Edema is the accumulation of excessive fluid in the interstitial spaces of the body’s tissues causing them to swell. Edema can be classified as systemic or localized. When fluid is diffusely distributed in the interstitial space of tissues in the body, it is systemic edema (often depressed); when fluid accumulates in the local interstitial space of tissues, it is localized edema; when it occurs in the body cavity, it is called effusion, such as pleural effusion, peritoneal effusion, pericardial effusion. In general, the term edema, does not include localized edema of internal organs, such as cerebral edema, pulmonary edema, etc. Systemic edema: cardiogenic edema, nephrogenic edema, hepatogenic edema, dystrophic edema, systemic edema of other causes (e.g. mucinous edema, pharmacologic edema, idiopathic edema, etc.); Localized edema: thrombophlebitis, elephantiasis, local inflammation, trauma or allergy, etc.