HRCT 3D VR Measurements Of Structures In Normal Inner Ear And Clinical Application Of MRI In Sensorineural Hearing Loss

Part 1 HRCT 3D VR measurements of normal structures in inner ear[Objective]The main anatomic structures of normal inner ear were measured using HRCT 3D VR reconstruction. The statistically significant difference of the parameters among various age groups, different genders and between left and right ear were compared. The reference value of measurements parameters in normal inner ear were obtained, which was helpful in the diagnosis of the inner ear malformations and artificial cochlea preparation.[Materials and methods]1. Clinical data114 patients(60 males and 54 females,0-67 years old, mean=35.4years), a total of 228 ears without inner ear problems, were divided into 5 groups according to the following age standards:group A, younger than 20 years; group B, the age between 21 to 30 years; group C, the age between 31to40 years; group D, the age between 41to 50 years; group E, the ones older than 50 years.Inclusion criteria:all the patients hadn’t had any significant sensorineural hearing loss symptoms, and were scanned with ear HRCT and showed no inner ear malformations, fractures, tumors, sclerosis and other lesions. These patients for innear HRCT examination were mainly due to the following reasons:chronic otitis media, otitis extema, and nasopharyngeal etc.2. InstrumentCT scanner:Siemens SOMATOM Definition dual-source CT, with Syngo 2008G post-processing workstation.3. Scanning methodSpecial inner ear scan was used. (1) Scanning range:from mastoid tip to the upper part of the temporal bone petrous, including the entire inner ear. (2) Scan parameters:tube voltage 120Kv and tube voltage 320mA, detector 0.6mm×64, pitch5mm, tube rotation time 0.5s/rot,5mm high-resolution acquisition. Bone reconstruction algorithm was performed in unilateral small vision, reconstruction vision 10×10cm, reconstruction thickness 0.6mm.4. Data processing and analysisAfter HRCT scan, all the data were transferred to an offline workstation named Syngo 2008G which was equipped with a automatic post-processing inner ear volume rendering technique software package. Three-dimensional reconstruction of the bony labyrinth was performed, the surrounding structures were cutted, and adjusted the threshold in order toget clear inner ear three-dimensional images. The main structures of inner ear were measured in reconstruction images by adjusted the angle and using a ruler tool in the workstation tool. The main structures of inner ear were included the length of vestibular, the width of vestibular, the width of superior semicircular canal, the diameter of the ampulla of the superior semicircular canal, the diameter of the superior semicircular canal bony island, the width of lateral semicircular canal, the diameter of the lateral semicircular canal bony island, the width of posterior semicircular canal, the diameter of canal for the cochlear nerve, the length of cochlear base, the width of cochlear base, the height of cochlear, the angle between of the first and second turn.5. Statistics analysisSSPSS 20.0 software package were applied to statistical analysis in this study. The measurement data were recorded as (mean±SD). The statistically significant difference was set at P<0.05.(1) Parameters among various age groups were compared with One-Way ANOYA. (2)Parameters between different genders were compared with independent Sample T-Test, and parameters between left and right ear were compared with Matched T-Test. (3)The correlation of parameters of inner ear with age was analyzed by the Pearson correlation coefficient for bivariate analysis.[Results]1. There were no statistically significant differencesin the parameters of normal inner ear structure between different genders, between left and right ear and among various age groups (P>0.05).2. The mean parameters of normal inner ear structure were obtained:[Conclusions]1. The major structures of inner ear, such as the vestibule, semicircular canals, cochlear could be clearly shown, and the diameters of the structures of inner ear could be measured by using HRCT scan VR reconstructionimages.2.There were no statistically significant difference in the parameters of normal inner ear structure between different genders, between left and right ear, and among various