Small Animal Radiology and Ultrasound: A Diagnostic Atlas and Text

Chapter Five The Skull 627
Fig. 5-20 A 3-month-old male
Labrador Retriever with an enlarged
left mandible. The oblique lateral
view revealed a markedly expanded
body of the mandible. The revealed
body was relatively radiolucent in its
center but contained some highly
dense toothlike structures (black
arrow) that were poorly formed.
Diagnosis: Odontoma, previously
referred to as adamantinoma.
An uncommon lytic lesion that may have radiographic and histologic attributes suggesting
a malignant bone tumor but that is actually a benign, nonneoplastic process is central
giant cell granuloma of bone. 68
Trauma. Trauma to the calvarium can cause permanent or transitory neurologic
changes without overt fractures. In those cases in which there is radiographically apparent
bony damage, the most common finding is a linear defect in the bone with minimal
displacement of fracture fragments (Fig. 5-21). It is important to differentiate vascular
channels that create relatively smooth lucencies with sclerotic borders and branching
patterns from the more irregular fracture lines. Skull fracture fragments may be
depressed into the brain. This is most common with fractures of the dorsal or lateral portions
of the skull.
Fractures of the base of the skull, middle ear, and temporomandibular joints may be
difficult to assess. If fractures of the osseous bullae are present, the fragments may be displaced
into their lumen. Fractures of the temporomandibular joints are uncommon but
may occur in association with luxations. Luxations of the temporomandibular joints may
be best noted on the lateral oblique or dorsoventral views. The luxation will be apparent
because of the loss or distortion of the normally smooth, semilunar shape of the joint space
or positioning of the condyloid process cranially or caudodorsal to the mandibular fossa of
the temporal bone (Fig. 5-22). In cats, temporomandibular joint injury should be suspected
when dental malocclusion is present, with or without mandibular symphyseal separation.
Fractures of the retroarticular process, mandibular fossa, zygomatic portion of the
temporal bone, and condylar process of the mandible are seen in association with
temporomandibular joint luxation in cats. 69 Subluxations are very difficult to evaluate
(Fig. 5-23). Although fractures affecting the temporomandibular joints usually involve the
mandible (condyloid process), fractures of the temporal bone may occur also. Fractures in
this region are particularly difficult to demonstrate and multiple oblique projections may
be required.
The zygomatic processes and maxillae are susceptible to fracture and are readily evaluated.
Zygomatic fractures usually involve the most lateral portion of the zygomatic arch but
may involve other sites as well. Maxillary fractures are usually linear with minimal displacement
unless the fracture lines encircle the muzzle (Fig. 5-24).