Pulmonary Embolism vs. Pulmonary Infarction: Key Distinction
Pulmonary embolism (PE) is the acute vascular event—a blood clot obstructing pulmonary arteries—while pulmonary infarction is a potential complication occurring in approximately 30% of PE cases, representing actual tissue death (necrosis) of lung parenchyma that develops when distal arterial occlusion leads to ischemia, hemorrhage, and ultimately irreversible tissue damage 1.
The Pathophysiologic Sequence
Pulmonary Embolism: The Initial Event
- PE is the thrombotic obstruction of pulmonary arteries
- Can occur at any level of the pulmonary arterial tree (central or peripheral)
- Represents the acute vascular insult itself
- Does not necessarily cause tissue death
Pulmonary Infarction: The Tissue Consequence
When PE occurs, the following cascade may lead to infarction 1:
- Distal arterial occlusion blocks normal pulmonary arterial blood flow
- Bronchial arteries compensate by becoming the primary perfusion source
- Higher systemic pressure in bronchial circulation (compared to pulmonary circulation) causes increased capillary blood flow
- Alveolar hemorrhage results from erythrocyte extravasation due to elevated capillary pressure
- If hemorrhage cannot be resorbed, tissue necrosis and infarction develop over months, eventually forming a fibrotic scar
Critical Clinical Distinctions
Location Matters
Pulmonary infarction predominantly occurs with distal (peripheral) arterial occlusions, not central emboli 2. Central PE rarely causes infarction because collateral circulation can adequately compensate. This explains why massive central PE can be hemodynamically catastrophic yet not produce infarction, while smaller peripheral emboli frequently do.
Timing and Diagnosis
A crucial pitfall: The diagnosis of pulmonary infarction cannot be confirmed at the time of acute PE diagnosis 1. The infarcted area is only replaced by fibrotic scar over months, meaning what appears as consolidation on initial imaging represents hemorrhage that may progress to true infarction.
Clinical Presentation Differences
PE Without Infarction
- Dyspnea (often sudden)
- Tachycardia
- Hypoxemia
- May be asymptomatic if small
PE With Infarction 3, 4
- Pleuritic chest pain (most frequent—occurs because infarcts are always peripheral along visceral pleura)
- Hemoptysis (much rarer than commonly believed)
- More likely to present with pleural pain (OR 2.7)
- Associated with more proximal PE on imaging (OR 1.6)
- Predicts greater functional impairment at 3 months (OR 3.03)
Radiologic Recognition
Imaging Characteristics of Infarction 3
Abandon the "wedge-shaped" teaching—this is outdated and causes missed diagnoses:
- Peripheral location along pleural surfaces (costal, diaphragmatic, mediastinal, or interlobar)
- Convex margin toward the hilum (semicircular or cushion-like, NOT triangular)
- Sharp free margin
- Focal hyperlucent areas within the consolidation on CT
- The apical portion is typically spared due to collateral flow
Common Misdiagnoses
Infarctions are frequently mistaken for:
- Pneumonia (most common error)
- Lung cancer
- Other pleural-based consolidations
Risk Factors for Infarction in PE Patients 3
Independent predictors include:
- Younger age
- Increasing body height
- Active cigarette smoking
- Presence of heart disease (hemorrhage progresses to infarction more readily) 2
Clinical Implications
Why This Distinction Matters
Symptom interpretation: Pleuritic pain and hemoptysis suggest infarction, which may be the first manifestation of PE 3
Prognosis: Patients with radiologic signs of infarction report more functional impairment at 3-month follow-up 4, though no difference in adverse events (recurrent thrombosis, readmission, mortality)
Treatment approach: Both require anticoagulation, but infarction may necessitate additional pain management and monitoring for complications (pneumonia, post-PE syndrome) 1
Follow-up counseling: Patients with infarction should be informed about potential persistent symptoms and functional limitations
Key Pitfall to Avoid
Do not assume all pleural-based consolidations in PE patients represent pneumonia or require antibiotics. The incidence of pneumonia-like lesions is significantly higher in PE patients (36.9%) compared to DVT patients (26.3%) 5, and many represent hemorrhagic infarction rather than infection. Distinguish based on clinical context, fever patterns, and inflammatory markers rather than imaging alone.