| Part1Detection of hypoplasia of bony cochlear nerve canal by virtual endoscopy:a pilot studyPurpose:To retrospectively examine the feasibility of computed tomographic (CT) virtual endoscopy (VE) in the evaluation of hypoplasia of bony cochlear nerve canal (BCNC) on the basis of absence of helix-like shape.Material and Methods:Twenty ears in14consecutive patients (mean age5.5years, range1-15years,6boys,8girls) diagnosed with hypoplasia of BCNC were included in this work. One hundred ears in50gender-and age-matched individuals (mean age6.6years, range1-15years,29boys,21girls) without inner ear disease and internal auditory canal (IAC) malformations served as controls. Three patients and9control subjects were scanned with a four-section multi-detector CT scanner (MX8000, Philips Medical Systems). Eleven patients and41control subjects were scanned with a16-section multi-detector CT scanner (Somatom Sensation16; Siemens Medical Solutions) or a64-section multi-detector CT scanner (Somatom Sensation Cardiac64; Siemens Medical Solutions). Each subject's head was placed in a neutral position, without chin tilt, to approximate the Reid base line. Scanning direction: Cephalocaudal. Both temporal bones were covered by the original scan. Image acquisition and reconstruction parameters for the individual CT scanners were as follows:Parameters for the MX8000were120kV;150mAs;0.6-mm section thickness;0.5-mm detector collimation;0.875beam pitch;50%reconstruction interval and bone algorithm reconstruction kernel;250mm field of view. Parameters for the Sensation16or Sensation64were120kV;150mAs;0.6-mm section thickness;0.6-mm detector collimation;0.5beam pitch;50%reconstruction interval and B70reconstruction kernels;250mm field of view, gvyThe BCNCs of all subjects were endoscopically traversed using3D software program (Fly Through,3D). The view axis was set perpendicular to the examined surface. VE perspective created from the inner margin of the anteroinferior quadrant of the fundus of the IAC to look toward the base of the modiolus, shows the anatomical shape of the BCNC by rotating the viewing point and standing point, or revolving the virtual camera around the viewing axis. If the VE was performed applying low value of850to1150and high value of3071, a helix-like shape appeared in the cochlear area where it corresponded with the tractus spiralis foraminosus. The central canal of the cochlea was defined as the foramen below the anterior part of the transverse crest. Helix-like shape was defined as the spiral fissure in the cochlear area, which runs around the central canal of the cochlea. A positive result on CT VE was defined as absence of helix-like shape or central canal of the cochlea. A negative result on CT VE was defined as presence of helix-like shape or central canal of the cochlea.The presence or absence of helix-like shape was evaluated by two independent reviewers. The value of VE for the diagnosis of hypoplasia of BCNC was assessed with clinical results and routine radiologic evaluation as the reference standard. Quantitative variables between the case group and the control group were tested with the Mann-Whitney U test, and differences in categorical data were tested with the χ2test and Fisher exact tests, if appropriate. Inter-observer agreement was calculated. Sensitivity, specificity, accuracy and the Youden index were selected to test the diagnostic ability of the VE.Results:Of the120ears evaluated in this study,20(11right ears and9left ears) had hypoplasia of BCNC. There was no significant difference with respect to age (P=0.335), sex (P=0.314) and side (P=0.683) between the case and control subjects. Absence of helix-like shape was found in the cochlear area of17of20ears in patients with hypoplasia of BCNC but in none of the control subjects. Three of20(15%) ears of case subjects showed the presence of helix-like shape. Inter-observer agreement was substantial (K=0.773). The diagnostic rates of absence of helix-like shape for hypoplasia of BCNC in terms of sensitivity, specificity, accuracy and the Youden index were85%,100%,98%, and0.85respectively. There were significant differences between the two groups with respect to VE findings for absence of helix-like shape (P<0.001). Five of20(25%) ears of case subjects had absence of the central canal of the cochlea. All of the ears of control subjects had presence of the central canal of the cochlea. The diagnostic rates of absence of the central canal of the cochlea for hypoplasia of BCNC in terms of sensitivity, specificity, accuracy and the Youden index were25%,100%,88%, and0.25, respectively. The comparison of the absence of central canal of the cochlea for the hypoplasia of BCNC between the two groups reached statistical significance. Compared with the absence of central canal of the cochlea, the absence of helix-like shape was found to have better sensitivity and accuracy in the detection of the hypoplasia of BCNC despite the similar specificity (P <0.001).Conclusion:The absence of helix-like shape at VE images offers high sensitivity, specificity and accuracy for the detection of the hypoplasia of BCNC with a substantial interobserver agreement. The absence of helix-like shape at VE images may be used as a potentially useful sign in the diagnosis of hypoplasia of BCNC. Part2Diagnostic Value of Bent-Lever Planes in Detecting Abnormality of the Malleus-Incus ComplexPurpose:To retrospectively investigate the diagnostic value of the bent lever planes in detection of abnormality of malleus-incus complex.Material and Methods:Eighty five ears in74patients (45male patients,29female patients; mean age,35.7years; age range,3-77years) with surgically proved abnormality of malleus-incus complex comprised our study population. Eleven