Small Animal Radiology and Ultrasound: A Diagnostic Atlas and Text

72 Small Animal Radiolo g y and Ultrasono graphy
Fig. 2-45 A 3-year-old male Yorkshire Terrier that had been
attacked by a larger dog was in shock and had dyspnea. The ventrodorsal
radiograph reveals an abnormal separation between the left
fifth and sixth ribs (large, straight arrow). There is gas in the soft tissues
around this area (small arrows). Pleural fluid density, presumably
a blood clot, is present at the site (large, curved arrow). No
evidence of pneumothorax is noted. Diagnosis: Intercostal tear of
the left fifth intercostal space, pleural hematoma, and subcutaneous
emphysema.
R I B T U M O R A N D I N F E C T I O N
Tumor and infection may involve the ribs, and both productive and destructive bony
lesions may be identified. Infection may be hematogenous, may extend from the chest wall,
or may extend from the pleural space. Osteomyelitis is usually proliferative with minimal
amounts of bony destruction. Rib tumors may be primary or metastatic. Fibrosarcoma,
chondrosarcoma, and osteosarcoma may arise from the rib or costal cartilage. These
tumors may grow inward and produce large extrapleural masses (Fig. 2-46). Rib destruction
or soft-tissue calcification or both may be evident radiographically. Displacement or
invasion of adjacent ribs may occur. Metastatic lesions are often small when detected and
may be proliferative, destructive, or both. Cortical expansion, a soft-tissue mass, or both
may be identified. The cortical malalignment usually associated with rib fracture will not
be present unless a pathologic fracture has occurred. Pleural fluid, often bloody, is a common
secondary finding with invasive rib tumors.
THORACIC WALL ANOMALIES
Several types of chest wall deformity have been described. Pectus excavatum, also called
funnel chest or chondrosternal depression, is a reduction in the dorsoventral thoracic
diameter due to displacement of the sternum dorsally into the thorax (Fig. 2-47). 74,79 This
usually displaces the cardiac silhouette to one side or the other and creates soft-tissue shadows
that overlie the lung and create difficulty in cardiac and pulmonary evaluations. In the
lateral radiograph, the sternum may be superimposed on the cardiac silhouette and curvature
of the ribs may be observed.
Pigeon breast, another chest wall deformity, may be acquired in dogs with cardiomegaly
secondary to congenital heart disease (Fig. 2-48). It has no clinical significance.
The sternum is angled excessively in a caudoventral direction, producing a dorsoventral