Disk Displacement of the Temporomandibular Joint: Sonography Versus MR Imaging

Rüdiger Emshoff 1 Siegfried Jank 1 Stefan Bertram 1 Ansgar Rudisch 2 Gerd Bodner 2 Received July 3, 2001; accepted after revision December 17, 2001. 1 Department of Oral and Maxillo-Facial Surgery, University of Innsbruck, Maximilianstr. 10, A-6020 Innsbruck, Austria. Address correspondence to R. Emshoff. 2 Department of Radiology, University of Innsbruck, Anichstr. 35, A-6020 Innsbruck, Austria. AJR 2002;178:1557 1562 0361 803X/02/1786 1557 American Roentgen Ray Society Disk Displacement of the Temporomandibular Joint: Sonography Versus MR Imaging OBJECTIVE. The purpose of this study was to determine the value of dynamic sonography in the evaluation of internal derangements of a temporomandibular joint (TMJ) during maximal mandibular range of motion. SUBJECTS AND METHODS. Maximal mandibular range of motion was performed during high-resolution sonography of the TMJ in 64 consecutive patients (128 joints; nine males and 55 females; age range, 17 65 years; mean age, 35 years 6 months), all of whom subsequently underwent MR imaging. MR imaging confirmed disk displacement with reduction in 27 joints and disk displacement without reduction in 60 joints of the 128 examined. The high-resolution sonography and MR imaging findings for these 27 and 60 TMJs, respectively, were analyzed. RESULTS. Dynamic high-resolution sonography performed during the maximal range of motion helped to detect 81 instances (93%) of internal derangement, 22 instances (82%) of disk displacement with reduction, and 50 instances (83%) of disk displacement without reduction. There was one false-positive finding for internal derangement. The accuracy of prospective interpretation of high-resolution sonograms of internal derangement, disk displacement with reduction, and disk displacement without reduction was 95%, 92%, and 90%, respectively. CONCLUSION. When real-time images are interpreted by expert radiologists, dynamic sonography performed during maximal mandibular range of motion may provide valuable information about disk displacement of the TMJ. I nternal derangements of the temporomandibular joint (TMJ) are one of the most common forms of temporomandibular disorders. The term internal derangement refers to clinical criteria for classifying TMJ disorders but is generally used to denote an abnormal position of the articular disk relative to the mandibular condyle and the articular eminence. The disorders have been associated with characteristic clinical findings such as pain, joint sounds, and irregular or deviating jaw function [1, 2]. Arthrography and MR imaging are common diagnostic methods for the evaluation of disk displacement. Arthrography as a dynamic investigation technique for the disk condyle relationship has been shown to provide a diagnostic accuracy of 83% when combined with videofluoroscopy [3], whereas MR imaging has a diagnostic accuracy of 95% when coronal and sagittal imaging techniques are combined [4]. However, arthrography is invasive and may be complicated by pain, disk perforation, and allergic reactions; MR imaging poses a problem in terms of clinical availability and cost. Sonography allows dynamic visualization of the soft-tissue structures of the TMJ. Although some reports in the literature discuss the use of sonography in the diagnosis of disk displacements [5 7], little attention has been directed toward the types of internal derangements. The purpose of this study was to describe the technique of high-resolution sonographic evaluation of an internal derangement and to discuss the reliability of the sonographic findings. Subjects and Methods From June 2000 to March 2001, 64 consecutive patients with symptoms of TMJ internal derangement were referred for MR imaging of the TMJ. There were 55 females and nine males whose ages AJR:178, June 2002 1557

Emshoff et al. ranged from 17 to 65 years (mean age, 35 years 6 months). High-resolution sonography was performed immediately after MR imaging. The findings on sonography and MR imaging in these 64 patients (128 joints) were analyzed. All sonograms were obtained and interpreted prospectively by a radiologist who had no knowledge of the results of the MR imaging. Sonography was performed using a 12-MHz linear array transducer on an HDI 5000 scanner (Advanced Technology Laboratories, Bothell, WA). Dynamic imaging for the full range of motion in the mandibular opening was used to evaluate the presence or absence of disk displacement at closed-mouth and maximal open-mouth positions. The orientation of the scanning was based on a standardized protocol to obtain cross-sections intersecting the anterosuperior joint compartment in a sagittal-to-frontal plane. With the patient in a supine position, we placed the transducer over the TMJ, parallel to the long axis of mandibular ramus. The transducer was tilted until the optimal visualization was obtained (Fig. 1). On the sonograms, the disk is visualized as a thin homogeneous, hypoto-isoechoic band lying adjacent to the inferior relation (overlying the mandibular condyle). The bony landmarks of the mandibular condyle and the articular eminence are visualized as hyperdense lines. We identified the course of the disk s motion