Pleural effusions in superior vena cava syndrome: prevalence, characteristics, and proposed pathophysiology

This review highlights recent data detailing the prevalence and characteristics of pleural effusions occurring in patients with superior vena cava syndrome.

Numerous case reports have described pleural effusions in conjunction with the superior vena cava syndrome. Recent data suggest that these effusions occur in 60% of superior vena cava syndrome cases. The effusions are small, usually occupying less than half the affected hemi-thorax, and occur about equally on either side or bilaterally. Although previously thought to be largely transudates, a large case series found that 18% of the effusions were chylous, with the remainder being exudates. None of the effusions sampled in the series were transudates. Occluded lymphatic flow from increased hydrostatic pressure in the superior vena cava and left brachiocephalic vein probably contributes to the development of chylous pleural fluid. The pathophysiology of the exudative effusions, however, remains unknown. Many factors, including diuresis, small pulmonary emboli, and the underlying inflammatory or malignant condition all likely contribute.

Chylous or exudative pleural effusions occur in most patients with superior vena cava syndrome. The effusions are usually small and resolve upon correction of the underlying superior vena cava obstruction.