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| REVIEW ARTICLE |
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| Year : 2013 | Volume
: 1
| Issue : 3 | Page : 99-103 |
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Magnetic resonance imaging of temporomandibular joint disc abnormalities: A pictorial essay
Galal Omami
Department of Oral Medicine and Radiology, Benghazi University College of Dentistry, Benghazi, Libya
| Date of Web Publication | 7-Feb-2014 |
Correspondence Address:
Galal Omami
College of Dentistry, Benghazi University, Benghazi
Libya
 Source of Support: None, Conflict of Interest: None  | Check |
DOI: 10.4103/2321-3841.126742
Internal derangement is the most common pathological condition affecting the temporomandibular joint (TMJ). Magnetic resonance imaging (MRI) of TMJ is principally directed toward assessment of the soft-tissue abnormalities in terms of internal derangement. This pedagogical article describes anatomy and biomechanics and provides a pictorial overview of the MRI findings of the disc abnormalities of TMJ. Keywords: Articular disc, internal derangement, magnetic resonance imaging, temporomandibular joint
How to cite this article:
Omami G. Magnetic resonance imaging of temporomandibular joint disc abnormalities: A pictorial essay. J Oral Maxillofac Radiol 2013;1:99-103 |
How to cite this URL:
Omami G. Magnetic resonance imaging of temporomandibular joint disc abnormalities: A pictorial essay. J Oral Maxillofac Radiol [serial online] 2013 [cited 2023 Mar 21];1:99-103. Available from: https://www.joomr.org/text.asp?2013/1/3/99/126742 |
| Introduction | |  |
Temporomandibular joint (TMJ) is a diarthroidal synovial joint capable of both translation (sliding) and rotation. It is composed of the mandibular condyle, the glenoid (temporal) fossa and the articular eminence (tubercle) with the interposed fibro- cartilaginous disc (meniscus). The articular disc is a biconcave fibro-cartilaginous structure interposed between the mandibular condyle and the temporal bone component of the joint. In a sagittal section, the normal disc appears biconcave, with the anterior and posterior thicker parts of the disc referred to as the anterior and posterior bands; respectively. In closed mouth position, the posterior band is located just above the condyle and the central thin zone is located between the anterior pole of the condyle and the posterior slope of the articular tubercle [Figure 1]. The anterior band is located under the articular tubercle. Posteriorly, the disc is attached to the temporal bone and to the condyle by the posterior disc attachment (retrodiscal tissue). This region is also referred to as the bilaminar zone because histologic studies indicated that the upper part was elastic tissue (superior lamina) and the lower part consisted of more fibrous tissue (inferior lamina). The bilaminar zone is a highly vascular component containing the branches of the auriculotemporal, masseteric and posterior deep temporal nerves and vessels. Anteromedially, the disc merges with the upper head of the lateral pterygoid muscle. The primary function of the disc is to permit a greater range of motion in a relatively small joint by dividing the joint cavity into two separate upper and lower compartments. Rotation and translation occur in both the upper and lower joint spaces. However, translation occurs predominantly in the upper space and rotation occurs predominantly in the lower joint space. [1]  | Figure 1: T1-Weighted sagittal magnetic resonance images in (a) closed- and (b) open-mouth positions showing normal disc positions (arrows)
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Internal derangement is an abnormality in the position of the articular disc relative to the condylar head resulting in mechanical interference with the normal joint dynamics. [2] Anterior (pure anterior, antero-medial, or antero-lateral) disc displacement is the most common type of internal derangement. [3],[4] Posterior disc displacement does occur, but it is rare [Figure 2]. The combination of anterior and lateral or medial displacement is called rotational displacement, whereas pure lateral or pure medial displacement is called sideways displacement. [5],[6],[7] When the disc is anteriorly displaced in the closed-mouth position but reduces (returns) to a normal position during opening, it is called anterior disc displacement with reduction (ADDwR) [Figure 3]. However, when the disc is persistently anteriorly placed regardless of the condyle position, it is called anterior disc displacement without reduction (ADDw/oR) [Figure 4]. In ADDwR, when an anteriorly displaced disc returns to a normal position, a click is usually heard during the opening. When the jaw closes, the disc again displaces anteriorly, usually during the last phase of the closing movement of the jaw and again a click is commonly heard. The closing click is usually less prominent than the opening click. [8] The clicking sound is caused by the impact of the condyle hitting the temporal eminence after the condyle has passed under the posterior band of the disc. [8],[9] ADDw/oR is usually associated with joint locking (limited mouth opening). This occurs when the condyle is located behind the thick posterior band of the disc and the whole disc is bunched up anteriorly. [10] Hence, a click usually indicates an ADDwR. A lock usually indicates ADDw/oR. Thus, a clicking joint does not lock and a locking joint does not click, at the same time. | Figure 2: Sagittal T1-weighted magnetic resonance image in open-mouth position shows condylar hypermobility (white arrow) and posterior displacement of articular disc (black arrow)
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 | Figure 3: T1-Weighted sagittal magnetic resonance images in (a) closed- and (b) open-mouth positions showing anterior disc displacement with reduction (arrows)
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 | Figure 4: T1-Weighted sagittal magnetic resonance images in (a) closedand (b) open-mouth positions showing anterior disc displacement without reduction (arrows)
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The standard magnetic resonance imaging (MRI) protocol of TMJ includes oblique sagittal and oblique coronal images perpendicular and parallel to the long axis of the condylar head. Sagittal images should be obtained in both closed- and open-mouth positions to determine the disc dynamics. Coronal images are usually obtained only in the closed-mouth position.
