We often have patients present to us for coughing. Our job is to determine if it is heart disease or pulmonary disease. So
the purpose of this lecture is to review thoracic radiology and some radiographic pitfalls you should avoid. To show the importance
of differentiating between heart and pulmonary disease, the Journal of Prehospital Emergency Care evaluated the appropriateness
of diurectic administration in humans. They found that diuretics were inappropriately administered in 42% of cases. Administration
was potentially harmful in 17% of patients. In patients with pneumonia, dehydration, and sepsis diuretic administration is
contraindicated. One dose of diuretic decreases mucociliary apparatus function in pneumonia.
In humans one dose of diuretic increased mortality rate of patients without cardiac disease in 7 of 9 patients or 78%. Not
proven in animals....but could it be the same for our patients?
So our coughing patient again. We take thoracic radiographs and need to evaluate the cardiac silhouette first. We ask , "Is
it big or not???" Remember normal cardiac dimensions on the lateral view the height of the heart is ⅔ of thoracic cavity.
The height of the heart evaluates the left heart – specifically the left ventricle. Also on the lateral view, a normal heart
will be 2.5-3.5 intercostal spaces in width. The width of the heart evaluates the right heart. On the DV/DV view, the distance
between the heart and chest wall should be relatively equal on each side. The heart is less than 50% of thoracic cavity on
the DV/VD view. The trachea deviates away from the vertebral bodies on the lateral view. The left and right main stem bronchi
are superimposed just caudal to the carina. The caudal cardiac waist curves cranially to the carina on the lateral view. A
lot of people talk about "sternal contact" to evaluate the heart. This is quite a variable finding and Increased sternal contact
may be breed or age associated. Obliquity can make evaluation of the heart difficult. The trachea can artifactually be parallel
to the vertebral bodies with obliquity. Mild obliquity can cause the left main bronchi to be dorsally displaced and also make
the caudal cardiac silhouette straight. You can see that a lateral view is obliqued by looking at the rib heads, they should
be superimposed. Obliquity of the ventrodorsal view can cause the right (or left) heart appear larger. Make sure you look
at the dorsal spinous processes to assess whether the VD view is straight. They should appear as triangles centered over the
vertebral bodies.
Next we'll look at the thoracic vasculature. It is important to be able to look for congestion. Cardiac patients will have
large vessels or a large vein, whereas patients with pneumonia or sepsis will have small vessels. Normal pulmonary vasculature
on the lateral view is easiest to evaluate in the cranial ventral thorax. The artery is dorsal and the vein is ventral and
between these two is a bronchus. The artery and vein should be similar in size. These should be compared to the width of the
proximal 4th rib. You should compare the vessels to the smaller rib (which is the down side rib – there is less magnification).
In patients with pulmonary venous congestion, the vein is larger than the artery and larger than the proximal 4th rib. Another
vessel that you can look at is the caudal vena cava. Normally it extends from caudal to cranial and angles ventrally. When
the heart is enlarged, the caudal vena cava is either horizontal or angles dorsally between the diaphragm and caudal cardiac
waist. And lastly when there is pulmonary venous congestion, you are evaluating the left heart. If right heart disease is
present, look for hepatic venous congestion. IN order to do this, let's review the location of a normal liver silhouette.
On the lateral view the gastric axis should be parallel with the intercostal spaces. IN deep chested dogs, the gastric axis
can be perpendicular to the vertebral bodies and still be normal. On the VD view, the gastric axis is normally perpendicular
to spine at the level of the 10th - 12th thoracic vertebral bodies. By comparison to the normal liver, when hepatic venous
congestion is present, the gastric axis is caudally deviated and the caudal hepatic margins are rounded. Ascites may be present
as well. 
