The temporomandibular joint (TMJ) connects the jawbone to the skull, playing a role in essential functions like chewing and speaking. Magnetic Resonance Imaging (MRI) is a tool used to assess the TMJ, helping distinguish between normal and abnormal findings.
Understanding TMJ MRI
Magnetic Resonance Imaging uses strong magnets and radio waves to generate detailed images of soft tissues and bones. This imaging method is particularly useful for the TMJ because it provides clear visualization of structures such as the articular disc, joint capsule, ligaments, and surrounding muscles. A significant advantage of MRI is that it does not use ionizing radiation, unlike X-rays or CT scans.
MRI is preferred over other imaging techniques for assessing the TMJ because it offers superior contrast for soft tissues, which are frequently involved in TMJ disorders, unlike X-rays or CT scans that primarily show bones. A TMJ MRI may be ordered for individuals experiencing persistent pain, clicking sounds, jaw locking, or limited jaw movement, as it can help identify the underlying causes of these symptoms.
Normal TMJ MRI Findings
A healthy, functional temporomandibular joint on an MRI scan presents with specific characteristics. The articular disc, a biconcave fibrous structure positioned between the condyle of the mandible and the temporal bone, plays a role in smooth joint movement. In a closed-mouth position, the posterior band of this disc typically sits directly above the condylar head, around the 11–12 o’clock position.
The condyle, which is the rounded end of the jawbone, and the glenoid fossa, a depression in the temporal bone, should exhibit smooth, well-defined cortical bone surfaces. These smooth surfaces indicate an absence of erosions or degenerative changes. When the mouth opens, the condyle normally translates forward beneath the articular eminence, with the disc maintaining its position between the two bones.
The joint space, which is the area between the condyle and the fossa, should appear appropriate in size, indicating no significant fluid accumulation or inflammation. Surrounding tissues, including the joint capsule, ligaments, and masticatory muscles, should also appear typical, without signs of thickening or abnormalities.
Abnormal TMJ MRI Findings
Deviations from the normal appearance of the TMJ on an MRI can indicate various problems within the joint. One common abnormality is disc displacement, where the articular disc moves from its normal position relative to the condyle. This displacement can occur in different directions, such as anteriorly (forward), posteriorly (backward), medially (inward), or laterally (outward).
Disc displacement is further categorized by whether it reduces, meaning the disc returns to its normal position upon mouth opening, or if it remains displaced. Anterior disc displacement with reduction often causes a clicking sound as the disc moves. In contrast, disc displacement without reduction can lead to limited jaw opening and persistent pain, as the disc remains out of place even with jaw movement.
Degenerative joint disease, also known as osteoarthritis, presents with several distinct signs on an MRI. These include the formation of bone spurs (osteophytes), subchondral cysts (fluid-filled sacs within the bone), erosions of the bone surfaces, and flattening of the condyle or fossa. These changes indicate wear and tear within the joint, similar to osteoarthritis found in other joints.
Joint effusion, which is the presence of excess fluid within the joint space, suggests inflammation or injury. While small amounts of fluid can be normal, a significant effusion often correlates with pain and disc displacement.
Bone marrow edema appears as a change in the signal intensity within the bone, indicating inflammation or stress. This finding is often associated with internal derangement, osteoarthritis, or joint effusion within the TMJ. Perforations, or tears, in the articular disc or the retrodiscal tissues (the tissue behind the disc), can also be detected. These perforations are often found in advanced stages of TMJ dysfunction. Although less common, MRI can also identify tumors or other lesions within or near the joint, providing a comprehensive view of the joint’s condition.
Interpreting TMJ MRI Results
Interpreting TMJ MRI results requires a comprehensive approach that integrates various pieces of information. The MRI scan is one component of this diagnostic process. Clinical examination, which includes assessing the patient’s symptoms and performing a physical evaluation of the jaw, is equally important. A thorough patient history, detailing the onset and nature of symptoms, also contributes to understanding the overall picture.
A specialized medical doctor, known as a radiologist, interprets the MRI images and compiles a detailed written report. This report describes all findings, whether normal or abnormal, and provides a professional assessment of the joint’s condition. The radiologist’s report is then sent to the referring clinician, such as a dentist, oral surgeon, or another specialist.
The clinician integrates the MRI findings with the patient’s symptoms, medical history, and results from other diagnostic tests. This holistic approach allows the clinician to form an accurate diagnosis. For instance, an MRI showing disc displacement without reduction combined with a patient’s reported jaw locking and pain helps confirm a specific TMJ disorder. The insights gained from the MRI can influence treatment decisions, ranging from conservative management, such as physical therapy or splint therapy, to surgical interventions in more severe cases. However, MRI findings do not always perfectly align with a patient’s symptoms; some individuals may have abnormal MRI findings without experiencing significant pain, while others may have pain despite a seemingly normal MRI.