Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Simpo PDF Merge and Split Unregistered Version - http://www.simpopdf.com C. GRACE PETRIKOWSKI isorders of tlJe temporomandibular joint are -that interfere with the normal form or function of the joint. These disorders include dysfunction of the articular disk and associated ligaments and muscles, joint arthritides, inflammatory lesions, neoplasms, and growth or developmental abnormalities. including diagnostic imaging, before commencing treatment. The clinical signs and symptoms of :Otherdisorders of the TMJ may include swelling in and around the joint, an elevated temperature, and rednessof the overlying skin. Clinical Features 'Iemporomandibular joint ('I'MJ) dysfunction is the most common jaw disorder, with 28% to 86% of adults and adolescentsshowing one or more clinical signs or symptoms,A higher incidence of the disorder has been reported in females, although the reason for this preponderance is not clear. Signs and symptoms of dysfunction may include one or more of the following: pain in the TMJ or ear or both, headache, muscle tenderness,joint stiffness, clicking or other joint noises, reduced range of motion, locking, and subluxation. In most casesthe clinical signs and symptoms are transitory, and treatment is not indicated. However, a small percentage of patients (5%) suffer severe dysfunction (e.g., severe pain, marked functional impairment, or both), which requires a thorough diagnostic workup, ~jl5 ""UY"'Y TMJ imaging may be necessaryto supplement information obtained from the clinical examination, particularly when an osseous abnormality or infection is suspected,conservative treatment has failed, or symptoms are worsening. Diagnostic imaging also should be considered for patients with a history of trauma, significant dysfunction, alteration in range of motion, sensory or motor abnormalities, or significant changes in occlusion. TMJ imaging is not indicated for joint sounds if other signs or symptoms are absent or for asymptomatic children and adolescentsbefore orthodontic treatment. The purposes of TMJ imaging are to evaluate the integrity and relationships of the hard and soft tissues,confirm the extent or stage of progression CHAPTER 25 DIAGNOSTIC IMAGING OF THE TEMPOROMANDIBULAR 539 JOINT Simpo PDF Merge and Split Unregistered Version - http://www.simpopdf.com importance of understanding the range of normal appearance. The extreme aspects of,the condyle are called the medialpoleand lateralpoles.The long axis of the condyle is slightly rotated on the condylar neck such that the medial pole is angled posteriorly, forming an angle of 15 to 33 degrees with the sagittal plane. The two condylar axes typically intersect near the anterior border of the foramen magnum in the submentovertex projection. Most condyles have a pronounced ridge oriented mediolaterally on the anterior surface, marking the anteroinferior limit of the articulating area. This ridge is the upper limit of the pterygoid fovea,a small depression on the anterior surface at the junction of the condyle and neck. It is the attachment site of the superior head of the lateral pterygoid muscle and should not be mistaken for an osteophyte (spur), which indicates degenerative joint disease. Although the mandibular and temporal components of the TMJ are calcified by 6 months of age, complete calcification of cortical borders may not be completed until 20 years of age. As a result, radiographs of condyles in children may show little or no evidence of a cortical border. In the absence of disease,the cortical borders in adults are visible radiographically. A layer of fibrocartilage covers the condyle but. is not visible radiographically. of known disease, 'and evaluate the effects of treatment. The clinician must correlate the radiographic information with the patient's history and clinical findings to arrive at a final diagnosis and plan the management of the underlying disease process. . A thorough understanding of the anatomy and morphology of the TMJ is essential so that a normal variant is not mistaken for an abnormality. The TMJs are unique in that although they constitute two separate joints anatomically, they function together as a single unit. Eachcondyle articulates with the mandibular fossa of the temporal bone. A disk composed of fibrocartilage is interposed between the condyle and mandibular fossa. A fibrous capsule lined with synovial membrane surrounds and enclosesthejoint. Ligaments and muscles restrict or allow movement of the condyle. CONDYLE The condyle is a bony, ellipsoid structure connected to the mandibular ramus by a narrow neck (Fig. 25-1). The condyle is approximately 20 mm long mediolaterally and 8 to 10mm thick anteroposteriorly. The shape of the condyle varies considerably; the superior aspect may be flattened, rounded, or markedly convex, whereas the mediolateral contour usually is slightly convex. These variations in shape may cause difficulty with radiographic interpretation; this underlines the A FIG. 25-1 MANDIBULAR FOSSA The glenoid (mandibular) fossa is located at the inferior aspectof the squamous part of the temporal bone and is composed of the glenoid fossaand articular eminence of the temporal bone (Fig. 25-2, A). It is some- B Mandibular condyle. The medial pole (arrow) is on the right in each case. A, Anterior aspect. B, Superior aspect. PART V 540 RADIOGRAPHIC INTERPRETATION OF PATHOLOGY Simpo PDF Merge and Split Unregistered Version - http://www.simpopdf.com ~ FIG. 25-2 A, Basal view of the skull showing the mandibular fossa. AE, Articular eminence; A7; articular tubercle; CC, carotid canal; EAM, external auditory meatus; Mf; mandibular fossa; Sf; squamotympanic fissure; ZA, zygomatic arch. B, Pneumatization of the articular eminence with a mastoid air cell (panoramic view) (arrow). (B, Courtesy Dr. D. Tyndall and Dr. S.R. Matteson, Chapel Hill, N.C.) times described as the temporalcomponentof the 'I'MJ. The articular eminence forms the anterior limit of the glenoid fossa and is convex in shape. Its most inferior aspectis called the summitor apexof the eminence. In a normal TMJ, the roof of the fossa,the posterior slope of the articular eminence, and the eminence