Why all the heavy breathing? Radiography of pulmonary pathology (Proceedings)

Initially we have to review all the normal structures on a thoracic radiograph before we can begin to discuss pathology. So a review....There are three main normal structures in the lungs: the interstitium, airways, and vessels. The interstitium is the supporting structure of the lungs. The bronchi are the large airways and can be seen as they taper and converge together toward the lung. These are so thin they are radiolucent when normal. Mineralization of the bronchial wall (does not cause thickening just increased visualization) can be an age related change. The vessels are thicker than the bronchi and diverge as they extend into the periphery. In a lateral view, the artery is dorsal, the bronchus is in the middle, and the vein is ventral. In left lateral recumbency, the right cranial lobar artery and vein should be the same diameter. The diameter of each vessel should not exceed the smallest diameter of the right 4th rib. On the VD view, the artery is lateral and the vein is axial. The caudal lobar pulmonary artery and vein are similar in size. In the dog, the diameter of these two vessels should not exceed the diameter of the 9th rib. In a cat the vessels are compared to the size of the 10th rib.

It is important to be able to distinguish inspiratory from expiratory radiographs because expiratory films can artifactually appear to have pathology. The post cardiac triangle (the area of the lungs that is caudal to the heart, cranial to the diaphragm and ventral to the caudal vena cava will be large if inspiratory exposure. The lumbodiaphragmatic angle (where the caudal dorsal lung extends adjacent to the lumbar spine on a lateral view) is at or caudal to T12 on an inspiratory film. The costodiaphragmatic angle (where the diaphragm meets the costal arches on a VD view) should be at or caudal to T10 on an inspiratory film. The diaphragmatic cupula will be at or caudal to T8 on an inspiratory VD view. The retrosternal lucency dorsal to the sternum on a lateral view will extend to the 5th sternal segment during inspiration. The apex of the left cranial lung lobe on a lateral view will extend cranial to the first rib on a full inspiratory film. Poor exposure can also be problematic. Underexposure will simulate disease while overexposure will mask disease.

Now onto pathology. We will start with a bronchial pattern. A bronchial pattern is caused by infiltration of the airway by inflammatory cells, edema, neoplastic cells, or mineral. Chronic bronchitis can be due to allergic, parasitic, or inflammatory etiologies. Edema from cardiac disease can cause what appears to be a bronchial pattern but it is actually a peribronchial infiltrate. With bronchoalveolar carcinoma a primary bronchial pattern is seen with concurrent interstitial and alveolar patterns as well. This is considered a mixed pattern. Mineralization of the bronchi can occur with diseases such as Cushings disease. Bronchiectasis is an increased diameter of bronchi or lack of tapering as they extend into the periphery. This represents end stage of chronic bronchial disease and can be secondary to ciliary dyskensis. Feline bronchial lung disease (a syndrome) presents with prominent bronchial markings, 37% have concurrent alveolar lung disease, 10% have collapse of the right middle lung lobe and 10% have pulmonary overinflation due to air trapping. Radiographically bronchial disease appears as "tram lines" which are thickened paired linear/ branching lines which converege as they are traced into the lung periphery or "donuts" which are thickened bronchi viewed in cross section.

There are two types of interstitial patterns. Nonstructured and structured (nodular). Nonstructured is identified as infiltration of lung with soft tissue opaque material. This results in increased pulmonary opacity and decreased visualization of pulmonary vasculature. The pulmonary vascular markings are obscured but not obliterated. This can be described in four different ways: hazy (fog-like), short linear fuzzy soft tissue pulmonary markings (called reticular or linear interstitial), numerous punctate dot-like opacities (called miliary interstitial), and small irregular to round very fuzzy soft tissue aggregate opacities usually seen in conjunction with short fuzzy linear markings (called reticulonodular). Diseases which cause an interstitial pattern include 1) interstitial fibrosis – aging or scarring from chronic lung disease 2)

Interstitial pulmonary edema – perihilar in location with associated cardiomegaly and pulmonary venous congestion 3) Granulomatous (fungal) pneumonia - reticulonodular manifestation is frequent and 4)