Last revised by Daniel J Bell on 14 Jan 2020

A pseudochylothorax (plural: pseudochylothoraces), also known as a pseudochylous effusion, chyliform effusion, cholesterol effusion, or cholesterol pleurisy, is a rare cause of pleural effusion due to the accumulation of a cholesterol crystal-rich fluid within the pleural space.

The exact incidence of pseudochylothorax is unknown, however it is thought to be very uncommon 1,2. Indeed, the literature reports less than 200 cases 3.

Patients generally present with a slowly progressive course of varying degrees of respiratory distress and chest pain, depending on the amount of fluid that has accumulated 1,2,4,5.

The pathogenesis of pseudochylothoraces is yet to be fully elucidated 2,4,5. Generally, pseudochylothoraces are a complication or evolution of chronic exudative pleural effusions, typically associated with a fibrotic and thickened pleura 2,4,5. However, there are relatively recent case reports of more rapid onset pseudochylothoraces occurring in the absence of significant pleural thickening or chronicity 2,4,5.

The most common etiologies are tuberculosis and rheumatoid arthritis 1,2,4,5. Other far less common causes include neoplasm (e.g. lung cancer) and other infections (e.g. syphilisechinococcosis1,2,4,5.

The fluid in a pseudochylothorax is an exudate, typically with a high cholesterol content 5. A pleural fluid-to-serum cholesterol ratio of >1 is diagnostic, and differentiates it from a similarly appearing chylothorax 5.

Pseudochylothoraces can be appreciated on any form of conventional chest imaging, such as plain radiograph or CT. Typically, they are unilateral with features that are indistinguishable from those of any other pleural effusion 3,5. In most cases, they are associated with ipsilateral pleural thickening 3,5.

A pseudochylothorax should be drained if symptomatic 2,5. Otherwise, the exact management strategy will depend on underlying etiology 2,5. For example, in pseudochylothoraces secondary to rheumatoid arthritis, aggressive management of the rheumatoid arthritis often resulted in improvements of pleural collections 2,5.

Pseudochylothorax was first described by Bruce F Weems, an American physician, in 1918 6.

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