A bad leg
Your senior house officer visited a 74 year old man in the emergency department. He shows you a photograph of his right lower leg taken after he had examined it (figure).
The causes of unilateral pitting oedema tend to relate to focal pathology or localised factors. Infection and inflammation causes oedema through the tissue response via the immune system. It can also result from impaired fluid drainage, namely of venous blood or lymph fluid. Blockage of outflow, leakage of vessels, or immobility and failure of muscle pumps can all lead to unilateral oedema.
Bilateral causes tend to be due to systemic pathology. Cardiac failure is a failure of the heart muscle pump. Renal hypoperfusion leads to volume retention via the rennin-angiotensin-aldosterone mechanism. Pump failure and fluid retention leads to venous volume overload. Dependent pitting oedema, pulmonary oedema, ascites, and raised jugular venous pressure result.1