Page 50 - Atlas of Small Animal CT and MRI

1.3

Temporomandibular joint

Normal temporomandibular joint Temporomandibular dysplasia

The normal temporomandibular joint (TMJ) includes Temporomandibular dysplasia has been reported in
the articular surfaces of the condyloid process of the several canine breeds, including Dachshunds, Cocker
mandible and the mandibular fossa of the temporal Spaniels, Cavalier King Charles Spaniels, and Irish
4,5
bone, between which lies a cartilaginous articular disc. Setters. The disorder is clinically characterized by
These structures are surrounded by a joint capsule and temporomandibular joint laxity, resulting in subluxation
supported by a lateral ligament and adjacent muscles or luxation, and an inability to close the mouth. CT
of mastication. High‐resolution imaging protocols are imaging features include flattening of the condyloid
1,2
necessary to visualize these structures. Osseous process and mandibular fossa and hypoplasia of the
structures are well visualized on CT images, although retroarticular process (Figure 1.3.5). Although overt
the intrinsic soft tissues of the joint are not clearly luxation is uncommon, the joint frequently appears
delineated (Figure 1.3.1). On MR images, the condyloid incongruent or subluxated (Figure 1.3.6). As with other
process and region of the mandibular fossa appear T1 forms of dysplasia, the phenotypic expression of this
and T2 hyperintense centrally, as a result of medullary disorder is variable, and imaging findings may be subtle
fat, with a well to poorly defined signal void peripherally in some patients.
defining the subchondral bone margins. The articular Craniomandibular osteopathy
disc is sometimes visible and has T1 iso‐ to hyperinten-
sity and variable T2 intensity compared to muscle Craniomandibular osteopathy is an autosomal recessive
(Figure 1.3.2). 3 developmental disease primarily affecting young West
Highland White and other Terriers but also reported in
6–8
Developmental disorders a number of other breeds. Clinical signs include
swelling of the jaw due to bilaterally symmetrical new
Subchondral cysts bone production, which can involve the mandibular
Subchondral bone cysts are occasionally seen in the body, ramus, and articular parts of the mandible. With
condyloid process and are often clinically silent. Some severe manifestations, proliferative new bone encases
cysts appear to be closed, while others may communicate the temporomandibular joints and extends to the tem-
with the joint space at the caudal aspect of the process. On poral regions of the calvarium. Although radiographic
CT images, cysts appear as spherical defects with well‐ evaluation usually suffices for diagnosis of the disorder,
demarcated dense bone margins (Figure 1.3.3). On MR CT imaging may be useful to more accurately character-
images, cysts are typically T2 hyperintense and T1 hypoin- ize the extent of temporomandibular joint involvement.
tense centrally with a well‐defined signal void peripher- CT imaging features include symmetrically distributed
ally because of the dense bone margin (Figure 1.3.4). uniformly dense proliferative medullary and external

Atlas of Small Animal CT and MRI, First Edition. Erik R. Wisner and Allison L. Zwingenberger.
© 2015 John Wiley & Sons, Inc. Published 2015 by John Wiley & Sons, Inc.
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