What is Pericardial Thickening?
Pericardial thickening is an abnormal increase in the thickness of the pericardium (the fibrous sac surrounding the heart) beyond the normal range of 1.2 to 1.7 mm, which can be detected on advanced cardiac imaging and is associated with various pericardial diseases including acute pericarditis, recurrent pericarditis, and constrictive pericarditis. 1
Normal Pericardial Anatomy
The pericardium normally appears as:
- A thin curvilinear structure measuring 1.2 to 1.7 mm in thickness 1
- On MRI: appears as a hypointense (dark) line surrounded by bright mediastinal and epicardial fat 1
- On CT: appears as a 1-2 mm thin density, best visualized anterior to the right ventricle 2
Any pericardial width >4 mm is regarded as abnormal on CT and cardiac MRI 1
Clinical Significance and Associated Conditions
Pericardial thickening occurs in several distinct disease states:
Acute Pericarditis
- Thickened pericardial layers with variable pericardial effusion 1
- Shows enhancement after contrast administration on CT 1
- Strong pericardial late gadolinium enhancement (LGE) on cardiac MRI 1
Constrictive Pericarditis
- Thickened pericardial layers that may be mild to moderate in degree 1
- Thickening most pronounced at the base of ventricles (right ventricle > left ventricle), atrioventricular grooves, and atria 1
- Creates a rigid, deformed pericardium that compresses cardiac contents 1
- May progress to calcification 3
Recurrent Pericarditis
- May show heterogeneous distribution of thickening due to adhesions 1
Critical Diagnostic Caveats
Important pitfall: A thickened pericardium does not always indicate constrictive pericarditis 3. Conversely, constrictive pericarditis can occur without pericardial thickening 3, making this a challenging diagnosis that requires correlation with hemodynamic findings.
In constrictive pericarditis specifically, CMR is particularly valuable for identifying atypical presentations with minimally thickened pericardium 1. The thickening may be accompanied by fibrotic fusion of pericardial layers and epicardial involvement 4.
Imaging Modalities for Detection
Cardiac MRI is the preferred imaging modality for optimal assessment of pericardial thickening 1, offering:
- Precise delineation of pericardial thickness 5
- Tissue characterization capabilities 1
- Assessment of inflammation via late gadolinium enhancement 1
- Evaluation of hemodynamic consequences 1
CT is complementary, particularly for detecting calcification 2, though it may fail to visualize the pericardium in more than half of normal individuals and patients with localized disease 6.
High-frequency ultrasound shows promise for detailed pericardial assessment, with superior resolution compared to CT for visualizing the apical pericardium 6, though this remains primarily a research tool.
Functional Consequences
When pericardial thickening progresses to constriction, it results in:
- Decreased pericardial compliance 1
- Restriction of diastolic cardiac filling 5, 3
- Ventricular interdependence with characteristic septal bounce 1
- Equalization of diastolic pressures across cardiac chambers 4
The thickened, rigid pericardium essentially creates a fixed cardiac volume, preventing normal diastolic expansion and leading to symptoms of right heart failure including venous congestion, ascites, and peripheral edema 1.