patients had bilateral disease. All of the subjects were scanned with a16-section multi-detector CT scanner (Somatom Sensation16; Siemens Medical Solutions, Forchheim, Germany). The head of each subject was placed in a neutral position, without chin tilt, to approximate the Reid base line. Both temporal bones were covered by the original scan. The transverse images were acquired with a slice thickness of0.6mm, increment of0.3mm (kV,120; mAs,350; pitch,0.8). The raw data were reconstructed by using a bone algorithm and a display field of view of12cm.The bent lever planes for each ear were independently generated at the workstation by two radiologists. The anatomic location and orientation of the structures to be evaluated were confirmed on images in axial and coronal planes of reference. These planes were made in the axial image positioning the reference lines following the line that connected neck of malleus with incudostapedial articulation; in coronal image positioning the reference lines parallel to the long process of incus. For each ear, the acquired data sets were reformatted as S-T-S MIP using a slab thickness of3mm. The radiologists reviewed these planes and were required to comment on the various segments (head of the malleus, neck of the malleus, manubrium of the malleus, incudomalleolar joint, short process of the incus, body of the incus and long process of the incus) of the malleus-incus complex. They were also required to identify whether the various parts of malleus-incus complex and its abnormality can be shown in a single bent lever plane. They made a record independently, then, met with each other to go over every case and come to a consensus evaluation used as the final interpretation. According to this the observers assigned a value of abnormality (positive) or continuity (negative) to the various segments of malleus-incus complex. We took intraoperative findings for ossicular abnormality of various segments of malleus-incus complex as reference standard to evaluate the diagnosis made by the two reviewers. Differences in categorical data were evaluated with the McNemar test. The sensitivity, specificity, negative predictive value, Youden index and interobserver agreement were calculated.Results:The number of direct axial images in detection of abnormality of various segments of malleus-incus complex in85ears were the head of the malleus (n=21), neck of the malleus (n=20), manubrium of the malleus (n=23), incudomalleolar joint (n=7), short process of the incus (n=25), body of the incus (n=35) and long process of the incus (n=63). The number of bent lever planes in detection of abnormality of various segments of malleus-incus complex in85ears were the head of the malleus (n=20), neck of the malleus (n=19), manubrium of the malleus (n=26), incudomalleolar joint (n=10), short process of the incus (n=28), body of the incus (n=34) and long process of the incus (n=66). Intraoperative or pathological findings for lesion location of various segments of malleus-incus complex were head of the malleus (n=22), neck of the malleus (n=21), manubrium of the malleus (n=27), incudomalleolar joint (n=11), short process of the incus (n=26), body of the incus (n=35) and long process of the incus (n=68).The head of the malleus, neck of the malleus, manubrium of the malleus, incudomalleolar joint, body of the incus and long process of the incus of85ears and their abnormalities can be demonstrated in a single bent lever plane. The short process of the incus of85ears and its abnormality must be demonstrated in several bent lever planes. There was no significant difference between bent lever planes and direct axial images in identifying abnormality of the various segments of malleus-incus complex.The sensitivity of bent lever planes in detection of abnormality of various segments (head of the malleus, neck of the malleus, manubrium of the malleus, incudomalleolar joint, short process of the incus, body of the incus and long process of the incus) of malleus-incus complex were90.9%,90.5%,96.3%,90.9%,71.4%,94.3%and97.1%and the specificity were100.0%,100.0%,100.0%,100.0%,89.5%,98.0%and100.0%. The negative predictive value of bent lever planes in detection of abnormality of various segments were96.9%,97.0%,98.3%,98.7%,86.4%,96.1%and89.5%. The Youden index of bent lever planes in detection of abnormality of various segments were0.909,0.905,0,963,0.909,0.609,0.923and0.971. The Youden index of the bent lever planes for the assessment of various segments of malleus-incus complex was high for the components of malleus, incudomalleolar joint, body of incus, long process of incus, less for short process of incus. While studying the malleus, the Youden index of bent lever planes was found to be highest for its manubrium, minimum for its neck and intermediate for its head. High Youden index was achieved with bent lever planes for assessment of incudomalleal joint. In the evaluation of the incus, bent lever planes maintained its high Youden index with regards to evaluation of the body, and long process.The interobserver agreement for the two radiologists in identifying abnormality of the malleus-incus complex with use of bent-lever planes were head of the malleus (k=0.90), neck of the malleus (k=0.94), manubrium of the malleus (k=0.95), incudomalleolar joint (k=0.89), short process of the incus (k=0.75), body of the incus (k=0.85) and long process of the incus (k=0.93).Conclusion:The bent lever planes may replace direct axial images to show discontinuity of malleus-incus complex. The most segments of malleus-incus complex and their abnormality can be demonstrated in a single bent lever plane, which is is intuitive for radiologists.
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