Chest X-ray

  A chest X-ray, commonly abbreviated CXR, is a projection radiograph (X-ray), taken by a radiographer, of the thorax which is used to diagnose problems with that area.

The typical radiation dose to an adult from a chest x-ray is around 6 mrem.^[1]

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Problems identified through chest x-rays

Examples of such problems include but are not limited to:

• Pneumothorax, sometimes tension pneumothorax (though this is usually diagnosed clinically because of its acute nature)
• Rib fracture
• Air space disease/consolidation (e.g. pneumonia)
• Interstitial lung disease (e.g. idiopathic pulmonary fibrosis (IPF), lung cancer, active tuberculosis)
• Cardiac silhouette enlargement - congestive heart failure, pericardial effusion, hypertrophic cardiomyopathies
• Pleural effusion
• Peritonitis
• Hiatal hernia
• Emphysema
• Pulmonary embolism (rarely) - usually CXR is normal
• Dissecting aortic aneurysm (due to trauma, advanced/untreated syphilis, connective tissue disorders)

Chest X-Rays are among the most common films taken, being diagnostic of so many important problems.

Features that are typically examined on a chest X-ray

Every doctor will have a different approach to examining chest X-rays. A commonly used mnemonic for what to look for on a chest X-ray is: It May Prove Quite Right (but) Stop And Be Certain How Lungs Appear:

• I = Identification (name, age, sex, indication for X-ray)
• M = Markers (differentiate left from right - diagnose dextrocardia)
• P = Position - the spinous process of T4 should be between the heads of the clavicle (if it isn't the body is rotated)
• Q = Quality - is the film penetrated properly. In a properly penetrated film the vertebral interspaces should be visible behind the central (cardiac) shadow
• R = Respiration - chest X-rays are typically done with full inspiration
• (but)
• S = Soft tissue - look for subcutaneous emphysema (suggestive of trauma), soft tissue swelling
• A = Abdomen - look for free abdominal air (suggests penetrating trauma, peritonitis, or recent surgery)
• B = Bone - look for fractures (these tend to be at the lateral aspects because of the mechanics - bending moment largest at lateral aspect)
• C = Central shadow (cardiac silhouette) - greater than 50% of lateral distance in frontal view at the diaphragm suggests cardiac enlargement (usually secondary to heart failure) or a pericardial effusion). A widened mediastinum may suggest aortic dissection.
• H = Hila (of the lungs) - can be affected in lung disease, malignant processes and infection (hilar lymphadenopathy).
• L = Lungs - for consolidation, interstitial lung disease (reticular, nodular or reticulonodular), honeycombing, miliary pattern, granulomas, lung masses
• A = Absent structures/Apices of the lung (for pneumothorax)

Another approach is to examine first any major abnormality, and then "review areas":

• the apices,
• the hila,
• behind the heart (it must be remembered that lung can be seen through the heart),
• the cardiophrenic angles,
• the costophrenic angles,
• beneath the diaphragm, and then
• bone and soft tissues.

Views

Typical views

• Frontal (view)
  • PA (posterior-anterior) - pt faces AWAY from x-ray source - x-rays pass from their source to patients back through the body to exit through the anterior body wall to expose the film
  • AP (anterior-posterior) -pt FACES the x-ray source - these are typically done in the ICU
• Lateral (view)

The most common view is the PA (posterior-anterior) and is frequently done with a left lateral view (so one can identify the location of abnormalities in 3-D space). PA views are generally preferred to AP views (which are often done with mobile/portable X-ray equipment), but much less convenient in the ICU setting or when a patient cannot otherwise leave their bed. PA views are preferred because the central shadow is better defined, the magnification of the heart is reduced, and less of the lungs obscured by the heart/pericardial sac.

