CT Image Analysis Of Congenital External And Middle Ear Malformation

ObjectiveTo describe and analyze the temporal bone high-resolution computed tomography (HRCT) images in congenital aural atresia (CAA) patients, in order to1) clarify the abnormal developments of the middle ear anatomical landmarks such as facial nerve, sinus tympani, round window and ossicular chain;2) establish the distributional relationship of abnormal structures;3) clarify the development trends of middle ear malformations, which facilitate the assorting surgical candidates of CAAs and provide the basis for preoperative evaluation.Design/Patients1. Fifty CT scans from25patients (6bilateral cases) with CAA were selected, and postoperative cases and inner ear malformation were excluded.2. Thirty-one CAA ears were graded in Jahrsdoerfer score system and the middle ear target structures were described of abnormal morphology.3. Oblique axial multiplanar reconstruction (MPR) located along the long axis of Posterior semicircular Canal ampulla provides the best depiction of the round window and of the mastoid segment of facial nerve. Measure and compare target distances in atretic ears and nonatretic ears in CAAs. These included mastoid segment of facial nerve to round window horizontal line distance (Q1), mastoid segment of facial nerve vertical line to round window midpoint distance (N2), mastoid segment of facial nerve directly to round window midpoint distance (Z3), sinus tympani cross-sectional area (A5CM2), the deepest and/or farthest point of sinus tympani cross-sectional bottom (S point) to round window midpoint distance (WRW2), S point to mastoid segment of facial nerve distance (WFN1), mastoid segment of facial nerve to posterior semicircular canal or its extended line vertical distance (FNSSC). Determine correlations between the degree of anterior dislocation of the facial nerve and the shape of sinus tympani.4. Oblique planes of section were adjusted to optimally depict the given structures. Measure and compare ossicular distances at each MPR plane in atretic ears and nonatretic ears in unilateral CAA, including the distance from facial nerve to round window (r_fp/r_fm), distance from round window to incudostapedial joint (r_isj), the distance from round window to the stapes front crus (r_sa), distance from round window to the short process of the incus (r_isp), oval window diameter (ow). Paired-t test was used to compare differences between groups. Differences with significant was got linear correlations between groups of data.Results1. Jahrsdoerfer scoring CAA ears were graded from0point to9points, averaging6.06points,67.7%lies to≥6points. Prevalence of anatomic variants was as follows:ossicular chain malformation67.7%, including Incudo-malleolar fusion45.2%, incudostapedial joint disconnect29%, stapes malformation32.3%(rudimentary stapes19.4%and absent stapes12.9%); oval window atresia6.5%; round window stenosis3.2%; facial nerve malformation77.4%; middle ear space reduced48.4%; mastoid poorly pneumatized16.1%; microtia100%.2. Mastoid segment of facial nerve to round window horizontal line distances in atresia ears decreased when compared to non-atresia ear, which meant the mastoid segment of facial nerve tended to anteriorly dislocate in atresia ears of CAAs. The distribution of the data presented that atresia group lay below the2mm line while non-atresia group lay above the2mm line. Therefore the anterior dislocation of the mastoid segment of facial nerve was defined to Q1<2mm in this study. 3. The sinus tympani cross-section shapes were classified into three categories:cup-shaped, pear-shaped and boot-shaped. Area measurement indicated that cup-shaped and pear-shaped sinus tympani were small size, but boot-shaped sinus tympani were large size. There were significant differences of the sinus tympani cross-sectional areas between the boot-shaped group and cup-shaped group, as well as the boot-shaped group and pear-shaped group. Boot-shaped sinus tympani characterized by varying degrees of spacial enlargement and deep lateral extension, which were only seen in the CAA ears with anteriorly dislocated mastoid segment of facial nerve.4. Facial nerve anterior displacement distance (Q1) had a significant negative correlation with both the sinus tympani area (A5CM2) and sinus tympani extension distance (WRW2). That is, when mastoid segment of facial nerve located anteriorly, the sinus tympani extend laterally and backwards.5. The distances from round window to the short process of the incus (r_isp) in atretic ears differed significantly with those in control ears. The r_isp length correlated significantly with the r_fp length (i.e. the distance from facial nerve to round window).ConclusionThe part of pictorial review describes the application of high-resolution computed tomography, especially the use of MPR and VR technology, to the investigation and pre-operative grading of the congenital aural atresia. The part of middle ear measurements presents the three anatomic variants of the sinus tympani encountered in CAA patients with congenital malformation of the middle ear. Malformations of the boot-shaped sinus tympani are often found in association with facial nerve anterior dislocation anomalies. The position of the mastoid segment of facial nerve in relation to the extension and volume of the sinus tympani will determine the method of surgical approach. There may be some developmental associations between mastoid segment of facial nerve location and sinus tympani extension. Since the two structures share a common origin as the Reichert cartilage of the second pharyngeal arch, lack of ossification and excessive absorption of mesenchymal were presumed to be the cause of the extension type of sinus tympani found in the CAA patients.