Small Animal Radiology and Ultrasound: A Diagnostic Atlas and Text

196 Small Animal Radiolo g y and Ultrasono graphy
A
B
Fig. 2-176 A 4-year-old male mixed breed dog with a history of respiratory distress and fever occurring
1 week following treatment for heartworm disease. A, In the initial thoracic radiograph there is
a local area of interstitial density in the caudal dorsal lung (open arrows). This is indicative of pulmonary
thrombosis or embolization secondary to heartworm treatment. B, On the follow-up radiograph,
repeated 10 days after initial evaluation, an enlarged irregular pulmonary artery is evident in
the caudal dorsal lung lobe (closed arrows). This most likely represents thrombosis of the pulmonary
artery. Diagnosis: Pulmonary thrombosis and embolization secondary to treatment for dirofilariasis.
density due to oligemia distal to the arterial thrombosis. Rarely, an enlarged major lobar
artery, compared with its paired vein, may be seen if a comparatively large embolus lodges
in such a vessel. More commonly, an alveolar pattern infiltrate due to the hemorrhage,
necrosis, and inflammation is present. These patterns are seen only if major pulmonary
arteries are occluded. Obstruction of minor arteries will not lead to radiographic changes,
because the collateral circulation present at that level prevents significant oligemia to the
tissues. If a thrombosis is caused by dirofilariasis, enlarged, tortuous, or irregularly shaped
pulmonary vessels usually are visible.
Air embolism from diagnostic procedures, such as pneumocystography, or surgical
procedures may result in cardiac arrest or difficulties. 554 Minor embolizations probably are
not clinically recognized. Severe embolizations usually result in cardiac arrest and death.
Because air has a different radiographic density than blood, the air may be visible within
the heart and pulmonary arteries in severe cases.
LU N G L O B E T O R S I O N
Lung lobe torsion usually occurs with hydrothorax. A solitary lung lobe that has a severe
alveolar pattern infiltrate and also has an abnormal shape may be seen. 555-557 The involved
lung lobe will become dense, and air bronchograms may be evident early in the disease.
Later, the lung will fill completely with fluid and the air bronchograms will disappear (Figs.
2-63 and 2-177). The main lobar bronchus may remain aerated and visible for a short distance.
Abrupt termination of the bronchus after it branches from the trachea may be seen.
The right middle lung lobe is affected most frequently, with the right and left cranial lung
lobes the next most frequent. 67 Lung lobe torsion is more common in deep-chested breeds
of dogs but may be seen in other breeds as well as in cats. 150,558-560 Although rare, torsion
of multiple lobes over time has been reported in a dog. 556