Abscesses are collections of pus in confined tissue spaces, usually caused by bacterial infection. Symptoms include local pain, tenderness, warmth, and swelling (if abscesses are near the skin layer) or constitutional symptoms (if abscesses are deep). Imaging is often necessary for diagnosis of deep abscesses. Treatment is surgical drainage and often antibiotics.

Etiology

Numerous organisms can cause abscesses, but Staphylococcus aureus is the most common. 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 (see Bacterial Skin Infections: Cellulitis) 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 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, and trauma.

Symptoms and Signs

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, and inanition due to anorexia and increased metabolic needs.

Diagnosis

• 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

• Surgical drainage
• 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. All pus, necrotic tissue, and debris should be removed. 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.

If the abscess is deep (eg, intra-abdominal) or if there is surrounding cellulitis, systemic antimicrobial drugs are indicated as adjunctive therapy; they 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 deep or surrounded by significant cellulitis.

Last full review/revision October 2012 by Allan R. Tunkel, MD, PhD