Thoracic and abdominal radiology pearls (Proceedings)
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.