[Efficient diagnosis of pleural effusion]

Abstract

Under physiological conditions the pleural cavities contain a few millilitres of a fluid film with a protein content of about 1.7 g%. Because of the different capillary pressure, there is a regular flow of fluid from the parietal pleura to the visceral pleura. In cases of increased hydrostatic pressure or reduced colloid osmotic pressure in the absence of pleural disease, transudation takes place; in disturbances of permeability resulting from various types of inflammation, neoplasms or vascular disorders, and in disturbances of lymph backflow, exudates are formed. A pleural effusion is easily recognizable in typical cases. Reference is made to particular radiological manifestations which are not always correctly interpreted, viz. subpulmonary effusion, encapsulated interlobar effusion ("vanishing tumour") and predominantly mediastinal effusion. Precise examination of the neighbouring organs, together with thoracentesis and pleural biopsy, are decisive for the etiological diagnosis. When examining the effusion, it is of great importance to differentiate between transudate and exudate. Light's definition of transudate proved to be valid in this study (protein content below 3 g% and LDH index below 0.6). For the basic examination, we further recommend cytology and--to save time--tuberculosis bacteriology as well. The significance, sensitivity and specificity of various other chemical tests are discussed. For diagnostic strategy it is always necessary to take into consideration the entire clinical situation, including radiology and laboratory tests. With this proviso, a specific investigation scheme may be recommended. After application of the usual diagnostic methods, including pleural biopsy, aetiologically unclear effusions remain in about 20-25% of cases. Approximately 2/3 of these can be diagnosed by means of optimized biopsy technique under thoracoscopy and are predominantly tumoral effusions. Approximately 1/3 (5-10% of the total number) still remain unclear as "idiopathic" effusions, even after thoracoscopy. The relative importance of early diagnosis of a malignant pleural effusion is discussed.