False colour nuclear magnetic resonance (NMR) image of a transverse section through the chest of a person suffering from Hodgkin's disease, showing massive pleural effusion and pericardial effusion. Pleural effusion involves the introduction of fluid into the pleural cavity surrounding the lungs, and appears as the large white areas at bottom left & top right (ie both lungs are affected). Pericardial effusion means fluid accumulation in the pericardium (the membranous sac surrounding the heart), and is represented by the central white area. Both types of effusions occur in advanced cases of Hodgkin's disease, a cancer of the lymphatic system.