Pulmonary Radiology

Introduction

Before interpreting any image, the physician should take certain preparatory steps. The same systematic approach should be followed every time.

• Confirm name, date, and time on all images.
• Obtain records of patient’s medical history and physical examination.
• Confirm appropriate exam and technique for desired pathology.
• Compare any available images of the same area obtained with the same method.
• Determine orientation of image:
  • Right or left marker on X-ray
  • In the United States, standard exam views place a marker (dot) to patient’s right.
  • For CT/MRI: On axial view, the image is sliced and viewed from inferior to superior (as if looking from the patient’s feet up).

Chest X-ray

Indication

Medical indications:

• Emergency care:
  • Shortness of breath
  • Chest pain
  • Chest trauma
• Routine care:
  • Signs and symptoms of pulmonary infection
  • Hemoptysis 
  • Suspected mass
  • History of ingested/inhaled foreign object
• Monitoring:
  • Progression of pulmonary disease
  • Tuberculosis screening

Nonmedical indications:

• Verification of correct placement of IVs, lines, and tubes 
• Postoperative

Advantages:

• Low cost 
• Low radiation dose 
• Ubiquitous availability
• Fast

Disadvantages:

• Poor resolution of soft tissue
• Exposure to ionizing radiation
• Patient must hold still for image.

Exam technique

Positioning:

• Rotation:
  • There should be no rotation.
  • Spinous processes midway between medial ends of clavicles
• Visualization:
  • Lungs should be fully visible from apexes, above clavicles, to bases.
  • Performed during inspiration: 7–10 posterior ribs visualized above diaphragm
  • No superimposition of chin over neck or arms over peripheral chest

Positioning for specific views:

• Posteroanterior (PA):
  • Board is against anterior chest.
  • X-ray beams posterior to anterior direction through patient
• Anteroposterior (AP):
  • Board is against back.
  • X-ray beams anterior to posterior direction through patient
• Lateral (from side):
  • Patient is upright.
  • Board is against left or right (L or R) side.
• Lateral decubitus (from side laying down): 
  • Patient is supine.
  • Board is against side.
  • Patient is usually left side down on table.

Penetration:

Penetration is the degree to which radiation has passed through body, resulting in a darker or lighter image.

• Good penetration:
  • Ribs are only faintly visible behind the heart. 
  • Vascular markings are clear but not prominent. 
• Underpenetration: Film appears whiter and features are less apparent.
• Overpenetration: Film appears darker and features are less apparent.

Interpretation and evaluation

Systematic approach:

• Inside-out approach (central to peripheral):
  • Heart → mediastinum and hilum → lungs/lung borders → chest wall → abdomen
  • Once an abnormality is noted, use the pattern approach to come up with differential diagnoses.
• ABCDEFGHI approach:
  • A: airway/airspace
  • B: bones and soft tissue
  • C: cardiac 
  • D: diaphragm
  • E: effusions (pleural)
  • F: fields, fissures, and foreign objects
  • G: great vessels, gastric bubble
  • H: hilum
  • I: general impression

Different views are used to evaluate different portions of the chest:

• AP and PA:
  • Lung fields
  • Mediastinum 
  • Blood vessels
  • Pleural cavity
• Lateral:
  • Retrosternal space
  • Retrocardiac space 
• Lateral decubitus: layering of fluid/air (e.g., pneumothoraxes, pleural effusions)

Normal findings

AP/PA view:

• Heart and mediastinum:
  • Trachea midline
  • Shadow of superior vena cava (SVC) immediately to right of mediastinum
  • Right and left hila
  • Right (right atrium) and left (left ventricle) heart borders are clearly visible.
  • Portions of ascending and descending aorta are visible.
• Lungs: 
  • Right and left upper lobes should be visible and clear.
  • Right and left lower lobes should be visible and clear.
  • Note: Right middle lobe is not well visualized from the PA or AP views, as it overlaps portions of upper and lower lobes.
  • Costophrenic and cardiophrenic angle should be sharp and visible.
  • Carina should be midline and faintly visible.
• Bones:
  • Clavicles are visible and intact.
  • Scapula
  • Spinous processes midline, aligned with trachea
• Organs:
  • Liver visible under right hemidiaphragm should be uniform with no free air.
  • Stomach and colon visible with air in lumen under left hemidiaphragm. 

