Imaging of Temporomandibular Joint

Abstract

The temporomandibular joint (TMJ) is crucial for proper mouth function, and issues with it can cause significant discomfort and reduce the quality of life for those affected. Over the years, TMJ imaging has advanced to enhance overall patient care, treatment planning, and diagnostic accuracy. Temporomandibular joint disorders (TMD) are complex and poorly understood conditions characterized by pain in the affected area and restricted jaw movements. Radiographic examination is a key part of the standard clinical assessment for patients with TMDs. Conventional imaging methods like CT scans and X-rays are being replaced by advanced techniques such as MRI, which provides superior visualization of soft tissues and higher diagnostic accuracy, especially with contrast-enhanced high-resolution MRI. The integration of three-dimensional (3D) imaging techniques, such as multi-detector CT (MDCT) and cone-beam computed tomography (CBCT), has reshaped the assessment of TMJ anatomy and pathology. This combination enables the visualization of the joint in multiple thin sections, aiding in identifying minor structural abnormalities. Additionally, techniques like ultrasound (USG) provide real-time insights into dynamic TMJ function, offering valuable information on joint movement and biomechanics. Despite these significant advancements, challenges persist, including the need for standardized imaging protocols, access to advanced technologies, and ongoing research to validate the clinical usefulness of newer imaging methods.

1. Introduction

The temporomandibular joint (TMJ) serves as a critical component of the craniofacial complex, facilitating essential functions such as mastication, speech, and facial expression. Pathological conditions affecting the TMJ, collectively known as temporomandibular joint disorders (TMD), can lead to debilitating pain, restricted jaw movement, and a decline in overall quality of life. Accurate diagnosis and effective management of TMJ disorders necessitate advanced imaging techniques that can provide detailed anatomical and functional information.

Temporomandibular joint (TMJ) pain is prevalent in the general population, with only 3–7% of patients seeking medical attention [1, 2].

TMDs often involve structural and functional changes in the TMJ and adjacent structures like muscles of mastication, ligaments, teeth, and periodontal tissue [3].

In recent years, there has been a remarkable surge in technological advancements within the field of medical imaging, offering clinicians clear insights into the intricacies of the TMJ. These developments have not only enhanced the ability to visualize the joint’s structures but also revolutionized our understanding of dynamic functional aspects. Different imaging modalities are available to image the TMJ, each with inherent strengths and weaknesses [4].

Traditional imaging methods, such as plain radiography and computed tomography (CT), have long been employed for TMD cases. While these techniques have proven valuable, the advent of magnetic resonance imaging (MRI) has brought an evolution to this field. MRI’s ability to provide high-resolution, multi-planar, thin-sectioned images without ionizing radiation makes it particularly well-suited for capturing the intricate soft tissue anatomy of the TMJ, including the articular disc, ligaments, and surrounding musculature [5].

Beyond conventional imaging, three-dimensional (3D) technologies, such as cone-beam computed tomography (CBCT) and multi-detector CT (MDCT) have opened in a new era of precision in TMJ evaluation. These modalities offer the slightest detail into bony anatomy, allowing clinicians to identify subtle structural abnormalities and facilitating the development of customized treatment strategies. Moreover, advanced contrast-enhanced MRI techniques contribute to even superior diagnostic accuracy by highlighting specific pathological features [6, 7].

Ultrasound and functional imaging methods, have added a dynamic dimension to TMJ assessment. Real-time visualization of joint movements and biomechanics provides clinicians with invaluable information for a comprehensive understanding of TMJ function. This real-time data can aid in the diagnosis of conditions related to joint dynamics, leading to more effective and targeted interventions [8].

While these advancements hold immense promise, challenges do persist, including the standardization of imaging protocols, accessibility to cutting-edge technologies for developing nations and the need for continued research to validate the clinical efficacy of these newer imaging modalities. This exploration of recent advancements in TMJ imaging sets the stage for a more in-depth examination of each modality’s strengths and weaknesses and the potential contributions to advancing the field of maxillofacial diagnostics and therapeutics.

