Chest X-ray

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

Indentification (name, age, sex, indication for X-ray)
Markers (differentiate left from right - diagnose dextrocardia)
Position - the spinous process of T4 should be between the heads of the clavicle (if it isn't the body is rotated)
Quality - is the film penetrated properly. In a properly penetrated film the vertebral interspaces should be visible behind the central (cardiac) shadow
Respiration - chest X-rays are typically done with full inspiration
Soft tissue - look for subcutaneous emphysema (suggestive of trauma), soft tissue swelling
Abdomen - look for free abdominal air (suggests penetrating trauma, peritonitis, or recent surgery)
Bone - look for fractures (these tend to be at the lateral aspects because of the mechanics - bending moment largest at lateral aspect)
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.
Hila (of the lungs) - can be affected in lung disease, malignant processes and infection (hilar lymphadenopathy).
Lungs - for consolidation, interstitial lung disease (reticular, nodular or reticulonodular), honeycombing, miliary pattern, granulomas, lung masses
Absent structures/Apices of the lung (for pneumothorax)

Mnemonic

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)
M = Markers (left vs. right)
P = Position (rotation)
Q = Quality (penetration of film)
R = Respiration (full inspiration?)
(but)
S = Soft tissue
A = Abdomen
B = Bone
C = Central shadow
H = Hila
L = Lungs
A = Absent structures/Apices

Typical views

Frontal (view)
- PA (posterior-anterior)
- AP (anterior-posterior) - 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 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

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:

External links

Introduction to chest radiology: a tutorial for learning to read a chest x-ray

Database of chest radiology related to emergency medicine