Small Animal Radiology and Ultrasound: A Diagnostic Atlas and Text

640 Small Animal Radiolo g y and Ultrasono graphy
with hypertrophic osteodystrophy and those seen with craniomandibular osteopathy. The
abnormal metaphyseal bony proliferation may result in an angular limb deformity similar
to that of hypertrophic osteodystrophy. The lesion of the appendicular skeleton regresses
in a manner similar to that of the skull.
Temporomandibular Subluxation and Ankylosis. Temporomandibular subluxation, or
dysplasia, has been associated with chronic intermittent open-mouth locking of the temporomandibular
joint in the dog and cat. 104-106 Radiographic changes include an abnormally
shaped temporomandibular joint space; flattened mandibular condyles; small, flat
mandibular fossae; and an enlarged, hypoplastic, or missing retroglenoid process. In some
patients, the temporomandibular joint conformation may appear normal. When the jaw is
locked open, the abnormal temporomandibular joint subluxates and the jaw shifts to the
opposite side, becoming locked. Locking of the jaw also may occur secondary to trauma,
without evidence of preexisting joint abnormality.
Ankylosis of the temporomandibular joint may occur as a primary or secondary event.
Causes may include tumors, infections, trauma, or degenerative changes. Radiographic
findings may include new bone formation, either tumor bone or periosteal new bone. 107
Remodeling of the temporomandibular joint or obliteration of the joint space may be
noted also. 107,108
Idiopathic Hyperostosis of the Calvarium. A condition has been described in young
Bullmastiff dogs in which there was cortical thickening of frontal, temporal, and occipital
bones with an irregular bony proliferation. 109
Thickening of the Osseous Tentorium Cerebelli. The tentorium cerebelli is a thin bony
protrusion extending rostrally from the dorsal part of the occipital bone and from the dorsal
caudal portions of the parietal bones dividing the cerebellum and brain stem from the
cerebrum (caudal fossa from the cranial fossa). On occasion radiographic changes may be
noted. With marked hydrocephalus the size of this structure may be diminished markedly.
Tumors also may affect the tentorial process, causing either destruction or production of
bone (Fig. 5-36). Thickening or enlargement of the tentorium may be observed, especially
in cats. The significance of this finding is not known.
Metabolic Diseases. Metabolic diseases that affect calcium metabolism, such as primary,
secondary, and tertiary hyperparathyroidism, or others, may be evaluated radiographically.
The mandible is a convenient site for this evaluation because these conditions may cause a
generalized loss of density in the lamina dura dentes, which is the cortical bone of the tooth
alveolus. 110 In more advanced disease there may be a fractures, generalized demineralization
of the entire skull, enlargement of the bony structures, and soft-tissue swelling. 111-114
The enamel of the teeth is one of the last areas to be depleted of calcium; therefore the
appearance of teeth floating in soft tissue develops (Fig. 5-37).
N A S A L PA S S AG E S A N D S I N U S E S
Many diseases that affect the nasal passages and sinuses can cause radiographically apparent
changes. 115–117 These include allergic, parasitic, bacterial, fungal, traumatic, foreign
body, and neoplastic diseases. Parasitic causes include Capillaria, 118 Eucoleus, 119
Baylisascaris, Linguatula, 120 and Pneumonyssus. 121 Fungal causes include Aspergillus,
Cryptococcus, Penicillium, Rhinosporidium, 122 and Actinomyces. Many different neoplasms
may occur within the nasal cavity including adenocarcinoma, nonkeratinizing squamous
cell carcinoma, chondrosarcoma, lymphoma, and fibrosarcoma. Less commonly encountered
tumors of the nasal cavity include mast cell tumor, meningioma, melanoma, transmissible
venereal tumor, squamous cell carcinoma, and osteosarcoma. 123–127 The
radiographic findings are never specific for a tumor type.
Radiographic evaluation of the nasal cavity is performed to identify the location and
extent of the lesion that is producing the patient’s clinical signs. In most cases, a definitive
diagnosis cannot be made based on the radiographic appearance of the lesion. However,
radiography is still useful because it provides information relative to localization and extent