itself form an S shape when viewed in the sagittal plane. The most lateral aspect of the eminence consists of a protuberance,called the articular tubercle, which is a ligamentous attachment. The squamotympanic fissure and its medial extension, the petrotympanic fissure, form the posterior limit of the fossa.The middle portion of the roof of the fossa forms a small portion of the floor of the middle cranial fossa,and only a thin layer of cortical bone separates the joint cavity from the intracranial subdural space. The spine of the sphenoid forms the medial limit of the fossa. Fossa depth varies, and the development of the articular eminence relies on functional stimulus from the condyle. For example, the mandibular fossa is very flat and underdeveloped in patients with micrognathia or condylar agenesis.The fossaand articular eminence develop during the first 3 years and reach mature shape by the age of 4 years; young infants lack a definite fossa and articular eminence. All aspectsof the temporal component may be pneumatized with small air cells derived from the mastoid air cell complex (Fig. 25-2, B). Pneumatization of the articular eminence is seen radiographically in approximately 2% of patients. Like the condyle, the mandibular fossa is covered with a thin layer of fibrocartilage. INTERARTICULAR DISK The interarticular disk (meniscus), composed of fibrous connective tissue,is located between the condylar head and mandibular fossa. The disk divides the joint cavity into two compartments, called the inferior (lower) and superior (upper) joint spaces,which are located below and above the disk, respectively (Fig. 25-3). A normal disk has a biconcave shape with a thick anterior band, thicker posterior band, and a thin middle part. The disk also is thicker medially than laterally. The medial and lateral margins of the disk blend with the capsule. The thin central portion normally serves as an articulating cushion between the condyle and articular eminence. The anterior band is thought to be attached to the superior head of the lateral pterygoid muscle, and the posterior band attachesto the posterior retrodiskal tissues (also called the posterior attachment).The junction between the posterior band and posterior attachment usually lies within 10 degrees of vertical above the condylar head. The disk and posterior attachment are collectively called the softtissue componentofthe TMJ During mandibular opening, as the condyle translates downward and forward, the disk, also moves :J CHAPTER 25 DIAGNOSTIC IMAGING OF THE TEMPOROMANDIBULAR 541 JOINT Simpo PDF Merge and Split Unregistered Version - http://www.simpopdf.com . Joint space { Synovial membrane Superior, I Inferior \ / Interarticular disk, LaterC11 I pterygoi;:: , Superiorbelly. muscle Inferiorbelly- l . c~nective Articular surfaces, Articular eminence ~ Superior lamina } -posterior tissue attachment " Synovial membrane A Middle cranial '"'~~_/ Inferior Articular surfaces- / jJOlnt space Interarticula r disk _Articular eminence Mandibular condyle Lateral capsular wall Medial collateral ligament' Medial capsular c FIG. 25-3 TMj anatomy. A, Lateral view. B, Sectioned cadaver specimen In the same orientation. Af, Articular eminence; /0, interarticular disk; LPM,lateral pterygoid muscle; MC, mandibular condyle; PA,posterior attachment. C, Coronal view. (Courtesy Dr. W.K. Solberg, Los Angeles, Calif.) forward and rotates so that its thin central portion remains between the articulating convexities of the condylar head and articular eminence. Laterally and medially, the disk attaches to the condylar poles, helping to ensure passivemovement of the disk with the condyle so that the condyle and disk translate forward together to the summit of the articular eminence. As the mandible opens, the condyle also rotates against the lower surface of the disk in the inferior joint space.On mandibular closing, this process reverses,with the disk moving back with the condyle into the mandibular fossa. superior lamina stretches and allows the dISk to move forward with condylar translation. The inferior lamina attaches to the posterior surface of the condyle. The posterior attachment is covered with a synovial mem.brane that secretessynovial fluid, which lubricates thejoint. As the condyle moves forward, tissuesof the posterior attachment expand in volume, primarily as a result of venous distention, and as the disk moves forward, tension is produced in the elastic posterior attachment. This tension is thought to be responsible for the smooth recoil of the disk posteriorly as the mandible closes. POSTERIOR ATTACHMENT TMJ BONY RELATION5HIPS (RETRODISKAl TISSUES) The posterior attachment consistsof a bilaminar zone of vascularizedand innervated loose fibroelastic tissue. The superior lamina, which is rich in elastin, inserts into the posterior wall of the mandibular fossa. The RadiograPhicjoint spaceis a general term used to describe the radiolucent area between the condyle and temporal component (see Fig. 25-3). This general term should not be confused with the terms suPerior joint spaceand inferiorjoint spacedescribed earlier, which refer 542 PART V RADIOGRAPHIC INTERPRETATION OF PATHOLOGY Simpo PDF Merge and Split Unregistered Version - http://www.simpopdf.com to soft tissuespacesabove and below the disk. The radiographic joint space contains the soft tissue components of the joint. The left and right condylar positions within the fossa can be determined and compared by the dimensions of the radiographic joint spaceviewed on corrected lateral tomographs. A condyle is positioned concentrically when the anterior and posterior aspectsof the radiolucent joint space are uniform in width. The condyle is retruded when the posterior joint spacewidth is less than the anterior (Fig. 25-4) and protruded when the posterior joint spaceis wider than the anterior. . The diagnostic significance of mild or moderate condylar eccentricity is not clear; condylar eccentricity is seen in one third to one half of asymptomatic individuals and is not a reliable indicator of the soft tissue statusof the joint, particularly because the shape of the condylar head is not concentric to the shape of the fossa. Markedly eccentric