22. Necrosis and gangrene

1. Definition

• Necrosis → death of cells or tissues in a living organism
• Gangrene → necrosis of tissue in contact with the external environment, with drying or putrefaction; black colour from iron sulphide (haemoglobin breakdown)
• Sequestrum → piece of dead tissue separated from living tissue (bone)
• Infarct → necrosis of part of an organ from arterial occlusion

2. Aetiology

Ischaemic (circulatory)

• Arterial occlusion → atherosclerosis, embolism, thrombosis
• Arterial injury, ligation
• Arteritis → Buerger's disease
• Vasospasm → Raynaud's, ergotamine
• Diabetic microangiopathy
• Venous gangrene → phlegmasia caerulea dolens
• External compression → tight plaster, tourniquet, strangulated hernia, volvulus, pressure ulcers

Physical

• Mechanical trauma, crush
• Thermal → burns, frostbite
• Electrical injury
• Radiation

Chemical

• Acids → coagulative necrosis
• Alkalis → liquefactive necrosis
• Intra-arterial injection of drugs

Infective

• Clostridia → gas gangrene
• Necrotising fasciitis
• Fournier's gangrene → scrotum, perineum
• Meleney's synergistic gangrene

Neurotrophic

• Peripheral neuropathy (diabetes, leprosy), spinal cord injury → pressure ulcers

3. Pathological characteristics

Types of necrosis

• Coagulative → protein denaturation; heart, kidney, spleen infarcts
• Liquefactive (colliquative) → enzymatic digestion; brain, abscess
• Caseous → tuberculosis
• Fat necrosis → pancreatitis, breast trauma
• Fibrinoid → vessel walls in vasculitis

Dry gangrene (mummification)

• Slow arterial occlusion, little fluid in tissue, no infection
• Tissue dries, shrinks, becomes black and hard
• Clear line of demarcation → granulation tissue between living and dead tissue
• Little toxin absorption → mild general symptoms
• Spontaneous separation (auto-amputation)

Wet gangrene

• Sudden arterial occlusion, venous obstruction, oedema, infection
• Putrefactive bacteria → tissue swelling, liquefaction
• No demarcation, rapid spread
• Severe toxin absorption → sepsis, high mortality
• Internal organs → always wet (bowel, appendix, gallbladder)

4. Clinical characteristics

Dry gangrene

• Starts at the toes or fingertips
• Black, dry, wrinkled, cold, insensate tissue
• Line of demarcation → red zone of inflammation between live and dead tissue
• Absent distal pulses
• General condition preserved

Wet gangrene

• Swollen, oedematous, blue-black or greenish skin
• Blisters with dark fluid
• Foul smell, discharge
• Crepitus with gas-forming organisms
• Fever, tachycardia, toxaemia, septic shock

5. Diagnosis

Laboratory

• Leucocytosis, CRP, blood cultures
• Blood glucose, HbA1c
• Renal function, creatine kinase

Imaging

• Duplex ultrasound, CT angiography → level of arterial occlusion
• X-ray → gas, osteomyelitis
• Ankle-brachial pressure index (ABPI)

6. Treatment: principles

General

• Convert wet gangrene to dry → keep dry, open to air, antiseptic dressings
• No elevation of an ischaemic limb
• Antibiotics → wet gangrene, sepsis
• Control diabetes, fluids, analgesia
• Treat the cause → revascularisation (angioplasty, bypass, embolectomy), anticoagulation
• Stop smoking

Local and surgical

• Dry gangrene:
  • Wait for demarcation
  • Necrectomy or amputation through the line of demarcation
  • Revascularisation first if possible → lower amputation level
• Wet gangrene:
  • Urgent amputation or radical debridement above the infection
  • Guillotine amputation in sepsis, then definitive amputation later
• Amputation levels → toe, ray, transmetatarsal, below-knee, above-knee
• Visceral gangrene → resection of the organ (bowel resection, appendicectomy, cholecystectomy)

7. Complications

• Sepsis, septic shock
• Spread of infection
• Acute kidney injury
• Loss of limb
• Death