The Air Bronchogram Sign

On the normal chest x-ray, we see air in the trachea and proximal bronchi because they are surrounded by the soft tissue (water density) of the mediastinum. In the lungs, however, the bronchi are not visible. The only branching structures visible in the lungs are the pulmonary vessels (water density) surrounded by air.

1 The linear markings seen in the lungs are basically blood vessels, which are: A. air density B. bone density C. water density D. run perpendicular to the x-ray beam	1 C. water density (soft tissue)
Because bronchi have very thin walls, contain air, and are surrounded by air-filled alveoli, the intraparenchymal bronchi __________ visible on a normal chest x-ray. A. are B. are not	B. are not
In *Figure 7-1A* , the branching pulmonary vessels are visible in the lung. The trachea and proximal main bronchi ( arrows ) are surrounded by mediastinal soft tissue and are visible. The peripheral bronchi are not visible. On computed tomography (CT), the bronchi are normally visible through much of the lung. In *Figure 7-1B* **, a right bronchus ( arrow ) appears tubular (in plane) and a left bronchus ( arrow ) appears circular (perpendicular to plane). Figure 7-1C** , a coronal CT reconstruction, shows the distal trachea, carina, and intraparenchymal bronchi in plane ( upper arrow ), perpendicular ( middle arrow ) and oblique ( lower arrow ) as a tube, circle, and oval.
2 To visualize the bronchi, we used to instill an opaque material (iodinated oil) into the bronchial lumen. The “positive” contrast bronchogram is seldom performed now because patients __________ having thick oily goop dumped into their bronchi. A. loved B. hated	2 B. hated
*Figure 7-2A* *shows a bronchogram with iodinated contrast medium filling normal medial bronchi and dilated lateral bronchi (bronchiectasis). CT has replaced bronchography. In a different patient,* *Figure 7-2B* *shows multiple dilated bronchi in cross-section on the left and relatively normal bronchi on the right in cross section (perpendicular).* *Figure 7-2C* *is a coronal CT scan that shows the left lower lobe bronchiectasis longitudinally.*
3 Do we ever see normal bronchi on a chest x-ray? Sure we do! When the lung is consolidated and the bronchi contain air, the dense lung delineates the air-filled bronchi. Visualization of air in the intrapulmonary bronchi on a chest roentgenogram is called the air bronchogram sign. The presence of an air bronchogram indicates __________. A. normal lung B. interstitial thickening C. emphysema D. alveolar consolidation	3 D. alveolar consolidation
4 Figure 7-3A simulates the normal lung using two straws. Straw V (vessel) contains water, and straw B (bronchus) contains air. They are x-rayed in air. Straw _____________ is (are) easily seen. A. V B. B C. V and B Figure 7-3A Courtesy of Ms. Ann Gorman, Medical College of Wisconsin, Milwaukee	4 A. V
Straw B is much less visible because there is air inside and outside the thin-walled straw.
5 Figure 7-3B portrays a diseased (consolidated) lung; the straws are immersed in water. Straw B is now visible; this is the ________ sign. A. air bronchogram B. silhouette C. fissure Figure 7-3B	5 A. air bronchogram
Straw V now disappears, which is the ________ sign. If you missed this, review questions 1-4. A. air bronchogram B. silhouette C. fissure sign	B. silhouette
*Figure 7-4* *is a scout view of a patient with left lower lobe pneumonia. The bronchi appear as branching black tubes in the consolidated lung behind the heart. In* *Figure 7-5* *, the CT scan shows a right middle lobe air bronchogram. Interstitial thickening elsewhere in the right lung does not give an air bronchogram.*
6 Copyright BEETLE BAILEY ©2005 by King Features Syndicate, Inc. World rights reserved.	6 “Doctors without borders.”
7 Soft tissue and air density are involved in the air bronchogram and silhouette sign. If an air-filled bronchus is to be seen, it must be surrounded by ____________ density. A. decreased B. increased	7 B. increased (soft tissue or water)
Conversely, if a pulmonary vessel is to be seen, it must be surrounded by _________. Not seeing the lung vessels is a variation of the silhouette sign. A. pleural effusion B. alveolar consolidation C. aerated lung	C. aerated lung
*Figure 7-6A* is a radiograph of a patient with bilateral consolidation. The right upper lobe bronchi are visible (arrows), but the pulmonary vessels are not. Arrows indicate air bronchograms in the right upper lobe.