Lateral view:

• Heart and mediastinum:
  • Retrosternal space is clear.
  • Anterior (right ventricle) and posterior (right atrium) heart borders are clearly visible.
  • Entire descending aorta should be visible.
• Lung:
  • Viewed from the right, all 3 lobes of right lung should be visible, and from the left, only 2.
  • Posterior costophrenic angle should be sharp.
• Bones: Thoracic spine has regular curve.

Pathologic findings

• A: airway/airspace
  • Airway:
    • Deviated trachea
    • Asymmetric or evidently deformed bronchial tree
  • Airspace:
    • Areas of increased density (mass, atelectasis, infection, foreign object, etc.)
    • Areas of decreased density (pneumothorax, hemothorax)
• B: bones and soft tissue
  • Bones:
    • Fractures
    • Dislocation of ribs, clavicles, or shoulders
    • Spinal abnormalities
• C: cardiac 
  • Enlarged heart (normal-sized heart is roughly ½ the width of chest), suggesting cardiac failure
  • Blurring of cardiac silhouette suggests something (mass, infection, fluid) in front of it.
  • Oddly shaped heart suggests congenital abnormalities:
    • Boot-shaped: tetralogy of Fallot
    • Snowman-shaped: total anomalous pulmonary venous return
    • Globular heart: pericardial effusion
• D: diaphragm
  • Asymmetric:
    • Phrenic nerve palsy
    • Congenital malformation
    • Severe trauma
  • Incomplete:
    • Diaphragmatic hernia
• E: effusions (pleural)
  • White area at base of lungs
  • White area pushing against parenchyma on sides of lungs
• F: fields, fissures, and foreign objects
  • Distortion of normal anatomy landmarks may suggest mass.
  • Radiopaque foreign bodies
  • Radiolucent foreign bodies are detectable by the collapse of lung parenchyma beyond them
• G: great vessels, gastric bubble
  • Gastric bubble:
    • Should be present on left side under diaphragm
    • Absence points to GI pathology.
• H: hilum
  • Calcifications
  • Malformation of blood vessels
  • Masses
• I: general impression
  • Is there anything abnormal not explained by the patient’s pathologic condition?

Computed Tomography

Indication

Medical indications:

• Follow-up of suspicious chest X-ray imaging:
  • Mediastinal widening
  • Suspected pulmonary mass
  • Atypical pneumonia
  • ARDS
  • Concern for intravascular pathology
• Malignancy:
  • Staging of primary tumor
  • Detection of metastases 
  • Evaluation of lymph nodes 
• Major trauma:
  • Evaluation of neck and thoracic spine
  • Concern for subtle pathology not seen on X-ray

Advantages:

• Excellent anatomical detail resolution 
• Structures can be seen in 3 dimensions.
• Often gold standard for pulmonary examination

Disadvantages:

• Involves high radiation dose
• Not ubiquitously available
• Patient must hold still for exam.
• Expensive to perform

Exam technique

Standard CT scanning:

• Patient lies supine on table. 
• Table is moved in CT scanner, which rotates around patient.
• Patient is instructed to hold breath and remain still for scan (seconds).
• Exams can be done with or without IV or oral contrast.
• Timing of IV contrast dye can help direct radiologic inquiry for certain areas of lungs:
  • CT angiography: Pulmonary blood vessels are visible.
  • CT with IV contrast: for aortic enhancement (e.g., dissection protocols) or for organ enhancement (e.g., preferred in trauma to detect active bleeding)

Special forms:

• High-resolution CT of chest:
  • Does not use contrast
  • Perform 3-dimensional (3D) reconstructions for additional imaging method and assistance in CT-guided surgeries
• CT pulmonary angiography:
  • Used to obtain details of pulmonary arterial system
• CT angiography or aortography:
  • Used to obtain details of arterial system
  • Requires a rapid infusion of contrast dye

Interpretation and evaluation

• Interpretation should follow systematic and reproducible pattern.
• Select appropriate window view for tissue evaluated:
  • Lung
  • Bone
  • Mediastinal
• Review patient’s history/examination.
• Compare to available recent imaging of area of interest.
• Orient image:
  • Axial images are viewed as if looking from the patient’s feet up.
  • Sagittal and coronal can vary.
• Identify landmark anatomical structures.
• Observe for “continuity” of structures while scrolling through image slices.

Normal findings

• Pulmonary tissue:
  • Uniformly dark gray tending toward black
  • Minor and major fissures of the right lobe and major fissure of left lobe visible
• Airways:
  • Larynx, trachea, and bronchi are visible as black air-filled spaces.
  • Smaller 
• Heart:
  • All 4 chambers visible 
  • Pericardium should not be distinguishable in healthy individuals.
• Blood vessels:
  • Blood-filled structures appear brighter in CT with contrast.
  • Major vessels (pulmonary arteries and veins, aorta, and superior vena cava) continuous with heart
  • Each smaller (black) bronchus is paired with blood vessel (white).
• Bony structures:
  • Ribs, vertebrae, clavicles, scapulae, and humeri should be visible and lightest in color (most dense structures).
• Abdominal structures:
  • Diaphragm should be visible dividing lungs from viscera.
  • Liver should be visible, uniformly colored, with the exception of vasculature, under right hemidiaphragm.
  • Gastric bubble, bowel visible under left hemidiaphragm.

Pathologic findings

• Pulmonary parenchyma:
  • Opacity:
    • Suggests consolidation/infection
    • Usually also visible on X-ray 
    • CT allows for better anatomical localization (e.g., lobar, diffuse, dependent) and qualification (e.g., patchy, loculated).
  • Loss of lung volume (atelectasis):
    • Lung collapse 
    • CT allows for better identification of etiology (compressive, obstructive, cicatrization).
  • Hyperinflation:
    • Destruction of tissue distal to terminal bronchiole
    • Most commonly seen in emphysema
    • CT is more sensitive than X-ray for diagnosis and allows for better qualification of disease.
  • Nodules and malignancies:
    • Nodules < 1 cm in diameter are not reliably evaluated by radiography.
    • CT allows for detailed evaluation and follow-up monitoring.
    • Calcifications, location, and size all help distinguish benign lesions from more worrisome pathology.
• Pulmonary interstitium:
  • Multiple etiologies, including viral infection and chemotherapy
  • Reticular, nodular, or reticulonodular pattern
  • CT allows for better characterization of pattern than X-ray.
• Pleura and pericardium:
  • CT allows for detailed qualification and provides landmarks for treatment.
  • Free air between membranes appears dark.
  • Fluid in membrane will appear different shades depending on etiology.
• Great vessels:
  • Aortic dissection and aneurysm:
    • Contrast CT is method of choice.
    • Double lumen is visible on image.
  • Pulmonary embolism:
    • Contrast CT is method of choice.
    • Filling defect is visible on image.

Magnetic Resonance Imaging

Indication

Medical indications:

• Detailed evaluation of soft tissue organ structures:
  • Thymus 
  • Myocardium 
• Vascular disease:
  • Aorta
  • Pulmonary artery 
• Evaluation of chest wall:
  • Infection
  • Tumor
  • Disease extending into or from pleura
• Evaluation of paraspinal masses:
  • Superior to CT because spinal bone can create CT artifact

Advantages:

• Provides higher level of imaging and detail of internal organs, bones, soft tissue, and blood vessels than chest X-ray or CT
• Can be used for evaluation of pregnant patients
• Used as adjunct to previous test

Disadvantages:

• ↑↑↑ Cost
• Takes much longer to perform than chest X-ray or even CT
• Not suitable for all patients:
  • Implants (particularly metal ones) distort image.
  • Requires patient to be in loud, enclosed space.
  • Patient must stay still to allow for adequate images.

