Chest ImagingExudative effusion
pleural effusion that occurs when there is increased
permeability of abnormal
pleural capillaries with leakage of high molecular weight proteins and cells into the
pleural space (see
pleural effusion). Exudates are usually, but not always, unilateral.
The commonest causes are infection and malignancy of the lung or pleura. Other causes include trauma, collagen vascular disease, pulmonary embolism and exudates secondary to abdominal disease such as pancreatitis or subphrenic abscess. In addition the pleural space may contain blood, chyle, bile, cerebrospinal fluid or any intravenous infusion given to the patient.
Exudates should be distinguished from transudates. The main distinguishing features on biochemical analysis of the pleural fluid are a high specific gravity (> 1.016), a high protein content (> 3g/dl or pleural fluid to serum protein ratio of > 0.5) and a high LDH (> 200 IU/L or pleural fluid to serum ratio of > 0.6). Chest ultrasonography and CT can be useful in distinguishing between exudates and transudates. Ultrasound features which indicate that an effusion is an exudate include the presence of septa or debris and evidence of pleural thickening (Fig.1). On CT exudates are often associated with evidence of enhancement of the pleura and extrapleural fat following intravenous contrast injection. Both Chest ultrasonography and CT are commonly used to guide aspiration.
CF - HM
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Ultrasound imaging of right basal pleural effusion demonstrates multiple septa (arrows). Biochemical analysis confirmed that the effusion was an exudate.
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Exudative effusion, Fig.1 | |