This case features a patient with a history of end-stage renal disease with a small-moderate, asymptomatic pleural effusion and probable adjacent atelectasis, found incidentally but illustrating some of the classic ultrasound findings and signs in a pleural effusion. Visualization of the thoracic spine sign is highly suggestive of a pleural effusion, with the following sonomorphologic hallmarks further increasing diagnostic confidence ¹

• the quad sign defines the boundaries of a pleural effusion
  • laterally, two anechoic posterior rib shadows, superficially the parietal pleura, and the visceral pleura (or "lung line") is found deep
• the sinusoid sign is an inspiratory decrease in the size of the effusion
  • the "jellyfish sign," is a subtype

This is a free-flowing, simple effusion, evidenced by its dependent location, anechoic and homogenous nature, lack of septations, and absence of the plankton sign.

Learning points:

• recognize the sonographic features of a pleural effusion when performing lung ultrasonography
  • the quad sign
  • the sinusoid sign
    • subtype is the jellyfish sign
• pathology of the underlying lung may be visible
  • the tissue-like sign
  • the shred sign