal bone. METHODS: HRCT data of 10 normal temporal bones were reconstructed two-dimensionally in two non-orthogonal planes. Parallel to the plane defined by the superior semicircular canal (defined as transverse) as well as perpendicular to the plane defined by the superior semicircular canal (defined as longitudinal). This was done using commercially available software. Sixteen surgically important relationships between neural, vascular and/or bony structures were measured and analyzed. RESULTS: Quantitatively, wide variations were obtained in the measurements obtained from images of both non-orthogonal planar orientations. These variations were not age or sex dependent. Qualitatively, the images obtained highlight the anatomy of the temporal bone and skull base as it will be encountered during otologic surgery, since the surgical visual axis is along the long axis of the temporal bone. CONCLUSIONS: The reformatted images in non-orthogonal planes were superior to the axial and coronal series because they condensed critical relationships into a single perspective which promoted an intuitive understanding of the surgical approach. These reconstructed images show wide differences in quantitative measurements between surgically relevant landmarks. The protocol can be easily implemented in the clinical setting and is a potentially valuable educational tool. We recommend that non-orthogonal reconstructed images be routinely included with orthogonal temporal bone HRCT scans.     

CT多平面重组在大前庭水管综合征诊断中的应用

目的探讨CT多平面重组（mulitiplanar reformation，MPR）在大前庭水管综合征诊断中的应用价值。方法选取31例前庭水管扩大患者轴位扫描原始图像、利用原始图像获取对称性轴位MPR图像及前庭水管最大显示MPR图像，比较三种图像中前庭水管的显示情况。结果轴位扫描图像显示前庭水管左右对称3例（9．68％），两种经MPR处理后图像均显示前庭水管左右对称；原始扫描图像前庭水管长肢全程显示24例，未全程显示不能进行前庭水管经线测量7例；30例患者前庭水管最大显示MPR图像上可全程显示前庭水管长肢并进行测量。结论前庭水管最大显示MPR图像能对称显示双侧前庭水管全程显示前庭水管长肢，对前庭水管扩大的准确测量具有重要意义。     

Chronic sphenoid sinusitis revisited: comparison of multidetector axial sections, multiplanar reconstructions, and virtual sinoscopy with endoscopic sinus surgery

OBJECTIVES: To assess the role of multidetector computed tomography (CT) and CT virtual sinoscopy in the evaluation of chronic sphenoid sinusitis and to compare the imaging findings with functional endoscopic sinus surgery. DESIGN: Prospective study. SETTING: Tertiary care teaching hospital. PATIENTS: Thirty patients with chronic sphenoid sinusitis referred for preoperative CT. INTERVENTIONS: Thin-section helical axial CT was performed using a multidetector CT scanner with multiplanar reformation (MPR) and volume-rendered or virtual sinoscopy images. Sixty sinuses were divided into quadrants for analysis. Extrasinus extension was labeled as the "fifth quadrant." MAIN OUTCOME MEASURES: Imaging findings were compared with those of functional endoscopic sinus surgery, and accuracy of the imaging modality was determined. RESULTS: Multidetector CT (axial CT and MPR) was found to be 100% sensitive, specific, and accurate in the evaluation of extent of sinusitis, status of the sinus septum, integrity of the optic nerve canal in relation to the sinus, and type of sinus pneumatization. Axial CT and MPR images showed sensitivity of 98% and specificity of 92% compared with functional endoscopic sinus surgery in evaluating the ostia. Regarding carotid canal integrity, axial CT and MPRs were 100% sensitive and 98% specific. Virtual sinoscopy showed sensitivity and specificity of 67% and 92%, respectively, for the 22 ostia that could be visualized and evaluated using this modality. CONCLUSIONS: Axial multidetector CT with secondary MPRs provide the necessary preoperative information regarding extent of disease and sphenoid sinus anatomy. Virtual sinoscopy is a navigational aid, an adjunct to endoscopy, and an educational tool for surgeons-in-training.     

人工耳蜗植入术后植入电极的影像学检查

目的 探讨建立螺旋CT扫描及三维重建技术观察人工耳蜗植入电极方法，并比较X线摄片方法与螺旋CT扫描三维重建方法的耳蜗内电极的影像学特征及其临床应用价值。方法 18例人工耳蜗植入患者全部作术后X线摄片检查。其中9例用经眼眶前后位摄片，9例采用侧斜位60。摄片。3例患者施行术后螺旋CT扫描及内耳三维重建方法。结果 2种投射头位的X线摄片均可显示电极形态及单个电极对，可间接判断电极在耳蜗内的植入深度。螺旋CT扫描三维重建图可直观地显示耳蜗形态、电极形态及其在耳蜗内植入的深度，可清晰识别单个电极对。结论 螺旋CT扫描三维重建方法可直观观察植入电极的形态及位置，可准确判断电极在耳蜗内植入的深度，有其独特的临床应用价值。     

