Both. The pleural space is in direct anatomic contiguity with the lung interstitium. Thus, the interstitial edema of left-sided heart failure, as it is mobile, easily enters the pleural space. However, pleural fluid is absorbed into the parietal pleural lymphatics and thus into the systemic venous system. Therefore, right-sided heart failure with systemic venous hypertension may also lead to pleural effusions.
What disease processes mimic congestive heart failure on the chest x-ray?
Multiple disease processes of the lungs may occupy the same spaces‚ peribronchovascular interstitium, interlobular septa, air space, and pleura‚ as the edema of congestive heart failure. These disease processes, when accompanied by a prominent-looking heart, may mimic congestive failure. Examples are airways disease with thick bronchi which may be mistaken for edema, early acute respiratory distress syndrome (ARDS, injury edema), diffuse pneumonias, and occasionally, lymphangitic spread of carcinoma. It is impossible to distinguish renal failure and consequent fluid overload from congestive heart failure.
What is the differential diagnosis of a big, baggy-looking heart on the chest x-ray (e.g., cardiomegaly without specific chamber enlargement)?
Cardiomyopathy (of multiple causes)
Polyvalvular disease (becoming rarer with decrease in rheumatic fever).
This appearance is sometimes called a water bottle‚ heart, because the normal chamber outlines cannot be seen. I personally have not seen many water bottles‚ of that shape, but perhaps your grandmother had a hot water bottle that looked like that.