Treatment of Small Subsegmental Pulmonary Emboli
For these 2 small subsegmental pulmonary emboli, you should first perform bilateral lower extremity compression ultrasound to exclude proximal deep vein thrombosis (DVT), then make a risk-stratified treatment decision: anticoagulate if high-risk features are present (active cancer, prior VTE, persistent risk factors, limited cardiopulmonary reserve) or consider clinical surveillance without anticoagulation if low-risk and DVT is excluded. 1
Yes, This Means Blood Clots in the Lungs
The radiology report describes 2 small blood clots (pulmonary emboli) in the right lung's blood vessels—specifically in the right middle lobe and lower lobe at the subsegmental level 1. These are peripheral, small clots that require careful management decisions.
Critical First Step: Rule Out DVT
Before deciding whether to withhold anticoagulation, you must perform bilateral lower extremity compression ultrasound to exclude proximal deep vein thrombosis. 1 This is non-negotiable because:
- Isolated subsegmental PE is frequently associated with DVT 1
- If proximal DVT is found, full anticoagulation is mandatory regardless of the small PE size 1
- Withholding anticoagulation without excluding DVT is a critical error 1
Risk Stratification Determines Treatment
The American College of Chest Physicians provides a risk-based approach for subsegmental PE management 1:
Low-Risk Patients (Consider Clinical Surveillance)
Clinical surveillance without anticoagulation may be appropriate for low-risk patients (weak recommendation, low-certainty evidence) 1. Low-risk characteristics include:
- No active cancer 1
- No prior VTE history 1
- Provoked PE with resolved risk factor 1
- Good cardiopulmonary reserve 1
Important caveat: Recent evidence suggests this approach may carry higher VTE recurrence risk than initially thought. A large prospective study was prematurely interrupted after showing higher-than-acceptable recurrence rates in untreated low-risk SSPE patients 2. One study of patients with small PE diagnosed by V/P SPECT who did not receive long-term anticoagulation showed 4% DVT recurrence at 90 days 3.
High-Risk Patients (Anticoagulate)
Anticoagulation is recommended over clinical surveillance for high-risk patients (weak recommendation, low-certainty evidence) 1. High-risk characteristics include:
- Active cancer (approximately 20% recurrence rate in first 12 months—anticoagulation strongly recommended regardless of subsegmental location) 1
- Prior unprovoked VTE 1
- Persistent risk factors 1
- Limited cardiopulmonary reserve 1
If You Choose Anticoagulation
Prefer direct oral anticoagulants (DOACs) over vitamin K antagonists: specifically apixaban, rivaroxaban, dabigatran, or edoxaban 1, 4. For rivaroxaban specifically:
- Initial dosing: 15 mg twice daily with food for 21 days 5
- Maintenance: 20 mg once daily with food thereafter 5
- Minimum duration: At least 3 months 1, 4
Contraindications to DOACs: Do not use in severe renal impairment (CrCl <15 mL/min for rivaroxaban) or antiphospholipid syndrome 1, 4, 5.
Alternative approach: If DOACs are contraindicated, use low molecular weight heparin (LMWH) or fondaparinux overlapping with warfarin until INR reaches 2.0-3.0 4.
If You Choose Clinical Surveillance
Provide thorough patient education about warning signs requiring immediate return: 1
- New or worsening shortness of breath
- Chest pain
- Leg swelling or pain
- Hemoptysis
Close follow-up is essential, though the optimal surveillance protocol remains undefined 1.
Confirm the Diagnosis
The European Society of Cardiology suggests considering further imaging to confirm PE when isolated subsegmental filling defects are seen on CTPA, as some may represent false-positive findings or imaging artifacts 1, 2. This is particularly important if clinical probability is low.
Special Considerations
Incidentally discovered asymptomatic subsegmental PE: The European Society of Cardiology recommends treating the same as symptomatic PE with standard anticoagulation regimens (weak recommendation, moderate-certainty evidence) 1.
Historical Context on Treatment Necessity
Older guidelines questioned whether treatment is mandatory for subsegmental PE 4. Early data suggested untreated patients with smaller emboli had much lower recurrence rates than previously assumed—one series showed only 10 recurrences (none fatal) among 308 hip replacement patients with postoperative PE who were not anticoagulated 4. However, current evidence and guidelines favor a more cautious, risk-stratified approach given the potential for serious consequences 1, 2.
Common Pitfalls to Avoid
- Never withhold anticoagulation without first excluding proximal DVT 1
- Do not assume all subsegmental filling defects are true PE—consider confirmatory imaging if clinical probability is low 1
- Do not underestimate risk in cancer patients—they require anticoagulation regardless of subsegmental location 1
- Do not use DOACs in severe renal impairment or antiphospholipid syndrome 1, 4
The Bottom Line
The risk-benefit ratio of anticoagulation for subsegmental PE remains unclear, and randomized trial data are lacking 2, 6. In real-world clinical practice, given the potentially serious consequences of recurrent VTE and the relatively favorable safety profile of modern anticoagulants, most clinicians favor anticoagulation for at least 3 months unless clear contraindications exist or the patient is definitively low-risk with negative DVT screening. 4, 1