Computed tomography in maxillofacial trauma

Computed tomography (CT) has become the key diagnostic modality in the evaluation of head trauma. Experience with CT in the preoperative assessment of maxillofacial injuries is limited, however. Plain films and multidirectional tomography have been used until now to define fractures in the facial region. We examined 27 patients sustaining maxillofacial trauma with CT scans. Ten patients were studied in the coronal plane, 12 in the axial plane, and the reMayning 5 in both the axial and coronal planes. Polycycloidal tomography in the coronal and/or sagittal plane was obtained in 18 patients for comparison with the CT scan. Fracture lines, bony fragments, and associated skeletal deformities were clearly identified by CT scan in all 27 patients permitting the diagnosis of zygomatic, orbital floor, nasoethmoidal complex, LeFort, temporal bone, frontal sinus, and mandible fractures. More importantly, concommitant intracranial injuries including epidural and intracerebral hematomas, traumatic encephalocoele, and pneumocephalus were readily seen. In addition, facial and orbital soft tissue structures including the globe, optic nerve, orbital fat, and extraocular muscles were easily examined by adjusting the CT level and window settings. Overall, CT yielded additional information not available from polytomography in 15 of 18 cases when both modalities were used. Multidirectional tomography is currently superior to CT scanning if fine, intrinsic bone detail is required. However, we have found that complex fractures with fragmentation are more easily identified on CT scans than conventional tomography because of superior contrast resolution of computed tomography. With improved spatial resolution, CT scanning may totally supplant multidirectional tomography in the evaluation of maxillofacial trauma.     

Correlation of high resolution computed tomography and gross anatomic sections of the temporal bone. Part III. Cochlear and vestibular aqueducts

Gross anatomic sections of isolated temporal bones (TB) were compared with high resolution computed tomography (CT) scans obtained utilizing contiguous 1.5-mm thick slices in the transaxial, coronal, and sagittal planes. Each TB was then sectioned at 2.0-mm intervals in planes parallel to those of the CT scans. Both the cochlear and vestibular aqueducts were best visualized in the coronal plane; the transaxial plane proved less reliable and the sagittal plane was not useful at all. The cochlear aqueduct in the coronal plane appears as a funnel-shaped configuration with its widest portion opening into the subarachnoid space. The vestibular aqueduct at its opening into the epidural space is well visualized in the coronal plane, and as it traverses the bone toward the vestibule it appears as an oval to spherical lucency, whereas in transaxial sections it is seen as a small longitudinal lucency.     

成人面神经管螺旋CT曲面重建图像的解剖学研究

目的探讨螺旋CT曲面重建图像对面神经管解剖学研究的参考价值.方法对50例正常成人(100侧)面神经管进行螺旋CT曲面重建,描述正常成人面神经管曲面重建图像的解剖特征,并进行测量.结果 50例正常人的轴位和冠状位曲面重建图像,可在一幅图像上清晰显示双侧面神经管结构,显示率100%,矢状位曲面重建图像只能完整显示单侧面神经管结构;三个方位曲面重建图像上能较准确测得面神经管长径和宽径,测量值差异无显著性意义(P>0.05),而对弯曲部的显示、测量和对毗邻结构的显示,不同方位有各自价值和限度.结论螺旋CT面神经管曲面重建图像具有简便、实用、准确、直观等优点,是目前研究面神经管影像解剖的良好方法.对面瘫定位诊断具有重要指导意义.     

How best to present the radiological picture of the temporal bone today?

The detailed evaluation of anatomy and pathology of the temporal bone requires imaging modalities that are superior to plain x-ray films. Conventional polytomography has today largely been replaced by high-resolution CT. High-resolution CT provides excellent demonstration of the delicate bony structures and provides superior information about the soft tissues. The axial 1 mm scans of a complete temporal bone examination can be reformated in any number of planes. These reconstructions display the temporal bone in various projections. This theoretically well-founded procedure of individual processing has proven to be highly practical in more than 1000 examinations of the skull base. High-resolution CT with image reconstruction is the diagnostic method of choice for the evaluation of the skull base and especially the temporal bone, as the complex anatomy is best demonstrated by this technique. Six axial computed tomographic scans are demonstrated in detail. The special value of multiplanar reconstructions is illustrated by reconstructions in the coronal, sagittal and longitudinal plane.     

