Based on my CT scan, into which anatomic category (central/proximal, lobar, or peripheral/distal) do my pulmonary emboli fall?

Understanding Your Pulmonary Embolism Location on CT

Your CT scan will categorize your pulmonary emboli as either central (in the pulmonary trunk or main pulmonary arteries), lobar (in arteries feeding individual lung lobes), or subsegmental/peripheral (in the smallest branches of the pulmonary arteries). 1, 2

How to Read Your CT Report

The anatomic classification system used in modern CT pulmonary angiography (CTPA) follows a hierarchical structure based on where the blood clots are located:

Central/Proximal PE

• Clots located in the pulmonary trunk (the main vessel leaving the right side of your heart) or the main pulmonary arteries (the left and right branches)
• These are sometimes called "saddle emboli" when they straddle the bifurcation
• This location typically indicates more severe disease 1, 2

Lobar PE

• Clots in the arteries leading to individual lobes of your lungs
• Intermediate severity classification
• Falls between central and peripheral in terms of vessel size 2

Subsegmental/Peripheral PE

• Clots in the smallest branches of the pulmonary arteries
• Also called "distal" PE
• Generally considered less severe, though still requiring treatment in most cases 1, 2

Why Location Matters for Your Care

The location of your clots directly impacts treatment decisions and prognosis, though location alone does not determine mortality risk. 2, 3

Clinical Significance:

Central PE patients:

• More frequently show signs of right heart strain (RV/LV ratio >1.0, septal deviation)
• More likely to receive systemic thrombolysis (9.8% vs 2.0% for peripheral PE)
• More likely to receive advanced endovascular therapy (11.3% vs 0.7% for peripheral PE)
• However, hospital mortality rates are similar to peripheral PE (5.3% vs 6.6%) 3

Subsegmental PE patients:

• May be candidates for observation without anticoagulation in select circumstances
• Generally managed with anticoagulation alone
• Less likely to require advanced interventions 2

Important Caveats

Location is only one piece of the puzzle. The 2025 ESC consensus statement emphasizes that your overall risk stratification depends on multiple factors beyond just clot location 2:

• RV/LV ratio (right-to-left ventricle size ratio >1.0 indicates strain)
• Pulmonary artery diameter (should be smaller than the aorta)
• Septal deviation (the wall between heart chambers bowing toward the left)
• Biomarkers (troponin, BNP levels)
• Clinical stability (blood pressure, heart rate, oxygen levels)

A critical finding: While central PE correlates with more severe hemodynamic compromise and higher rates of right ventricular dysfunction, multivariate analysis shows that central location itself is not an independent predictor of mortality when other factors are controlled 3, 4. This means your doctors will look at the complete picture, not just where the clots are located.

What Your Report Should Include

According to the 2025 international consensus guidelines, your CTPA report should specify 2:

1. Exact location of clots (central, lobar, or subsegmental)
2. RV/LV ratio measurement
3. Pulmonary artery trunk diameter
4. Septal deviation (if present)
5. Signs of chronic disease (organized mural thrombi, complete occlusions, intravascular webs, RV hypertrophy)

These findings help your medical team determine whether you need anticoagulation alone, systemic thrombolysis, or catheter-directed interventions.