Chest X-Ray Terminology

• Study notes relating to chest x-rays

Terminology

• Radiolucent refers to a dark pattern and indicates the presence of air, which is normal.
• Radiodense/opacity refers to a white pattern, indicating solid or fluid, which is normal for bones and organs.
• Infiltrate is an ill-defined radiodensity, as seen in atelectasis.
• Consolidation is a solid white area, as seen in pneumonia or pleural effusion.
• Hyperlucency indicates extra pulmonary air, as seen in COPD, asthma, or pneumothorax.
• Vascular markings refer to lymphatics, vessels, and lung tissue; they are increased with CHF and absent with pneumothorax.
• Diffuse refers to a spread throughout, as seen in atelectasis or pneumonia.
• Opaque refers to fluid or solid, as seen in consolidation.
• Bilateral indicates both sides.
• Unilateral indicates one side.
• Fluffy infiltrates indicate diffuse whiteness with a butterfly/batwing pattern, as seen in pulmonary edema.
• Patchy infiltrates indicate scattered densities, as seen in atelectasis.
• Platelike infiltrates indicate thin-layered densities, as seen in atelectasis.
• Ground glass/honeycomb indicates reticulogranular distribution through both lung fields, as seen in ARDS or fibrosis.

Different Densities

• Air appears black because it absorbs x-rays the least, resulting in a dark shadow (radiolucent), and is found in the lungs, stomach, or intestines.
• Bone absorbs the most x-ray energy, resulting in a white shadow (radiopaque), and is found in the ribs and clavicles.
• Fat, soft tissue, and fluid have varying degrees of gray.

PA (Postero-Anterior) Chest Film

• A PA chest film is created in the radiology department with the patient usually standing.
• The X-ray beam passes from posterior to anterior (PA), with the film placed against the patient's chest.
• It usually results in high-quality film with minimal magnification of the heart shadow.

AP (Antero-Posterior) Chest Film

• Taken with a portable x-ray machine.
• The X-ray source is in front of the patient, and the film is behind the patient.
• AP films are often more difficult to read because the quality is not as good as PA film.
• The heart shadow is more magnified with AP film since the heart is closer to the x-ray source and farther from the film.
• Rotation of patients is more likely.

Technical Factors

• In a supine position, the diaphragm is elevated.
• On an AP film, the heart appears larger because it is more anterior.
• Penetration refers to the amount of x-ray exposure.
• Overpenetrated film will appear too black.
• Underpenetrated film will appear too white.
• Tissues that absorb the least amount of energy and appear black in an x-ray film are called "RADIOLUCENT."

Indications for CXR

• Unexplained dyspnea
• Severe persistent cough
• Hemoptysis
• Fever and sputum production
• Acute severe chest pain
• Positive TB skin test
• ETT placement (Endotracheal Tube)
• Placement of pulmonary artery catheter, central venous pressure catheter
• Elevated or changing plateau pressure during mechanical ventilation
• Sudden decline in oxygenation

Approach to Reading Chest Film

• A disciplined approach is needed.
• First, ensure the name on the film matches the patient being evaluated.
• Second, evaluate the technical quality of the film, including proper patient position and x-ray penetration.
• Third, systematically evaluate all anatomical structures seen on film following a prescribed series of steps.

Other important factors

• In a pulmonary embolism (PE), the CXR may appear normal at first.
• Chronic COPD patients' CXR may also appear normal.
• There may be a lag time behind clinical conditions of the patient.
  • For example, aspiration pneumonia with fever and cough can take 12-24 hours to show

Assessment

• Airways (trachea midline or shift)
• Bones and soft tissues (vertebral bodies & spinal process)
• Cardiac Silhouette & mediastinum (enlarged, deviated)
• Diaphragm (gastric bubble, flattening, right slightly higher than the left because of liver)
• Effusions (pleural), lateral decub to rule out (R/O) effusion
• Fields - lung fields
• Lines, tubes, and previous surgeries

Important Info

• Should be taken of full inspiration otherwise it may make the heart appear larger and airways with volume loss

Assessment of Structures

• Chest wall and mediastinum:
  • Symmetry of chest
  • Rib fractures
  • Bone changes
  • Heart size
  • Presence of free air or fluid
• Lung evaluation:
  • Size, density, and symmetry
  • Lung edges in frontal and lateral films
  • Vascular markings
  • Presence of free air or fluid
  • Consolidations and infiltrates

Hydrothorax/Pleural Effusions

• More commonly called a pleural effusion.
• A blunted costophrenic angle on a chest x-ray indicates pleural effusion is present.
• About 200 mL or plural fluid will blunt costophrenic angle.
• Best chest x-ray view for detecting small pleural effusions is lateral decubitus.
• Pus in pleural space is called EMPYEMA
  • Empyema commonly refers to pus-filled pockets that develop in the pleural space.

Pneumothorax

• Refers to collection of air in the pleural space.
• May occur spontaneously, with trauma, or with invasive procedure.
• May occur with mechanical ventilation and is called barotrauma in such cases.
• Pneumothorax causes the lung margin to pull away from the chest wall in the affected region.
• The presence of air can be better visualized by comparing inspiratory vs. expiratory CXRs.

