MRI for Pericarditis: Heart Inflammation

What Is Pericarditis?

Pericarditis is inflammation of the pericardium — the thin, two-layered sac that surrounds and protects the heart. The pericardium contains a small amount of fluid (15-50ml) that lubricates the heart's movement as it beats. When the pericardium becomes inflamed, it can cause sharp chest pain, pericardial effusion (excess fluid around the heart), and, in severe cases, cardiac tamponade (dangerous compression of the heart by accumulated fluid).

Pericarditis is the most common pericardial disease encountered in clinical practice. It accounts for approximately 5% of emergency department presentations with chest pain (excluding those with heart attacks). Annual incidence in the UK is estimated at 27 per 100,000 population.

The majority of cases (80-90%) are idiopathic or viral — meaning the exact cause isn't identified or is presumed to be a viral infection. Other causes include autoimmune diseases (lupus, rheumatoid arthritis), post-myocardial infarction (Dressler syndrome), post-cardiac surgery (postcardiotomy syndrome), tuberculosis, bacterial infection, malignancy, and uraemia (kidney failure).

The clinical spectrum ranges from a single acute episode (resolving within weeks) to recurrent pericarditis (one of the most challenging conditions in cardiology, with recurrence rates of 15-30% after a first episode and up to 50% after a second). Constrictive pericarditis — chronic thickening and scarring of the pericardium that restricts heart filling — is a rare but serious long-term complication.

Why Cardiac MRI Is Used for Pericarditis

Acute pericarditis is typically diagnosed clinically (chest pain, pericardial rub, ECG changes) and confirmed with echocardiography (showing pericardial effusion). Cardiac MRI adds value in several important scenarios:

• Confirming pericardial inflammation: CMR (cardiac MRI) directly visualises pericardial inflammation using late gadolinium enhancement (LGE) and T2-weighted oedema imaging. This is useful when the diagnosis is uncertain or when distinguishing pericarditis from myocarditis (inflammation of the heart muscle itself) or myopericarditis (both together).
• Assessing myocardial involvement: Up to 30% of pericarditis cases have concomitant myocarditis. Identifying myocardial involvement (myopericarditis) changes the management — activity restriction is more stringent, and some treatments differ.
• Constrictive pericarditis: CMR is the best non-invasive test for diagnosing constrictive pericarditis — showing pericardial thickening, calcification (indirectly), and the characteristic septal bounce (abnormal interventricular septal motion).
• Differentiating constrictive pericarditis from restrictive cardiomyopathy: These two conditions present similarly (heart failure with preserved ejection fraction) but require very different treatments. CMR features can distinguish between them.
• Effusive-constrictive pericarditis: A combination of pericardial effusion and constriction. CMR demonstrates both the effusion and the pericardial thickening/enhancement.
• Recurrent pericarditis — guiding treatment: CMR can show whether active pericardial inflammation persists, helping guide decisions about anti-inflammatory therapy duration and when it's safe to taper or stop treatment.
• Excluding other causes of chest pain: CMR simultaneously assesses myocardial function, coronary artery anatomy (MR coronary angiography, though limited), and alternative diagnoses.

MRI Sequences Used

• Cine SSFP (balanced steady-state free precession): The workhorse of cardiac MRI — produces "movie" images of the heart beating. Shows ventricular function, wall motion, pericardial effusion, and — critically — the septal bounce of constrictive pericarditis (an abnormal fluttering or bouncing movement of the interventricular septum during early diastole).
• T2-weighted STIR or T2-prepared SSFP: Detects oedema. Inflamed pericardium appears bright (high signal) on T2-weighted images. This is one of the direct signs of active pericardial inflammation.
• T2 mapping: Quantitative technique that measures the T2 relaxation time of the myocardium. Elevated T2 values indicate oedema and active inflammation. Particularly useful for detecting subtle myocardial involvement (myopericarditis).
• T1 mapping and ECV (Extracellular Volume): Native (pre-contrast) T1 values are elevated in inflamed tissue. Post-contrast T1 mapping allows calculation of ECV, which is increased in inflammation, oedema, and fibrosis.
• Late Gadolinium Enhancement (LGE): Acquired 10-15 minutes after gadolinium injection. Inflamed or fibrotic pericardium enhances brightly. LGE of the pericardium is one of the most specific signs of pericarditis on CMR. If myocardial LGE is also present (typically in a non-ischaemic, subepicardial or mid-wall pattern), this indicates myopericarditis.
• Real-time cine during free breathing: For patients who can't hold their breath (common in acute, unwell patients). Allows assessment of septal motion and ventricular interdependence without breath-holding.
• Black-blood T1 spin echo: Good for measuring pericardial thickness. Normal pericardium is 1-2mm thick. Thickened pericardium (>4mm) supports the diagnosis of constrictive or effusive-constrictive pericarditis.