by having the patient slightly move the mandible. We found that during the dynamic evaluation, the sonographic beam must be kept in exactly the same orientation to the diskal surface to avoid artifactual changes in diskal echogenicity. Scanning 60 or more off the plane perpendicular to the long axis of the disk leads to nonvisualization of the disk. Scanning parallel to the joint space is of limited use because a lack of bony landmarks makes orientation difficult. However, once the disk is localized in a sagittal or coronal direction, the transducer is tilted perpendicular to the joint to determine the position of the disk in the sagittal direction. In evaluating findings of the closed mouth, we considered the position of the disk to be normal if the intermediate zone of the disk was located between the anterosuperior aspect of the condyle and the posteroinferior aspect of the articular eminence. Disks with the intermediate zone located anterior to this position were considered displaced. In evaluating findings of the open mouth, the position of the disk was considered normal if the intermediate zone of the disk was located between the condyle and the articular eminence of the condyle (Fig. 1). At the time of MR imaging, the diagnosis of disk displacement was made by a second radiologist. MR imaging was performed with a 1.5-T MR scanner (Vision; Siemens, Erlangen, Germany) and a dedicated circular polarized transmit receive TMJ coil. The data were collected on a 252 256 matrix with a field of view of 145 mm, giving a pixel size of 0.60 0.57 mm. With the patient in a supine position, 15 coronal slices and eight parasagittal slices were obtained of the TMJs in each patient using a turbo spin-echo proton density weighted sequence (TR/TE, 2800/15) with thin slices of 3 mm. MR images were corrected to the horizontal angulation of the long axis of the condyle. Each patient received an individual nonferromagnetic intermaxillary device to help in obtaining the different open-mouth positions. Sequential bilateral images were obtained of the closedmouth and the maximal open-mouth positions. The MR images selected for analysis of the disk condyle relationship depicted the disk, condyle, articular eminence, and glenoid fossa. The disk position was considered normal if the posterior band of the disk was located at the 12-o clock or superior position relative to the condyle. Disk displacement was diagnosed in patients in whom the posterior band of the disk was in an anterior, anteromedial, anterolateral, medial, or lateral position relative to the superior part of the condyle [4]. The MR images were interpreted without knowledge of the findings of the other study. Diagnosis of the functional disk condyle relationship was categorized as normal (absence of internal derangement) or as disk displacement with or without reduction. The categorization was based on whether disk displacement was evident in the closed-mouth position and whether the displacement was or was not A associated with an interposition of the disk between the condyle and the articular eminence in the openmouth position [4] (Figs. 2 and 3). Results Dynamic high-resolution sonography revealed 81 internal derangements, all of which were verified on MR imaging. In these 81 TMJs, MR imaging confirmed disk displacement with reduction in 22 cases and disk displacement without reduction in 50 cases. In the six cases in which sonography produced false-negative results, MR imaging revealed a medially displaced disk in the closed-mouth position (Table 1). MR imaging revealed 87 cases of internal derangement: 22 true-positive findings of disk displacement with reduction, five false-negative findings of disk displacement with reduction, 50 true-positive findings of disk displacement without reduction, and 10 false-negative findings of disk displacement without reduction. The sensitivity of MR imaging for detecting disk displacement with reduction in the pres- C B Fig. 1. Drawings illustrate examination and analysis of temporomandibular joint (TMJ) disk position using high-resolution sonography. A, Drawing shows technique of examining TMJ region with sonographic transducer positioned against patient s face overlying zygomatic arch and TMJ. B, Depiction of location of disk intermediate zone relative to condyle (C) and articular eminence (E) at closed-mouth position. Top = anterior, left = superior. C, Depiction of location of disk intermediate zone relative to condyle (C) and articular eminence (E) at maximal open-mouth position. Top = anterior, left = superior. 1558 AJR:178, June 2002