age groups (P>0.05).3. A normal range of parameters of normal inner ear structure in our country was got by using HRCT VR reconstruction, which provided a detail data basis, reliable imaging data for the diagnosis of inner ear malformations, preoperative screening of cochlear implantation, cochlear electrode formulation and the evaluation of surgery path.Part 2 Clinical application of MRI in sensorineural hearing loss[Objective]The advantages of different MRI techniques and post-processing methods for the display of the inner ear, were discussed respectively.The inner ear morphology and auditory nerve diameter were compared between patients with sensorineural hearing loss and normal people, in order to choose reasonable and effective scanning sequence and the best post-processing method for the patients with sensorineural hearing loss, which provide a valid imaging basis for the clinical diagnosis of sensorineural hearing loss, etiology judgment of sensory deafness, treatment and cochlear implantation.[Materials and methods]1. Clinical data11 patients, a total of 19 ears with congenital sensorineural hearing loss (8 males and 7 females,2-67 years old, mean age of 21.5 years,3 unilateral),inclusion criteria: poor hearing since childhood, bilateral hearing threshold more than 90Bb,with clinical hearing tests diagnosis of SNHL.16 patients, a total of 22 ears with acquired sensorineural hearing loss (8 males and 8 females,16-61 years old, mean age of 21.5 years,10 unilateral ear), inclusion criteria:sudden hearing loss more than 30dB with unknown reasons, accompanied by dizziness, nausea, vomiting and other symptoms, with clinical hearing tests diagnosis of SNHL.Normal group with 18 cases, a total of 36 ears (8 males and 10 females,17～74 years old, mean age of 44years,all bilateral ears), inclusion criteria:normal hearing, no personal and family history of ear disease, no history of dizziness, no history of ototoxic drug use, no ear and head trauma, no abnormal brain signal change on routine head MRI examination.2. Instrument and scanning methodAll the MRI examinations were performed on GE Signa EXCITE HD 3.0T MR scanner or Netherlands Philips Achieva3.0T MR scanner using an 8-channel phase array head coil. All the patients underwent conventional axial MR T1-weighted imaging (TIWI), T2-weighted imaging (T2WI). Special inner ear scanning sequences was as followings:(1)Axial 3D FIESTA scanning range:from mastoid tip to the upper part of the temporal bone petrous, including the entire inner ear, scanning parameters as follows: TR3.7ms, TE1.4ms, FOV200×200mm, matrix320x320,0.8mm thickness with 0 mm gap, NEX=2, flip angle60°,RF bandwidth41.67MMz;Axial T2WDRIVE scanning range the same as axial 3D FIESTA, scanning parameters as follows:TR1500ms, TE195ms, FOV140×140mm, matrix480x480, 0.7mm thickness with 0 mm gap, NEX=2,RFbandwidth657.9MMz.(2)Oblique sagittal FS-T2WI image:images ofaxial FSE-T2WI sequence of a reference, sagittal images were obtained in the oblique plane perpendicular to the long axis of the IAC, bilateral simultaneous localization, bilateral ears were scanned at the same time,12 slices of each side, a total of 24 slices of bilateral ears. Signa EXCITE HD3.0T MR scannerscanning parameters as follows:TR3125ms, TE130ms, FOV200x200 mm,2mm thickness with 0.2 mm gap,RF bandwidth 31.25MMz, matrix 320x320, NEX=2; Netherlands Philips Achieva3.0T MR scanner scanning parameters as follows:TR3000ms, TE50ms, FOV 100x100 mm,2mm thickness with 0.2mmgap,RFbandwidth217.7MMz,matrix 320 x320,NEX=2.3. Data processing and analysisAfter MRI scan, all the original 3D and Oblique sagittal FS-T2WI image data were transferred to ADW 4.3 workstation and Philips workstation with post processing tools for the following post processing:(1)The original images were reconstructed by using the methods of maximum intensity projection (MIP), volume rendering (VR) and multi planar reconstruction (MPR), and membranous labyrinth, internal auditory canal structure could be stereoscopicl displayed clearly. The IAC was determined to be abnormal if it was smaller than 4 mm in either the vertical or transverse diameter.