🫁 CXR Signs in Pulmonary Embolism
Chest X-ray signs classically associated with pulmonary embolism (PE). Most CXR findings are non-specific; these signs may aid in diagnosis but have limited sensitivity.
| Sign | Pathophysiology | Sensitivity | Specificity | PPV |
|---|
| Westermark sign | Focal oligemia | 11% | 92% | 33% |
| Hampton hump | Pulmonary infarction | Rare | High | High when present |
| Fleischner sign | Dilated proximal PA | Uncommon | Moderate | Moderate |
| Palla sign | Enlarged right descending PA | Low | Moderate | Low |
| Knuckle sign | Abrupt PA cutoff | Low | High | High when present |
Westermark Sign
Nils Westermark, Swedish radiologist
Description: Focal region of decreased vascular markings (oligemia) in the affected lung field, distal to a pulmonary embolism. Results from dilation of pulmonary arteries proximal to the embolus combined with collapse of distal vasculature, creating a sharp "cut-off" appearance.
Classic Appearance: Wedge-shaped or geographic area of rarefaction in the lung periphery with sharply demarcated margins, representing the zone of oligemia.
Differential Diagnosis: Hypovolemia, pneumothorax, emphysema, Swyer-James syndrome
Ref: Ray J. Can J Cardiol 2003; Worsley D et al. Radiology 1993 (PIOPED Study)
Hampton Hump
Aubrey Otis Hampton, 1940
Description: A shallow wedge-shaped opacity in the lung periphery with its base against the pleural surface, representing pulmonary infarction distal to an occluded pulmonary artery. The convex apex points toward the hilum.
Classic Appearance: Pleural-based triangular or wedge-shaped consolidation with rounded apex pointing centrally. Usually in the lower lobes. May contain air bronchograms. Typically appears 1–3 days after PE.
Accuracy
High when present
⚠️ Image unavailable — search Wikimedia Commons: Hampton hump pulmonary embolism
Fig: Hampton hump shown in CT (blue arrow) — wedge-shaped peripheral opacity representing pulmonary infarction. (Wikipedia/Radiology case)
Differential Diagnosis: Pneumonia, pulmonary contusion, pleural effusion, tumor infarction, Wegener's granulomatosis
Ref: Hampton AO, Castleman B. Am J Roentgenol Radium Ther 1940; PIOPED Study 1993
Fleischner Sign
Felix Fleischner
Description: Enlargement (dilation) of the proximal pulmonary arteries due to acute obstruction by pulmonary embolism. The affected artery appears engorged proximal to the embolus.
Classic Appearance: Prominent, enlarged main or lobar pulmonary arteries bilaterally or unilaterally. May show abrupt narrowing ("cut-off") at the site of embolism. Visible on both CXR and CT.
Differential Diagnosis: Pulmonary hypertension, high output states, PA aneurysm, mediastinal tumors
Ref: Kumaresh A et al. J Clin Imaging Sci 2015; Cooksley T et al. J Emerg Med 2012
Palla Sign
A. Palla, radiologist
Description: Enlargement of the right descending pulmonary artery (RDPA), seen as a rounded opacity in the right lower lobe on chest X-ray, due to acute pulmonary artery distension from proximal embolism.
Classic Appearance: Prominent right descending pulmonary artery causing enlargement of the right hilum. RDPA diameter > 16 mm on frontal CXR is considered abnormal. May appear as a rounded "palla" shadow in the right lower zone.
Differential Diagnosis: Pulmonary hypertension, right heart failure, emphysema, mediastinal lymphadenopathy
Ref: Palla A et al. Chest 1983; Stein et al. Am J Med 1975
Knuckle Sign
Also called "Pulmonary artery cutoff sign"
Description: An abrupt, sharp cutoff of a pulmonary artery branch at the site of embolic occlusion, with subsequent reconstitution of the vessel distally (the "knuckle" shape at the cut-off point).
Classic Appearance: On CXR, appears as a truncated pulmonary artery with a rounded, knuckle-like terminus. Best seen in interlobar arteries. On CT/MRA, corresponds to the "polo mint" sign or filling defect.
Differential Diagnosis: Pulmonary artery sarcoma, extrinsic compression by tumor, vasculitis
Other CXR Findings in PE
Yale Sign (Tubular Sign)
Columnar lucency representing a pulmonary artery casting of a embolus within the vessel lumen. Rare finding.
McCullough Sign
Enlargement of the azygos vein (> 7mm) associated with acute PE and right heart strain. Non-specific.
plicae sign
A thin curvilinear density representing the imprint of the embolus on the vessel wall, with collateral vessels.
Normal CXR in PE
Up to 70–80% of confirmed PE cases have normal or non-specific CXR findings. A normal chest X-ray does NOT rule out pulmonary embolism. V/Q scan or CTPA remains essential.
Clinical Pearl Summary
| Scenario | Most Useful Sign |
|---|
| MASSIVE PE with hemodynamic compromise | Fleischner sign (dilated proximal PA), Knuckle sign |
| Smaller PE with infarction | Hampton hump |
| Focal oligemia pattern | Westermark sign |
| Right lower lobe opacity | Palla sign, Hampton hump |
| Routine screening / rule-out PE | Remember: CXR is NON-SPECIFIC — use Wells criteria + D-dimer, confirm with CTPA or V/Q |
🔑 Key Point: All CXR signs in PE have low sensitivity but variable specificity. When present, they modestly increase pre-test probability. When absent, they do NOT rule out PE. CT Pulmonary Angiography (CTPA) remains the diagnostic standard.