died on March 8, 2005. At the time of his death, he was a
Professor of Radiology, Epidemiology and Biostatistics, Boston
University School of Medicine, Boston Medical Center, Boston,
At the time this article was written, all of the remaining
authors were affiliated with Boston University School of Medicine
as medical students, residents, or fellows; they have now moved
to other facilities.
is Director of Breast MRI, Department of Radiology, Lakey Clinic,
is a radiologist with Sullivan's Island Imaging, LLC, Sullivan's
is Staff Radiologist, Department of Radiology, Caritas St.
Elizabeth's Medical Center, Boston, MA. At the time this paper
was a medical student at the Boston University School of
This article is adapted from a presentation that was given at
the 2002 meeting of the American Roentgen Ray Society, Atlanta,
Magnetic resonance imaging (MRI) has replaced computed
tomography (CT) and arthrography as the primary modality in the
evaluation of the temporomandibular joint (TMJ). Direct
visualization of the disk afforded by MRI is a distinct advantage
Despite the superior resolution of CT and limited visualization of
cortical bone by MRI, most osseous pathology is accurately
Intra-articular abnormalities are readily visible on MRI images,
providing further information not available with other imaging
The TMJ is a ginglymoarthrodial (hinge and glide) articulation
with some degree of diathrosis (free motion) formed by the
mandibular condyle and glenoid fossa of the temporal bone
(Figure 1). Within this synovial joint is a fibrous disk or
meniscus that divides the joint into superior and inferior
compartments that do not communicate unless disk integrity is
compromised. The biconcave disk has 3 functional segments: A thick
posterior band that is separated from the anterior band by the thin
intermediate zone. Multiple ligamentous attachments provide disk
stability. Posteriorly, the bilaminar zone attaches the disk and
capsule to the condyle and temporal bone. Laterally, the disk is
continuous with an unnamed ligament attaching to the neck of the
condyle. The superior belly of the lateral pterygoid muscle inserts
into the anterior portion of the disk.
The surrounding supporting ligamentous structures are the
temporomandibular, sphenomandibular, and stylomandibular ligaments.
The temporomandibular ligament provides lateral support extending
from the zygomatic process of the temporal bone to the condylar
neck. The sphenomandibular and stylomandibular ligaments provide
medial support coursing from the spine of the sphenoid bone to the
lingual of the mandibular foramen and from the styloid process to
the mandibular ramus, respectively. No discrete ligaments are
normally observed anteriorly or posteriorly around the joint.
The relationships of the structures of the TMJ change with mouth
position. When the mouth is closed, the disk is positioned at
approximately 11 o'clock with respect to the mandibular condyle;
the posterior segment of the disk caps the apex of the mandibular
condyle. As the jaw opens, the disk remains between the condyle and
the articular eminence as the condyle translates anteriorly. The
thin intermediate zone of the disk is interposed between the
condyle and the articular eminence in the fully open mouth position
Imaging the TMJ
A small surface coil is placed over the TMJ; a bilateral
examination can be performed with coupled coils. Images are
obtained in the open-and closed-mouth positions to assess the
position and reducibility (or recapture) of the articular disk.
This is facilitated by placing a specialized device in the
patient's mouth to keep it open and by instructing the patient to
bite down on it for the closed-mouth views.
From axial localizing images, sagittal and coronal planes are
prescribed. Imaging is most commonly performed in these planes in
order to document the position of the disk. Oblique sagittal and
coronal images can be oriented to the condyle, but are unnecessary
to demonstrate internal derrangements.
T1-weighted sagittal images are the cornerstone of the TMJ
examination; the anatomy is clearly depicted, and the imaging plane
is optimal for assessing articular disk position. T2-weighted
images are useful for detecting degenerative periarticular changes
and the presence of a joint effusion.
Fat saturation or inversion recovery renders these findings more
Gradient-echo techniques have been implemented to obtain
cine-loop motion studies. Three-dimensional volume acquisitions
allow a volume of tissue to be imaged rapidly and subsequently
viewed in any plane. The use of intra-articular and intravenous
gadolinium may provide utility in certain clinical instances-for
instance, the inflamed synovium or an inflamed arthropathy will
avidly enhance after the administration of intravenous gadolinium.
An abnormal position of the disk constitutes internal
derangement. The cause is usually not elicited; postulated causes
include trauma, malocclusion, bruxism, stress, and primary osseous
The disorder is 3 to 5 times more common in females and commonly
manifests by the fourth decade. Initially, there is anterior
displacement of the disk that reduces with jaw opening. As the
fibers of the posterior bilaminar zone loosen, the disk no longer
reduces. Disk deformity ultimately results and secondary osseous
and articular abnormalities ensue.
Abnormal disk morphology and position are the earliest and most
sensitive signs of internal derangement. The earliest finding is
often T2 hyperintensity in the bilaminar zone. Disk degeneration is
reflected as desiccation or loss of signal that is typically
intermediate on T1weighted images and hyperintense on T2-weighted
Disk deformity may also develop; the disk may become biconvex,
thickened, or folded among other previously described morphologic
abnormalities. Late in the course of the disease, the disk or
bilaminar zone may perforate.