(2)Observation of cochlear nerve diameter:In the Oblique sagittal FS-T2WI image, combined, with axial and T2WDRIVE sequence and 3D FIESTA sequence image, the four nerves including facial nerve, superior vestibular nerve, inferior vestibular nerve were clearly displayed in the internal auditory canal. According to the accepted standard imaging diagnosis of cochlear nerve dysplasia:in the sagittal plane, the caliber of the cochlear nerve was compared with the facial nerve, the superior and inferior vestibular nerves, and the contralateral cochlear nerve. We designated the cochlear nerve as small when it appeared decreased in size compared with the other nerves of the IAC. We designated the cochlear nerve as absent when it could not be identified on the axial, coronal, and oblique plane sagittal images.4. Statistics analysis:SPSS 20.0 software package were applied to statistical analysis in this study. The statistically significant difference was set at P<0.05. The caliber of the cochlear nerve among congenital sensorineural hearing loss group, acquired sensorineural hearing loss group and normal group were compared with multiple independent sample Kruskal-Wallis H test.[Results]1. Among 11 patients, a total of 19 ears with congenital sensorineural hearing loss. Adrenal myelinopathy was found in 1 cases.11 ears were found with inner ear malformations, among them,2 ears of cochlear aplasia with vestibular and semicircular canal malformations, internal auditory canal stenosis,1 ear with vestibular aqueduct and Lateral semicircular canal malformation,6 ears with internal auditory canal stenosis alone,2 ears with enlarged vestibular aqueduct. Among the 11 ears with inner ear malformations,4 ears were found with absent cochlear nerve. Among the remaining 15 ears,10 ears with cochlear nerve dysplasia,3 ears with cochlear nerve diameter equal to the same side nerve or contralateral cochlear nerve diameter,2 ears with cochlear nerve diameter larger than the facial nerve or contralateral cochlear nerve diameter. Among 16 patients, a total of 22 ears with acquired sensorineural hearing loss, no inner ear malformations were found,9 ears with cochlear nerve dysplasia or absent,9 ears with cochlear nerve diameter equal to the same side nerve or contralateral cochlear nerve diameter,4 ears with cochlear nerve diameter larger than the facial nerve or contralateral cochlear nerve diameter. In normal group with 18 cases, a total of 36 ears,no ears with cochlear nerve dysplasia or abent,15 ears with cochlear nerve diameter equal to the same side nerve or contralateral cochlear nerve diameter,21 ears with cochlear nerve diameter larger than the facial nerve or contralateral cochlear nerve diameter.2. There was a significant statistically difference of the caliber of the cochlear nerve among congenital sensorineural hearing loss group, acquired sensorineural hearing loss group and normal group(P<0.001);there wasno statistically significant difference of the caliber of the cochlear nerve between congenital sensorineural hearing loss group and acquired sensorineural hearing loss group(P<0.001); there was a significant statistically difference of the caliber of the cochlear nerve between congenital sensorineural hearing loss groupand normal group, acquired sensorineural hearing loss group and normal group(P<0.001).[Conclusions]1. MRI scan of the inner ear with 3D FIESTA, T2WDRIVE sequence, combined with MPR, MIP and VR reconstruction image, the membranous labyrinth, internal auditory canal structure etc. of inner ear could be observed clearly by any angle, multi-direction, which was significant for the diagnosis of inner ear malformations and judgment for the cause of sensorineural hearing loss. Sagittal images obtained in the oblique plane perpendicular to the long axis of the IAC best distinguish each of the four major nerves of the IAC:facial, cochlear, superior vestibular, and inferior vestibular nerves,whichcould provide important radiological basis for the assessment before cochlear implantation.2. There was a significant statistically difference of the caliber of the cochlear nerve among congenital sensorineural hearing loss group, acquired sensorineural hearing loss group and normal group(P<0.001).3. For patients with sensorineural hearing loss, routine brain MRI scan could clearly show white matter lesions, which has important clinical significance to determine the cause of sensorineural hearing loss.Combining with MRI inner ear scanning, routine brain MRI scan was necessary before the cochlear implant surgery.