2. Temporomandibular radiography

The use of conventional radiography for the accurate evaluation of the TMJ is restricted by the presence of structure superimposition. There are various views that demonstrate the temporomandibular joint. Structure superimposition limits the use of conventional radiography for proper TMJ examination. There are various views that demonstrate the temporomandibular joint.

• Trans-Cranial View

• Trans-pharyngeal View

• Trans-orbital View

• Reverse Towne’s Projection

2.1 Trans-cranial view

It is also known as Lindblom’s view. This technique is particularly effective in detecting arthritic changes on the articular surface, assessing the bony relationship of the joint, despite not detecting changes on the central and medial surfaces [9, 10, 11]. This view is taken with the patient’s mouth in three positions (Figures 1 and 2).

1. Open mouth.

2. Rest position.

3. Closed mouth.

Figure 1.

Transcranial projection, the central ray is oriented at a 25° positive angle and 20° anteriorly centered over the TMJ of interest, (A) Mouth closed. (B) Mouth open.

Figure 2.

Transcranial view – Mouth closed position transcranial view – Mouth open position.

2.1.1 Indications

1. To study the position of the condyles in the glenoid fossa.

2. To study the joint space, i.e. the space between the articulating surfaces of the glenoid fossa and the condyles for either partial or complete obliteration (ankylosis).

3. To study antero-posterior mobility. (Hypermobility, i.e. dislocation and subluxation.)

4. To study osseous change such as flattening in arthritis.

2.1.2 Limitations

• Sub-condylar fractures cannot be seen because of superimposition of ipsilateral petrous bone and posterior clinoid process of sella turcica on the neck of the condyle.

• The radiograph shows only the lateral part of the joint space.

2.2 Trans-pharyngeal view

It is also known as Infracranial or McQueen Dell Technique (Figures 3 and 4).

Figure 3.

(A) Trans-pharyngeal projection. The central ray is oriented superiorly 5° to 10° and posteriorly approximately 10°, centered over the TMJ of interest. The mandible is positioned at maximal opening. (B) Trans-pharyngeal projection showing positioning from above, showing the X-ray beam aimed slightly posteriorly across the pharynx.

Figure 4.

Trans-pharyngeal view.

The view is a lateral projection of the medial surface of the condylar head and neck, typically taken in the mouth open position, allowing the joint to be projected into the nasopharynx shadow, increasing joint contrast [9, 10, 11].

2.2.1 Indications

1. TMJ pain dysfunction syndrome

2. Joint disease such as osteoarthritis and rheumatoid arthritis.

3. Pathological conditions affecting the condylar head such as cysts or tumors.

4. Condylar head and neck fractures [10].

2.3 Trans-orbital view (Zimmer projection)

This is the conventional frontal TM joint projection is highly effective in delineating joints with minimal super impositions, resulting in a relatively true ‘enface’ projection (Figure 5).

Figure 5.

Trans-orbital projection. The central ray is oriented downward approximately 20° and laterally approximately 30° through the contralateral orbit, centered over the TMJ of interest.

2.3.1 Indications

1. To study medio-lateral displacement of the condyle.

2. To study superior surfaces of the condyle for osteophytes, etc.

3. To study the relationship of the condyle to the articular eminence in the medio-lateral plane.⁵

2.4 Reverse Towne’s

This projection is useful in viewing the condylar head and neck. The original Towne’s view, an AP projection, was intended to show the occipital region and condyles, but due to conventional dental skull views being taken in the PA direction, the reverse Towne’s (PA) projection is used (Figures 6 and 7) [11].

Figure 6.

(A) The patient is in a forehead-nose position with an open mouth and an X-ray beam aimed upwards at 30°, as shown in the reverse Towne’s projection positioning diagram; (B) the radiographic baseline is horizontal and perpendicular to the film.

Figure 7.

Reverse Towne’s view.

2.4.1 Indications

• High condylar necks fractures

• Intra-capsular TMJ fractures

• Examining the quality of condylar head articular surfaces in TMJ disorders

• Condylar hypoplasia or hyperplasia.

