Update on uncommon pleural effusions.

Although infections, malignancies and heart failure are responsible for the majority of pleural effusions, there are many other causes and several uncommon but distinctive types of pleural fluid. For this update we have chosen several uncommon forms of pleural effusions or disorders in which there have been recent advances in our understanding over the past several years. Chylothorax, pseudochylothorax and urinothorax are associated with characteristic clinical contexts and pleural fluid parameters but are likely underdiagnosed. Yellow nail syndrome is a rare disorder that can be associated with chylothorax and manifests multisystem features. Recognition of these entities is important because each of these disorders is associated with distinctive aetiology and management modalities. Correct diagnosis depends on the clinician's awareness of the clinical contexts and manifestations along with diagnostic pleural fluid findings in these disorders.