Transudates

• Congestive heart failure (40%): 80% bilateral, ± cardiomegaly on CXR occasionally exudative (especially after aggressive diuresis or if chronic)

• Cirrhosis (“hepatic hydrothorax”): diaphragmatic pores allow passage of ascitic fluid often right-sided (²∕³) & massive (even witho marked ascites)

• Nephrotic syndrome: usually small, bilateral, asymptomatic (r/o PE b/c hypercoag)

• Other: PE (usually exudate), malignancy (lymphatic obstruction), myxedema, CAPD

• Atelectasis NB:

• Cerebrospinal filuid leak into pleural space

• Heart failure

• Hepatic hydrothorax

• Hypoalbuminemia

• iatrogenic

• nephrotic syndrome

• peritoneal dialysis

• urinothorax