The Prescription of Diagnostic Images forTemporomandibular Joint Disorders

Michael J. Pharoah, DDS, MSc,FRCDtC)

Professor and HeadOrai RadiologyFaculty of DentistryUniversity of TorontoToronto, Ontario, Canada

Correspondence to:Dr Michael J, PharoahFaculty of DentistryUniversity of Toronto124 Edward StreetToronto, OntarioW5C 1G6 CanadaFax'416-979-4936Email: michael,pharoah@utoronto.ca

The selection of the appropriate imaging modality for thediagnosis of various disorders of the temporomandibular¡oint (TMJ) can be difficult, due in part to recent develop-

ment of imaging modalities. Practitioners responsible for the diag-nosis and treatment of temporomandibular disorders may not befully aware of the strengths and weakness of each modality; nordoes the profession have the benefit of years of experience in theapplication of these new modalities. For those practitioners whoare not intimately involved with diagnostic imaging of the TMJ,an available set of guidelines concerning the application of diag-nostic imaging to disorders of the TMJ would be useful.

In the absence of clear research and long-term experience withnew imaging modalities, the production of a set of guidelines ischallenging and may ultimately be based on the various experi-ences of the authors. Also, there is a danger inberent in the formu-lation of guidelines. Guidelines may promote a cookbook-likeapproach, which lacks the judgment necessary for rhe prescriptionof imaging based on the merits of each specific case. The applica-tion of imaging to an individual patient should be based on theinformation provided by the clinical features and, in some cases,may be based on something as ethereal as a hunch. In this respect,diagnosis may be more an art than a science. However, the pro-duction of guidelines is a beginning point and can be helpful aslong as these guidelines are never viewed as bemg infallible hut,rather, are open to challenges. Changes should occur with furtheradvances in knowledge, experience, and technology. To date, themost comprehensive document, which does not purport to be a setof guidelines btit instead is a position paper, has been produced bythe American Academy of Oral and Maxillofacial Radiology,'This document provides excellent information about the applica-tion of diagnostic imaging to various diseases and abnormalities ofthe TMJs.

There are many factors that should be considered in attemptingto create a set of guidelines. The cost of each imaging modalityand thus the total financial burden upon society and upon theindividual patient should be considered. Is there a less expensivemethod that can provide the necessary information? The radiationdose may be a consideration, especially in situations where diag-nostic imaging is being employed as a screening tool. Researchfindings indicating the sensitivity and specificity of a particularimaging modality should also be considered. However, these stud-ies often fail to consider the practical overriding parameters, which

Key words: temporomandibular joint imaging, modalities,selection criteria, guidelines

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include the quality of tbe images and the experi-ence and knowledge of those who analyze theimages. The guidelines must have a clear, clinicalapplication. Lastly, the guidelines must be continu-ally tested and cballenged by considering the accu-racy of differing imaging modalities and whetherthe findings were useful in hoth the development oftreatment plans and in treatment outcomes.

Selection Criteria

With this article, 1 would like to take a differentapproach, one that assumes that tbe clinician doesnot know the true nature of the abnormality. Inother words, imaging is required for a diagnosis tobe made. It should be clear that much of the fol-lowing is based on personal experience. The firststep is the development of selection criteria forpatients vifho require diagnostic imaging. A decisionto proceed with imaging should be based on infor-mation obtained from the patient history and fromclinical exammation of the patient. The prescrip-tion of imaging should never be based on a generalroutine. Also, a contraindication is the perceivedneed to estabhsb the absence of disease for medical-legal reasons, for instance, before orthodontic treat-ment is commenced. Attempts to obtain previousfilms of tbe joint should also be made.

Diagnostic imaging may be ordered for the stag-ing of disease. For example, a diagnosis ofosteoarthritis may be clear from rhe clinical infor-mation, but radiographs may be ordered, not toprovide a diagnosis, but to establisb tbe degree ofjoint involvement. This establishes a baseline,whicb is important for future studies to evaluatethe success or failure of the treatment provided.Because of the extreme variation in the normalmorphology of the TMJ, films of both left andright joints should always be taken to provide acomparison. There must he a reasonable anticipa-tion that the information from tbe radiologie examwill aid in establishing an accurate diagnosis andthat this information will infitience the treatmentplan for the patient.

