Edema is the accumulation of fluid in tissues. It is caused by an imbalance between forces holding fluids in the vasculature and tissues 1. Fluids are normally held in a steady state between tissues and vasculature by homeostasis between these forces (Starling equation) 2:
- capillary hydrostatic pressure: drives fluid out of the vasculature into tissues
- plasma colloid osmotic pressure: keeps fluid in the vasculature, preventing extravasation into the tissues
- tissue colloid osmotic pressure: keeps fluid in the tissues
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Clinical presentation
Pathology
Etiology
- increased capillary hydrostatic pressure
- congestive cardiac failure
- venous obstruction, compression, or thrombosis
- ascites
- constrictive pericarditis
- arteriolar dilatation
- reduced plasma colloid osmotic pressure
- ascites and liver cirrhosis
- nephrotic syndrome
- malnutrition
- protein-losing enteropathy
- increased tissue colloid osmotic pressure
- increased vascular permeability
- inflammation, e.g. trauma, hypersensitivity response, infection 4
- infection
- reduced lymphatic clearance
- lymphedema
- lymphatic obstruction
- increased salt retention (causes both increased hydrostatic pressure and reduced plasma colloid osmotic pressure by fluid retention)
- renal insufficiency
Radiographic features
MRI
Soft tissue edema presents as non-enhancing, diffuse or focal low T1, high PD/T2 signal reticulated signal in the subcutaneous fat and superficial fascia 4.
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