How is Fournier's gangrene diagnosed?

Diagnosis of Fournier's Gangrene

Fournier's gangrene is primarily a clinical diagnosis made by focused history and complete physical examination including digital rectal examination, supplemented by CT imaging in stable patients with equivocal findings, but imaging must never delay surgical intervention. 1

Clinical Diagnosis

History and Physical Examination

• Obtain a focused medical history and perform a complete physical examination including digital rectal examination in all suspected cases. 1
• Look specifically for: perineal/genital/perianal tenderness, induration, cyanosis, gangrene, and subcutaneous crepitation (crepitus). 2
• Physical examination alone establishes the diagnosis in 95% of cases. 3
• Severe pain disproportionate to physical findings is often the earliest reliable symptom, typically beginning approximately 24 hours after infection. 4
• Skin changes progress rapidly from initial pallor to bronze discoloration, then purplish-red appearance, with bullae filled with reddish-blue fluid in later stages. 4

Laboratory Investigations

In patients with signs of systemic infection or sepsis, obtain:

• Complete blood count 1
• Serum creatinine and electrolytes 1
• Inflammatory markers (C-reactive protein, procalcitonin) 1
• Blood gas analysis 1

Mandatory diabetes screening:

• Check serum glucose, hemoglobin A1c, and urine ketones in all patients to investigate undetected diabetes mellitus (strong recommendation). 1

Risk Stratification Scores

• Use the Laboratory Risk Indicator for Necrotizing Fasciitis (LRINEC) score for early diagnosis. 1, 5
• Use the Fournier's Gangrene Severity Index (FGSI) for prognosis and risk stratification. 1, 5

Imaging Studies

CT Scan (Preferred Modality)

• In hemodynamically stable patients with suspected Fournier's gangrene, consider performing a CT scan. 1
• CT has sensitivity of 90% and specificity of 93.3% for necrotizing soft tissue infections. 6, 7
• CT findings include: asymmetric fascial thickening, subcutaneous emphysema (hallmark finding but not present in all cases), soft tissue stranding, fluid collections, and abscess formation. 8, 7
• CT helps determine disease extent, identify infection source, and evaluate fascial plane involvement. 6, 8, 7

Ultrasound (Alternative)

• Ultrasound can detect subcutaneous gas, scrotal skin thickening, soft tissue inflammation, collections/abscesses, and paratesticular fluid. 6
• Gas in testicular tissue appears with characteristic findings and is highly specific (94%) for necrotizing infection. 6
• Use bedside ultrasound when CT is contraindicated, unavailable, or patient transport is unsafe. 6

Critical Imaging Caveats

Imaging must NEVER delay surgical intervention when necrotizing infection is clinically suspected (strong recommendation). 1, 6

In hemodynamically unstable patients persisting after proper resuscitation, proceed directly to surgery without any imaging including CT. 1, 6

Time to surgery is the most critical determinant of outcome in a disease with 20-50% mortality. 6

Microbiological Confirmation

• Gram stain of tissue obtained during surgical exploration shows large, spore-forming gram-positive bacilli and other organisms. 4
• Blood cultures are positive in 5-30% of related cases. 4
• The infection is typically polymicrobial involving both aerobic organisms (Streptococcus, Staphylococcus, E. coli) and anaerobic bacteria. 9

Diagnostic Algorithm

For patients with obvious clinical findings (tenderness, induration, crepitus, gangrene):

• Proceed immediately to surgical exploration without imaging. 6, 2

For hemodynamically stable patients with equivocal clinical findings:

• Obtain CT scan to confirm diagnosis and assess extent. 6, 7
• If CT unavailable or contraindicated, use bedside ultrasound. 6

For hemodynamically unstable patients:

• Proceed directly to surgery after resuscitation, avoiding CT imaging. 1, 6

Common Pitfalls

• The diagnosis is frequently unsuspected until gas is detected or systemic toxicity appears; early severe pain should trigger immediate evaluation even without other findings. 4
• A rather innocuous early lesion may evolve to full manifestation over 24 hours. 4
• Never delay surgical intervention to obtain imaging when clinical suspicion is high. 1, 6