Exam technique

Positioning:

• Supine on table
• Table is advanced into scanner.
• Patient is instructed to remain still for scan.
• MRI scanner rotates around patient.

MRA:

• To examine blood vessels
• Exams can be done with or without IV contrast.
• Advancements have allowed medicine to create both 2D and 3D image reconstructions.

Views:

• T1-weighted scans: Tissues with high fat content (e.g., white matter) appear bright/white and compartments filled with water (CSF) appear dark/black.
• T2-weighted scans: Compartments filled with water (CSF) appear bright/white and tissues with high fat content (e.g., white matter) appear dark/black.
• Images oriented in 3D slices: 
  • Coronal 
  • Sagittal
  • Axial

Interpretation and evaluation

• Interpretation should follow a systematic and reproducible pattern.
• Review patient’s history/examination.
• Compare to available recent imaging of the area of interest.
• Orient image.
• Identify landmark anatomical structures.
• Observe for “continuity” of structures while scrolling through image slices.

Normal findings

• Thymus:
  • Size:
    • Largest in ages 12–19 years, then involutes
    • Round soft tissue masses 7 mm after age 19
  • Shape:
    • Convex, straight, or concave edges based on patient’s age 
    • Soft tissue lobulation
• Myocardium:
  • Statistically normal parameters:
    • Muscle thickness
    • Ventricular size
    • End diastolic volume
• Detailed anatomy of soft tissue structures:
  • Spinal cord
  • Pulmonary parenchyma
  • Diaphragm
  • Top of liver
  • Vasculature

Pathologic findings

• Thymus:
  • Hyperdensities:
    • Nodules
    • Masses
  • Increased size/changes in texture:
    • Malignancy
• Myocardium:
  • Changes in size, shape, or thickness:
    • Myocarditis
    • Cardiac sarcoidosis
    • Takotsubo cardiomyopathy
    • MI with nonobstructed coronary arteries (MINOCA)
    • Cardiomyopathies
• Blood vessels:
  • Double-lumen sign:
    • Aortic dissection
  • Change in pulmonary vein diameter:
    • Pulmonary hypertension

Mnemonic

MRI T2 = H20 is white

Ultrasonography

Indication

Medical indications:

• Imaging of areas filled with fluid:
  • Ascites
  • Edema
• Imaging when radiation is contraindicated:
  • Pregnancy
  • High predisposition to malignancy
• Specific settings include:
  • Trauma
  • Suspected infection of the lung parenchyma and pleura
  • Evaluation of cardiac anatomy and function
  • Procedural

Advantages:

• Can be performed at the bedside
• Fast to perform
• Low cost
• No exposure to ionizing radiation
• Works well for imaging soft tissue

Disadvantages:

• Quality depends on the experience of the user.
• Image resolution can vary.

Exam technique

• Transthoracic:
  • Probe is placed on external chest wall over area of interest.
  • Ultrasound beam is oriented to desired anatomy.
• Transesophageal:
  • Probe is placed in patient’s esophagus.
  • Allows for closer imaging of mediastinal structures 
• Imaging planes:
  • Sagittal (or longitudinal): along long axis of structure being evaluated
  • Transverse: perpendicular to sagittal plane
• Types of images:
  • Static images (photographs)
  • Cine images: captured during real-time scanning
• Image definition or sharpness of image generated can be characterized in terms of:
  • Axial definition: 
    • Differentiation of 2 objects close to each other, parallel to beam
    • Determines depth of ultrasound beam; quality impacted by beam penetration
  • Lateral definition: 
    • Differentiation of 2 objects on plane perpendicular to beam
    • Determines ability of probe to distinguish structures perpendicular to beam
    • Primarily determined by beam width

Interpretation and evaluation

• Interpretation of ultrasounds is challenging even for trained practitioners.
• Should follow systematic and reproducible pattern
• Review patient’s history/examination.
• Compare to available recent imaging of area of interest.
• Fluid appears dark on ultrasound.
• Doppler functionality can be used to determine flow of blood.

