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Pulmonary

Chest imaging

ABCDEF: Airways/quality, Bones, Cardiac silhouette, Diaphragm, Effusions, Fields/foreign bodies.

Madison Masters5 min6 questions1 trials

How to read a film

Read every chest radiograph the same way, every time. The ABCDEF pass is slower than “glance and guess,” and it catches the missed pneumothorax, the malpositioned tube, and the small effusion hiding on the lateral.

ABCDEF — one pass, six jobs
  1. A

    Assess quality, airways, always compare

    Rotation: spinous processes bisect the clavicular heads. Inspiration: 9–10 posterior ribs. Penetration: vertebral bodies visible through the heart. Airways: narrowing, deviation, foreign body. Always pull the prior film.

  2. B

    Bones and soft tissue

    Subcutaneous air, rib fractures, cervical ribs. Soft-tissue swelling can be the only clue to a missed trauma film.

  3. C

    Cardiac silhouette, mediastinum, hilum

    AP films enlarge the heart. Cardiothoracic ratio >50% suggests cardiomegaly on a PA film only. Widened mediastinum is generally >8 cm — first exclude rotation.

  4. D

    Diaphragm and gastric bubble

    Left hemidiaphragm is usually lower. Flattening is sensitive for emphysema. A missing gastric bubble on the left is a hint, not a diagnosis.

  5. E

    Effusions

    Blunting of the costophrenic angle. Small fluid is seen first on the lateral. Upright PA misses fluid until >250 mL; recumbent films are worse. Lateral decubitus: free-flowing fluid layers, loculated fluid does not.

  6. F

    Fields and foreign bodies (lines)

    Focal vs diffuse: PTX, pneumonia, edema. Silhouette sign = a density against a normal border. ETT tip 3–5 cm above the carina.

↑ intrapleural pressure pushes the trachea (PTX). ↓ intrapleural pressure pulls it (atelectasis / mucus plug).

Schematic normal PA chest radiograph labeled ABCDEF
Normal PA film. Use this as the mental template before you name a pathology.
Schematic lateral chest radiograph highlighting the posterior costophrenic sulcus
Lateral film: the posterior costophrenic sulcus is where a small effusion hides first.

Trachea, push vs pull

Side-by-side schematic of tracheal deviation from pneumothorax versus atelectasis
Left: tension physiology pushes the trachea away. Right: volume loss pulls it toward the white-out.

Pushes (↑ intrapleural pressure)

  • Tension pneumothorax
  • Large pleural effusion
  • Massive hemothorax
  • Large mass

Pulls (↓ volume)

  • Lobar atelectasis / mucus plug
  • Fibrosis / pneumonectomy
  • Scarring after TB
  • Unilateral hypoplasia

Pattern recognition on CXR

Schematic right lower lobe pneumonia
RLL pneumonia. Silhouettes the diaphragm, spares the right heart border — the density is posterior and basal.
Schematic cardiogenic pulmonary edema
Cardiogenic edema: large heart, bat-wing perihilar haze, Kerley B lines, blunted angles. If the heart is small, think ARDS or non-cardiogenic.
Schematic right pneumothorax with visceral pleural line
Pneumothorax: visceral pleural line with no markings beyond it. On a supine film look for the deep sulcus sign.
Schematic right pleural effusion with meniscus
Effusion: homogeneous base, meniscus climbing the chest wall, no air bronchograms. Atelectasis enhances with contrast and can improve when prone; effusion does not.
SignMeansWhere to look
Silhouette signPulmonary density touching a normal border erases itRML erases the right heart; RLL erases the diaphragm; lingula erases the left heart
Air bronchogramPatent airway inside consolidated lungPneumonia > atelectasis; also pulmonary edema, hemorrhage
Kerley B linesThick interlobular septaCHF, lymphangitic spread
Deep sulcusSupine PTX collecting anterior-caudalICU films — do not wait for an upright
Bat-wing / perihilarCentral alveolar fillingCardiogenic edema, DAH, PCP (bat-wing GGO on CT)

CT chest — windows and patterns

CT is for an abnormal CXR you cannot characterize, or a normal CXR you do not believe. HRCT (<2 mm, non-contrast) is the study for diffuse parenchymal disease: inspiratory, expiratory, supine, and prone.

  • Scout first — anatomy and tubes at a glance.
  • Soft-tissue window: mediastinum, heart, vessels. LV > RV normally. Main PA diameter should be less than the ascending aorta; PA ≥29 mm has PPV 97% for pulmonary hypertension.
  • Lung window: parenchyma. Inspiratory HRCT: round trachea. Expiratory HRCT: D-shaped trachea; air trapping declares itself.
  • Coronary calcium is visible even on non-contrast studies — mention it.
Six-panel schematic of common CT chest patterns
CT pattern atlas. Name the pattern first, then the etiology. Tree-in-bud is small-airway filling ().
PatternWhat you are seeingFirst etiologies
ConsolidationComplete alveolar filling; dense attenuation that obscures vessels ± air bronchogramsPneumonia > malignancy
Ground-glass (GGO)Partial filling; hazy ↑ attenuation that does not hide architectureInfection, edema, blood, fibrosis, malignancy
Tree-in-budFilled centrilobular bronchioles — branching dotsInfection including TB, CTD, ABPA, CF, tumor emboli
Emphysema / blebAirspace >1–2 cm; bleb is the smaller cousinCOPD, congenital, spontaneous PTX
Mosaic attenuationPatchy ↑ and ↓ attenuation from air trapping, poor perfusion, or GGO. Expiratory images worsen air trappingHypersensitivity pneumonitis, obstruction, CTEPH, infection, edema
HoneycombingStacked cystic airspaces. Microcystic <4 mm, macrocystic >4 mmNSIP often <4 mm; IPF / UIP often >4 mm
Subpleural reticulationSeptal lines ~1 cm from the pleuraUIP > NSIP; can be aging
BronchiectasisIrreversibly dilated airways; tram-tracks, signet-ringPost-infectious, CF, NTM, traction from fibrosis
Atelectasis vs effusionAtelectasis enhances with contrast and can improve prone; effusion is homogeneousDo not call both without a decubitus or CT