Chest x-ray

Chest x-ray (CXR) is one of the most commonly performed imaging studies in clinical practice. CXR is a quick, noninvasive, and relatively low-radiation method to evaluate conditions and monitor procedures related to the heart and main vessels, lungs, airways, bones, and soft tissues of the thorax. Verification of patient and study data, view, and technical quality is essential before interpreting a CXR. Radiological interpretation should be performed using a systematic approach (e.g., the ABCDEFGHI mnemonic) to minimize errors while also integrating clinical findings to formulate a diagnostic impression.

General information on x-ray technology is found in “Radiography.”

CXRs are used in the evaluation of several conditions and to monitor various procedures, including: ^[1][2]

• Clinical findings that require further assessment, e.g.:
  • Respiratory (e.g., dyspnea, pathological breath sounds)
  • Cardiovascular (e.g., chest pain, heart murmur)
  • Gastroesophageal (e.g., hiatal hernia)
• Patients with polytrauma, chest trauma
• Critical care patients (e.g., upon admission, to monitor for complications)
• Chronic conditions (e.g., to monitor neoplasms, COPD)
• Postprocedural patients: to confirm the position of tubes and devices, e.g., endotracheal or nasogastric tube placement, cardiac implantable electronic devices (CIEDs)

A routine CXR upon admission is not required if patients do not have cardiothoracic symptoms or conditions. ^[1]

There are no absolute contraindications to performing a CXR. Radiation exposure is a common concern.

• The radiation dose of a single CXR has not been associated with an increase in negative health outcomes. ^[3][4]
• Always follow the ALARA principle and radiation safety protocols when performing a CXR.
• Pregnancy and fetal radiation exposure
  • The fetal radiation dose of a two-view CXR is classified as very low. ^[1][5]
  • There is no evidence of increased fetal risks or pregnancy loss with typical CXR doses. ^[5][6]

Consider the clinical indication carefully before exposing a patient to even small doses of radiation.

We list the most important contraindications. The selection is not exhaustive.

Patient and study data ^[2][7][8]

Verify the following:

• Patient's name and date of birth
• Date and type of study

Views ^[2][7][8]

• Posteroanterior (PA) view
  • Patient position: standing with the chest as close to the x-ray detector as possible
  • Preferred view: provides the most accurate visualization of chest structures
• Anteroposterior (AP) view
  • Patient position: sitting or lying, with the x-ray detector under the back
  • Alternative to PA view for patients who cannot stand (e.g., intubated patients, patients in the ICU)
  • The cardiac silhouette and other mediastinal structures appear magnified.
• Lateral view
  • Patient position: standing with the left side as close to the x-ray detector as possible
  • Complement to the PA view: used to visualize the retrosternal and retrocardiac spaces
• Lateral decubitus view
  • Patient position: lying with the side of interest down, arms raised overhead; x-ray detector behind the back
  • Used to detect, e.g., small pleural effusion, pneumothorax

Technical quality ^[2][7][8]

Assess the following aspects of a CXR to ensure good technical quality:

• Penetration: The vertebral bodies should be visible through the heart shadow.
• Inspiration: At least 6 anterior and/or 10 posterior ribs should be visible. ^[7][8]
• Rotation: The distance between the medial end of the clavicles and the spinous process should be the same on both sides.

The study may need to be repeated if the data is incorrect or the quality is inadequate.

General principles ^[2][7][8]

• Verify patient and study data, view, and adequate technical quality of the study.
• Review the image from cranial to caudal and medial to lateral to ensure a comprehensive assessment and minimize errors.
• Utilize a systematic approach to CXR interpretation (e.g., the ABCDEFGHI approach).
• Assess for CXR emergency findings.

Obtain previous chest x-rays for comparison when available.

Do not delay treatment for expert interpretation of imaging studies if an emergency is clinically suspected.

ABCDEFGHI approach

• Airway
• Bones and soft tissue
• Cardiovascular
• Diaphragm
• Edges and effusions
• Fields
• Gastric bubble
• Hardware
• Impression

Always verify the view (e.g., AP or PA) and patient position (e.g., standing or supine) when interpreting a chest x-ray.

Airway

• Trachea: Trace down and identify deviations and/or narrowing.
  • There may be a slight, normal deviation to the right caused by the aortic knob.
  • Tracheal deviation can occur toward an affected lung field (e.g., lobar collapse, pulmonary fibrosis ) or away from it (e.g., tension pneumothorax ).
• Main bronchi: Identify the carina.
  • Should be a well-defined, midline angle
  • Identify deviations, deformities, surrounding masses, and dilation (e.g., tumors, bronchiectasis ).

Bones and soft tissue

• Bones: Trace the clavicles, posterior and anterior rib arches, scapulae, and vertebrae.
  • Should appear radiopaque with smooth and continuous edges without any irregularities or disruptions
  • Changes in density (e.g., areas of ↑ radiolucency) are seen in osteolytic lesions.
  • Disruptions of the bony cortex are seen in fractures.
  • Examine and compare the intercostal spaces: Widened intercostal spaces and horizontal ribs are signs of pulmonary hyperinflation.
• Soft tissue
  • Should appear homogeneous without any abnormal masses or irregularities
  • Confirm symmetric mammary shadows.
  • Evaluate for areas of increased radiopacity (e.g., cutaneous calcification) or radiolucency (e.g., subcutaneous emphysema ).