condylar positioning usually represents an abnormality. For example, inferior condylar positioning (widened joint space) may be seen in casesinvolving fluid or blood within the joint, and superior condylar positioning (decreased joint space or no joint space, with osseous contact of joint components) may indicate loss,.displacement, or perforation of intracapsular soft tissue components. Marked posterior condylar positioning is seen in some casesof disk displacement, and marked anterior condylar positioning may be seen in juvenile rheumatoid arthritis. CONDYLAR MOVEMENT The condyle undergoes complex movement during mandibular opening. Downward and forward translation (sliding) of the condyle occurs, whereby the A superior surface of the disk slides against the articular eminence; at the same time a hingelike, rotatory movement occurs with the superior surfac~ of the condyle against the inferior surface of the disk. The extent of normal condylar translation varies considerably. In most individuals, at maximal opening the condyle moves down and forward to the summit of the articular eminence or slightly anterior to it (see Fig. 25-4). The condyle typically is found within a range of 2 to -5mm posterior and 5 to 8mm anterior to the crest of the eminence. Reduced condylar translation, in which the condyle has little or no downward and f{)rward movement and does not leave the mandibular fossa,is seen in patients who clinically have a reduced degree of mouth opening. Hypermobility of the joint may be suspected if the condyle translates more than 5 mm anterior to the eminence. This may permit anterior locking or dislocation of the condyle if a superior movement also occurs above and anterior to the summit of the articular eminence. The type of imaging technique selecteddepends on the specific clinical problem, whether imaging of hard or soft tissuesis desired, the amount of diagnostic information available from a particular imaging modality, the cost of the examination, and the radiation dose. In most casesthe imaging protocol begins with hard tissue imaging to evaluate the osseouscontours, the positional relationship of the condyle and fossa,and the range of motion, although a combination of imaging techniques may be indicated. Soft tissue imaging is indicated when information about disk position, morphology, or integrity is needed or to image abnormalities in the ~ \,; FIG. 25-4 Corrected lateral (sagittal) tomograms. A represents a lateral image slice, and B represents a medial image slice of the same joint. Notice that the condyle appears centered in the lateral image and retruded in the medial image. C, Open view showing the degree of condyle translation during mandibular opening. rl """ CHAPTER 25 DIAGNOSTIC IMAGING OF THE TEMPOROMANDIBULAR 543 JOINT Simpo PDF Merge and Split Unregistered Version - http://www.simpopdf.com FIG. 25-5 Panoramic view. The right condyle is smaller than the left and is not smoothly corticated. Tomograms later showed marked erosive changes of the right condylar head. muscles or surrounding tissues.A summary of the diagnostic information provided by eachimaging technique is presented in Table 25-1. HARD TISSUE IMAGING Panoramic Projection Becausethe panoramic projection provides an overall view of the teeth and jaws, it servesas a screening projection to identify odontogenic diseasesand other disorders that may be the source of TMJ symptoms,Some panoramic machines'have specific TMJ programs, but these are of limited usefulness becauseof thick image layers and the oblique, distorted view of the joint they provide, which severely limits image quality, Gross osseouschangesin the condyles maybe identified, such as asymmetries,extensive erosions, large osteophytes, or fractures (Fig. 25-5). However,no information about condylar position or function is provided because the mandible is partly opened and protruded when this radiograph is exposed,Also, mild osseouschanges may be obscured,and only marked changes in articular eminence morphology can be seen as a result of superimposition by the skull baseand zygomatic arch. For these reasons,the panoramic view does not provide an adequate examination of the hard tissuesof the joints. Transcranial Projection The transcranial projection provides a sagittal view of the lateral aspectsof the condyle and temporal component. The patient is positioned in a cephalostat; the x-ray beam is directed downward from the opposite side, through the cranium and above the petrous ridge of the temporal bone, at a 25-degreepositive angle centered through thejoint. The horizontal direction of the beam mav be individually corrected for the condylar long axis (see Conventional Tomography, Chapter 13), an average 20-degree anterior angle may be used. The film cassetteis placed on the side to be imaged (Fig. 256). A routine transcranial seriesincludes projections of both TMJs in the closed and maximally open positions (Fig. 25-7). Becauseof the positive beam angulation, the central and medial aspectsof the joint are projected inferiorly, and only lateral joint contours are visible in this pro- \ / A A 250 to \ 'f--:::::=:~-=-"~ \ B ',~200 FIG. 25-6 Transcranial projection. A, The central ray is oriented at a 25-degree positive angle from the opposite side (8) and anteriorly 20 degrees, centered over the TM] of interest. ,+, , 544 PART V RADIOGRAPHIC INTERPRETATION OF PATHOLOGY Simpo PDF Merge and Split Unregistered Version - http://www.simpopdf.com IMAGING TECHNIQUE* Arthridites + ++ Developmental abnormalities -1-t- Trauma (fracture) Asymmetry -to + + " + + ++ + -t- 1-1+ -t-t- -t-t- -to + + ++ T "t- Soft Tissue Disk perforation joint effusion JOintspace calcifications Modified from Brooks SL et al: Imaging of the temporomandibular joint, position paper ot the American Acatlemy ot Ural anti Maxiliotacial KatllOlogy, Ural :)urg Oral Pathol Oral Radiol Endod 83:609,1997. *-, Does not provide diagnostic information for the abnormality; +, only occasionally useful; ++, often useful; +++, almost always useful. tWhen including arthrocentesis. jection. l'he Ipsl1ateralpetrous ndge otten ISsupenmposed over the condylar neck, which may obscure osseouschanges in the condyle or temporal component. The