Tension Pneumothorax

• Represents a serious medical emergency.
• Occurs when air within the pleural space is under pressure.
• Air accumulates in pleural space on inspiration but cannot exit on exhalation.
• A chest film will show a shift of the mediastinum away from the pneumothorax.
• Requires immediate decompression with chest tube or needle aspiration of trapped air.
• Can lead to cardiac tamponade and hemodynamic collapse.

Pulmonary Infiltrates

• Are seen on chest radiograph when alveoli fill with watery fluid (edema), pus (pneumonia), blood (alveolar hemorrhage), or fat-rich material (alveolar proteinosis).
• Appears as white shadows in the lung.
• Air bronchogram refers to the phenomenon of air-filled bronchi (dark) being made visible by the opacification of surrounding alveoli (grey/white).

Pulmonary Edema

• Pulmonary edema due to left heart failure is a common finding on a chest radiograph.
• Left heart failure causes enlargement of pulmonary blood vessels in the apex of the lung (cephalization).
  • Cephalization is when blood vessels to the apices of the lungs are the same size or larger than the blood vessels to the bases.
• Kerley B-lines are often seen with pulmonary edema due to left heart failure.
• A chest radiograph often shows an enlarged heart and pleural effusion with CHF.

Interstitial Disease

• A chest radiograph usually shows diffuse, bilateral infiltrates.
• Infiltrates may look like scattered, ill-defined nodules.
• May have different types of Interstitial Lung Diseases (ILDs); two the most common are:
  • Idiopathic pulmonary fibrosis
  • Sarcoidosis
• "Honeycomb" appearance can occur with idiopathic pulmonary fibrosis, collagen vascular disease, asbestosis, chronic hypersensitive pneumonitis, medications induced (amiodarone).

ARDS

• Ground glass appearance
• Honeycomb pattern
• Diffuse bilateral radiopacity

Atelectasis

• Defined as a collapsed or airless condition of the lung.
• Common findings on chest radiographs, especially in postoperative patients.
• When localized to a subsegmental portion of lung, it's called "plate atelectasis".
• Lobar atelectasis occurs when a major bronchus is obstructed by a mucus plug, tumor, or foreign body.
• Signs of volume loss include elevation of the hemidiaphragm and shift of the hilum towards the affected side.
• Transcription may read "infiltrate", which describes an ill-defined radiodensity.

Hyperinflation

• Commonly seen with emphysema.
• Other signs of hyperinflation include:
  • Flattening of hemidiaphragms
  • Large retrosternal airspace
  • Narrowed mediastinum
  • Increased AP diameter
  • Emphysema causes a loss of visible blood vessels in the lung.
• Thumb sign can indicate Epiglottitis.
• Steeple sign can indicate Croup.

Catheters, Lines, & Tubes

• A chest radiograph is obtained after placement of an endotracheal tube, CVP line, or pulmonary artery catheter.
• The film helps confirm the tube or catheter is in the correct position.
• The tip of the endotracheal tube should be 2-6 cm above the carina with the patient's head in a neutral position, below the vocal cords, at the level of the aortic knob or notch.
• A pacemaker should be positioned in the right ventricle.
• A pulmonary artery catheter should be in the right lower lung field.
• Chest tubes should be in the pleural space surrounding the lungs.
• A nasogastric tube and feeding tubes should be positioned in the stomach 2-6 cm below the diaphragm.

CAT SCAN

• Computed tomography (CT) is very helpful in certain situations.
• CT visualizes structures cross-sectionally with great detail up to ~2mm structure inside the lung.
• CT scanning creates images looking like "slices" of the patient's chest (5 to 7 mm thick).
• Conventional CT scanning is used to evaluate lung nodules & masses, great vessels, mediastinum, & pleural disease.
• Iodinated contrast is sometimes used to make the blood appear more dense and allows blood vessels to be distinguished from soft tissue structure (DYE's can cause fatal responses!).
• CT scans are the standard for diagnosing a pulmonary embolism.

High Resolution Cat Scan

• High-resolution CT (HRCT) scanning examines 1 mm slices of lung, producing greater lung detail.
• High-resolution CT scanning is ideal for evaluating diffuse parenchymal lung disease, such as:
  • Interstitial lung disease
  • Emphysema
  • Bronchiectasis

Magnetic Resonance Imaging

• Uses radio waves from realigning Hydrogen nuclei to generate MRI image (no x-rays are used)
• Most often used to image the mediastinum, hilar regions, and large vessels in the lungs
• MRI has limitations in chest medicine
  • Cannot be used in patients with a pacemaker
  • Tracheostomy tube safety
  • Metal objects cannot be used near MRI machine (i.e., gas cylinders)

Ultrasound

• Images created by passing high-frequency sound waves into the body & detecting sound waves that become back (echo) from tissues of the body
• Ultrasonic evaluation of the lung can be performed, but is limited
• Uses portable equipment
  • Commonly used to guide placement of central and arterial catheters, & to detect & quantify pleural effusions
• Very common in an emergency setting or the ICU