The position of the disk must be assessed first on sagittal
closed-mouth images. The disk most commonly displaces anteriorly or
anterolaterally. However, the disk can become displaced in any
direction; medial and lateral disk displacements account for up to
30% of cases.
Early in the course of the disease, the disk may reduce in position
(Figure 3). With progression, the disk does not reduce during mouth
opening (Figure 4). Finally, an irreducible disk may become
adherent and remain fixed anteriorly during both mouth opening and
closing (Figure 5). Fluid may accumulate within the joint. Cortical
erosions, followed by condylar head flattening and anterior
osteophytosis, develop. Subchondral marrow edema followed by
low-signal sclerosis is the natural progression.
The TMJ is susceptible to the same varieties of arthritis that
involve other joints in the body. Inflammatory arthritis and
degenerative arthritis are the most common offenders; however,
other types of arthritis known to involve the TMJ include:
Infectious, posttraumatic, and metabolic arthritis.
Among the inflammatory arthritides affecting the TMJ, rheumatoid
arthritis is the most common and has received the most coverage in
the literature. The abnormalities described in the TMJ are similar
to those in other synovial joints afflicted with rheumatoid
arthritis (Figure 6). The advantage of MRI in evaluating
involvement of the TMJ in rheumatoid arthritis is its ability to
reveal the soft-tissue abnormalities. The inflammatory synovial
pannus eventually destroys the disk and its supporting structures,
resulting in abnormal disk position, abnormal morphology, and
possibly complete destruction of the disk. The presence of a joint
effusion can be depicted with T2-weighted images. Direct
visualization of the synovial pannus with T1-weighted
postgadolinium images has been reported with variable success.
In any event, synovial enhancement is nonspecific and may occur in
any inflammatory process, including osteoarthritis.
Despite the superiority of CT in depicting osseous anatomy, the
ability of MRI to depict the bony abnormalities of rheumatoid
arthritis has been shown to equal CT.
Destruction of the condyle and articular eminence are typical
findings, and marrow signal abnormalities may reflect edema or,
occasionally, subchondral sclerosis. Eventually, bony apposition
ensues with destruction of the intervening soft-tissue structures.
Because the bony and soft-tissue findings in rheumatoid arthritis
are frequently bilaterial, both TMJs should be imaged.
In degenerative arthritis of the TMJ, MRI initially reveals
subchondral changes, such as increased T2 hyperintensity and cysts.
These findings are shared by primary and secondary osteoarthritis.
Secondary osteoarthritis can be associated with previous trauma,
surgery, internal derangement, or congenital malformation. The
common end point is subchondral sclerosis, marginal osteophytes,
condylar flattening, occasional subchondral cysts, and distortion
of the disk due to adhesions.
In advanced cases, fusion of the joint may occur (Figure 7).
Innumerable conditions can affect the normal development of the
TMJ, including hereditary and nonhereditary syndromes, postnatal
trauma, infection, radiation, and endocrine and dietary
The uniting feature of these disparate entities is their effect on
the growing condyle. The result is a spectrum of abnormalities,
ranging from condylar agenesis to condylar hyperplasia.
Condylar agenesis is associated with congenital syndromes, such
as otomandibular dysostosis, hemifacial microsomia, and
mandibulofacial dysostosis. Depending on the extent of involvement,
the condyle, glenoid fossa, coronoid process, ramus, and even the
mandibular body may be absent. Deficiencies in the external ear,
the auditory canal, and the middle and inner ear may also be
Condylar hypoplasia is more commonly the result of a postnatal
insult, such as trauma, infection, or radiation. Altered condylar
morphology is assocated with a shallow sigmoid notch, a short ramus
and mandibular body, and underdevelopment of the glenoid fossa
(Figure 8). Soft-tissue abnormalities, such as deficiencies in the
external ear, are not a feature of condylar hypoplasia.
Although condylar hyperplasia can result from hereditary
syndromes and endocrine disturbances, the most common cause is
idiopathic unilateral condylar hyperplasia. The condyle may be
morphologically normal, or elongation of the condylar process may
be noted. The mandibular ramus and body may be elongated, which
will result in chin deviation toward the unaffected side when
Dislocation of the TMJ usually occurs anteriorly. Displacement
posteriorly, superiorly, or medially is prohibited by the contour
of the ipsilateral glenoid fossa. Laterial displacement is
prevented, as the medial wall of the contralateral glenoid fossa
confines the contralateral condyle. A dislocation in any direction
except anterior implies a fracture of either the articular fossa or
An anteriorly dislocated mandibular condyle is visualized
anterior and superior to the articular eminence (Figure 9). A
patient with a dislocated mandible is unable to close his or her
mouth. Conversely, in subluxation, the condyle reduces in the
Other stigmata of traumatic injury can be readily appreciated on MR
images of the TMJ, such as fractures, bone marrow edema, and
The exquisite tissue contrast of MRI is optimal for visualizing
the soft tissue and periarticular structures of the TMJ. Careful
attention to technique with dedicated coils and high spatial
resolution are essential. Dynamic maneuvers (opening and closing
the mouth) are a necessary component of the examination to assess
the position of the articular disk (which usually dislocates
anteriorly). MRI is capable of demonstrating abnormalities of the
disk, its supporting structures, synovium, and periarticular
structures associated with internal derangement, degenerative and
inflammatory arthropathies, and developmental and traumatic