Cochlear orientation and dimensions of the facial recess in cochlear implantation

OBJECTIVE: To study the dimensions of the facial recess and the spatial relationship between the facial recess and the cochlea, using CT scanning in cochlear implantees. METHOD: In 29 cochlear implantees, preoperative CT scans of the temporal bone were compared with findings done at surgery. The dimensions of the facial recess and the relationship between the facial recess and the cochlea were both measured on a viewing station and classified on printed films by 3 blinded and independent reviewers. RESULTS: No significant relations could be found between either intuitive classification of facial recess width or electrode array insertion feasibility and the measurements with the viewing station. The 3 reviewers had large interobserver variability. In 5 cases, neither intuitive review of the CT scans nor viewing station measurements could predict any of the problems encountered during surgery. CONCLUSION: Our findings show that intuitive review was not reliable in classifying facial recess width. Viewing station measurements, in classifying the spatial relation between the facial recess and the cochlear basal turn, need a more detailed review in terms of the relationship with the operation direction and the orientation of the basal turn of the cochlea. Advanced imaging techniques, specifically multislice CT, might improve the diagnostic capabilities.     

MRI versus CT in assessment of cochlear patency in cochlear implant candidates

OBJECTIVE: To investigate how cochlear patency as seen on preoperative CT and MRI scans correlates with findings at surgery in cochlear implant patients. MATERIAL AND METHODS: CT and MRI scans of 25 patients were reviewed by 3 independent observers. The reviewers classified the cochlear patency and recorded the location of any suspected decrease in patency. Their results were compared with the findings noted during surgery. RESULTS: Decreased cochlear patency was found in six patients at surgery. The mean sensitivity/specificity of CT and MRI assessment was 33%/88% and 41%/91%, respectively. CONCLUSION: Our study suggests that CT, using axial and semi-longitudinal planes, is equivalent to MRI in predicting cochlear patency.     

Preoperative cochlear implant imaging: is magnetic resonance imaging enough?

OBJECTIVE: To investigate the accuracy of magnetic resonance imaging (MRI) as a preoperative imaging technique for cochlear implant candidates. STUDY DESIGN: Retrospective, blinded. SETTING: Tertiary medical center. PATIENTS: 31 cochlear implant candidates with various causes of hearing loss. INTERVENTION: Cochlear implant patients received preoperative high-resolution temporal bone computed tomography (CT), and high-resolution T2-weighted fast spin echo MRI (FSE-MRI). The images were read independently of each other and in a blinded manner by two neuroradiologists. The imaging results were also correlated with intraoperative findings. MAIN OUTCOME MEASURES: Lack of agreement between the findings for either imaging technique; also, lack of agreement between imaging findings and intraoperative findings. RESULTS: FSE-MRI is equal to CT imaging in the detection of abnormalities of cochlear patency. It is better than CT imaging in detecting cochlear dysplasia and large vestibular aqueducts, and in determining the presence of the cochlear nerve. CONCLUSION: FSE-MRI is accurate in predicting inner ear anomalies and obstruction of the cochlear lumen. It also adds information not gathered from CT imaging, such as the presence and size of the cochlear nerve.     

Development of the mouse cochlea database (MCD)

The mouse cochlea database (MCD) provides an interactive, image database of the mouse cochlea for learning its anatomy and data mining of its resources. The MCD website is hosted on a centrally maintained, high-speed server at the following URL: http://mousecochlea.umn.edu. The MCD contains two types of image resources, serial 2D image stacks and 3D reconstructions of cochlear structures. Complete image stacks of the cochlea from two different mouse strains were obtained using orthogonal plane fluorescence optical microscopy (OPFOS). 2D images of the cochlea are presented on the MCD website as: viewable images within a stack, 2D atlas of the cochlea, orthogonal sections, and direct volume renderings combined with isosurface reconstructions. In order to assess cochlear structures quantitatively, "true" cross-sections of the scala media along the length of the basilar membrane were generated by virtual resectioning of a cochlea orthogonal to a cochlear structure, such as the centroid of the basilar membrane or the scala media. 3D images are presented on the MCD website as: direct volume renderings, movies, interactive QuickTime VRs, flythrough, and isosurface 3D reconstructions of different cochlear structures. 3D computer models can also be used for solid model fabrication by rapid prototyping and models from different cochleas can be combined to produce an average 3D model. The MCD is the first comprehensive image resource on the mouse cochlea and is a new paradigm for understanding the anatomy of the cochlea, and establishing morphometric parameters of cochlear structures in normal and mutant mice.     

高分辨率CT对颞骨外伤性面瘫的诊断价值

目的：探讨高分辨率CT（HRCT）对颞骨外伤性面瘫的诊断价值及对手术的指导意义。方法：据临床资料和颞骨HRCT表现,对29例拟行手术治疗的颞骨外伤性面瘫患者提出预测性诊断,并与术中所见进行对比。结果：CT显示骨折线走行情况与术中所见基本符合,不同类型的骨折引起的神经损伤具有各自的特点。面神经损伤的直接征象包括骨折线贯穿骨管、骨管断裂或断离;间接征象包括面神经局部增粗、骨管壁密度降低、膝状神经窝扩大、面神经受压等。各种征象与术中所见的符合率均在90％以上。结论：HRCT可明确显示颞骨骨折线的位置及走行,有助于判断面神经损伤范围、程度以及邻近结构破坏情况,为临床诊断及治疗提供可靠依据。