Pericardial effusion

Imaging description Pericardial effusion is caused by the obstruction of the lymphatic or venous drainage from the heart [1]. Accumulation of pericardial fluid above 50 ml is abnormal, which corresponds to 4 mm thickness of the pericardium on cross-sectional imaging [2, 3] (Figure 63.1). Simple effusions tend to have the attenuation of water on CT (<10 HU) (Figures 63.2 and 63.3), while exudative (20–60 HU) or hemorrhagic (60–80 HU) effusions have attenuation values greater than that of water [2, 4]. Pericardial effusions accompanied by pericardial thickening are suggestive of inflammatory pericarditis [4]. MRI can be helpful in characterizing pericardial effusions [3–5] (Figure 63.4). Signal characteristics may help distinguish pericardial fluid from thickening or may distinguish between simple and exudative or hemorrhagic transudative effusions. Simple effusions have no or very little T1-weighted signal intensity, while exudative or hemorrhagic effusions often are medium or high signal intensity on T1 sequences [3–5]. Importance Pericardial effusions are often asymptomatic but large effusions may be symptomatic and, therefore, are important to identify in order to alert the clinician. Occasionally the cause of a pericardial effusion can be identified on cross-sectional imaging, especially in cases of hemopericardium.