PLEURAL EFFUSION
The spine sign extending above the diaphragm is most commonly used to look for a pleural effusion. As a rule of thumb, 1-2 vertebrae would be a small effusion (approx 250ml), 2-4 vertebrae moderate (approx 500ml) and 4-6 vertebrae large (approx 1L) (1).
The appearance of the effusion can give you a clue to its cause (2,3)
ANECHOIC
Anechoic (black) effusions are typically transudates, especially if found bilaterally. However, they could also be early exudates.
ECHOGENIC
PLANKTON SIGN
The presence of small echogenic foci floating in the fluid. It is present with exudates eg pus, blood (clip below)
Same as plankton but in the clinical scenario of a haemothorax
EMPYEMA
On US, empyema looks almost like consolidated lung. The fluid has a tissue like homogenous echogenicity. Echogenic locules of gas with tiny reverberation artefacts float in the fluid. However, unlike air bronchograms, these locules do not have the typical branching pattern of bronchioles.
SEPTATIONS
Septations are more common with empyemas and malignant effusions. Septations suggest thoracocentesis should not be performed in ED.
REFERENCES
1. Tsai, Tzu-Hsiu; Yang, Pan-Chyr. Ultrasound in the diagnosis and management of pleural disease. Current Opinion in Pulmonary Medicine 9(4):p 282-290, July 2003.
2. Sajadieh H, Afzali F, Sajadieh V, Sajadieh A. Ultrasound as an alternative to aspiration for determining the nature of pleural effusion, especially in older people. Ann N Y Acad Sci. 2004;1019:585–92.
3. Brogi E, Gargani L, Bignami E, Barbariol F, Marra A, Forfori F, Vetrugno L. Thoracic ultrasound for pleural effusion in the intensive care unit: a narrative review from diagnosis to treatment. Crit Care. 2017 Dec 28;21(1):325.