Pericardial effusion
Is it pericardial, how big, where, what is it made of — and is it compressing anything?
Numbers to remember
- End-diastolic echo-free space: <10 mm small, 10–20 mm moderate, >20 mm large [31]
- Pericardial fluid sits anterior to the descending aorta in PLAX; pleural fluid sits posterior to it
- Rate matters more than size: a rapid small effusion can cause tamponade; a slow large one may not [31,177]
- Large effusion >3 months without inflammation → consider drainage (risk of progression to tamponade) [125,177]
Questions echo must answer
Echo is the first-line test for suspected pericardial effusion [31,125]. It answers five questions:
- Is it pericardial?Separate it from pleural fluid, epicardial fat and ascites.
- How large, and where?Circumferential or loculated; size at end-diastole [31].
- What does it look like?Clear, fibrinous strands, echogenic material (blood, pus, tumour), clot after surgery.
- Is there haemodynamic compromise?Chamber collapse, respiratory Doppler variation, IVC → see Tamponade [24,149].
- Where to drain?Best entry site and depth to the fluid [31,149].
The cause is established clinically: inflammation, malignancy, infection (TB in endemic areas), hypothyroidism, renal failure, post-MI or post-procedure, and aortic dissection [31,125,201].
Acquisition protocol
- PLAXFluid anterior to the descending aorta; measure at end-diastole. Look for anterior fat or fluid.
- PSAXDistribution around the LV.
- A4CLateral and apical collections, RA and RV collapse.
- SubcostalAnterior (RV) and inferior collections. This is often the best drainage window; measure depth from the skin.
- IVCSize and collapse.
- M-modeRV free-wall diastolic motion; RA collapse timing.
- DopplerMitral and tricuspid inflow respiratory variation, hepatic vein flow [24].
- Post-surgicalLook for localised clot behind the RA or LV; TOE if TTE is inconclusive [24].
- Pericardial vs pleural (relation to the descending aorta)
- Maximal end-diastolic depth and location
- Circumferential vs loculated
- Content (clear / strands / echogenic)
- Chamber collapse
- IVC
- Respiratory Doppler variation
- Best drainage window and depth
Diagnosis & severity
| Size (end-diastole) | Depth [31] |
|---|---|
| Small | <10 mm |
| Moderate | 10–20 mm |
| Large | >20 mm |
| Differential | Clue |
|---|---|
| Pleural effusion | Posterior to the descending aorta in PLAX; no pericardial reflection; lung inside it |
| Epicardial fat | Anterior only, granular, moves with the heart; common in older, obese and diabetic patients |
| Ascites | Below the diaphragm; falciform ligament in the subcostal view |
| Haemopericardium / clot | Echogenic, may be localised (post-surgery, dissection, rupture) |
Key pointSize does not equal compromise. The pericardial pressure–volume relationship is steep once the reserve volume is used up, so the rate of accumulation determines tamponade [31,177].
Thresholds that change management
- Tamponade, or suspected bacterial or neoplastic effusion → pericardiocentesis or surgical drainage [31,125,177].
- Effusion with suspected aortic dissection → do not drain percutaneously; emergency surgery [9,31].
- Large chronic effusion (>3 months) without inflammation → consider drainage because of the risk of later tamponade [125,177].
- Small to moderate effusion with pericarditis → anti-inflammatory therapy and follow-up echo [125].
- Hypothyroidism can produce large, slowly accumulating effusions that rarely cause tamponade; thyroid replacement resolves them [201].
- ESC triage score combines aetiology, clinical presentation and imaging to time drainage [149].
Pitfalls & mimics
PitfallFat is not fluid. An anterior echo-free or granular space with no posterior fluid is almost always epicardial fat. Draining it is dangerous.
- Pleural effusion mistaken for pericardial: use the descending aorta in PLAX and the subcostal view.
- Loculated post-operative effusions compress a single chamber (often the RA or LV) without the classic signs. Use TOE [24].
- Gain too low makes fibrin and clot invisible.
- Measure at end-diastole, perpendicular to the wall. The systolic space looks bigger.