image of the condyle, temporal component, and joint space is distorted, and condylar position cannot be reliably determined, particularly if the horizontal beam angle is not individualized for each patient. The transcranial projection is useful for identifying grossosseouschanges on the lateral aspectof the joint only, displaced condylar fractures, and range of motion (open views). degrees trom the anterior (Yig. ~5-~); the hIm cassette is placed on the side being imaged. The patient opens the mouth maximally to avoid superimposition of the condyle on the temporal component. Because of the negative beam angulation, this view depicts the medial aspect of the condyle. The transpharyngeal view provides limited diagnostic information because the temporal component is not imaged well (Fig. 25-9). The transpharyngeal projection is effective for visualizing erosive changesof the condyle rather than more subtle changes. Transpharyngeal (parma) t'rO)ectlon The transpharyngeal (Parma) projection provides a sagittal view of the medial pole of the condyle. The xray beam is directed superiorly at -5 degrees through the sigmoid notch of the opposite side and 7 to 8 Transorbital Projection The transorbital projection is similar to the transmaxillary projection in that both provide an anterior view of the TMJ, perpendicular to transcranial and transpharyngeal projections. In the transorbital view, the CHAPTER 25 DIAGNOSTIC IMAGING OF THE TEMPOROMANDIBULAR 545 JOINT Simpo PDF Merge and Split Unregistered Version - http://www.simpopdf.com IMAGING TECHNIQUE* SKULLVIEWS CONVENTIONAL COMPUTED TOMOGRAPHY TOMOGRAPHY MAGNETIC ARTHROGRAPHY RESONANCE IMAGING ++ +t+ +++ + ++- +1-+ + ++ ++ +++ ++ -++ ++ + +t+ c+++ ++ Tt+ patient's head is tilted downward 10 degreesso that the canthomeatalline is horizontal (Fig. 25-10). The x-ray beam is directed from the front of the patient through the ipsilateral orbit and TMJ of interest. The film cassette is placed behind the patient's head, perpendicular to the x-ray beam. The patient opens maximally or, as an alternative, protrudes the mandible, thereby positioning the condyle at the summit of the articular eminence and avoiding superimposition of the articular eminence or skull base on the condyle. The entire mediolateral dimension of the articular eminence, condylar head, and condylar neck is visible, which makes this view particularly useful for visualizing condylar neck fractures. The morphology of the convex surface of the condylar head can be evaluated,making this projection a useful adjunct to transcranial and transpharyngeal projections in the diagnosis of gross +++ Ii + degenerative changes or other anomalies (Fig. 25-11). The usefulnessof this projection is limited by the ability of the condyle to move to the summit of the articular eminence. If condylar motion is limited, only the condylar neck is visible becauseareasof the joint articulating surfaces are obscured by superimposition of the temporal component on the condylar head. A similar projection is the reverse open Towne's projection, which sometimes is used to image condylar neck fractures, particularly if medial displacement has occurred, because the condylar head and neck are visualized in the frontal plane. Submentovertex (Basal) Projection The submentovertex (SMV) projection provides a view of the skull base and condyles superimposed on the condylar necks and mandibular rami. For this reason PART V 546 RADIOGRAPHIC INTERPRETATION OF PATHOLOGY Simpo PDF Merge and Split Unregistered Version - http://www.simpopdf.com B FIG. 25-7 Transcranial projections of the left TM). The profile of the lateral aspect of the condylar head is indicated by an arrow. Note the degree of translatory movement between the closed view (A) and the open view (8). FIG. 25-8 Transpharyngeal projection. A, The central ray is oriented superiorly 5 to 10 degrees and (8) posteriorly approximately 10 degrees, centered over the TMJ of interest. Note that the mandible is positioned at maximal opening. the SMV projection often is used to determine the angulations of the long axis of the condylar head for corrected tomography (see Chapter 11 for technique). This view may be used as an adjunct to views depicting the TMJs in the lateral plane and is particularly useful for evaluating facial asymmetries, condylar displacement, or rotation of the mandible in the hori- FIG. 25-9 Transpharyngeal projection showing the condyle at the articular eminence. The zygomatic arch is superimposed over the glenoid fossa. zontal plane associated with trauma or orthognathic surgery. Conventional Tomography Tomography is a radiographic technique that produces multiple thin image slices, permitting visualization of an anatomic structure essentially free of superimpositions of overlapping structures (see Chapter 13). Because this technique can provide multiple image r ~: ~ ~ CHAPTER Z.5 UIAI.JNU:' IlL IMAI.JINI.J Ut ..MI: II:Mt'UKUMAI"U'DULAK :>4/ IUI"" Simpo PDF Merge and Split Unregistered Version - http://www.simpopdf.com \ '\ -.. """'" ~ / '" I-IL.. Z~-l U IranSOrOI1:alproject:lon. I ne cenual ray ISorlemea aownwara apprOXlmal:elY 10 degrees and laterally approximately 30 degrees through the ipsilateral orbit, centered over the TMJ of interest. tiLl. ~3-1 I Irilll~UrUllill VIt:W ~IIUWIIIY lIl~ LUIIUYI~ (arrow) below the articular eminence. The mastoid process partly obscures the articulating surface on the most medial aspect. Sllces at rlgllt allgl~~ UllUUgll UI~ jUllll, II l~ ~Up"llUl lU the transcranial view in depicting true condylar position and revealing osseouschanges. For these reasons, tomography is a valuable adjunct to plain film radiography and can provide information that may not be available with plain films alone. lomograpns typIcallY are exposea ill me sagllIal (lateral) plane with several image slices in the closed (maximal intercuspation) position and usually only one image in the maximal open position. In "corrected" sagittal tomography, the condylar long axis with respect to the midsagittal plane is determined using an SMV projection (Fig. 25-12): The patient's head is then rotated to this angle, permitting alignment of image slices perpendicul,ar to the condylar long axis. This