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An abscess is a circumscribed collection of pus usually caused by microorganisms. Abscesses can occur anywhere in the body—in hard or soft tissue, organs or An amoebic abscess caused by Entameoba histolytica. Phototake (CN) /Phototake NYC. Reproduced by permission. confined spaces. Due to their fluid content, abscesses can assume various shapes. Their internal pressure can cause compression and displacement of surrounding tissue, resulting in pain. An abscess is part of the body's natural defense mechanism; it localizes infection to prevent the spread of bacteria.

Any trauma such as injury, bacterial or amoebic infection, or surgery can result in an abscess. Microorganisms causing an abscess may enter tissue following penetration (e.g., a cut or puncture) with an unsterile object or be spread from an adjacent infection. These microorganisms also are disseminated by the lymph and circulatory systems.

Abscesses are more likely to occur if the urinary, biliary, respiratory, or immune systems have impaired function. A foreign object such as a splinter or stitch can predispose an area to an abscess. The body's inflammatory response mechanism reacts to trauma. The area involved has increased blood flow; leukocytes (mostly neutrophils) and exudates (fluid, typically serum and cellular debris) escape from blood vessels at the early stage of inflammation and collect in any available space. Neutrophils release enzymes which are thought to help establish the abscess cavity. The exudate attracts water, causing swelling in the affected area. Usually the body removes various exudates with its circulatory and lymphatic systems. When the body's immune response is altered by disease, extreme fatigue, or other predisposing factors as mentioned above, resolution of the inflamed area is slow to occur. If the affected area does not heal properly, an abscess can form.

Symptoms of an abscess vary according to location. Fever and pain can be present while dysfunction of an organ system sometimes is the symptom. An abscess can rupture and drain to the outside of the body or into surrounding tissue where the fluid and debris can be re-absorbed into the blood stream. Occasionally surgical drainage or antibiotics are needed to resolve an abscess.

See also Immune system.

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