Sonography and MR Imaging of the Temporomandibular Joint A B C Fig. 2. Temporomandibular joint (TMJ) of 32-year-old woman. Diagnosis of disk displacement with reduction was based on MR imaging findings. A, Longitudinal high-resolution sonogram obtained in closed-mouth position shows anterosuperior TMJ compartment and disk (arrows) anterior to condyle (arrowheads). E = articular eminence, D = disk, C = condyle. B, Sagittal MR image obtained in closed-mouth position shows anterosuperior TMJ compartment and disk (arrows) anterior to condyle. C, Longitudinal high-resolution sonogram obtained in maximal open-mouth position shows anterosuperior TMJ compartment and disk (arrows) superior to condyle (arrowheads). E = articular eminence, D = disk, C = condyle. D, Sagittal MR image obtained in maximal open-mouth position shows anterosuperior TMJ compartment and disk (arrows) superior to condyle. ence of a disk displacement with reduction was 82%; in the presence of a normal disk position, sensitivity was 95%. For disk displacement without reduction, sensitivity was 83% in the presence of a disk displacement and 96% in the presence of a normal disk position (Tables 1 and 2). Of TMJ positions diagnosed as disk displacement on high-resolution sonography, MR imaging showed 22 disk displacements with reduction (82%) and 50 disk displacements without reduction (83%). Of the TMJ positions shown on high-resolution sonography as normal disk positions, MR imaging showed that five were disk displacements with reduction (95%) and 10 were disk displacements without reduction (87%) (Tables 1 and 2). The accuracy of prospective interpretation of high-resolution sonograms of internal derangement, disk displacement with reduction, and disk displacement without reduction was 95%, 92%, and 90%, respectively (Table 2). Discussion The close association between symptoms of TMJ internal derangements and disk displacement has been emphasized in the literature. AJR:178, June 2002 Symptoms of TMJ internal derangements may resolve spontaneously, and conservative treatment with occlusal splints has been successful [8]. However, the disorder is frequently accompanied by severe, persistent pain, and in such cases, surgical repair is advocated. The techniques of arthroscopic lysis and lavage [9], repositioning the displaced disk [10], and diskectomy [11] have been previously described. Arthrography and MR imaging of the soft-tissue components of the TMJ may not be always available. Arthrography is an invasive technique; cost and availability concerns limit the use of MR imaging. Thus, most management approaches for patients with TMJ disorder are symptom-based. For this reason, several studies have been conducted to determine the accuracy of clinical and adjunctive diagnostic tests; the accuracy rates of the tests for TMJ internal derangements have ranged from 43% to 90% [6, 12 15]. Although sonography has been advocated for diagnosis [5], its reliability as an aid in diagnosing disk displacement has not been critically studied. A recent study using static sonography concluded that interpretation by an experienced clinician of properly obtained sonograms has a diagnostic accuracy of D 55%. Differences in interpretations occurred when disk displacements were evaluated separately at different open-mouth positions [6]. Patients in the study who had a prospective diagnosis of TMJ internal derangement then underwent dynamic high-resolution sonographic evaluation (with a 12-MHz probe) during maximal mandibular range of motion. Accuracy for diagnosis of internal derangement, disk displacement with reduction, and disk displacement without reduction based on prospective interpretation of high-resolution sonograms was 95%, 92%, and 90%, respectively. High-resolution sonography allowed greatly improved diagnostic efficacy because of a more defined tissue differentiation and enhanced near-field clarity. Furthermore, the advantage of dynamic high-resolution sonography in investigating the disk condyle relationship during repeated motion at the respective open-mouth positions probably made the structures involved more clearly distinguishable. There are pitfalls in diagnosing disk displacements on the basis of the dynamic high-resolution sonographic findings during maximal mandibular range of motion. If the transducer is not tilted to obtain 1559

Emshoff et al. cross-sections appropriately intersecting the disk in the frontal plane, the disk may become hypoechoic, resulting in a falsenegative diagnosis of displacement. Degeneration or partial rupture of the disk may cause errors in interpretation while the disk is being located and maximal mandibular range of motion is being performed. It is important to scan the entire length of the upper joint compartment both transversely and especially longitudinally to look for the fibrillar pattern of a degenerated disk (Fig. 4). Most disk displacements that were missed on high-resolution sonography were positioned laterally or medially. Sideways and rotational components are difficult to completely evaluate with the current high-resolution sonographic techniques (Fig. 5). The upper TMJ compartment may be filled with fluid or fibrous tissue, especially if the disk has been displaced for a long time. Nearly all false-positive interpretations of disk displacements in our study were caused by synovial effusion simulating anterior disk displacement (Fig. 6). Differentiation on high-resolution sonography between disk displacement and fibrous structures sometimes was impossible (Fig. 7). It is possible that some of the disk displacements diagnosed with high-resolution sonography were not visible to the radiologist on the MR images and that MR imaging is an imperfect standard of reference. In our study, judgments about disk position were made using the sagittal and coronal views. Arthroscopic or surgical confirmation of imaging results was not available for our