Introduction
This topic covers acute diffuse purulent infection of loose tissue, called phlegmon, and the long-lasting purulent processes that follow acute infections which were not fully treated. Exam answers should explain how phlegmon differs from a localized abscess, which tissue planes it follows, and why it can become life-threatening quickly.
Definition and classification
A phlegmon is an acute suppurative inflammation of loose connective, fatty or intermuscular tissue. It has no capsule and no sharp border, so pus and oedema spread along fascial planes and between muscles. An abscess is a circumscribed collection of pus walled off by granulation tissue; the difference in borders is the key point. A chronic purulent infection is a persistent suppurative process lasting weeks or months. Typical forms are chronic abscess, fistulas and sinus tracts, chronic osteomyelitis and chronic empyema.
Causes and pathogenesis
The most common causative agent is Staphylococcus aureus, followed by beta-haemolytic streptococci. Deep or contaminated infections often contain mixed aerobic and anaerobic flora from the skin or bowel, and Escherichia coli or Pseudomonas may be involved in hospital-acquired cases. Clostridial species are important in necrotizing forms. Predisposing factors include diabetes, obesity, immunosuppression, peripheral vascular disease, injection drug use, trauma, foreign bodies and poor hygiene.
- Entry through a skin break, a wound, an injection, or haematogenous spread from a distant focus
- Bacterial enzymes such as hyaluronidase, coagulase, streptokinase and leukocidins break down tissue barriers
- Neutrophil infiltration and exudate raise tissue pressure, causing ischaemia and necrosis
- Spread along fascial planes, lymphatics and veins to adjacent compartments
- In chronic infection, incomplete drainage, a foreign body or low-virulence organisms keep the process going, and granulation tissue and fibrosis form a capsule and sinus tracts
Typical sites of phlegmon include subcutaneous tissue, intermuscular spaces, the palm and fingers (palmar space infection), the paraproctal and ischiorectal regions, the retroperitoneum and pelvis, and the neck. Infection of the submandibular and sublingual spaces (Ludwig angina) is especially dangerous because it can compromise the airway.