Chest X-rays are a foundational tool in diagnostic imaging. While newer, more advanced imaging techniques are available, chest radiographs remain a critical part of medical diagnostics. In fact, over 21 million chest X-rays are requested each year in England alone.
Given their prevalence, accurate interpretation of chest X-rays is crucial to providing effective patient care. A systematic approach is key to minimizing errors and ensuring nothing is missed during the review. That’s where the ABCDE approach comes in.
This article focuses on the ABCDE CXR approach to reading chest X-rays. It’s aimed at nurses and other allied health professionals who regularly interpret these images. We’ll cover technical quality assessment (using the RIPE framework) and systematic interpretation (using the ABCDE method). Finally, we’ll discuss common abnormalities seen on chest X-rays.
How Chest Radiographs are Generated and Patient Positioning
A chest radiograph, or CXR, is a type of X-ray that allows healthcare providers to visualize the structures inside your chest, including your heart, lungs, and blood vessels.
How Chest Radiographs are Generated
X-rays are a type of electromagnetic radiation that can pass through body tissues. Different tissues absorb X-rays in different amounts. This creates a contrast that allows the radiologist to see the various structures.
Structures that block more of the X-rays, such as bones, appear white on the image. These are called radiopaque structures. Areas that allow more of the X-rays to pass through, such as air-filled spaces in the lungs, appear black. These are called radiolucent structures.
Patient Positioning
The standard chest X-ray involves either a posterior-anterior (PA) view or an anterior-posterior (AP) view.
The PA view is generally preferred because it minimizes the amount of magnification of the heart. In this view, the X-ray beam enters through your back (posterior) and exits through your chest (anterior).
However, some patients are unable to stand for the PA view. In these cases, an AP view is used, where the X-ray beam enters through your chest and exits through your back. It’s important to remember that AP views can make the heart appear larger than it actually is.
Ordering a Chest X-Ray
The key idea behind ordering any medical test is “right test, right time, right patient.” Before ordering a chest X-ray, make sure it’s actually the right test for what you’re trying to learn. Sometimes, other imaging methods might be better.
When you request the X-ray, give the radiologist all the information they need:
- Full details about the patient’s health, including their history, your assessment, and what you found during the exam.
- Any past medical issues and current treatments.
- Specifically, what question are you hoping the X-ray will answer?
The more information you provide, the better the radiologist can tailor the imaging and interpret the results.
Anatomy Relevant to Chest X-ray Interpretation
Knowing the anatomy of the chest is key to reading chest x-rays. Here are some important structures to look for:
Bony Structures
On a chest x-ray, you should be able to identify and trace the ribs (both anterior and posterior) and recognize the clavicles and their relationship to the mediastinum. You should also be able to recognize the thoracic vertebrae.
Mediastinum and Heart
You should be able to identify the right and left heart borders, as well as locate the aortic knob and main pulmonary artery. Being able to trace the trachea and carina is also important.
Lungs and Pleura
Divide the lungs into zones (upper, middle, and lower) and identify the major and minor fissures. You should also be able to locate the hila and note their normal appearance.
Diaphragm and Costophrenic Angles
Assess the height and contour of the diaphragmatic domes and ensure the costophrenic angles are sharp and clear.
Technical Quality Assessment: The RIPE Method
Before you dive into interpreting a chest X-ray, it’s essential to make sure the image itself is of good quality. One handy mnemonic for assessing quality is RIPE, which stands for Rotation, Inspiration, Projection, and Exposure.
Rotation
To check for rotation, look at the spinous processes (the bony projections you can feel down your spine) in relation to the clavicles (collarbones). If the distance between the spinous processes and each clavicle is equal, there’s likely no rotation. If the patient is rotated, it can distort the appearance of structures in the mediastinum (the space in the chest between the lungs).
Inspiration
Adequate inspiratory effort is crucial for a good chest X-ray. Count the number of visible posterior ribs (the ribs you can see from the back). Ideally, you should be able to see 9-10 posterior ribs. If the patient didn’t take a deep enough breath, it can mimic certain lung conditions.
Projection
Confirm whether the X-ray is a PA (posterior-anterior, taken with the beam going from back to front) or AP (anterior-posterior, taken with the beam going from front to back) projection. AP views are often taken in patients who are too sick to stand. Keep in mind that heart size and mediastinal width can appear different depending on the projection.
Exposure
Exposure refers to the penetration of the X-ray beam. Ideally, you should be able to just barely see the vertebrae through the heart. If the image is overexposed, the lung markings will appear faint. If it’s underexposed, the lung markings will be exaggerated.
Systematic Interpretation: The ABCDE Approach
To make sure you don’t miss anything crucial, radiologists typically use a systematic approach to reading a chest X-ray. A common one is called the ABCDE approach. Here’s how it works:
A: Airway
First, look at the trachea, or windpipe. Is it in the midline? Can you identify the carina, where the trachea branches into the left and right main bronchi? Look for anything that might be pushing or pulling the trachea out of position, and check for any signs of obstruction.
