As we saw before, a simple transudative pleural effusion is anechoic. On the other hand, presence of echogenicities in the effusion is suggestive of complex/exudative pleural effusion. The term ‘plankton sign’ is often used to indicate debris appearing as swirling, punctiform echoes in such effusions and may indicate infection or hemothorax depending on the clinical context. Rarely, it can be seen in simple effusions after aggressive diuretic therapy. As the collection progresses, fibrin is activated and septations or loculations appearing as thin hyperechoic lines begin to form within the fluid collection, resembling a ‘spider web’. This is an important finding because effusions with loculations are more likely to require interventions such as intra-pleural instillation of fibrinolytic/enzymatic therapy via chest tube or surgical treatment.

Following are several examples of complex pleural effusion/empyema.

Here’s a case highlighting the importance of repeat POCUS when a patient’s improvement is not as expected. The initial image shows a consolidated lung with minimal movement, surrounded by a small pleural effusion—findings suggestive of pneumonia in a patient with fever and leukocytosis. The patient initially showed improvement on antibiotics for a couple of days but then began spiking fevers again with worsening leukocytosis. Repeat POCUS revealed a complex pleural effusion with septations and echogenic material of varying echogenicities, indicative of empyema.