Pulmonary Radiology

Pulmonary, or chest, imaging includes imaging of the lungs and surrounding structures in the thorax. Imaging of the chest represents a substantial portion of the imaging tests that are routinely performed. Common imaging methods include X-ray, CT, MRI, and ultrasonography (US). Each imaging method has advantages and disadvantages. Radiology exams, once completed, are read and interpreted by board-certified, fellowship-trained radiologists; however, most physicians should know the basics of how to interpret these images.

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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

CT scan device

Photograph of CT scanner:
The motorized table moves the patient through the scanner, which contains the X-ray tube and detectors.

Image: “UPMCEast CTscan” by daveynin. License: CC BY 2.0

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
Normal lung ultrasound

Normal lung ultrasound:
(A): The pleural lines (arrows): The A-lines, or horizontal lines arising from the pleural line, are separated by regular intervals that are equal to the distance between the skin and the pleural line.
(B): M-mode shows the pleural line. Under the pleural line is the seashore sign (sandy pattern) due to the lung dynamics and pleural sliding. The horizontal lines are A-lines, separated by regular intervals (arrows).

Image: “Normal lung ultrasound” by Department of Critical Care, University Medical Center Groningen, University of Groningen, Hanzeplein 1, Groningen, 9700 RB, The Netherlands. License: CC BY 2.0

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

References

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