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Abnormalities::Chest radiograph

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Abnormalities

Nodule

A nodule is a discrete opacity in the lung which may be caused by:

There are a number of features that are helpful in suggesting the diagnosis:

  • rate of growth
    • Doubling time of less than one month: sarcoma/infection/infarction/vascular
    • Doubling time of six to 18 months: benign tumour/malignant granuloma
    • Doubling time of more than 24 months: benign nodule neoplasm
  • calcification
  • margin
    • smooth
    • lobulated
    • presence of a corona radiata
  • shape
  • site

If the nodules are multiple, the differential is then smaller:

Cavities

A cavity is a walled hollow structure within the lungs. Diagnosis is aided by noting:

  • wall thickness
  • wall outline
  • changes in the surrounding lung

The causes include:

Pleural abnormalities

Fluid in space between the lung and the chest wall is termed a pleural effusion. There needs to be at least 75ml of pleural fluid in order to blunt the costophrenic angle on the lateral chest radiograph, and 200ml on the posteroanterior chest radiograph. On a lateral decubitus, amounts as small as 50ml of fluid are possible. Pleural effusions typically have a meniscus visible on an erect chest radiograph, but loculated effusions (as occur with an empyema) may have a lenticular shape (the fluid making an obtuse angle with the chest wall).

Pleural thickening may cause blunting of the costophrenic angle, but is distinguished from pleural fluid by the fact that it occurs as a linear shadow ascending vertically and clinging to the ribs.

Diffuse shadowing

The differential for diffuse shadowing is very broad and can defeat even the most experienced radiologist. It is seldom possible to reach a diagnosis on the basis of the chest radiograph alone: high-resolution CT of the chest is usually required and sometimes a lung biopsy. The following features should be noted:

Pleural effusions may occur with cancer, sarcoid, connective tissue diseases and lymphangioleiomyomatosis. The presence of a pleural effusion argues against pneumocystis pneumonia.

Reticular (linear) pattern
(sometimes called "reticulonodular" because of the appearance of nodules at the intersection of the lines, even though there are no true nodules present)
Nodular pattern
Cystic
Ground glass
Consolidation

Signs

  • The silhouette sign is especially helpful in localizing lung lesions. (e.g., loss of right heart border in right middle lobe pneumonia),<ref name="OBGYN">Chest X-Ray, OB-GYN 101: Introductory Obstetrics & Gynecology. © 2003, 2004, 2005, 2008 Medical Education Division, Brookside Associates, Ltd. Retrieved 9 February 2010.</ref>
  • The air bronchogram sign, where branching radiolucent columns of air corresponding to bronchi is seen, usually indicates air-space (alveolar) disease, as from blood, pus, mucus, cells, protein surrounding the air bronchograms. This is seen in Respiratory distress syndrome<ref name="OBGYN"/>
  • The "bean" sign first described by Professor Keval Pandya is the appearance of a sharply circumscribed bean shaped nodule on chest X-ray which has a high sensitivity and specificity (92% and 88%) for the presence of miliary TB.

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Abnormalities
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