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Densities in CXR

• Air
• Bone
• Liquid

Air bronchogram

• Ability to visualize distal bronchial tree as air filled dark tubular structures is called air bronchogram.
• Visualization of lumen as opposed to visualization  of wall. When the wall of the bronchial tree is visualized it is called thickened bronchi
• This occurs when the alveoli are filled or atelectatic and the bronchial tree is patent.
• Alveolar filling displaces air with a liquid density and  provides a contrast to visualize air filled bronchi
• Presence of air bronchogram indicates alveolar process

Bronchial Visibility

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

1. 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.

2. 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.

Silhouette sign:

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.

Pleural disease can obliterate all of the silhouettes.

Infiltrate

Radiological Characteristics

• Liquid density less than a segment
• With alveolar features

Etiology

• Tuberculosis
• Viral Pneumonia
• Alveolar cell carcinoma

Unilateral opacification

1. Massive pleural effusion
   • Opacification associated with signs of expanded lung volume
   • Larger hemi thorax
   • Deviation of Mediastinum to opposite side
2. Complete atelectasis of Lung
   • Opacification associated with signs of loss of lung volume
   • Smaller hemi thorax
   • Deviation of Mediastinum to same side

Acute Diffuse alveolar Disease

Radiological Characteristics

• Soft fluffy lesions
• Coalescing lesions
• Air bronchogram
• Butterfly/Medullary distribution
• Cortical distribution
• Alveologram
• Segmental/Lobar density

Common Etiology

• Water
  • Pulmonary edema
• Blood
  • Coag defect
  • Goodpastures
  • SLE
  • Wegners
  • Pulmonary hemosiderosis
• Inflammatory exudate
  • ARDS
  • CMV
  • Pneumocysis
  • Mycoplasma
  • Influenza
  • Leigionella

Calcified miliary Lung nodules

Calcified hilar nodes

Segmental density

• Bronchial segment

  • Endobronchial lesion

    • Cancer

    • Foreign body

    • Granuloma

    • Benign tumor

  • Aspiration

• Vascular segment

  • Pulmonary infarct

    • Pulmonary embolus

    • Invasive Aspergillosis

 

Hyperinflation

Radiological Characteristics

• Dark lung fields
• low flat diaphragm
• Vertical heart
• Increased retrosternal air
• Infracardiac lung
• Widened sternal angle

Etiology

• Asthma
• Emphysema
  • Lack of vascular markings in the periphery
  • Presence of blebs: Prominent lines not corresponding to fissures could be walls of blebs.

 

 

Fungous ball Radiological characteristics cavity Ball inside Crescent of air Etiology Aspergillus

Contents of Cavity Air fluid level Abscess Hemorrhage Mass Fungous ball Irregular density: stalagmites Lung cancer

Unilateral Hyperlucency 

• Pneumothorax
• Swyer James syndrome
• Agenesis of Pulmonary artery
• Unilateral partial airway obstruction of large airway

Bronchogram

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.

Pleural effusion

Radiological Characteristics :

1. Homogenous density
2. in base in upright film
3. obliterating costophrenic angle
4. meniscus high in axilla (visual illusion)
5. shift of Mediastinum to opposite side with large effusions
6. Loss of diaphragmatic Silhouette

Common Etiology

• Congestive hear failure
• Cancer
• Tuberculosis
• Hemothorax
• Para pneumonic
• Empyema
• Rheumatoid arthritis

Pleural masses

Radiological Characteristics

• 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.

Etiology

Mesothelioma

Metastatic lesions

• Thymoma
• Cystadenocarcinoma

Plasmacytomas