Pericardial effusion CT and MRI
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor-In-Chief: Cafer Zorkun, M.D., Ph.D. [2]; Varun Kumar, M.B.B.S.
CT and MRI
Cross-sectional imaging by CT or MRI is very sensitive in the detection of generalized or loculated pericardial effusions. Some fluid in the pericardial sac contributes to the apparent thickness and should be considered normal. Commonly, free-flowing fluid accumulates first at the posterolateral aspect of the left ventricle, when the patient is imaged in the supine position.
Estimation of the amount of fluid is possible to a limited extent based on the overall thickness of the crescent of fluid. Compared to cardiac ultrasound, CT and MRI may be particularly helpful in detecting loculated effusions, owing to the wide field of view provided by these techniques. Hemorrhagic effusions can be differentiated from a transudate or an exudate based on signal characteristics (high signal on T1-weighted images) or density (high-density clot on CT). Pulsation artefacts may cause local areas of low signal in a hemorrhagic effusion. Effusions are often incidentally noted on CT scans obtained for other indications.
Pericardial thickening (thickness >4 mm) is difficult to differentiate from a small generalized effusion. Both entities will reveal a low signal/density line that is thicker than the normal pericardial thickness. In acute pericarditis, the pericardial lining can show intermediate signal intensity and may enhance after gadolinium administration.
CT
- CT attenuation measurements also enable the initial characterization of pericardial fluid.
- A fluid collection with attenuation close to that of water is likely to be a simple effusion.
- Attenuation greater than that of water suggests malignancy, hemopericardium, purulent exudate, or effusion associated with hypothyroidism.
- Pericardial effusions with low attenuation also have been reported in cases of chylopericardium.
Images shown below are courtesy of RadsWiki
MRI
A pericardial effusion is black on spin echo images and in contrast is bright on gradient echo images. Small to moderate sized pericardial effusion occupy the space anterior to the right ventricle and are usually 5 mm or greater. A large pericardial effusion is often circumferential.
Insight into the composition of the pericardial effusion can be gleaned based upon the following characteristics:
- Transudates: low signal on T1-weighted images but high signal on T2-weighted and gradient echo images.
- Exudates: Intermediate signal on both types of sequences.
- Hemorrhagic effusions: Wide range of signal intensity on spin-echo sequences that is dependent upon the age of the effusion.
- The appearance of pericardial fluid is different on SE and GRE cine MR images.
- Nonhemorrhagic fluid has low signal intensity on T1-weighted SE images and high intensity on GRE cine images. Conversely, hemorrhagic effusion is characterized by high signal intensity on T1-weighted SE images and low intensity on GRE cine images.
- When an effusion is secondary to malignancy, an irregularly thickened pericardium or pericardial nodularity may be depicted on MR images.