3. Computed tomography (CT)

For the assessment of the TMJ, computed tomography (CT) has shown to be an invaluable tool. CT has been employed in the detection of uncommon disorders such synovial osteochondromatosis as well as bony abnormalities of the TMJ. A wide range of osseous pathological alterations, including osteophytes, condylar erosion, fractures, ankylosis, dislocation, internal disc derangement diagnosis, and growth anomalies such condylar hyperplasia, can be well visualized with CT.

Research conducted on autopsy specimens revealed that CT has a 100% specificity, 100% positive predictive value, and 78% negative predictive value for identifying alterations in the bone [12]. Nevertheless, the very high radiation dose, equipment accessibility, and expensive cost have restricted it’s widespread use in TMJ evaluation [11, 13].

Multi-detector CT (MDCT) is more widely available and better tolerated. In both closed and open mouth postures, MDCT is carried out without the need for intravenous or intra-articular contrast media. Multi-planar reconstructions are performed using bone and soft-tissue techniques in the coronal oblique, parallel to the long axis of the mandibular condyle and sagittal oblique planes, perpendicular to the long axis of the mandibular condyle [14].

For acquisition, the slice thickness and interval should be between 0.5 and 1 mm. Coronal images are reconstructed parallel to the mandibular condyles, with a slice thickness and inter-slice gap of 2–3 mm. Sagittal images are reconstructed from the raw data perpendicular to the plane of mandibular condyles as seen on axial plane (Figure 8) [15].

Figure 8.

Technique of reconstruction. A, B: Sagittal images are reconstructed perpendicular to the glenoid fossa plane.; C, D: Reconstructed coronal pictures are oriented perpendicularly to the sagittal image plane.; E, F: The 3D reformatted and reassembled panoramic image accurately depicts the anatomy of the joint. (Source: [15]).

The multi-planar reconstructions are examined using a DICOM viewer (Figure 8). In order to identify any anomalies in the imaging volume, that might be incidental or the cause of symptoms resembling TMJ dysfunction, the source axial images are also examined. It has been discovered that MDCT is a helpful imaging test for the accurate diagnosis of internal disc derangement, arthritis, and other various TMJ disorders [14]. The normal appearance of the TMJ on a CT scan is as shown in Figure 9.

Figure 9.

Normal CT anatomy of the temporomandibular joint. (a) The mandibular condyle (C) is seated inside the glenoid fossa (gf) of the temporal bone in this oblique sagittal reconstruction at the bone window, created with the use of a bone reconstruction algorithm. The external auditory canal (eac) is posterior to the temporal bone’s articular eminence (ae). (b) A bone reconstruction algorithm is used for oblique coronal reconstruction at the bone window. The coronal dimension of the condyle is broad. The zygomatic process’s base is located laterally (rz). (c) Oblique sagittal reconstruction in the closed-mouth position employing soft-tissue windows and a soft-tissue reconstruction method. The anterior band (thick arrow) and posterior band (arrowhead) are easily apparent. The thin intermediate zone (thin arrow) is located at the narrowest point between the condyle and the articular eminence. The posterior boundary of the posterior band is often located at the 12 o’clock position. (d) Soft-tissue oblique sagittal reconstruction in an open mouth position. The condyle has moved anteriorly onto the articular eminence, causing the disc to shift anteriorly as well. The anterior band (thick arrow), posterior band (arrowhead), and intermediate zone (thin arrow) are again illustrated.

4. Cone beam computed tomography (CBCT)

Cone beam CT (CBCT), introduced in 1982, is a low-dose technique for visualizing bony structures in the head and neck. Despite limitations like high radiation doses and long scanning times, CBCT offers high spatial resolution and less scanning time, making it the preferred imaging modality for maxilla-mandibular regions. Compared to multi-slice CT, CBCT produces high-resolution multi-planar images with a reduced dose of radiation [12]. CBCT has a higher sensitivity of 0.80 for detecting degenerative TMJ changes, with diagnostic accuracy dependent on defect size, with high sensitivity for condylar defects compared to CT [7, 16]. Caruso et al.’s study suggests that CBCT 3D Imaging improves detection of changes in condylar shape, and clarifies condyle position in the glenoid fossa [17].