B: Breathing
Next, assess the lungs and pleura, the membranes that line the lungs and chest cavity. Are the lung fields symmetrical? Are they clear, or are there any opacities (areas that look whiter than they should), signs of consolidation (where the air spaces in the lungs are filled with fluid), or effusions (fluid buildup)? Check for pneumothorax, where air leaks into the space between the lung and chest wall, causing the lung to collapse; this will appear as an absence of lung markings.
C: Circulation
Now, take a look at the heart and great vessels (aorta, pulmonary artery, etc.). Is the heart enlarged (cardiomegaly)? What’s the width and contour of the mediastinum, the area between the lungs that contains the heart, great vessels, trachea, and esophagus? Look for any abnormalities in the great vessels.
D: Diaphragm
Assess the diaphragmatic domes, the curved muscles at the base of the chest that separate the chest from the abdomen. Are they the right height and shape? Are the costophrenic angles, where the diaphragm meets the chest wall, sharp and clear? Look for any signs of air under the diaphragm, which could indicate a perforated abdominal organ.
E: Everything Else
Finally, examine everything else: the bones (ribs, clavicles, vertebrae) for fractures or lesions, the soft tissues for any masses or swelling, and look for any foreign bodies like lines, tubes, or pacemakers.
Common Chest X-ray Abnormalities
A chest X-ray can reveal a lot about what’s going on in your chest. Here are some of the abnormalities that doctors look for when reading a CXR.
Pulmonary Edema
Pulmonary edema appears on an X-ray as:
- Kerley B lines (thickened interlobular septa)
- Possible cardiomegaly (enlarged heart)
- A “batwing” appearance of central edema
Pulmonary edema is often caused by heart failure or acute respiratory distress syndrome (ARDS).
Consolidation
Consolidation shows up as:
- A homogeneous opacity in the lung field
- Air bronchograms (air-filled bronchi within the consolidated area)
Consolidation is typically caused by pneumonia but can also be due to pulmonary infarction or malignancy.
Pneumothorax
A pneumothorax is marked by:
- Absence of lung markings in the pleural space
- A visceral pleural line
- A deep sulcus sign (in supine patients)
Types of pneumothorax include spontaneous pneumothorax, tension pneumothorax (which is life-threatening), and traumatic pneumothorax.
Pulmonary Embolism
Pulmonary embolism is often subtle and nonspecific on an X-ray, but you might see:
- Westermark’s sign (focal oligemia)
- Hampton’s hump (wedge-shaped opacity)
A CT pulmonary angiography (CTPA) is the gold standard for diagnosis. The chest X-ray is used to rule out other causes of chest pain and shortness of breath.
Cardiomegaly
To assess cardiomegaly, doctors:
- Assess the heart size
- Compare the heart size to the chest width
Cardiomegaly can be caused by hypertension, valvular heart disease, or cardiomyopathy, and it can lead to heart failure. Note that Ampanozi G et al (2018) found that comparing fist size to heart size is not a reliable way to assess cardiomegaly.
Cancer
Cancer can appear as:
- A solitary pulmonary nodule
- A mass lesion
- Hilar enlargement
- Pleural effusion
Early detection is key since lung cancer is a leading cause of cancer death. Early detection improves the prognosis.
When to ask for help
Even with a systematic approach like the ABCDEs, interpreting a chest X-ray can be tricky. Don’t hesitate to consult a radiologist or a more experienced colleague in these situations:
- Complex or uncertain cases: If you’re unsure about your interpretation, or if you see multiple unusual things on the image, it’s always best to get a second opinion.
- Discrepancies: If the X-ray doesn’t seem to match what’s going on with the patient, talk to someone. The clinical picture should always make sense with the radiographic findings.
- Need for more imaging: Sometimes, an X-ray just isn’t enough to get a clear picture. If you think a CT scan or other advanced imaging is needed, discuss it with a senior colleague.
The Bottom Line
Being able to interpret a chest X-ray is a crucial skill for healthcare providers. It requires a systematic approach, including an assessment of the image’s technical quality and how it relates to the patient’s clinical picture.
That’s why it’s so important to use the RIPE and ABCDE methods. RIPE helps you make sure the image is clear and properly exposed, while ABCDE provides a structured framework for your interpretation. These tools help make sure you don’t miss anything important.
Remember, continuous learning is key. Stay up-to-date on the latest guidelines and best practices in radiology. Don’t hesitate to consult with radiologists and more experienced colleagues when you need a second opinion or run into a challenging case. Deep knowledge of anatomy, image quality, and specific pathologies is critical for accurate and effective chest X-ray interpretation. By using these methods, improving your knowledge, and collaborating with peers, you can improve your ability to use chest X-rays to benefit patient care.