Additional views

• Decubitus - useful for differentiating pleural effusions from consolidation (e.g. pneumonia). In effusions, the fluid layers out (by comparison to an up-right view, when it often accumulates in the costophrenic angles).
• Lordotic view - used to visualize the apex of the lung, to pick-up abnormalities such as a Pancoast tumour.
• Expiratory view - helpful for the diagnosis of pneumothorax
• Oblique view

Abnormalities

Nodule

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

• Neoplasm: benign or malignant
• Granuloma: tuberculosis
• Infection: round pneumonia
• Vascular: infarct, varix, Wegener's granulomatosis, rheumatoid arthritis

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
• calcification
• margin
  • smooth
  • lobulated
  • presence of a corona radiata
• shape
• site

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

• infection: tuberculosis, fungal infection, septic emboli
• neoplasm: e.g., metastases, lymphoma, harmatoma
• sarcoidosis
• alveolitis
• auto-immune disease: e.g., Wegener's granulomatosis, rheumatoid arthritis
• inhalation (e.g., pneumoconiosis)

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:

• cancer (usually malignant)
• infarct (usually from a pulmonary embolus)
• infection: e.g., Staphylococcus aureus, tuberculosis, Gram negative bacteria (especially Klebsiella pneumoniae), and anaerobic bacteria.

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 X-ray, and 200ml on the posteroanterior chest X-ray. On a lateral decubitus, amounts as small as 5ml of fluid are possible. Pleural effusions typically have a meniscus visible on an erect chest X-ray, 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 is 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 X-ray alone: high-resolution CT of the chest is usually required and sometimes a lung biopsy. The following features should be noted:

• type of shadowing (lines, dots or rings)
  • reticular (crisscrossing lines)
  • nodular (lots of small dots)
  • rings or cysts
  • ground glass
  • consolidation (diffuse opacity with air bronchograms)
• location (where is the lesion worst?)
  • upper zone (e.g., sarcoid, tuberculosis, silicosis/pneumoconiosis, ankylosing spondylitis, Langerhans cell histiocytosis)
  • lower zone (e.g., cryptogenic fibrosing alveolitis, connective tissue disease, asbestosis, drug reactions)
  • central (e.g., pulmonary oedema, alveolar proteinosis, lymphoma, Kaposi's sarcoma, PCP)
  • peripheral (e.g., cryptogenic fibrosing alveolitis, connective tissue disease,chronic eosinophilic pneumonia, bronchiolitis obliterans organising pneumonia)
• lung volume
  • increased (e.g., Langerhans cell histiocytosis, lymphangioleiomyomatosis, cystic fibrosis, allergic bronchopulmonary aspergillosis)
  • decreased (e.g., fibrotic lung disease, chronic sarcoidosis, chronic extrinsic allergic alveolitis)

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 intesection of the lines, even though there are no true nodule present)

• cryptogenic fibrosing alveolitis
• connective tissue disease
• sarcoidosis
• radiation fibrosis
• asbestosis
• lymphangitis carcinomatosis

Nodular pattern

• sarcoidosis
• silicosis/pneumoconiosis
• extrinsic allergic alveolitis
• Langerhans cell histiocytosis
• lymphangitis carcinomatosis
• miliary tuberculosis
• metastases

Cystic

• cryptogenic fibrosing alveolitis (late stage "honeycomb lung")
• cystic bronchiectasis
• Langerhans cell histocytosis
• lymphangioleiomyomatosis

Ground glass

• Extrinsic allergic alveolitis
• Diffuse interstitial pneumonitis
• Alveolar proteinosis

Consolidation

• Alveolar haemorrhage
• Alveolar cell carcinoma
• vasculitis
• chronic eosinophilic pneumonia

Limitations

It must be remembered that while the chest X-ray is a cheap and safe method of investigating diseases of the chest, there are a number of serious chest conditions that may be associated with a normal chest X-ray and other means of assessment may be necessary to make the diagnosis:

• Asthma
• Chronic obstructive pulmonary disease
• Pneumocystis jiroveci pneumonia (PCP)
• Pulmonary embolism
• Smoke inhalation
• Foreign body inhalation