More specifically, the selection criteria shouldinclude clinical evidence of the presence of diseasewitbin the joint. Examples of clinical informationthat suggest the presence of disease witbin theTMJ include:

• Soft tissue swelling over the lateral aspect of thejoint

• Abnormal temperature or color of the skin overthe joint

• Recent changes in mandibular function (eg,decreased opening or deviation on opening)

• Recent changes in the occlusion (eg, develop-ment of an anterior open bite)

• Severe, unrelenting pain within the joint• Recent history of trauma to the joint ot

mandible• Severe restriction in the movement of the

mandible, which suggests ankylosis• Unusual symptoms or pain, which suggest the

presence of a giant cell reaction involving pros-thetic joints

The presence of joint clicking by itself does notrequire diagnostic imaging. Because of the markedprevalence of disc displacement, it is possible thatthis may be considered a variation of normal andnot a true abnormality of the joint. However, ifjoint clicking is accompanied by any of the abovecriteria, diagnostic imaging may be required. Also,when several modalities of treatment have beenapplied and fail, it would be reasonable to proceedwith imaging to confirm the diagnosis.

Imaging Modalities

If one assumes that there is a need for diagnosticimaging, knowledge of the available imagingmodalities is required before the prescription. Forthe purpose of simplification, the list of modalitiesavailable can be divided into those that can be usedfor the assessment of tbe hard tissues (bone com-ponents) and those for soft tissues (articular disc,bilaminar ligament, and surrounding muscles).

As noted below, arthrography or magnetic reso-nance imaging (MRI) can be applied to the evalua-tion of soft tissues. For the evaluation of hard tis-sues, imaging modalities include plain films,tomography, computed tomography (CT), andnuclear imaging (eg, most often technetium bonescan). Plain films include panoramic radiography,transcranial, transorblta!, transmaxillary, andsometimes various skull views. In my opinion, thepanoramic film should always be included in anysurvey of the TMJ. This film gives information thatmay be missed if the imaging is restricted to thearea of tbe joint. For instance, the panoramic imagemay reveal abnormal morphology such as hyper- orhypoplasia of the joint and/or mandible, hyperpla-sia of the coronoid processes, or the presence ofdisease that may masquerade as temporomandibu-lar disease. Examples would include inflammatorydisease, such as periapical pathology (especially ofmandibular molars) and the presence of neoplasia.

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Imaging Protocol for Hard Tissues

What would be a reasonable initial protocol forrbe assessment of hard tissue abnormalities.^ Thepanoramic film by itself is not a gond surveyinstrument because of the inherent distortion ofthe image of the joint. An initial survey shouldsupplement the panoramic film with views of thejoint from the lateral aspect and from the frontalaspect. Two viewing directions at righr angles willprovide enough information to permit a more 3-dimensional concept of the joint. If plain films areused alone, the lateral view would he provided bytbe transcranial film (unfortunately, this has con-siderable image distortion), and the frontal viewwould be provided by rhe transorbital or trans-maxillary view. Tberefore, tbis survey wouldinclude a panoramic film and transcranial (openand closed) and rransorbital views. If available,tomography will provide a better initial surveybecause rbere is less image distortion. Tbis surveywould include a panoramic film and lateral andanteroposterior tomographs (corrected to the longaxis of the condylar head). These 2 protocols canprovide an adequate initial survey. If these imagesare of good quality and there is no evidence of dis-ease, there may not be a need to continue with fur-ther imaging. However, if these images indicate thepresence of an abnormality, further diagnosticimages are likely required. The following sectionslist the criteria that indicate specific abnormalitiesand the types of images that should be used.

Neoplasia. If the initial images indicate the pres-ence of disease, such as a neoplasm, then furtherimaging of rhe hard tissues may be required.Genera! features thar suggest the presence of aneoplasm include irregular enlargement of thecondyle, bone destruction of rhe condyle orglenoid fossa, and soft tissue calcifications. Thenext imaging modality should be CT, to obtainbetter 3-dimensianal information and bone detailand ro increase tissue contrast (ability to differenti-ate different soft tissues). Magnetic resonanceimaging may be required if further informationregarding the extent of soft tissue invasion isrequired.

Septic Arthritis. If the initial images in conjunc-tion with the clinical information suggest the pres-ence of inflammatory disease within the joint (sep-tic arthritis), then CT and nuclear imaging may berequired ro confirm the diagnosis. Clinical signsmay include swelling, redness, and increased rem-perature in the tissue lateral to the joint. Oftenseptic arthritis is the result of spread of osteomyeli-tis of the mandible or inflammatory disease from

chronic mastoid or ear infections. A preliminarydiagnosis of osteomyelitis is indicated by the pres-ence of inflammatory periosteal new bone orsequestra in the mandible, and sclerosis of themastoid air cells suggests chronic inflammatorydisease. Usually CT is the most accurate method toconfirm the presence of osteomyelitis of themandible. Nuclear imaging can confirm a diagno-sis of septic arthritis by employing a tecbnetiumbone scan followed by a gallium scan.

Other Arthritides. Usually tomography will pro-vide adequate documentation of these abnormali-ties, but if more detail is required, then CT can beemployed.