patients. False-negative and false-positive imaging findings may not be reliably excluded in the absence of surgical confirmation. Studies in which MR imaging findings of the TMJ have been correlated to cryosectional morphology have shown high sensitivity, specificity, and diagnostic accuracy [4]. In addition, surgical confirmation of imaging findings may not be as precise as cryosectional observations because surgery does not provide a cross-sectional view. For these reasons, it seems justifiable to use the MR imaging findings as the gold standard. Observer variations are known to be present in any clinical experience and could substantially influence the process of diagnosis. It seems that, for our institution, the learning curve has leveled off. Although the issue was not a focus of our study, we found little variability among the error rates of the respective 5-month study periods. This finding implies 1560 that the radiologist involved in the sonographic evaluation is at an even level of the learning curve in experience, formal training, and continuing education. Preoperative or intraoperative recognition of an abnormality of the TMJ disk is essential to ensure a beneficial outcome [9, 16]. The results of therapy may be disappointing if disk displacements are overlooked [17 19]. The findings of high-resolution sonography could play an important part in determining patient care. The sonographic findings obtained before surgery may help in the selection of the optimal therapeutic approach. Sonography, despite its limitations, may provide valuable information about disk A B C D Fig. 3. Temporomandibular joint (TMJ) in 27-year-old woman. Diagnosis of disk displacement without reduction was based on MR imaging findings. A, Longitudinal high-resolution sonogram shows anterosuperior TMJ compartment in closed-mouth position and disk (arrows) anterior to condyle (arrowheads). E = articular eminence, D = disk, C = condyle. B, Sagittal MR image shows anterosuperior TMJ compartment in closed-mouth position and disk (arrows) anterior to condyle. C, Longitudinal high-resolution sonogram shows anterosuperior TMJ compartment in maximal open-mouth position and disk (arrows) anterior to condyle (arrowheads). E = articular eminence, D = disk, C = condyle. D, Sagittal MR image shows anterosuperior TMJ compartment in maximal open-mouth position and disk (arrows) anterior to condyle. TABLE 1 Interpretations of High-Resolution Sonographic Findings in 64 Patients (128 Temporomandibular Joints) Findings True-positive True-negative False-negative False-positive Internal Derangement Disk Displacement With Reduction Disk Displacement Without Reduction 81 40 6 1 22 96 5 5 50 65 10 3 AJR:178, June 2002

Sonography and MR Imaging of the Temporomandibular Joint TABLE 2 Reliability of Prospective Diagnoses Based on High-Resolution Sonographic Findings in 64 Patients (128 Temporomandibular Joints) Statistical Values Sensitivity (%; no.) Specificity (%; no.) PPV (%; no.) NPV (%; no.) Accuracy (%; no.) Internal Derangement Disk Displacement With Reduction Disk Displacement Without Reduction 93 (81/87) 98 (40/41) 99 (81/82) 87 (40/46) 95 (121/128) 82 (22/27) 95 (96/101) 82 (22/27) 95 (96/101) 92 (118/128) 83 (50/60) 96 (65/68) 94 (50/53) 87 (65/75) 90 (115/128) Note. High-resolution sonographic findings compared against standard of MR findings. PPV = positive predictive value, NPV = negative predictive value. Fig. 4. Temporomandibular joint (TMJ) in 39-year-old man. Diagnosis of disk displacement and degeneration was based on findings on MR imaging. Interpretation of sonographic findings resulted in falsenegative diagnosis. Longitudinal high-resolution sonogram shows anterosuperior TMJ compartment with disk disrupted in posterior (large arrows) and anterior (small arrows) parts. Anterior part of disk (small arrows) is displaced anteriorly to condyle (arrowheads). E = articular eminence, D = disk, C = condyle. Fig. 6. Temporomandibular joint (TMJ) in 35-year-old woman. MR imaging showed normal disk position with effusion. Interpretation of sonographic findings resulted in false-positive diagnosis. Longitudinal high-resolution sonogram shows anterosuperior TMJ compartment with disk (large arrows) superior to condyle (arrowheads) and presence of effusion (small arrows). E = articular eminence, D = disk, C = condyle, EF = effusion. AJR:178, June 2002 Fig. 5. Temporomandibular joint (TMJ) in 21-year-old woman. Diagnosis of medial disk displacement was based on findings on MR imaging. Interpretation of sonographic findings resulted in false-negative diagnosis. Longitudinal high-resolution sonogram shows anterosuperior TMJ compartment and disk (arrows) superior to condyle (arrowheads). E = articular eminence, D = disk, C = condyle. Fig. 7. Temporomandibular joint (TMJ) in 51-year-old woman. MR imaging showed normal disk position and degeneration. Interpretation of sonographic findings resulted in false-positive diagnosis. Longitudinal high-resolution sonogram shows anterosuperior TMJ compartment with disk (large arrows) superior to condyle (arrowheads) and presence of fibrous structures (small arrows). E = articular eminence, D = disk, C = condyle, F = fibrous structures. 1561

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