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Densities in CXR
|Pulmonary artery||Liquid density|
|Left atrium||Liquid density|
Bronchi are visible only up to 4th or 5th order of branching.
The thickness of cartilage decreases with each branching and the walls become progressively thin.
In addition they are surrounded by air filled alveoli and hence there is no contrast to be able to recognize the bronchi.
If the bronchi are recognizable beyond 5th order of branching it is abnormal. This can occur in
Visibility of Lumen: Alveolar filling will provide the necessary contrast. Recognizable bronchi as branching air filled lucencies in a density is called air bronchogram and indicates alveolar disease.
Visibility of wall: If the bronchi wall is thickened (Chronic bronchitis, Bronchiectasis) or there is cartilaginous calcification then you can recognize them also. There is no surrounding density in this instance.
Helps in localization of disease in Lungs and Mediastinum
Example: Consolidation of RLL and RML will project in the right lower lung field. We can use Silhouette sign to localize. RML is adjacent to right heart margin and does not reach diaphragm. Hence if the right heart margin is indistinct with a sharp diaphragm the lesion has to be in the RML. Of course lateral view will easily resolve whether it is RML or RLL lesion.
In order to use Silhouette sign you need to know the location of each Silhouette and the lobe adjacent to it.
|Right diaphragm||Right Lower lobe, Pleura|
|Right Heart margin||Middle lobe, Anterior Mediastinum|
|Ascending Aorta||RUL, Anterior Mediastinum|
|Aortic Knob||LUL, Posterior Mediastnum|
|Left Heart margin||Lingula, Anterior Mediastinum|
|Left Diaphragm||Left Lower lobe, Pleura|
Pleural disease can obliterate all of the silhouettes.
- Liquid density less than a segment
- With alveolar features
- Viral Pneumonia
- Alveolar cell carcinoma
Acute Diffuse alveolar Disease
- Soft fluffy lesions
- Coalescing lesions
- Air bronchogram
- Butterfly/Medullary distribution
- Cortical distribution
- Segmental/Lobar density
- Pulmonary edema
- Coag defect
- Pulmonary hemosiderosis
- Inflammatory exudate
Calcified miliary Lung nodules
|Histoplasmosis||Co-existing nodes and Splenic calcification|
|Chicken pox||No nodes No Splenic calcification|
Calcified hilar nodes
|Histoplasmosis||Multiple densities clumped together|
|Silicosis||Egg shell/Calcification of rim|
- Dark lung fields
- low flat diaphragm
- Vertical heart
- Increased retrosternal air
- Infracardiac lung
- Widened sternal angle
- Lack of vascular markings in the periphery
- Presence of blebs: Prominent lines not corresponding to fissures could be walls of blebs.
Crescent of air
Contents of Cavity
- Air fluid level
- Fungous ball
- Irregular density: stalagmites
- Lung cancer
- Swyer James syndrome
- Agenesis of Pulmonary artery
- Unilateral partial airway obstruction of large airway
Rarely done nowadays. because
- High resolution CT scan has replaced bronchogram
- Fiberoptic bronchoscopy affords easy visibility of Endobronchial lesions
Note the carina, Right main and left main
1, 2, 3 are Posterior , Anterior and Apical segments of RUL
4 and 5 are Lateral and Medial segments of RML
6, 7, 8, 9, 10 are Superior Medial, Lateral, Anterior and Posterior segments of RLL
Try to appreciate the three dimensional view of these segments. Appreciation of this is necessary to understand why certain segments are prone for aspiration. You have to think of it also on the position of the patient and determine which segment would be the site for aspiration based on gravity.
Radiological Characteristics :
- Homogenous density
- in base in upright film
- obliterating costophrenic angle
- meniscus high in axilla (visual illusion)
- shift of Mediastinum to opposite side with large effusions
- Loss of diaphragmatic Silhouette
- Congestive hear failure
- Para pneumonic
- Rheumatoid arthritis
- In the presence of pleural effusion pleural masses are not visible for lack of contrast.
- In the absence of fluid the margins of density are irregular along the periphery of lungs.
- With Pneumothorax the masses become easily visible.
- With CT chest the pleural masses are easily recognizable even in the presence of fluid.