minimizes geometric distortion of the joint and allows accurate assessmentof condylar position. Although a corrected tomographic technique is preferred, when not available,a 20-degreehead rotation toward the side of interest is superior to image slicesparallel to the midsagittal plane. To minimize patient movement in open views, a bite-block may be inserted between the patient's anterior teeth becauseit takes severalseconds to complete each tomographic exposure. It is desirable to supplement this examination with coronal (frontal) tomographs, particularly when morphologic abnormalities or erosive changes of the condylar head are suspected. For coronal tomographs, the patient is in a maximal open or protruded position, which brings the condyle to the summit of the articular eminence, free of superimposition of the posterior slope of the eminence. The entire condylar head is visible in the mediolateral plane (Fig. 25-13). \..ompU1:eo lomograpny Computed tomography (CT) is indicated when more information is needed about the three-dimensional shape and internal structure of the osseous compo- PART V 548 RADIOGRAPHIC INTERPRETATION OF PATHOLOGY Simpo PDF Merge and Split Unregistered Version - http://www.simpopdf.com nents of the joint or if information regarding the surrounding soft tissues is required. CT produces digital image slices (see Chapter 13). Multiple image slicesare made in both the axial and coronal planes, although the coronal imagesare the more useful. Data from axial and coronal scans can be manipulated to produce (reformat) images in the sagittal plane. Threedimensional reformatted images also can be produced. These are useful for assessingosseousdeformities of the jaws or surrounding structures. CT cannot produce accurate images of the articular disk. CT may be considered for determining the'presence and extent of ankylosis and neoplasms and the extent of bone involvement in some arthritides, imaging complex fractures, and evaluating complications from the use of polytetrafluoroethylene or silicon sheet implants such as erosions into the middle cranial fossa and heterotopic bone growth. SOFT TISSUE IMAGING FIG. 25-12 SMV projection. Tracing of angles between the long axis of each condyle and the midsagittal plane. For tomographic views the patient is rotated according to the measured angles to produce an undistorted radiographic view of each TM). FIG. 25-13 lar condyle. Frontal tomographic image of the mandibu- The soft tissuesof the joint can be imaged with magnetic resonance imaging (MRI) or arthrography. Conventional imaging techniques do not demonstrate disk position, morphology, or functiop. Soft tissue imaging is indicated when TMJ pain and dysfunction are present or when the clinical findings suggestdisk displacement along with symptoms that are unresponsive to conservative therapy. MRI and arthrography should be used only when information about the condition of the soft tissue components of the joint is required to formulate a treatment plan. The choice of technique depends on patient factors, such as allergy to contrast agents and claustrophobia, as well as on the cost,availability, and objectives of the imaging technique. Arthrography is superior for diagnosis of small disk perforations and joint adhesions. MRI can indicate a pathologic condition of the soft tissue through altered tissue signal, allowing evaluation of the disk and surrounding muscles, and can image joint effusion. The technique is noninvasive and does not use ionizing radiation. Arthrography with videofluoroscopy provides a superior motion study of the joint, although some MRI techniques can provide limited dynamic information. Arthrography Imaging of the hard tissuesshould be completed before arthrographic imaging is performed. Arthrography is a technique in which an indirect image of the disk is obtained by injecting a radiopaque contrast agent into one or both joint spaces under fluoroscopic guidance (Fig. 25-14). A perforation is detected by the flow of contrast agent into the superior joint space from the CHAPTER 25 DIAGNOSTIC IMAGING OF THE TEMPOROMANDIBULAR JOINT 549 Simpo PDF Merge and Split Unregistered Version - http://www.simpopdf.com a A FIG. 25-14 A and B, Arthrographs in which both the lower and upper joint spaces have been injected with contrast media (spaces appear white) that highlights the disc (black). In both images the anterior aspect of the patient is on the left side of the image. In A the posterior band (white arrow) and the anterior band (black arrow) are evident. B reveals a disc with an enlarged posterior band (arrow). lower space,and adhesions are detected by the manner in which contrast agent fills the joint space.Mter both spacesare filled, disk function is studied using fluoroscopy during open and closing movements. The fluoroscopic study usually is supplemented with tomographs of the joint. Arthrography is indicated when information about disk position, function, morphology, and the integrity of diskal attachments is required for treatment planning. The risks of this procedure include allergic reactio~nto the nonionic iodine contrast agent and infection. Draw- backs of this procedure are its invasive nature and its association with postoperative discomfort. Magnetic Resonance Imaging MRI uses a magnetic field and radiofrequency pulses rather than ionizing radiation to produce multiple digital image slice~ (see Chapter 13). BecauseMRI can provide superb imagesof soft tissues,this technique can be used for imaging the articular disk. MRI allows construction of images in the sagittal and coronal planes without repositioning the patient (Fig. 25-15). These DC FIG. 25-15 MRI of a normal TM!. A, Closed view showing the condyle and temporal component. The biconcave disk is located with its posterior band (arrow) over the condyle. B, Coronal image showing the osseous components and disk (arrows) superior to the condyle. (Courtesy Dr. Per-Lennart Westesson, Rochester, N.Y.) 550 PART V RADIOGRAPHIC INTERPRETATION Simpo PDF Merge and Split Unregistered Version - http://www.simpopdf.com images usually are acquired in open and closed mandibular positions using surface coils to improve image resolution. Sagittal