16. Phlegmon

1. Definition

• Phlegmon → acute diffuse purulent inflammation of loose connective tissue, spreading along tissue planes without a limiting membrane
• Differs from an abscess → no pyogenic membrane, no clear boundary
• Cellulitis → term used in English texts for the non-suppurative, early form

2. Aetiology and risk factors

• Streptococcus pyogenes → spreading, serous form
• Staphylococcus aureus → purulent form
• Gram-negative bacilli, anaerobes → putrefactive and necrotic forms
• Entry → wounds, injections, insect bites, spread from an abscess, lymphadenitis or osteomyelitis
• Risk factors → diabetes, alcoholism, immunosuppression, old age, poor hygiene

3. Pathogenesis

• Bacterial enzymes (hyaluronidase, streptokinase) → break down connective tissue
• Spread along the paths of least resistance:
  • Subcutaneous fat
  • Intermuscular and fascial spaces
  • Along vessels and nerves
  • Tendon sheaths
• Thrombosis of small vessels → tissue necrosis
• Weak or absent demarcation → wide spread, early toxaemia

4. Classification

By exudate

1. Serous → oedema, serous infiltrate; early stage
2. Purulent → pus diffusely impregnates the tissues
3. Putrefactive → anaerobes and Gram-negative flora; grey, foul-smelling, gas
4. Necrotic → large areas of dead tissue, sloughs

By depth

• Superficial (epifascial) → subcutaneous tissue
• Deep (subfascial) → intermuscular spaces, deep spaces of the neck, hand, foot

By site (special forms)

• Neck → Ludwig's angina (floor of the mouth, submandibular space)
• Mediastinum → mediastinitis
• Retroperitoneum → paranephritis, retroperitoneal phlegmon
• Pelvis → paraproctitis, parametritis
• Hand → deep palmar space infection
• Orbit → orbital cellulitis

By course

• Acute, chronic
• Woody phlegmon (Reclus) → chronic, hard, painless infiltrate of the neck from low-virulence flora

5. Clinical picture

Symptoms

• Rapidly increasing pain and swelling
• Fever 39–40 °C, chills
• Malaise, headache
• Loss of function

Signs

• Diffuse, tense, hot swelling without clear borders
• Redness, often less marked in deep phlegmon
• Tenderness, induration (infiltrate)
• Fluctuation → late, in areas of softening
• Regional lymphangitis, lymphadenitis
• Toxaemia → tachycardia, confusion
• Crepitus → gas-forming organisms

6. Diagnosis

Laboratory

• Leucocytosis, left shift, raised CRP
• Blood glucose
• Blood cultures, pus culture

Imaging

• Ultrasound → fluid in the tissue planes
• CT or MRI → deep phlegmon, extent, gas
• X-ray → gas in tissues

7. Differential diagnosis

• Abscess
• Erysipelas → sharp raised border, superficial
• Necrotising fasciitis → pain out of proportion, rapid spread, skin necrosis, crepitus
• Deep vein thrombosis
• Gas gangrene

8. Treatment

Conservative

• Serous stage only → antibiotics, rest, immobilisation, elevation
• If no improvement in 12–24 h → surgery

Surgical

• Wide incision over the whole infiltrate, opening all pockets and spaces
• Counter-incisions → for complete drainage
• Excision of necrotic tissue (necrectomy)
• Irrigation with antiseptics, drains, wound left open
• Daily dressings; repeat debridement as needed
• Later → secondary sutures or skin grafts

General

• Broad-spectrum intravenous antibiotics, then by culture
• Fluids, detoxification
• Correct blood glucose
• Tetanus prophylaxis
• Treat sepsis

9. Complications

• Lymphangitis, lymphadenitis
• Thrombophlebitis
• Sepsis, septic shock
• Spread to deep spaces → mediastinitis, retroperitoneum
• Airway obstruction → Ludwig's angina
• Erosion of vessels → secondary haemorrhage