Imaging diagnosis is crucial for evaluating TMJ conditions, assessing bone structures, and assessing the position of the condyle within the glenoid cavity. It helps confirm the progression of disorders and evaluate treatment effects. Other factors to consider include condylar fractures, neoplasms, malformations, and potential solutions to cranial vault continuity [18]. Normal anatomy of TMJ on a CBCT is as shown in Figure 10.

Figure 10.

Normal anatomy of TMJ as viewed on CBCT image. (Source: [19]).

5. Magnetic resonance imaging (MRI)

MRI, developed in 1977, is a non-invasive imaging technique that uses low-frequency radio waves to produce images. It uses protons to change position, producing signals based on tissue density. Tissue rich in water emits a hyper-signal, producing clear images, while tissues lacking water emit a hypo-signal, producing dark images. As a result, components richer in water, including muscle and fat, send intermediate signals that produce images in shades of gray, while cortical bone, which is poor in water, emits a hyposignal that results in a dark image [4]. MRI scans reveal high T1 signal intensity in condyle marrow fat, low signal intensity in cortical bone and disk due to low proton density and short T2, and high T2 and PD signal intensity in central disk (Figure 11) [8].

Figure 11.

Normal anatomy of TMJ on an MRI image.

MRI of the TMJ captures the disk and its relation to the condylar head, indicating TMJ dysfunction. Diagnosis depends on factors like joint effusion, ruptured retro-discal layers, and thickening of lateral pterygoid muscle attachment. Advanced degenerative joint disease is characterized by osteoarthritic changes. MRI is used to identify disk injuries, joint effusion, and differentiate between synovial proliferation and joint effusion. Gadolinium-enhanced MRI distinguishes proliferating synovium from joint effusion [9].

6. TMJ arthrography

Arthrography of the TM joint examines soft tissue state, including disk integrity and position, and provides evidence of internal disk derangement or perforation. It’s useful for diagnosing cases with minimal bone damage and clinical evidence suggesting disk derangement [10].

Dr. Fleming Norgaard introduced positive contrast agent in 1947 for TMJ visualization, but it wasn’t globally acclaimed until 1970 when Wilkes unmasked it in the US, by the inoculation of a radiopaque contrast material into the temporomandibular joint spaces, leading to single and double contrast techniques [20].

Procedure: TM joint arthrography involves catheterizing the upper and lower joint spaces and injecting 0.5–1 ml of radiographic contrast media, typically iodine compounds, into the lower and upper spaces (Figure 12) [10]. The contrast medium, containing 300 mg iodine/mL, should be administered in small amounts to the TMJ (1.5-2 ml), reducing the risk of idiosyncratic reactions as it is injected only into the joint compartments [21]. After joint space opacification, a series of radiographs/CBCT (Figures 13 and 14) are obtained with the jaws closed and in graduated stages of opening. Since there is not a known normal circumstance in which there is contact between the superior and inferior joint spaces, the disk appears as a radiolucent vacuum between two opaque regions of contrast media [10].

Figure 12.

Arthrographic technique. Left, the TMJ arthrogram site as well as the route for inserting the angiocatheter into the lower joint space are displayed. A sterile drape is placed over the preauricular area, and a 22-gauge angiocatheter is positioned perpendicular to the skin’s surface (arrow at the puncture site). The operator pushes the tool into the tissue until it makes touch with the condyle’s posterolateral surface. The angiocatheter would be positioned somewhat superior and anterior using the same approach, but with a reasonably broad opening. Right, the angiocatheter hub (arrow at the puncture site) is attached to the tube and syringe for the contrast medium injection. Slowly injecting contrast is done while being periodically observed via a fluoroscope. A stopcock at the synringe’s tip seals the system when the contrast agent is injected.

Figure 13.