Condylar Hyperplasia. In the initial examina-tion, rhe panoramic film may reveal a profoundasymmerry, indicating rbe presence of hyperplasiaof the mandibular condyle with varying degrees ofinvolvement of the mandibuiar ramus and body. Ifcorrective otrbognathic surgery is contemplated, itmay be important to determine whether there isactive condylar growrh. This is difficult to ascer-tain with a single srudy alone. Technetium honescans may be employed to determine the metabolicactivity of the bone of the mandibular condyle.Since rhe number of parameters influencing theresults of this study prohibit a meaningful valuefor bone activit>', it is reasonable to compare theactivity of one condyie to the other. However,abnormally bigh activity does not necessarily indi-cate continued growth of tbe byperplastic condyle,since otber conditions such as remodeling andosteoarthriris may result in increased activity. Thenuclear scan is more useful if bone activity is equalto that in the normal condyle, which indicates thatthere is no longer abnormal bone growth. Ifnuclear scans are not available or inconclusive, alongitudinal srudy may be employed. Lateraloblique cephalometric views of the mandihle, pro-jected at righr angles to the body of the mandible(using the submentovertex view of rhe mandible asa guide), are produced, and the mandibular lengthis measured. This can be repeated on an annualbasis to determine wbether the dimension of themandible has changed.

Trauma. In cases where there is a history oftrauma to the mandible or to the joint, the right-angled views, especially those in the anteroposte-rior direction, are of paramount importance. Ifgreater detail is required regarding the number andposition of bone fragments, then CT imagingshould he ordered. If further information is neededregarding the articular disc and surrounding liga-ments, then either MRI or arthrography is indi-cated.

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Ankylosis. Ankylosis may be suspected with aninability to move the mandible, especially witha history of previous trauma or arthritis.Approaches employing CT, specifically rhe coronalimage slices, are useful in detecting small regionsof ankylosis, which may not be apparenr in con-ventional tomographic images, and CT can help todetermine the exact extent of the ankylosis.

Prosthetic Joints. Where unusual symptoms orpain suggesr the presence of a giant celi reactiveiesion to a joint prosthesis, the initiai radioiogicseries of fiims may be omitted, and CT should beused. Coronal image siices are the most useful indetermining erosion of the glenoid fossa.

Imaging Protocol for Soft Tissues

Usually, diagnostic images of the soft tissues areordered to determine the direction and severity ofdisplacement of the articular disc and whetherthere is abnormal morphology of the disc. Eitherarthrography or MRl can he employed. There areseveral studies that compare these imaging modali-ties. Ofcen rhe conclusion is that MRI is moreaccurate and represents the gold standard,Fiowever, Eiedberg et ai,- in a review of ail the lit-erature, suggested that arthrography has the high-est diagnostic outcome for anterior disc positionbut noc for medial displacement. In realiry, it islikely that the 2 methods are comparable, witheach having its particular strengths and weak-nesses. Aiso, the parameters concerning the qualityof the images and the experience of the ciinieiananaiyzing rhe images are not factored into thesestudies. In reality, both of these factors have a pro-found effect on the accuracy of che findings.

When these 2 imaging modalities are compared,it is apparent char arthrography has the followingadvantages; the cost is lower, it provides a gooddynamic study of joint movement, and it candetect the presence of perforation and adhesions.

The disadvantages include its radiation dose, asmail amount of patient morbidity, and a lack oraccuracy in detecting medial dise displacements,Tbe advantages in the use of MRI include a lack ofionizing radiation dose, no apparenr patient mor-bidity, the abiliry to see surrounding soft tissuessuch as the muscles, and the ability to demonstrateabnormal tissue signals of che disc and condyie.Disadvantages include its bigher cost and minimalinformation regarding joint movement, perfora-tions, or adhesions. It is interesting to comparethese 2 modalities, but if the information, forexample the presence of a perforation, has noinfluence on the treatment provided, then it is ofacademic importance only and brings into ques-tion the need for these diagnostic images.

Conclusions

A different approach to the developmenr of guide-lines for the application of diagnostic imaging forahnormalities of the TMJ has been presented.Assuming that the elinieian does not know the ulti-mate diagnosis, this paper suggests an initial imag-ing protocol, along with supplemental images thatcan help in arriving at a diagnosis. Lastly, guide-lines are no more than suggestions, and the num-ber and types of images should be based solely onthe needs of individual patients.

References

1, Brooks SL, Brand JW, Gibbs SJ, Hellender L, Lurie AG,OmneU KA, et al. Imaging of the temporqmandibularjoint: A posirion paper of the American Academy of Oraland Maxillofacial Radiology. Oral Surg Oral Med OralPatbol Oral Radiol Endod 1997;S3:609-618.

2. I.iedberg J, Panmekiate S, Petersson A, Rolilin .VI.Evidence-based evaluation of tbree imaging metbods fortbe temporomandibular disc. Dentomaxillofac Radiol199â;25:234-241.

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