A pleural ultrasound image of a collapsed lung surrounded by pleural fluid ("jellyfish sign") may correspond to an intrapericardial mass

Abstract

Lung ultrasound has been shown to be a valuable diagnostic tool. It has become the main way to get to the diagnosis of pleural effusion with much more specificity and sensibility than the x-ray. The diagnosis of pleural effusion with ultrasound is easily obtained after the visualization of hypoechoic fluid surrounding the lung. Sometimes it appears as an image of a collapsed lung moving with the surrounded pleural fluid ("jellyfish sign"). Until now this sign was almost pathognomonic of pleural effusion, but we explore a case in which this sign could have led to a misleading diagnosis. We present the case of a child admitted to intensive care with respiratory distress. In the point of care lung ultrasound we believed to see a pleural effusion with a collapsed lung moving into the effusion. Due to the enlargement of the pericardial sac, we did not realize that what we thought to be the pleural space was in fact the pericardial space. Unfortunately, there was a more echogenic area inside the pericardial effusion which led to a misleading fake lung atelectasis with pleural effusion ("jellyfish sign"). The correct diagnosis was properly obtained after assessing a cardiac point of care ultrasound using a four chambers view. The left side of the thorax is more difficult to be sonographed than the right due to the presence of the heart fossa that occupies a significant part of that side. Obtaining the diagnosis of pleural effusion on that side is more difficult for this reason and can sometimes be misleading with a pericardial effusion. The presence of the "jellyfish sign" is not pathognomonic and may lead to an error if we are guided only by the presence of that sign. To avoid such a misleading diagnosis, we highly recommend performing a point of care cardiac ultrasound if a pleural effusion is primarily seen in the lung ultrasound.

Keywords: Flapping lung; Jellyfish sign; Pericardial effusion; Pleural effusion; Ultrasound.

Fig. 1

Jellyfish sign on ultrasound. Image with what seems to be a collapsed lung (small arrow) surrounded by fluid that looks like pleural effusion (big arrow). Notably, there is also a further effusion above the pericardium (star)

Fig. 2

Thoracic X-ray scan, showing an enlargement of the cardiac silhouette with the presence of bilateral pleural effusion

Fig. 3

Subcostal view by echocardiography, showing a pericardial effusion with a hyperechoic intrapericardial mass (arrow)

Fig. 4

Thoracic CT scan, showing a large pericardial effusion without masses or abscesses. The hyperechoic masses observed on ultrasound can be explained as areas with a more organized thick effusion. Bilateral pleural effusion is seen more on the left side