Not All Pericardiac Fluid Is Pericardial: Ultrasound of Pericardial Effusion and Two of Its Mimics

Focused cardiac ultrasound is emerging as a useful tool in preoperative evaluation and crisis management. Focused cardiac ultrasound’s scope of practice includes screening for the presence/absence of pericardial effusion.¹  Thus, practitioners of focused cardiac ultrasound should be able to differentiate a pericardial effusion from conditions that can mimic it, especially in an emergency. These focused cardiac ultrasound images were obtained in a patient who presented with hypotension and was found to have a trace pericardial effusion along with two other conditions that are often misdiagnosed as pericardial effusion.^2,3 

Fluid collections on ultrasound appear as anechoic/hypoechoic (dark) spaces with posterior acoustic enhancement (brightness deep to the effusion). In this parasternal long-axis view (PSLAX), two such fluid collections are seen posterior to the heart. In any parasternal long-axis view, fluid that dissects into the plane between the heart and descending aorta is pericardial whereas fluid deep to the heart unable to dissect into this plane is classically a left pleural effusion.³  Thus, this parasternal long-axis view shows a trace pericardial effusion and a large left pleural effusion containing atelectatic lung (Supplemental Digital Content 1, https://links.lww.com/ALN/C91).

In the subcostal four-chamber view (SC4C), two fluid collections appear superficial to the heart. In any subcostal four-chamber view, circumferential pericardial fluid follows the contours of the heart. In contrast, ascites fails to follow the contours of the heart and additionally contains an undulating falciform ligament²  (Supplemental Digital Content 2, https://links.lww.com/ALN/C92). Thus, this image shows the patient’s trace pericardial effusion and also prominent ascites.