Abscess

Abscesses are focal confined collections of suppurative inflammatory material and can be thought of as having three components ¹:

1. a central core consisting of necrotic inflammatory cells and local tissue

2. peripheral halo of viable neutrophils

3. surrounded by a 'capsule' with dilated blood vessels and proliferation of fibroblasts

Terminology

An abscess is akin to an empyema, as both are defined inflammatory collections. The difference is that an abscess occurs in the parenchyma of the affected organ while an empyema arises in a pre-existing cavity such as the pleural space. 

Clinical presentation

The presentation of an abscess is varied depending on the location and its infiltration and mass effect on local structures. Systemically, patients with abscesses can present with swinging pyrexia and raised inflammatory markers, which are resistant to antimicrobial therapy. Pain is a common accompanying symptom. The hallmark signs of subcutaneous abscesses are pain, warmth, redness, and swelling. 

Pathology

Etiology

Abscesses can be caused by bacteria, parasites, or fungi.

Location

Essentially any tissue in the body can play host to abscesses. Please refer to individual articles for further details:

• appendicular abscess

• Bartholin gland abscess

• Bezold abscess

• breast abscess

• Brodie abscess

• cerebral abscess

• dental abscess

• intratonsillar abscess

• liver abscess

• parapharyngeal abscess

• perianal abscess

• pericardial abscess

• perinephric abscess

• peritonsillar abscess

• pulmonary abscess

• prostatic abscess

• psoas abscess

• renal abscess

• retropharyngeal abscess

• scrotal wall abscess

• spinal epidural abscess

• splenic abscess

• soft tissue abscess

• spinal epidural abscess

• subcutaneous abscess

• subperiosteal abscess

• subphrenic abscess

• testicular abscess

• tubo-ovarian abscess

Radiographic features

Typical radiological appearances are of a central zone of necrotic inflammatory material encapsulated by a discernible wall. Exact features will vary depending on the tissue or organ within which the abscess is located. 

CT

• relatively low attenuation central necrotic component

• a well-defined fibrous capsule: can be irregular and thick when compared to the thin smooth wall of a simple cyst

• capsular ring enhancement with contrast: can be difficult to appreciate when the abscess is contained in a vascular structure like the liver where there is a concurrent parenchymal enhancement

• surrounding inflammatory changes (i.e. peritoneal fat stranding)

• a mass effect with effacement of adjacent structures

Nuclear medicine

The presence of an abscess in patients presenting with sepsis can be delineated by indium (In-111) labeled white cell scans, often in the setting of suspected abdominopelvic sepsis. Tracer accumulates in the region of the abscess, such as the right iliac fossa in an appendiceal abscess.

As abscesses usually have a thick wall with poor vascularity, indium-111 take-up can be a lengthy process and 48-hour delayed images are sometimes required. The sensitivity of this test is not thought to be affected by the use of concomitant antibiotics or steroids.

Treatment and prognosis

Treatment is guided by the size, accessibility, and clinical severity of sepsis in each case. Although abscesses may be treated medically with antibiotics, they often require percutaneous or surgical drainage. As abscesses have poor vascularity, high dose oral or parenteral treatment is preferred. Percutaneous drainage can be performed under ultrasound or CT guidance for abscesses within the thoracic or peritoneal cavity. Some abscesses will require open incision and drainage.

History and etymology

The word "abscess" is derived from the Greek work aposteme (άπό-ίστημι) meaning "throwing off of bad humors". The word first appeared in 1543 in a translation of a surgery text: "Aposteme - In latyne, it is called abscissas" ³.