Page 434 - Atlas of Small Animal CT and MRI

424 Atlas of Small Animal CT and MRI

technique consisted of dark blood, steady‐state free Cardiac chamber enlargement
procession cine, unenhanced and contrast‐enhanced T1‐ Left and right atrial/ventricular enlargement results
weighted imaging, and delayed inversion recovery from mitral or tricuspid insufficiency, respectively, and
prepped imaging. MR features included mixed T1 inten­ may be seen in patients imaged for reasons other than
sity, T2 hyperintense mural masses that variably enhanced cardiac disease. On unenhanced CT images, the dilated
following contrast administration. chamber is hypoattenuating compared to adjacent myo­
cardium. The presence of intravascular contrast media
Heart results in enhancement within the cardiac chambers,
which are well delineated by surrounding myocardium
Although cardiac CT and MRI are frequently used in peo­ (Figure 4.4.9). Pulmonary CT features of left ventricular
ple for diagnosis of coronary artery, myocardial viability, failure are described in Chapter 4.6.
and cardiac function disorders, there are only sporadic
reports of their use in clinical veterinary medicine. 9–16 This Myocardium
may be in large part due to the relative paucity of coronary CT and MR are not routinely used for evaluation of
artery disease in domestic animals and to the utility of cardiomyopathy since these disorders are well character­
ultrasound for diagnosis and monitoring of the common ized using conventional radiography and echocardiog­
cardiac disorders of dogs and cats. Rapid multislice CT raphy. However, ventricular chamber dilatation (dilated
scanning with prospective or retrospective cardiac gating cardiomyopathy) or myocardial thickening associated
is necessary to accurately depict cardiac anatomy with with reduced ventricular chamber volume (hypertrophic
minimal motion artifact. Cardiac MR imaging requires cardiomyopathy) may occasionally be seen in patients
specific imaging software and also employs cardiac gating with clinically silent or controlled cardiomyopathy
techniques. An in‐depth discussion of cardiac MR imag­ imaged for other reasons (Figure 4.4.10). Characterization
ing pulse sequences is beyond the scope of this text, but of myocardial perfusion deficits in cats with hyper­
studies typically include “dark blood” fast spin‐echo trophic cardiomyopathy using contrast‐enhanced MR
sequences, “bright blood” gradient‐recalled echo (GRE) or has been reported, although results were inconsistent
steady‐state free procession sequences, and inversion (Figure 4.4.11). The use of MR for anatomic and func­
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recovery (IR) and phase‐contrast sequences in both short tional myocardial imaging in veterinary medicine is
and long‐axis imaging planes. 17
otherwise limited. 20–23
Normal heart
The complex internal and external anatomy of the heart Neoplasia
Hemangiosarcoma is the most common cardiac neo­
and great vessels is depicted in Figure 4.4.5.
plasm of dogs and usually arises from the right atrium.
Developmental disorders Cardiac hemangiosarcoma can be either primary or
The imaging appearance of the various developmental metastatic, and hemopericardium is a frequent sequela
to erosion through the myocardium. Cardiac hemangio­
cardiac disorders depends on the specific anomaly. From sarcoma appears as a space‐occupying luminal mass that
a combination of two‐dimensional CT images and 3D may be isoattenuating to adjacent myocardium and
renderings, one can assess for chamber enlargement, enhances following contrast medium administration
presence of stenosis, poststenotic dilatation, intracardiac (Figure 4.4.12). Pericardial effusion may be evident in
or extracardiac shunting lesions, and other anatomic those patients with active pericardial hemorrhage. Other
defects (Figures 4.4.6, 4.4.7). CT is also useful for iden­ cardiac‐associated neoplasms occasionally encountered
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tifying cardiac vascular ring anomalies (Figure 4.4.8). include aortic body tumors (chemodectoma), lym­
phoma, and rhabdomyosarcoma (Figure 4.4.13). Other
Acquired disorders than hemangiosarcoma, cardiac metastasis is rare. 24,25
Acquired cardiac disorders in veterinary patients are
typically not evaluated using CT or MR since other diag­ Pulmonary vasculature
nostic tests yield satisfactory results. However, changes
in cardiac chamber volume and myocardial wall thick­ Oligemia
ness are frequently seen in patients undergoing thoracic Generalized pulmonary oligemia can occur from hypo­
imaging for other disorders. Coronary artery angiogra­ volemia, resulting in reduced pulmonary perfusion volume,
phy, another common use for CT in human medicine, is or may be regional, multifocal, or solitary and result from
likewise rarely used in veterinary medicine because of pulmonary artery branch occlusion or pulmonary arterial
the lack of significant coronary arterial disease. hypertension (Figure 4.4.14). Nonuniform pulmonary

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