8 What good is the air bronchogram sign? Well, for one thing, bronchi are pulmonary structures; visualization of the bronchi (air bronchogram) indicates a ____________ lesion, rather than a lesion elsewhere. A. pleural B. mediastinal C. pulmonary D. bronchiectatic	8 C. pulmonary
It means that the bronchi contain ___________. A. air B. pus C. mucus D. tumor	A. air
It means the adjacent lung is consolidated.
*Figure 7-6B* *shows extensive air bronchogram in left lower pneumonia.*
9 The air bronchogram may be seen in pneumonia, pulmonary edema, pulmonary infarction, and certain chronic lung lesions, as long as the bronchi are __________ and the surrounding lung is radiopaque (water density). A. straight B. parallel C. thick walled D. air filled	9 D. air filled
10 Do we always see an air bronchogram with pulmonary parenchymal consolidation? “Always,” of course, is _________ the answer in medicine. A. never B. always C. sometimes	10 A. never
If a bronchus is obstructed by tumor or filled with secretions, pulmonary consolidation _________ show an air bronchogram. A. would B. would not	B. would not
Patchy peripheral lung consolidation or interstitial disease usually does not cause enough lung opacity to produce an air bronchogram. Conditions that hyperinflate the lungs do not cause air bronchograms. In *Figure 7-6A* *, the right lower lobe and left lung pneumonia are not dense enough to cause air bronchograms.*
11 In pneumonia, if the bronchi are filled with secretions, there _________ be an air bronchogram within the lesion. A. would B. would not	11 B. would not
If a cancer obstructs a bronchus, an air bronchogram _________ be visible. A. would B. would not	B. would not
Interstitial fibrosis _________ cause an air bronchogram. A. would B. would not	B. would not
Asthma _________ cause an air bronchogram. A. would B. would not	B. would not
In *Figure 7-7A* *, there is no air bronchogram in the collapsed right upper lobe because the bronchi are full of mucous plugs. In this patient, a tumor obstructs the right upper lobe bronchus (* *Figure 7-7B* , arrow ).
12 The absence of an air bronchogram indicates the lesion may be ___________. A. pulmonary B. extrapulmonary C. pleural D. any of the above	12 D. any of the above
CLINICAL PEARL: Postoperative left lower lobe atelectasis is frequent and difficult to detect through the heart. Sometimes an air bronchogram seen through the cardiac shadow is the most definitive sign of left lower lobe consolidation. In *Figure 7-8* **air bronchograms ( arrows ) are visible through the density of the heart. There is also a silhouette sign of the medial diaphragm.**
13 So it’s easy! Remember, consolidated lobes may not show an air bronchogram if: (true or false)	13
The bronchi are full of secretions. A. true B. false	A. true
There is an aspirated foreign body in the bronchus. A. true B. false	A. true
There is not complete lung consolidation. A. true B. false	A. true
CLINICAL PEARL: An air bronchogram indicates open airways, strong evidence that the lung disease is not due to an obstructing tumor in a smoker.
14 Are there other uses of air bronchograms? If air-filled bronchi are very crowded together, this indicates ____________. A. overexpanded lung B. collapsed lung C. emphysema	14 B. collapsed lung (atelectasis)
The crowded air bronchograms suggest this is ____________ atelectasis. A. obstructive B. nonobstructive C. bronchiectasis	B. nonobstructive
In Figure 7-6B , the bronchi are normally spaced, whereas in Figure 7-8 they are crowded.
15 Several diseases may cause bronchiectasis. Instead of tapering, the bronchi ____________, as they course peripherally. A. fill with pus B. widen C. narrow D. disappear	15 B. widen (dilate)
*Bronchiectasis is difficult to diagnose and illustrate on an x-ray.* *Figure 7-9* **shows dilated bronchi ( arrows ) at the lung base. Figure 7-10A** shows dilated, thickened bronchi. Bronchi running in the axial plane are tubular ( straight arrows ), and bronchi running across (perpendicular to) the axial plane are circular ( curved arrow ). *Figure 7-10B* shows dilated bronchi completely filled with secretions in plane ( straight arrows ) and in cross-section ( curved arrow ).
*Anagram: Rearrange the letters in DORMITORY to form two words that better define it (answer at end of chapter).*