MRI is currently regarded as the gold standard for imaging TMJ internal derangements. MRI is capable of providing information on the disc morphology and position through high soft-tissue resolution without exposing the patient to ionizing radiation. However, the modality is limited by its high cost and lengthy scanning time. [10]
T1-weighted image sequences have greater latitude and therefore they are generally favorable for outlining morphology and better visualization of intra-articular tissue relative to the surrounding joint capsule and cortical bone. T2-weighted images in both sagittal and coronal planes are obtained routinely to detect joint effusion and inflammatory changes in the joint capsule. [11] The coronal images are valuable in identifying medial and lateral displacements of the disc [Figure 5]. The American Academy of Oro facial Pain recommends the diagnostic imaging analysis of TMJ dysfunction based on clinical evaluation of the joint and jaw muscles. [12]  | Figure 5: Coronal T1-weighted magnetic resonance image in closed-mouth position shows lateral displacement of articular disc (arrow)
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In MRI, the normal disc has the lowest signal intensity (i.e., darkest). In closed-mouth position, the normal disc is located with its posterior band immediately superior to the uppermost portion of condylar head (12 O'clock position). Anterior location of the disc from the 12 O'clock position in the closed-mouth position is generally regarded as anterior disc displacement (ADD). Thickening of the posterior discal attachment could occurs in some patients with ADD, appears as a band-like structure of low signal intensity replacing the normally bright signal from the posterior disc attachment (pseudo disc sign) [Figure 6]. Furthermore, the insertional area of inferior head of lateral pterygoid muscle could appear as a band of low signal intensity and confused for the articular disc (double disc sign) [Figure 7]. Stuck disc is a condition in which the disc remains in a fixed position relative to the glenoid fossa and the articular eminence in both closed- and open-mouth positions, usually due to fibrous adhesions. [13]  | Figure 6: Sagittal T1-weighted magnetic resonance image in closed-mouth position shows anteriorly displaced articular disc (arrow) and a hypointense band in the retrodiscal region (arrowhead) indicating thickening of posterior discal attachment "pseudo disc sign"
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 | Figure 7: Sagittal T1-weighted magnetic resonance image in closed-mouth position shows anteriorly displaced disc (arrow). Note the low signal intensity of lateral pterygoid tendon is parallel to the disc, giving a "double disc sign"
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Effusion is accumulation of excessive amount of fluid (usually inflammatory exudate) in the joint cavities. It is considered to be an early sign that may precede degenerative joint disease. Joint effusion is best depicted on T2-weighted MRI as high-signal intensity areas in the joint spaces [Figure 8] and [Figure 9]. Due to the arthrographic effect created by the high signal intensity of the joint effusion on T2-weighted images, these images also may be useful for outlining disc perforations [11] [Figure 10]. | Figure 8: Sagittal T2-weighted magnetic resonance image shows fluid effusion in superior joint cavity (arrow) and anterior displacement and folded deformity of articular disc (arrowhead)
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 | Figure 9: Sagittal T2-weighted magnetic resonance image in open-mouth position shows fluid effusion in the superior joint space (arrows) and high signal intensity in the glenoid fossa indicating retodiskitis (arrowhead)
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 | Figure 10: Sagittal T1-weighted magnetic resonance image in closed-mouth position shows anteriorly displaced and perforated articular disc (arrow)
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Other MRI observations associated with internal derangement include hypertrophy of lateral pterygoid muscle [Figure 11], rupture of retrodiscal ligaments, joint effusion and bone marrow edema of condylar head [Figure 12]. It is important for the radiologist to detect early MRI changes of TMJ that may proceed to advanced osteoarthritic changes [Figure 13]. | Figure 11: Sagittal T1-weighted magnetic resonance image in open-mouth position shows high signal intensity in superior belly of lateral pterygoid muscle indicating fatty replacement (arrow). Note the anterior displacement and biconvex deformity of articular disc (arrowhead)
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 | Figure 12: Sagittal T2-weighted magnetic resonance image shows fluid accumulation in superior joint space (arrowhead) and increased signal intensity of the condylar head indicating bone marrow edema (arrow)
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 | Figure 13: Sagittal T1-weighted magnetic resonance image in open-mouth position of osteoarthritic joint shows osteophyte formation (arrowhead) and anterior displacement and folded deformity of articular disc (arrow)
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| Conclusion | | |
In this article, we highlight MRI findings of soft-tissue abnormalities of TMJ and feel it will be of interest and aid learning for both radiology trainees and practitioners. This article should be a useful reference for maxillofacial radiologists and orofacial pain specialists as knowledge of disc abnormalities of TMJ is important for optimal patient care.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9], [Figure 10], [Figure 11], [Figure 12], [Figure 13]
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