Chapter 89

Subcutaneous abscesses are common in the Emergency Department. Approximately 1 to 2.5 percent of patients present with this chief complaint.1–3 Abscesses occur in numerous anatomical areas with varied etiology and bacteriology. Classically, an abscess is a tender and fluctuant mass located in the dermal or subdermal tissue. It demonstrates the classic inflammatory responses of rubor, tumor, dolor, and calor. Although the abscess is usually tender, the surrounding and underlying tissue should not be tender.4,5 There is minimal surrounding erythema in a mature abscess.

Incision and drainage is the definitive treatment of a soft tissue abscess.6 This procedure results in significant improvement in symptoms and a rapid resolution of the infection in uncomplicated cases.7 However, premature incision before localization of pus will not be curative and may be deleterious. In cases of immature abscesses or cellulitis, oral antibiotics and warm compresses may be of value in helping the infection to coalesce. These methods are not a substitute for incision and drainage and should not be continued for more than 24 to 36 hours without reassessment of the patient.

### Pathogenesis

An abscess is a localized collection of pus caused by suppuration buried in a tissue, organ, or confined space.8 Intact skin is very resistant to bacterial invasion. Localized pyogenic infections are usually initiated by a breakdown in the normal epithelial defense mechanisms in the normal host. Plugging of the ducts of a superficial exocrine gland, such as apocrine and sebaceous glands or a congenital cyst or sinus, may initiate the process. Occlusion prevents desquamation and provides a moist environment for organisms to proliferate. The combination of a high concentration of organisms, the presence of nutrients, and sufficient damage to the corneal layer to allow organisms to penetrate the skin defenses results in abscess formation.1,9

Abscesses may begin as a cellulitis with organisms that cause necrosis, liquefaction, and accumulation of leukocytes and debris. Early stages appear as an area of hyperemia and tender inflammation that later becomes fluctuant as an exudate of leukocytes, necrotic material, and cellular debris accumulates. This is followed by loculation and walling off of the pus. As the process progresses, the area of liquefaction increases until it “points” and eventually ruptures into the area of least resistance.5

The body area involved depends upon host factors such as drug use, employment-related exposures, or minor trauma.9,10 Areas with a compromised blood supply will be more prone to infection as normal host cellmediated immunity is not as available.9 The frequency of occurrence in different areas includes the buttocks and perirectal area in 25 percent of cases, the head and neck in 20 percent, the extremities in 18 percent, the axilla in 16 percent, and the inguinal area in 15 percent.1

### Bacteriology

The majority of abscesses are polymicrobial with the isolated ...

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