The differential diagnosis for pleural effusions is quite broad, but one of which must always include pulmonary venous embolism. Pleural effusions are the accumulation of fluid in the pleural space. What is the pleural space? The pleural space is what separates your lungs from your chest wall. It allows your lungs to expand and contract with every breath and not get stuck on your musculoskeletal organs.
Pleural effusions are most commonly divided into two broad categories: transudative or exudative. In general terms, transudative pleural effusions are a volume issue and exudative pleural effusions are a disease specific issue. In even more general terms, exudative=bad and transudative=good. Volume issues such as heart failure and poor nutrition are classic causes of transudative pleural effusions. Cancer, pneumonia, auto immune disorders and pulmonary venous embolism are classically associated with exudative effusions.
What are the criteria for determining if a pleural effusion is transudative or exudative? The Light criteria describes pleural effusions as exudative if one or more of the following criteria are met
- a pleural fluid:serum protein ratio > 0.5
- a pleural fluid:serum lactic dehydrogenase (LDH) ratio>0.6
- a pleural fluid LDH>200
It came somewhat as a shock to me when this 52 year old male presented to the hospital in acute hypoxemic respiratory failure after telling his wife that he felt short of breath for the last three weeks. Here is a picture of his xray. As you can see his pleural effusion was consuming most of his left lung parenchyma. Even stranger was the fact this guy had a negative CT of his chest just two months prior, when he presented to the hospital with atypical chest pain. To go from a normal CT scan of your lungs to this in just two months, and no other acute problems is a first for Happy. It became quickly apparent that an elevated D-dimer and bloody pleural effusion was unlikely to represent a transudative process, such as heart failure.
Further pulmonary venous embolism evaluation and diagnosis (CT angiogram of the chest) confirmed the presence of massive saddle pulmonary venous embolism. What was the source of this man's thromboembolic disease? Of course, his venous emboli came from his massive, asymptomatic and clinically unapparent deep venous thrombosis of his right leg. From groin to ankle a large deep venous thrombosis consumed his leg. Yet he had no symptoms. He had no swelling. No pain. No nothin'.
This makes for some interesting legal discussion for patients who may feel failure to diagnose an asymptomatic deep venous thrombosis before the clinical life threatening pulmonary venous embolism represents negligence on the part of the physician.
I forgot to mention that this man had a history of a pulmonary embolism five years prior, so pulmonary venous embolism was #1 on my list of the differential diagnosis, despite the terribly unusual presentation for pulmonary venous embolism this would represent. I would consider this a long tail presentation of a common medical condition. I've seen pleural effusions from pulmonary emboli before. But I've seen never them like this before.
This case also shows how important the history and physical examination is in developing the differential diagnosis. And why you must always be on your guard for unusual presentations of common disease. Something that the intensity of medical school and residency training turns just another provider into doctors.