(a) The placement of the needle during the anesthetic injection before the TMJ (left side) arthrography. Anesthesia is administered by placing the needle tip in close proximity to the upper posterior region of the lateral pole of the condyle. (b) A needle is positioned in close proximity to the articular tubercle’s posterior surface to administer anesthetic before injecting contrast material into the upper joint compartment.

Figure 14.

Normal temporomandibular arthrogram. Left, both upper and lower joint spaces are moderately opacified; jaws are opened approximately one fingerbreadth of interincisal distance. Portion of contrast medium is seen in anterior recesses. Posterior band (arrow) of disk is positioned directly above condyle. Right, jaws are opened farther and condyle is anteriorly translated to greater extent, obliterating contrast in both anterior recesses. Posterior band of disk (arrow) trails behind condyle. C, condyle; AE, articular eminence; EC, external ear canal.

6.1 Indications

• Symptoms of TMJ arthralgia/arthritis include pain during jaw movement and restricted opening.

• Conservative treatments such non-steroid anti-inflammatory medications, occlusal splints, and jaw exercises that did not significantly reduce pain.

• Indications of internal derangement or adhesion [21].

6.2 Diagnostic information obtained

• Dynamic information on joint components and disk movement.

• Static images of components with closed and open mouths.

• Observation of anterior or anteromedial disk displacement (Figure 15).

• Examination of disk integrity, perforations presence.

Figure 15.

TMJ arthrography (right side) demonstrates anterior disc displacement, reduction, and posterior attachment perforation. (a–c) an oblique transcranial projection that displays the joint’s lateral aspect. (d–f) corresponding photos with the joint components indicated and contrast media emphasized. (a, d) when the mouth is closed, a rupture in the disc’s posterior attachment allows contrast material to flow into the upper compartment (arrow). When the mouth is closed, both compartments loaded with contrast have an anterior disc displacement (b, e). (c, f) In the open mouth position, the disc is decreased and a posterior attachment defect is visible (arrow).

6.3 Advantages

• Fluoroscopically, abnormalities like discontinuation, any tear or adhesion can be appreciated. Action of the articular disc and fluid accumulation can be seen as well.

• Simultaneous sampling of synovial fluid and joint lavage.

• Enhancement of disc shape and position through tomography.

• Diagnosis of joint mice.

• Distinguishing internal derangement and inflammation.

6.4 Disadvantages

• Excludes severely deformed disc.

• Interpretation challenges due to medial or lateral articular disc displacements.

• Potential significant radiation exposure.

• Common procedure hitches: contrast medium extravasation, joint pain, minimal with non-ionic contrast media [20].

• Large needles and cannulas can be a cause of parotitis in arthrography.

• Transient facial paralysis is another complication when there is vigorous infiltration of lidocaine.

7. Ultrasonography (USG)

Ultrasonography (USG) is a cost-effective, non-invasive imaging method used for abdominal and extremity imaging. It was first used for diagnosing TMJ disorders in 1991, and with advancements in higher frequency probes and higher resolution devices, its scope is promising [22].

7.1 Ultrasound protocol

Conventional US transducer positions, in both closed-mouth (Figure 16 A,C) and open-mouth (Figure 16 B,D) positions, are parallel to the ramus of the mandible and the Frankfort horizontal plane, which is a plane that connects the highest point of the external auditory canal with the lowest point on the lower margin of the orbit. Normal transverse section ultrasound image of the mandible in the closed (E) and open (F) mouth positions.

Figure 16.

The TMJ is seen in a normal ultrasound scan in both the open-mouth (H) and closed-mouth (G) positions. The articular capsule is indicated by red arrows. Joint disk (JD) and mandibular condyle (MC).

The articular disk’s normal ultrasound appearance in the sagittal plane is an inverted hypoechoic C-shaped structure, as seen by the red circle. During the mouth opening, the mandibular condyle moves anteriorly, as indicated by the distance between the center of the condylar oval at the two positions (yellow dotted line) (Figure 16). In normal anatomy, the disk appears centrally in relation to the center of the mandibular condyle, however in pathological findings, it may be moved anteriorly or posteriorly (Figure 17) [23]. US effusion diagnosis was found to be more accurate than the gold standard MRI.

