Most Common Location for Pulmonary Embolism
Pulmonary emboli are most commonly found in the main, lobar, and segmental pulmonary arteries, with less frequent occurrence in subsegmental branches. 1
Anatomical Distribution of Pulmonary Emboli
Pulmonary embolism (PE) typically follows a predictable pattern of distribution based on blood flow and vascular anatomy:
Main/Lobar Pulmonary Arteries: These larger vessels are the most common sites for pulmonary emboli. Spiral CT provides excellent results for detecting emboli in these locations 1
Segmental Arteries: Frequently involved, though emboli may be more difficult to detect than those in larger vessels
Subsegmental Arteries: Less commonly the sole location of emboli, with studies showing isolated subsegmental PE occurs in only 6-17% of cases 1
The European Society of Cardiology guidelines note that diagnostic accuracy for PE decreases with diminishing vessel caliber, making interpretation more difficult in smaller vessels 1.
Origin of Pulmonary Emboli
Understanding the source of emboli helps explain their distribution:
Lower Extremity/Pelvic Veins: 70-90% of identifiable thromboemboli arise from the inferior vena cava territory, particularly the femoral and iliac veins 1
Pelvic Veins: Recent post-mortem data shows an increasing number of thromboemboli originating from peri-prostatic and peri-uterine plexuses 1
Upper Extremity Veins: Approximately 10-20% of emboli originate from thrombi in the superior vena cava territory, with increasing frequency due to indwelling catheters and other invasive procedures 1
Cardiac Origin: Plays only a minor role in the overall incidence of PE 1
Clinical Significance of Embolus Location
The location of pulmonary emboli has important implications:
Diagnostic Accuracy: Conventional pulmonary angiography has 98% co-positivity for PE in main/lobar arteries but only 66% for PE limited to subsegmental arteries 2
Treatment Decisions: Central PE (in main/lobar arteries) is more likely to receive catheter-directed therapies (18.3% vs 3.3% for peripheral PE) 3
Clinical Presentation: Peripheral PE is more likely to present with hypotension (46.4% vs 32.6%), while central PE is more likely to show right ventricular strain on imaging 3
Important Caveats
Diagnostic Challenges: Isolated subsegmental PE can be missed on spiral CT and may cause difficulties in interpretation of pulmonary angiography 1
Multiple Emboli: When a large embolus fragments in the heart, multiple emboli often shower the lungs, with an average of more than six emboli found within the pulmonary arterial system in patients with proven PE 1
Non-thrombotic Emboli: Various types of non-thrombotic emboli (fat, air, amniotic fluid, foreign material) can also occur in the pulmonary circulation, with different distribution patterns and clinical implications 1
Despite differences in treatment patterns based on clot location, recent research suggests that clot location may not significantly affect patient outcomes at 90 days, with age being the only independent predictor of death or right ventricular strain 3.