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  Extravasation is the leakage of a fluid out of its container. In the case of inflammation, it refers to the movement of white blood cells from the capillaries to the tissues surrounding them (diapedesis). In the case of malignant cancer metastasis it refers to cancer cells exiting the capillaries and entering organs. It is frequently used in medical contexts, either referring to urine, or to blood.   http://en.wikipedia.org/wiki/Extravasation

Extravasation is the accidental administration of intravenously (IV) infused medications into the extravascular space/tissue around infusion sites, either by leakage (e.g., because of brittle veins in very elderly patients), previous venipuncture (such as from blood drawn for laboratory tests prior to therapy), or direct leakage from mispositioned venous access devices. Extravasation of medication during intravenous therapy is an adverse event related to therapy that, depending on the medication, amount of exposure, and location, can potentially cause serious injury and permanent harm, such as tissue necrosis. Milder consequences of extravasation include irritation, characterized by symptoms of pain and inflammation, with the clinical signs of warmth, erythema, or tenderness.

http://en.wikipedia.org/wiki/Extravasation_%28intravenous%29