Etiology of Abscesses
Numerous organisms can cause abscesses, but the most common is
Organisms may enter the tissue by
Direct implantation (eg, penetrating trauma with a contaminated object)
Spread from an established, contiguous infection
Dissemination via lymphatic or hematogenous routes from a distant site
Migration from a location where there are resident flora into an adjacent, normally sterile area because natural barriers are disrupted (eg, by perforation of an abdominal viscus causing an intra-abdominal abscess)
Abscesses may begin in an area of cellulitis Cellulitis Cellulitis is acute bacterial infection of the skin and subcutaneous tissue most often caused by streptococci or staphylococci. Symptoms and signs are pain, warmth, rapidly spreading erythema... read more 
or in compromised tissue where leukocytes accumulate. Progressive dissection by pus or necrosis of surrounding cells expands the abscess. Highly vascularized connective tissue may then surround the necrotic tissue, leukocytes, and debris to wall off the abscess and limit further spread.
Predisposing factors to abscess formation include the following:
Impaired host defense mechanisms (eg, impaired leukocyte defenses)
The presence of foreign bodies
Obstruction to normal drainage (eg, in the urinary, biliary, or respiratory tracts)
Tissue ischemia or necrosis
Hematoma or excessive fluid accumulation in tissue
Trauma
Symptoms and Signs of Abscesses
The symptoms and signs of cutaneous and subcutaneous abscesses are pain, heat, swelling, tenderness, and redness.
If superficial abscesses are ready to spontaneously rupture, the skin over the center of the abscess may thin, sometimes appearing white or yellow because of the underlying pus (termed pointing). Fever may occur, especially with surrounding cellulitis.
For deep abscesses, local pain and tenderness and systemic symptoms, especially fever, as well as anorexia, weight loss, and fatigue are typical.
The predominant manifestation of some abscesses is abnormal organ function (eg, hemiplegia due to a brain abscess).
Complications of abscesses include
Bacteremic spread
Rupture into adjacent tissue
Bleeding from vessels eroded by inflammation
Impaired function of a vital organ
Inanition due to anorexia and increased metabolic needs
Diagnosis of Abscesses
Clinical evaluation
Sometimes ultrasonography, CT, or MRI
Diagnosis of cutaneous and subcutaneous abscesses is by physical examination.
Diagnosis of deep abscesses often requires imaging. Ultrasonography is noninvasive and detects many soft-tissue abscesses; CT is accurate for most, although MRI is usually more sensitive.
Treatment of Abscesses
Surgical drainage or percutaneous needle aspiration
Sometimes antibiotics
Superficial abscesses may resolve with heat and oral antibiotics. However, healing usually requires drainage.
Minor cutaneous abscesses may require only incision and drainage How To Incise and Drain an Abscess A soft-tissue abscess may need to be incised and drained. A soft-tissue abscess is typically a palpable, tender, red lump containing pus. There is usually localized induration and some "give"... read more . All pus, necrotic tissue, and debris should be removed. With larger abscesses (eg, > 5 cm), eliminating open (dead) space by packing with gauze or by placing drains may be necessary to prevent reformation of the abscess. Predisposing conditions, such as obstruction of natural drainage or the presence of a foreign body, require correction.
Deep abscesses can sometimes be adequately drained by percutaneous needle aspiration (typically guided by ultrasonography or CT); this method often avoids the need for open surgical drainage.
Spontaneous rupture and drainage may occur, sometimes leading to the formation of chronic draining sinuses. Without drainage, an abscess occasionally resolves slowly after proteolytic digestion of the pus produces a thin, sterile fluid that is resorbed into the bloodstream. Incomplete resorption may leave a cystic loculation within a fibrous wall that may become calcified.
Systemic antimicrobial drugs are not routinely given but are indicated as adjunctive therapy as follows:
If the abscess is deep (eg, intra-abdominal)
If abscesses are multiple
If there is significant surrounding cellulitis
Perhaps if size is > 2 cm
Antimicrobial drugs are usually ineffective without drainage. Empiric antimicrobial therapy is based on location and likely infecting pathogen. Gram stain, culture, and susceptibility results guide further antimicrobial therapy.
Key Points
Cutaneous and subcutaneous abscesses are diagnosed clinically; deeper abscesses often require imaging.
Usually, drain the abscess by incision or sometimes by needle aspiration.
Use antibiotics when abscesses are large, deep, or surrounded by significant cellulitis.