Figure 17.

On normal ultrasonography, the articular disc appears in the sagittal plane as an inverted hypoechoic c-shaped structure. Throughout the closed-mouth, half-open-mouth, and fully-open-mouth views, the disc maintains a consistent central appearance in relation to the center of the condyle, “c,” which is delineated by a central vertical line. The articular disc’s anterior (“ant”) and posterior bands appear to be symmetrical in size when viewed from the center of the condyle. A focused annotated view was supplied to help visibility, with the articular disc highlighted with a dotted contour.

Emshoff et al. [24] used a 7.5 MHz transducer, which demonstrated a sensitivity of 40–50% and specificity of 70%. Diagnostic accuracy was acceptable in both positions, but sensitivity decreased from closed to open mouth. In contrast, specificity increased from closed to open mouth position. Progressive use of transducers with higher frequencies, of 10 MHz or more, results in improved sensitivity, ranging from 60–90% [23]. Jank et al. [25] discovered that HR-US may detect TMJ pathology even before clinical symptoms manifested, which is especially important in the younger population to prevent further damage.

7.2 Indications

Injuries and inflammation of the tendons, ligaments, soft tissues, and bones should be investigated using US, particularly in cases of post-traumatic pain syndromes, restricted joint mobility, and post-traumatic disorders. Moreover, the diagnosis of degenerative illnesses and interventional procedure cases (biopsies, punctures, and intra-articular injections) can be aided by ultrasound scanning.

7.3 Advantages

• Allows real-time motion observation.

• Helps localize imaging to patient-directed pain regions.

• Evaluates claustrophobic patients with non-MRI compatible stents and implants.

• Visualizes cortical osseous defects like osteophytes and erosions.

• Partial limitation by patient body habitus.

• Allows acoustic windows by adjacent osseous structures.

7.4 Disadvantages

• Difficulty in visualizing medial and lateral disc displacements.

• Inadequate visualization of perforations and adhesions.

• Inability to visualize subcortical osseous abnormalities.

• Inherent operator dependence and learning curve.

8. Nucleide imaging

Nucleide imaging uses radioactive isotopes to examine the entire maxillofacial region and TMJ, detecting active inflammatory processes [26]. This method is unique in assessing physiologic changes due to biochemical alteration. It relies on the radiotracer method, which assumes that radioactive atoms or molecules in an organism behave identically to their stable counterparts due to their chemical indistinguishability [27]. Depending on the registration methods, the nuclear imaging methods are of three types:

1. Scintigraphy

2. Single photon emission computed tomography (SPECT)

3. Positron Emission Tomography (PET)

8.1 Scintigraphy

Traditional radiographs and advanced imaging techniques have limitations in determining structural changes, but bone scintigraphy can aid in diagnosing TMJ disease activity, determining remodeling and inflammation, and managing the condition. Bone scintigraphy involves injecting technetium diphosphonate 99 mTC into the circulation, and metabolic images are obtained 2–3 hours post-injection. An intravenous dose of 99 mTC is determined by 740 MBq × body weight/70 kg [28].

The bone tracer complex, 99 mTC, is activated by blood flow and calcium-containing crystals binding to phosphate. It produces c-radiation, detected by a scintillation camera indicating bone metabolic activity. Positive scans correlate with clinical signs and symptoms (Figure 18). However, a bone scan is non-specific and may show conditions like growth, healing bone, infection, arthritic changes, or tumors [29].

Figure 18.

Bone scintigraphy showing increased uptake in the left condyle.

Bone scintigraphy detects active joint changes, stability, and inflammation, which can influence treatment. Its ability to detect or rule out remodeling in the TMJ assessment can help determine the need for complex dental therapy. A study found 93% sensitivity and 86% specificity for scintigraphy as compared with 89% sensitivity and 27% specificity for tomography, in assessing TMJ pain and joint noise [29].

Bone scans aid in diagnosing conditions like TMJ disease, altering clinical diagnoses and treatment plans, and determining joint stability for dental rehabilitation, orthodontics, or orthognathic surgery. Negative scans indicate no active bony disease.