What Radiologists Look For

• Pericardial enhancement on LGE: Bright signal in the pericardium after gadolinium, indicating active inflammation or fibrosis. This is the hallmark CMR finding of pericarditis.
• Pericardial oedema: High signal in the pericardium on T2-weighted images, indicating acute inflammation.
• Pericardial effusion: Quantified as small (<10mm), moderate (10-20mm), or large (>20mm). The distribution (circumferential vs. loculated) and signal characteristics (simple fluid vs. complex/haemorrhagic) are noted.
• Pericardial thickness: Normal ≤2mm. Thickened pericardium (>4mm) in the context of heart failure symptoms suggests constrictive pericarditis. However, constrictive pericarditis can occur with normal pericardial thickness in some cases.
• Septal bounce: Abnormal fluttering or early diastolic bouncing of the interventricular septum on cine images — the hallmark of ventricular interdependence in constrictive pericarditis.
• Myocardial involvement: T2 oedema and/or LGE in the myocardium (particularly the subepicardial layer, closest to the pericardium) indicates myopericarditis. The pattern and extent of myocardial involvement are reported.
• Ventricular function: Left and right ventricular volumes, ejection fraction, and regional wall motion — all accurately quantified by CMR.
• Pericardial calcification: MRI is less sensitive than CT for calcification, but it may be seen as areas of very low signal (dark) on all sequences. CT is the preferred modality if calcific constrictive pericarditis is specifically suspected.

How to Prepare for the Scan

• No fasting required unless your department specifically requests it
• Continue all cardiac medications — beta-blockers, anti-inflammatories, colchicine, etc.
• You'll have ECG leads placed on your chest for cardiac gating — the scanner synchronises image acquisition to your heartbeat. Shaving a small area of chest hair may be needed for good electrode contact.
• Remove all metal — jewellery, bra with underwire, belt buckle
• If you have a pacemaker or ICD, cardiac MRI may still be possible with an MRI-conditional device, but this requires specific planning with the MRI department and cardiology team

What Happens During the Scan

Cardiac MRI is one of the more technically demanding scans. You'll lie on your back with ECG leads and a surface coil over your chest. A cannula is placed for gadolinium contrast.

The scan takes 45-60 minutes. You'll need to hold your breath for 10-15 seconds at a time, multiple times throughout the scan. Each breath-hold captures one or two slices of the heart. The radiographer will coach you carefully — "breathe in... breathe out... breathe in... hold... and breathe."

Between breath-holds, you'll breathe normally for 10-20 seconds to recover. If you find breath-holding difficult, let the radiographer know — they can adjust techniques and use shorter breath-holds or free-breathing alternatives.

Gadolinium is injected partway through the scan. After a 10-15 minute wait, the late gadolinium enhancement sequences are acquired. The total scan time includes this waiting period.

What MRI Can't Show

• Pericardial calcification: CT is far superior to MRI for detecting pericardial calcification, which can be the dominant finding in chronic constrictive pericarditis. If calcific constrictive pericarditis is suspected, CT should complement MRI.
• Coronary artery disease: While CMR can assess myocardial perfusion and detect ischaemic damage, it cannot reliably visualise coronary artery stenosis with the same detail as CT coronary angiography or invasive coronary angiography.
• Cause of pericarditis: CMR shows that the pericardium is inflamed but doesn't tell you why. The cause (viral, autoimmune, tuberculous, malignant) still requires clinical history, blood tests, and sometimes pericardial fluid sampling.
• Haemodynamic assessment: While CMR shows the anatomical and functional consequences of constriction, invasive cardiac catheterisation (measuring intracardiac pressures directly) remains the gold standard for confirming the haemodynamic significance of constrictive pericarditis.

Treatment Pathways After Diagnosis

• Acute pericarditis — first episode: NSAIDs (ibuprofen or aspirin) plus colchicine for 3 months. This combination reduces recurrence from 30% to about 17%. Activity restriction (avoiding strenuous exercise) until symptoms resolve and inflammatory markers normalise.
• Myopericarditis: Activity restriction is more stringent (3-6 months). Colchicine plus NSAIDs. Monitoring with CMR to confirm resolution of myocardial inflammation before return to exercise.
• Recurrent pericarditis: Colchicine as maintenance therapy. If resistant, low-dose corticosteroids (with very slow taper over months). For steroid-dependent or refractory cases, the interleukin-1 inhibitor anakinra (Kineret) has shown excellent results and is now recommended by ESC guidelines. Rilonacept (Arcalyst) is another IL-1 inhibitor approved for recurrent pericarditis in some countries.
• Constrictive pericarditis: Medical management initially (anti-inflammatory therapy, diuretics). If constriction persists despite 3-6 months of medical therapy (and CMR shows ongoing inflammation suggesting potentially reversible "transient constriction"), pericardiectomy (surgical removal of the pericardium) is the definitive treatment. This is a major operation with significant mortality (5-10%) and is performed at specialist centres.
• Pericardial effusion/tamponade: Large effusions causing haemodynamic compromise require pericardiocentesis (needle drainage). CMR is useful before and after drainage to assess the pericardium and plan further management.

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