Pseudochylothorax

Pseudochylothorax, 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.

Epidemiology

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

Clinical presentation

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.

Pathology

The pathogenesis of pseudochylothoraces is yet to be fully elucidated ^2,4,5. Generally, pseudochylothoraces are most often a complication or evolution of a chronic exudative pleural effusions, typically associated with a fibrotic and thickened pleura ^2,4,5. The most common aetiologies are tuberculosis and rheumatoid arthritis, with far less common causes including neoplasm (e.g. lung cancer) and other infections (e.g. syphilis, echinococcosis) ^1,2,4,5. However, although often considered to require chronicity and pleural thickening to develop, there are relatively recent case reports of more rapid-onset pseudochylothoraxpseudochylothoraces occurring in the absence of significant pleural thickening or chronicity ^2,4,5.

Aetiology

The most common aetiologies are tuberculosis and rheumatoid arthritis ^21,2,4,5. Other far less common causes include neoplasm (e.g. lung cancer) and other infections (e.g. syphilis, echinococcosis) ^1,2,4,5.

Markers

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.

Radiographic features

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.

Treatment and prognosis

A pseudochylothorax should be drained if symptomatic ^2,5. Otherwise, the exact management strategy will depend on underlying aetiology ^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.

History and etymology

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