8.2 Single photon emission computed tomography (SPECT)

The TMJ is appropriate for single-photon emission CT (SPECT) scanning because it is a small joint located near the base of the skull and the paranasal sinuses. SPECT imaging allows for high-quality images of the TMJ that are separated from other high bone density regions, which planar images cannot do.

The TMJ can be investigated using one of the following techniques:

1. The 3-phase approach includes a 30-second perfusion study where images are obtained at every 3-seconds with computed perfusion analysis, instantaneous soft-tissue views of the head and mouth, and delayed views of the TMJ.

2. Delayed images include SPECT scans and planar views in anterior, posterior, and lateral projections of TMJ.

Increased perfusion and hyperemia are reflected in abnormal activity in TMJ flow studies in inflammatory individuals, with mild to substantial increases on immediate and delayed views (Figure 19). Being a non-anatomical examination is the main drawback of SPECT scanning. Although a region of elevated uptake indicating healing phenomena or aberrant pressures on the TMJ can be quickly established, the origin of these results may remain elusive.

Figure 19.

Coronal and transaxial sections generated after single-photon emission computed tomography showing increased uptake in the right condyle.

SPECT using 99mTc MDP/HMDP is highly sensitive in detecting bone pathology, particularly TMJ meniscus abnormalities. Studies show a sensitivity of 68.75% and a specificity of 61.88%. Using SPECT scanning and semi-quantitative methods can improve results to 100% sensitivity and 83.33% specificity. Planar imaging can also detect additional lesions that resemble TMJ meniscus abnormalities and cause referred pain to the TMJ, such as upper cervical spine OA, bone metastases, and oral and sinus pathology. Although radionuclide imaging is highly sensitive, its specificity is low. Typically, any inflammatory/traumatic/neoplastic lesion exhibits enhanced isotope uptake, which is both advantageous and disadvantageous.

8.3 Positron emission tomography (PET)

Bone scans detect bone metabolic changes before structural changes, aiding early detection of TMD. However, due to a shortage of molybdenum-99, fluoride-18 positron emission tomography (18F-PET) is being considered for its superior sensitivity and image quality [30]. PET scans use a gamma camera and radiopharmaceuticals to detect metabolic processes. The most common radiopharmaceutical is 2-fluoro-2-deoxyglucose labeled with fluorine-18 (18FDG), which is up taken by areas with increased metabolism rates. PET-MRI is now used, combining CT, PET-CT, and MRI.

Patient preparation includes fasting for 6 hours, maintaining glucose level below 120mg/dl, hydration, and avoiding physical activity. PET scans should be performed 3 months post-surgery, which is up taken by areas with increased metabolism rates (Figure 20) [19, 31].

Figure 20.

Tempromandibular joint (TMJ) images obtained using positron emission tomography (PET). (a) Standard uptake value of the condylar head in sagittal view of the right TMJ. (b) Lateral pterygoid muscles and condyles seen in an axial view (LPM). (c) Sagittal image of the condyle and capsule in the left TMJ. (d) A coronal image showing the left and right TMJs. In RA-affected joints, inflammation (left >right) manifests as increased brightness. Increased brightness in the left condyle superiorly and laterally indicates increased absorption of 18-fluorodeoxyglucose (FDG). A comparison of the FDG uptake in the left and right condyle joints demonstrates the differences.

FDG-PET/CT has proven clinically useful in patients with TMD, osteoarthritis, and arthralgic TMJ and TMD osteoarthritis. Studies show high TMJ uptake ratios in patients with osteoarthritis, higher accuracy, and sensitivity compared to conventional bone scintigraphy. FDG PET’s resolution for bone fractures is comparable to skeletal scintigraphy. PET scan evaluation requires thorough correlation with patient’s medical history and other examinations, such as physical, laboratory, and diagnostic imaging. The mean effective dose for a PET scan is from 3 to 4 mSv (Table 1) [19].

9. Radiographic appearance of TMJ disorders

Table 1.

Depicting the clinical and radiographic features of various TMJ disorders/pathology.