wet gangrene

**Definition:** Necrosis of tissue (usually from ischemia) with superimposed bacterial infection. Neutrophils and bacterial/lysosomal enzymes cause liquefactive necrosis, which is superimposed on the underlying coagulative necrosis of ischemia.

**Pathophysiology:** - Ischemia or tissue injury (arterial occlusion, venous obstruction, trauma, burns, frostbite, strangulated hernia or bowel, torsion) leads to coagulative necrosis. - Bacteria invade the devitalized tissue, and neutrophils and microbial enzymes cause liquefaction. - Common organisms are polymicrobial: Staphylococcus aureus, streptococci, Enterobacteriaceae, Pseudomonas, and anaerobes (Bacteroides, Clostridium). - Moist tissue favors bacterial growth. Venous obstruction leaves the tissue congested with blood and fluid.

**Gross features:** - Swollen, cold, pulseless, soft, moist tissue. - Blisters or bullae, with discoloration (red-black to green). - Foul odor. - Poorly demarcated line between viable and necrotic tissue, so the infection spreads quickly.

**Clinical significance:** - Systemic toxicity: fever, tachycardia, hypotension, sepsis, septic shock, DIC. - Common sites: diabetic foot (the classic scenario, with peripheral arterial disease, neuropathy, and impaired immunity), lower extremities, and internal organs (bowel, appendix, gallbladder, lung). - Related forms: - **Gas gangrene** (Clostridium perfringens) is a type of wet gangrene with crepitus from gas in tissue and α-toxin (lecithinase, a phospholipase C) causing myonecrosis and hemolysis. - **Fournier gangrene** is necrotizing fasciitis of the perineum and genitalia. - **Necrotizing fasciitis** is a deep soft-tissue infection, often polymicrobial or from group A strep.

**Management:** - Emergent surgical debridement or amputation. - Broad-spectrum IV antibiotics covering gram-positive, gram-negative, and anaerobic organisms (e.g., piperacillin-tazobactam plus vancomycin, with or without clindamycin). - Revascularization when feasible, glycemic control, and supportive care.

**Dry vs. wet gangrene (high-yield comparison):** - **Dry gangrene:** - Cause: ischemia, typically chronic arterial insufficiency (atherosclerosis, diabetes, Raynaud, frostbite). - Infection: absent or minimal. - Necrosis: coagulative. - Appearance: dry, shriveled, black, mummified, with a clear line of demarcation. - Course: slow progression, with systemic toxicity unlikely. - **Wet gangrene:** - Cause: ischemia or injury with bacterial superimposition. - Necrosis: liquefactive. - Appearance: moist, swollen, foul-smelling, with poor demarcation. - Course: rapid progression, with sepsis common.

**Board pearls:** - Gangrene is a clinical or gross term for necrosis plus decay, not a distinct histologic pattern. Wet gangrene = coagulative necrosis + liquefactive necrosis from bacteria. - Gas gangrene: gram-positive rods, "double zone of hemolysis" on blood agar, and gas on imaging. - A diabetic with a foul, blistering, swollen foot and fever → wet gangrene → urgent surgery and antibiotics.