Acute Pulmonary Embolism with Peripheral Infarct

Hyperlucent right lung with perpherial opacity in the right lung base. Westermark Sign and Hampton's Hump - see below for descriptions of these signs.     Diagnosis: Acute Pulmonary Embolism with Peripheral Infarct

Differential Diagnosis – Unilateral Hyperlucent Lung

  Increased Transradiancy of Chest Wall Origin (Spurious)

• Congenital absence of pectoralis major muscle
• Mastectomy

Congenital Anomalies

• Absence or hypoplasia of one pulmonary artery
• Pulmonary agenesis
• Extrapulmonary sequestration

Intrinsic Obstruction of One Pulmonary Artery

• Embolus
• Tumor

Extrinsic Compression of One Pulmonary Artery

• Tumor
• Nodes

Compensatory Hyperinflation

• Atelectasis Status after lobectomy

Partially Obstructed Airways Intrinsic Obstruction of Major Bronchus

• Tumor—benign or malignant
• Postinflammatory stricture
• Foreign body
• Amyloid

Extrinsic Obstruction

• Congenital   
• Aberrant vessel   
• Extrapulmonary sequestration
• Tumor
• Nodes

Congenital Malformation of Bronchus Causing "Congenital Emphysema" Unilateral Acquired Bronchitis and Bronchiolitis Obliterans

• Swyer-James-Macleod syndrome

Parenchymal Findings in Acute PE

Signs on Chest Xray suggestive of PE

Westermark Sign: Oligemia (vasoconstriction) seen distal to a pulmonary embolus.
Hampton's hump: A wedge shaped, pleural based consolidation associated with pulmonary infarction.
Fleischner sign: Prominent central pulmonary artery

Statistically significant findings associated with PA

• wedge shaped parenchymal consolidation
• linear bands

No statistical difference in prevalence of non wedge shaped consolidation, areas of decreased attenuation, atelectasis, or pleural effusion

Coche et al. Radiology 1998

Parenchymal Consolidation in PE

Hemorrhage:

• Ischemic damage to endothelial and alveolar epithelial cells
• Red blood cells and fluid enter into air spaces

Hemorrhage with Infarct:

• Occurs in 10-15% of PE
• Pleural based opacity with apex directed toward hilum
• May contain central areas of low attenuation representing uninfarcted secondary pulmonary lobules

Pneumonia

• Seen with septic emboli or superimposed infection of infarcted lung

Hemorrhage vs. Infarct

• Consolidation rapidly clears (several days) in hemorrhage
• Consolidation slowly clears (weeks) in infarct which may give rise to linear bands

References

• E.E. Coche, N.L. Muller, K.I. Kim, B.R. Wiggs, and J.R. Mayo 
  Acute pulmonary embolism: ancillary findings at spiral CT 
  Radiology 1998 207: 753-758.
• Robert G. Fraser , J. A. Peter Par, Diagnosis of diseases of the chest, Saunders 1977
• http://www.mdconsult.com/das/book/body/143494216-2/0/1288/321.html