slicesshould be oriented perpendicular to the condylar long axis. The examinations usually are performed using Tl-weighted, protonweighted, or T2-weighted pulse sequences.Tl-we'ighted or proton-weighted images best demonstrate osseous and diskal tissues,whereas T2-weighted images demonstrate inflammation and joint effusion. Motion MRI studies durin~ opening and closing can be obtained by having. the patient open in a seriesof stepped distances and using rapid image acquisition. ("fast scan") techniques. Medial disk displacements are best detected using MRI. The change in tissue signal that results from tissue changes in the disk and retrodiskal tissue may make accurate identification of the disk difficult. MRI does not have the morbidity associatedwith the introduction of needles into the joint (as occurs in arthrography), but MRI is a more expensive examination and is contraindicated in patients who are pregnant or who have pacemakers, intracranial vascular clips, or metal particles in vital structures. Some patients may not be able to tolerate the procedure because of claustrophobia or an inability to remain motionless. Radiographic of the TMJ Abnormalities DEVELOPMENTAL ABNORMALITIES Developmental abnormalities may be broadly categorized as anomalies in the form and size of joint components. The most striking radiographic changes usually are seen in the condyle, although the temporal component also may be deformed, often remodeling to accommodate the abnormal condyle. Condylar articular cartilage is a mandibular growth site, and as a result, developmental abnormalities at this location may manifest as altered growth on the affected side of the condyle, mandibular ramus, mandibular body, and alveolar process on the affected side(s). CONDYLAR HYPERPLASIA Definition Condylar hyperplasia is a developmental abnormality that results in enlargement and occasionally deformity of the condylar head; this may have a secondary effect on the mandibular fossaas it remodels to accommodate the abnormal condyle. The etiology may be overactive cartilage or persistent cartilaginous rests,increasing the thickness of the entire cartilaginous and precartilagi- OF PATHOLOGY nous layers.This condition uslJallyis unilateral and may be accompanied by varying degre~s of hyperplasia of the ipsilateral mandible.' Clinical Features Condylar hyperplasia is more common in males,and it usually is discovered before the age of 20 years. The condition is self-limiting and tends to arrest with termination of skeletal growth, although in a small number of casescontinued growth and adult onsethave been reported. The condition may progress slowly or rapidly. PatientS have a mandibular asymmetry that varies in severity,depending on the degree of condylar enlargement. The chin may be deviated to the unaffected side, or it may remain unchanged but with an increase in the vertical dimension of the ramus, mandibular body, or alveolar process of the affected side. As a result of this growth pattern, patients may have a posterior open bite on the affected side. Patients may also have symptomsrelated to TMJ dysfunction and may complain of limited or deviated mandibular opening or both caused by restricted mobility of the enlarged condyle. Radiographic Features The condyle may appear relatively normal but symmetrically enlarged, or it may be altered in shape (e.g., conical, spherical, elongated, lobulated) or irregular in outline. It maybe more radiopaque becauseof the additional bone present. A morphologic variation manifesting as elongation of the condylar head and neck with a compensating forward bend, forming an inverted L, may be seen. Also, the condylar neck may be elongated and thickened and may bend laterally when viewed in the coronal (anteroposterior) plane (Fig. 25-16). The cortical thickness and trabecular pattern of the enlarged condyle usually are normal, which helps to distinguish this condition from a condylar neoplasm. The glenoid fossa may be enlarged, usually at the expense of the posterior slope of the articular eminence. The ramus and mandibular body on the affected side also may be enlarged, resulting in a characteristic depression of the inferior mandibular border at the midline, where the enlarged sidejoins the contralateral normal mandible. The affected ramus may have increased vertical depth and may be thicker in the anteroposterior dimension. Differential Diagnosis A condylar tumor, most notably an osteochondroma, is included in the differential diagnosis. An osteochondroma usually is more irregular in shapecompared with a hyperplastic condyle. Surface irregularities and continued growth after cessationof skeletal growth should CHAPTER 25 DIAGNOSTIC IMAGING OF THE TEMPOROMANDIBULAR JOINT 551 Simpo PDF Merge and Split Unregistered Version - http://www.simpopdf.com increase suspicion of this tumor. Occasionally a condylar osteoma or large osteophyte that occurs in chronic degenerative joint disease may simulate condylar hyperplasia. Treatment Treatment consisting of orthodontics combined with orthognathic surgery ideally should be attempted after condylar growth is complete. Determining when condylar growth has stopped may be difficult; imaging may include longitudinal radiographic studies to assessthe dimensions of the condyle and mandible, nuclear imaging techniques, 'or both. A lack of unusual bone activity, demonstrated in a technetium bone scan, is a useful indication of arrested condylar growth. PART V 552 RADIOGRAPHIC INTERPRETATION OF PATHOLOG' Simpo PDF Merge and Split Unregistered Version - http://www.simpopdf.com CONDYLAR HYPOPLASIA Definition Condylar hypoplasia is failure of the condyle to attain normal size because of congenital and developmental abnormalities or acquired diseasesthat affect condylar growth. The condyle is small, but condylar morphology usually is normal. The condition may be inherited or may appear spontaneously. Some caseshave been attributed to early injury or injury to the articular cartilage by birth trauma or intraarticular inflammatory lesions.. Clinical Features Condylar hypoplasia usually is a component of a mandibular growth deficiency and therefore often is associated with an underdeveloped ramus and (occasionally) mandibular body. Congenital abnormalities may be unilateral or bilateral and usually are manifestations of a more generalized condition (e.g., micrognathia, Treacher Collins syndrome); they also may be associatedwith congenital defects of the ear and zygomatic arch. Developmental abnormalities that manifest during growth usually are unilateral. Acquired abnormalities are the result of damage during the growth period from sources such as therapeutic radiation or infection that diminish or prevent further condylar growth and development. Patients with condylar hypoplasia have ~andibular asymmetry and may have symptoms of TMJ dysfunction. The chin commonly is deviated to the affected side, and the mandible deviates to the affected side during mandibular opening. Degenerative joint disease is a common long-term Radiographic Features The condyle may be normal in shap~ and structure but is diminished in size, and the mandibular fossa also is proportionally small. The condylar neck and coronoid process usually are very slender and in some casesare shprtened or elongated. The posterior border of the ramus and condylar neck may have a dorsal (posterior) inclination. The ramus and mandibular body on the affected side may also be small, resulting in a mandibular asymmetryand occasional dental crowding, depending on the severity of mandibular underdevelopment. The antegonial notch is deepened. The associated mandibular hypoplasia is more pronounced if the effect takes place early in life (Fig. 25-17). Differential Diagnosis Condylar destruction from juvenile rheumatoid arthritis may appear similar to that of hypoplasia. A surveyof other joints or testing for rheumatoid factor may be helpful. Changes in condylar morphology in severe degenerative joint diseaseor other arthritic conditions may have a similar appearance, although arthritic disease does not cause mandibular hypoplasia of the affected side unless it occurs during growth and other signs of arthritis are usually visible in the affected joint. Ireatment Orthognathic surgery, bone grafts, and orthodontic therapy may be required. JUVENILE ARTHROSIS Synonyms Boering's arthrosis and arthrosis deformans juvenilis sequela. FIG. 25-17 A panoramic film revealing hypoplasia ot the left condyle. In tnlS case tne hypoplasia is restricted to the condylar head and neck with minimum involvement of the mandibular ramus and body. r"APTI=g 7~ nIAr:"'{)~Tlr '~AAr:I'-Ir: nl: TWI: TFMPnRnMANDIBLJLAR ""~ IOINT Simpo PDF Merge and Split Unregistered Version - http://www.simpopdf.com Definition juvenile arthrosis, a condylar growth disturbance first described by Boering, manifests as hypoplasia and characteristic morphologic abnormalities. This condition may be a form of condylar hypoplasia but is thought to differ in that the affected condyle at one time ,was normal and became abnormal during growth. juvenile arthrosis may be unilateral or bilateral, and it predisDoses the TMT to secondary degenerative changes. Clinical Featur.esjuvenile arthrosis affects children and adolescents during the period of mandibular growth. It is more common in females. It may be an incidental finding in a panoramic projection, or the patient may have mandibular asymmetry, signs and symptoms of TMj dvsfunction. or both. Radiographic Features The condylar head develops a characteristic "toadstool" appearance, with marked flattening and apparent elongation of the articulating condylar surface and dorsal (posterior) inclination of the condyle and neck. The condylar neck is shortened or even absent in some cases, with the condyle resting on the upper margin of the ramus (Fig. 25-18). The articulating surface of the temporal component often is flattened. Progressive shortening of the ramus occurs on the affected side, and the antegonial notch may be deepened, indicating mandibular hypoplasia. In longstanding cases, superimposed degenerative changes may be present. Differential Diagnosis The radiographic appearance of juvenile arthrosis may be very similar to, and in some casesis indistinguish- able from, developmental hypoplasia of the condyle. Destruction of the anterior aspectof the condylar head from rheumatoid arthritis and severedegenerativejoint disease or severe condylar degeneration after orthognathic surgery or joint surgery also may simulate juvenilp ~rthrn~i~ Treatment Orthognathic surgery and orthodontic therapy may be required to correct the mandibular asymmetry.Caution should be exercised in undertaking orthodontic therapy becausestresson the joint may result in, further degeneration and orthodontic relapse. CORONOID HYPERPLASIA Definition Coronoid processhyperplasia maybe acquired or developmental, resulting in elongation of the coronoid process. In the developmental variant, the condition usually is bilateral. Acquired types may be unilateral or bilateral and usually are a response to restricted condylar movement caused by abnormalities such as ankvlosis. Clinical Features Bilateral developmental coronoid hyperplasia is more common in males, often commencing at the onset of puberty, although the condition was reported in a 3year-olc;i.Patients complain of a progressive inability to open the mouth and may have an apparent closed lock. The condition is painless. Radiographic Features Coronoid hyperplasia is best seen in panoramic, Waters', and lateral tomographic views and on CT FIG. 25-18 Juvenile arthrosis. The condylar heads have a "toadstool" appearance and are posteriorly inclined. The condylar necks are absent. 