Posterior ribs appear more horizontal than anterior ribs on CXR.

Cardiovascular

• The mediastinum is visualized as a radiopaque area with well-defined contours in the center of the CXR.
  • Loss of pulmonary volume (e.g., due to lobectomy, pneumonectomy, or atelectasis ) can cause a shift to the affected side.
  • A tension pneumothorax or a large pleural effusion can cause a contralateral shift.
• Trace the border between the aorta, trachea, and heart.
  • The aortic arch should appear as a smooth, rounded prominence on the left side of the mediastinum.
  • Abnormal aortic contour can be seen in, e.g., age-related aortic ectasia, aneurysmal dilatation, and dissection.
• Calculate the cardiothoracic ratio ; increases can be due to cardiomegaly or pericardial effusion.
• Trace the right and left heart contours and assess its components; request a lateral view if necessary.
  • The right atrium forms the right heart border; the left ventricle forms the left heart border.
  • Heart contours should be well-defined.
  • Poorly-defined heart contours can be caused by multiple conditions, e.g., pleural effusion, pneumonia, pericardial effusion, lymphadenopathy.
• Mediastinal widening can be caused by multiple conditions, e.g., mediastinal masses, aortic aneurysm, aortic dissection.

Diaphragm

• Trace both hemidiaphragms from the costophrenic angle to the vertebrae.
• The right hemidiaphragm should be slightly higher than the left. ^[7][8]
• Assess for diaphragmatic elevations (e.g., in atelectasis, phrenic nerve injury , hepatomegaly) or depressions (e.g., in tension pneumothorax , hyperinflation due to COPD ).
• Subdiaphragmatic free gas may be observed in pneumoperitoneum.

Edges and effusions

• Trace the lung borders and identify the cardiophrenic and costophrenic angles.
• Pleura and pleural spaces are not typically visible unless affected by a disease. ^[8]
  • Imaging findings in pneumothorax include the deep sulcus sign and a visible visceral pleura.
  • CXR findings in pleural effusion consist of a radiopaque area of variable size and conformation depending on the etiology and amount of fluid.
  • Pleural thickening can be visualized as areas of increased radiopacity, e.g., in mesothelioma.

A hemothorax is indistinguishable from a pleural effusion on CXR.

Fields

Compare the lung fields by assessing the following aspects:

• Lung volume: 6 anterior and/or 10 posterior ribs should be visible. ^[7][8]
  • Increased lung volume may be observed, e.g., in pulmonary hyperinflation in COPD.
  • Decreased lung volume may be observed, e.g., in interstitial lung disease, myasthenia gravis, obesity, and ascites.
• Lung density: should be relatively uniform across both lungs
  • Compare the right and left lung fields to assess for changes in density, e.g.:
    • Abrupt radiolucency in pneumothorax
    • Bilateral reticular, nodular, or linear opacities in interstitial lung disease
    • Bilateral diffuse opacities with or without Kerley B lines in pulmonary edema
  • Assess the upper, middle, and lower zones of each lung to identify focal changes in density, e.g.:
    • Pulmonary consolidation
    • Air bronchogram
    • Bronchiectasis
    • Solitary pulmonary nodules (< 3 cm) or masses (≥ 3 cm) ^[2][8]
• Lung hila
  • Visualized as two triangular areas superior to the cardiac silhouette ^[2][8]
  • Compare the right and left hila to assess for changes in hilar size (e.g., hilar lymphadenopathy in sarcoidosis or lymphoma ) and density (e.g., calcifications from granulomatous diseases including histoplasmosis and tuberculosis).
• Lung markings
  • Pulmonary vessels are easily visualized in the hilar areas and lower lung zones, becoming smaller and less visible toward the periphery and upper lung zones.
  • Increased lung markings in the upper lung zones are often observed in pulmonary edema and pulmonary hypertension.
  • Reduced lung markings are a feature of pneumothorax.

Gastric bubble and hardware

• The gastric bubble is frequently visible under the left hemidiaphragm.
• Confirm correct positioning of hardware (e.g., tubes, catheters, CIEDs).

Impression

• Gain an overall diagnostic impression by performing a clinical interpretation:
  • Combine all relevant radiological findings.
  • Incorporate clinical findings.
• Compare past CXRs if available.
• Initiate immediate treatment for CXR emergency diagnoses.

A systematic approach to CXR interpretation reduces errors and omissions.

CXR emergency findings ^[2][7][8]

Other common abnormal chest x-ray findings

• CXR findings in pneumonia
• CXR findings in pleural effusion
• CXR findings in atelectasis
• CXR findings in foreign body aspiration
• CXR findings in cardiogenic pulmonary edema
• CXR findings in noncardiogenic pulmonary edema
• CXR findings in COPD

• One-Minute Telegram 13-2020-1/3: Robots vs. residents: who can interpret chest x-rays better?

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