Page 435 - Atlas of Small Animal CT and MRI

Heart, Pulmonary Vasculature, and Great Vessels 425

perfusion results in regions of lower than expected attenu­ leads to main pulmonary artery enlargement and mosaic
ation on CT images, referred to as a mosaic pattern in the perfusion pattern (low‐attenuation areas due to oligemia).
human literature. Although CT features of pulmonary thromboembolism
have not been well described in domestic animals, clinical
Pulmonary hypertension experience suggests features are similar to those described
Pulmonary hypertension is the sequela to either increased in people (Figure 4.4.16). 27
flow resistance in the pulmonary arteries from vasocon­
striction, stenosis, pulmonary disease, or obstruction or Heartworm disease
from pulmonary venous congestion due to left heart fail­ Canine heartworm disease is endemic in many geo­
ure or other causes of disrupted venous return. Typical graphic areas and can cause profound cardiovascular and
CT features of pulmonary arterial hypertension in people pulmonary abnormalities associated with arteritis, pul­
include right heart, pulmonary trunk, and proximal lobar monary hypertension, vascular obstruction by adult
artery enlargement, with arterial narrowing or truncation filariae, and thromboembolism. These changes can be
peripherally, depending on the underlying cause. Lung amplified during adulticide treatment as a result of
parenchyma may also have a nonuniform density (mosaic pulmonary arterial showering of dying adult filariae. CT
pattern) associated with variable perfusion. CT features of features of heartworm infestation include mild but pro­
pulmonary venous hypertension include increased inter­ gressive enlargement of the lobar pulmonary arteries and
stitial to alveolar pulmonary attenuation due to pulmo­ intermittent periarterial interstitial infiltrates in the
nary edema and hemorrhage associated with small vessel prepatent phase of infection. Adult filariae have been
28
obstruction. We have observed similar imaging features detected in pulmonary arteries on contrast‐enhanced CT
26
28
in dogs and cats with pulmonary arterial and venous images. In dogs followed with serial CT examinations
hypertension (Figure 4.4.15). before and during adulticide therapy, peripheral arteries
increased in diameter in the first month following initia­
Pulmonary thromboembolism tion of treatment then subsided over a 15‐month period,
Pulmonary thromboembolism is often seen as a sequela although size did not reduce to pretreatment diameter.
of a hypercoagulable state or in patients with inflam­ Periarterial pulmonary infiltrates accompanied the arte­
matory pulmonary vascular disorders, such as heart­ rial changes in some instances. The increase in arterial
worm disease. In people, CT angiography is considered diameter was found to be due to arteritis and intralumi­
the imaging study of choice for diagnosis of pulmonary nal dead adult filariae lodged in the peripheral vessels,
thromboembolism, and characteristic imaging features and the eventual reduction in arterial diameter was
of acute and chronic forms have been described. In the thought to be associated with recanalization of affected
acute phase, blood clots are rarely seen on unenhanced vessels. Pulmonary infiltrates were found to be due to
CT images but are clearly seen as well‐defined filling pneumonia, thought to be an extension of the arteritis. 29
defects on contrast‐enhanced images, with arterial
enlargement sometimes present proximal to the site Great vessels
of obstruction and an abrupt termination of the
enhancing vessel distally with complete obstruction. Aortic mineralization
Partial obstruction results in eccentric filling defects. Radiographic and CT features of aortic mineralization
Widespread or large artery thromboembolism can result have been reported to involve primarily the aortic root
in right ventricular failure with associated distension of and arch. Mineralization is thought to represent dys­
the right ventricle, vena cava, and hepatic veins. Small trophic calcification associated with degeneration in the
artery embolism may result in focal pulmonary infarc­ tunica media in older dogs and was thought to be a clini­
30
tion in the periphery of the lung. These often have a cally silent finding. Aortic mineralization is occasion­
wedge shape corresponding to the geographic perfusion ally seen as an incidental finding on thoracic CT images
distribution of the affected vessel. in dogs and cats and will appear as focal or curvilinear
CT features of chronic pulmonary thromboembolism regions of high attenuation that follow the contour of the
in people are characterized by filling defects on contrast‐ vascular wall on transverse images (Figure 4.4.17).
enhanced images. Chronic thrombi are approximately
90 HU, so they will appear hyperattenuating compared Large vessel thrombosis
to patent vessels on unenhanced CT images. Affected Thrombosis of the aorta or vena cava is uncommon and
vessels are of smaller diameter than unaffected vessels. is usually a sequela of an underlying primary disorder
Development of collateral bronchial circulation may occur leading to hypercoagulability or vascular stasis
with chronic disease. Pulmonary arterial hypertension (Figures 4.4.18, 4.4.19). 31
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