Normal findings

• Lungs:
  • Ribs appear white.
  • Pleura (located just deep to ribs) is dark.
  • Multiple reflections of pleura are seen as equally spaced horizontal lines (A-lines)
  • Lung sliding seen as patient breathes.
• Heart:
  • Anatomy:
    • Myocardium
    • Valves
    • Chambers
  • Function:
    • Wall movement is coordinated.
    • Systolic and diastolic function appropriate
    • Flow through chambers and coronaries unimpeded

Pathologic findings

• Lungs:
  • Pleural effusion:
    • Patterns suggestive of fluid buildup
    • Hypoechoic space
  • Pneumothorax:
    • Absent lung sliding
    • Absent lung pulse
• Heart:
  • Anatomy:
    • Congenital abnormalities
    • Cardiac remodeling after MI
    • Cardiomyopathy
  • Function:
    • Systolic or diastolic insufficiency
  • Flow:
    • Valvular stenosis or regurgitation
    • Blockage of coronary arteries
• Procedural

Clinical Correlation

Pneumonia

• Can be seen on X-ray, CT, or MRI
• Consolidation (unilateral or bilateral):
  • Lobar pattern
  • Ground-glass pattern
  • Reticular or reticulonodular pattern
• +/– Air bronchograms, blunted costophrenic angle
• +/– Cavitation: round radiolucency surrounded by opacification
• +/– Abscess formation: air-fluid level

Malignancy

• Mass in lung tissue on chest radiology
• Can be seen on X-ray, CT, or MRI
• Number:
  • Single: usually primary
  • Multiple: metastasis
• Size: 
  • > 3 cm: mass
  • < 3 cm: nodule 
• Spiculated margins are usual.
• +/– Cavitation, calcifications, effusion, atelectasis, and hilar lymphadenopathy

Pneumothorax

• CT and MRI are more sensitive than X-ray.
• Visceral pleural white line: absence of lung markings peripheral to it
• Deep sulcus sign: inferiorly displaced, lucent costophrenic angle 
• Simple pneumothorax: no mediastinal shift
• Tension pneumothorax:
  • Mediastinal shift away from lucency
  • Compressed contralateral lung

Emphysema

• Seen on chest X-ray, CT, and MRI
• Hyperinflated lungs:
  • Flattened diaphragm
  • Hyperlucency 
  • ↑ AP diameter of chest
  • Widely spaced ribs
  • Narrow mediastinum
• +/– Bullae

Pleural effusion

• Seen on chest X-ray, CT, MRI, and ultrasonography (US)
• Fluid above diaphragm:
  • Appears black on US
  • White (hypodense) on CT and X-ray
  • On T2 MRI, water appears bright.
  • On T1 MRI, water appears dark.
• Supine, upright, and decubitus projections can be used for X-ray.
• On upright X-ray:
  • Blunted costophrenic angle
  • Meniscus sign
• Complete hemithorax opacification can occur +/– mediastinal shifting to other side
• Sinusoid sign on US: Lung moves within pleural fluid, seen on real-time examination.

Pulmonary edema

• Seen on chest X-ray, CT, and MRI
• Interstitial/parenchymal fluid in lungs
• Consolidation on imaging, usually bilateral
• +/– Air bronchograms, prominent lung vascularity, enlarged heart, Kerley A and B lines, and pleural effusions
• Classic bat-wing appearance from cephalization of pulmonary vasculature and fluid buildup

Atelectasis

• Seen on chest X-ray, CT, and MRI
• Lung tissue collapse
• Seen as opacification on imaging
• Types: 
  • Compressive: caused by mass, effusion, or a foreign object
  • Obstructive: obstruction of airflow
  • Cicatrization: scarring causing compression 
• +/– Displacement of: 
  • Fissures
  • Mediastinal structures
  • Hemidiaphragm