554 PART V RADIOGRAI?HIC INTERI?RETATION OF I?ATHOLOGY Simpo PDF Merge and Split Unregistered Version - http://www.simpopdf.com scans.The coronoid processesare elongated, and the tips extend at least 1 cm above the inferior rim of the zygomatic arch (Fig. 25-19). As a result, the coronoid processesmay impinge on the medial surface of the zygomatic arch during opening, restricting condylar translation. The coronoid processesmay have a large but normal shape or may curve anteriorly and may appear very radiopaque. The posterior surface of the zygomatic processof the maxilla may be remodeled to accommodate the enlarged coronoid process during function. The radiographic appearance of the TMJs usually is normal: Differential Diagnosis Unilateral casesshould be differentiated from a tumor of the coronoid process such as an osteochondroma or osteoma. Unlike coronoid hyperplasia, tumors usually have an irregular shape. The differential diagnosis also includes any causeof inability to open, such as soft tissue abnormalities and ankylosis, emphasizing the importance of including the coronoid process in imagesof the TMJs. An axial CT image with the patient in a wide-open position is useful in establishing coronoid interference to opening. Treatment Treatment consistsof osteotomy or surgical removal of the coronoid process and postoperative physiotherapy. BIFID CONDYLE Definition A bifid condyle has a vertical depression, notch, or deep cleft in the center of the condylar head seen in the frontal or sagittal plane or an actual duplication of the condyle, resulting in the appearance of a "double" or "bifid" condylar head. This condition may be unilateral or bilateral. It may result from an obstructed blood -supply or other embryopathy, although a traumatic cause has been postulated as a result of a longitudinal linear fracture of the condyle. Clinical Features Bifid condyle usually is an incidental finding in panoramic views or anteroposterior projections. Some patients have signs and symptoms of temporomandibular dysfunction, including joint noises and pain. Radiographic Features A depression or notch is present on the superior condylar surface,giving the anteroposterior silhouette a heart shape; in more severecasesa duplicate condylar head is present in the mediolateral plane (Fig. 25-20). The mandibular fossa may remodel to accommodate the altered condylar morphology. Differential Diagnosis A slight medial depressioh on the superior condylar surface maybe considered a normal variation; the point at which the depth of the depression signifies a bifid condyle is unclear. The differential diagnosis also includes a vertical fracture through the condylar head. Treatment Treatment is not indicated unless pain or functional impairment is present. Soft Tissue Abnormalities INTERNAL FIG. 25-19 Coronoid hyperplasia (sagittal tomogram). The coronoid process is elongated and extends above the inferior rim of the zygomatic arch (arrow) but otherwise is shaped normally. DERANGEMENTS Definition An internal derangement is an abnormality in the position and sometimes the morphology of the articular disk that may interfere with normal function. The disk most often is displaced in an anterior direction, but it may be displaced anteromedially, medially, or anterolaterally. Lateral and posterior displacements are extremely rare. Some hypothesize that disk displacements may be considered a normal variation based on the frequency of this finding in asymptomatic patients. The cause of internal derangements is unknown, ~ CHAPTER DIAGNOSTIC 25 IMAGING OF THE TEMPOROMANDIBULAR 555 JOINT Simpo PDF Merge and Split Unregistered Version - http://www.simpopdf.com ~ A FIG. 25-20 Bifid condyle. A, Sagittal tomogram showing a deep central notch with duplication of the condylar head (arrows). The glenoid fossa has remodeled (enlarged) to accommodate thecenter abnormal condyle. B, Coronal depression in the of the condylar head. tomogram. Another example. showing a although parafunction, jaw injuries (e.g., dIrect trauma), whiplash injury, and forced opening beyond the normal range have been implicated. Internal derangements can be diagnosed using either arthrography or MR!. In some instances the disk may resume a normal position with respect to the condyle (called redu'ctiona/the disk)during mandibular opening; when the disk remains displaced throughout the entire range of mandibular movement, the term nonreductionis used (Fig. 25-21). A chronically displaced disk may become deformed, losing its normal biconcave shape,and it may become thickened and fibrotic. Possible complications in long-standing chronic disk displacement are degenerative joint disease and per" foration through the disk or (more commonly) the posterior attachment. Clinical Features Disk displacement has been found both in symptomatic patients and in healthy volunteers, suggesting that it may be a normal variant and not necessarilya predisposing factor in TMJ dysfunction. It is not known why some disks remain displaced or why symptoms of pain and dysfunction are not found in all affected patients. Symptomatic patients may have a decreased range of mandibular motion. Internal derangements can be unilateral or bilateral; unilateral casesmay manifest clinically as mandibular deviation to the affected side on opening. Joint noises are common and may manifest as a click as the disk reduces to a normal position during mandibular opening and occasionally as a softer click as the disk becomes dIsplaced agam dUrIng manaIDular closing. Noises may be absent in chronically displaced, nonreducing disks, or crepitus may be heard. Patients may complain of pain in the preauricular region or headaches and may have episodes of closed or open locking of the joint. Patients may have to manipl,llate the mandible to open it fully past an apparent closed lock by applying medially directed pressure to the affected joint or mandible with the hand. Kaoiograpnlc t-eatures The disk cannot be visualized with conventional radiography or tomography; arthrography and MRI are the techniques of choice. Although a retruded condylar position has been associated with disk displacement, condylar position in maximal intercuspation is not a reliable indicator of disk displacement. Likewise,diminished range of motion at maximal opening is not a reliable indication of a nonreducing disk. DISk Displacement Identifying the disk may be difficult in casesof gross deformation of the disk and other soft tissue components. Anterior displacement is the most common disk displacement. When the mandible is in maximal intercuspation, partial or full anterior disk displacement is indicated by anterior location of the posterior band of the disk from the normal position, which is directly superior to the condylar head. The normal articulating surface of the disk (thin intermediate zone) is somewhat anteriorly positioned, and as a re~ult the osseous