What are the possible causes of a painful groin swelling associated with fever?

Groin Swelling with Fever: Differential Diagnosis

Painful groin swelling with fever represents a surgical emergency until proven otherwise, with the most critical diagnoses being vascular graft infection (if post-surgical), Fournier gangrene, inguinal abscess, and infectious lymphadenopathy—all requiring immediate imaging and potential surgical intervention. 1, 2

Life-Threatening Causes Requiring Emergency Intervention

Fournier Gangrene

• Presents with scrotal/perineal pain, erythema, edema, and systemic toxicity (fever, sepsis); any sign of tissue necrosis or subcutaneous crepitation mandates immediate emergency surgery without waiting for imaging. 2
• Subcutaneous crepitation is present in approximately 50% of cases and indicates gas in tissues. 2
• The infection progresses rapidly (hours to days) with accelerated clinical deterioration. 2
• Diabetes mellitus is the single most important risk factor, followed by immunocompromised status and obesity. 2, 3
• Mortality rates approach 20-50% if treatment is delayed. 2
• Critical pitfall: Never delay surgical debridement to obtain imaging when clinical suspicion is high—proceed directly to emergency surgery. 2

Vascular Graft Infection (Post-Surgical Patients)

• In patients with prior groin vascular surgery, painful erythematous groin swelling with or without draining wound/sinus tract is highly suggestive of vascular graft infection. 1
• Early-onset infections (<2 months post-op) present with fever, chills, leukocytosis, wound erythema, and signs of sepsis. 1
• Late-onset infections (>2 months post-op) are more indolent with local groin erythema, painful swelling, and sinus tract drainage. 1
• Complications include pseudoaneurysm formation, anastomotic rupture with life-threatening hemorrhage, and graft occlusion with distal ischemia. 1
• A draining sinus tract is the most obvious sign of graft infection. 1

Common Infectious Causes

Inguinal Abscess

• Presents as tender inguinal mass with fever and leukocytosis. 4
• Can extend from gastrointestinal, genitourinary, or retroperitoneal sites. 4
• The inguinal region communicates through several routes with peritoneal and retroperitoneal spaces, allowing infection to track from distant sources. 4
• Gram-positive pathogens are associated with hip/thigh muscle infections; gram-negative pathogens with GI/GU tract sources and psoas abscesses. 4
• CT imaging is essential for establishing diagnosis, determining extent of infection, and guiding surgical planning. 4

Infectious Lymphadenopathy

• Inguinal lymph nodes drain the external genitalia, inferior anal canal, perianal region, adjoining abdominal wall, and lower extremities. 4
• Lymphadenitis presents with tender, enlarged inguinal nodes and fever. 1
• Consider sexually transmitted infections (gonorrhea, chlamydia, syphilis) in sexually active patients. 1

Epididymitis with Extension

• In sexually active men <35 years, most commonly caused by C. trachomatis or N. gonorrhoeae. 1
• Typically presents with unilateral testicular pain and tenderness, hydrocele, and palpable epididymal swelling. 1
• Usually accompanied by urethritis (often asymptomatic). 1
• In men >35 years or those with recent urinary instrumentation, consider gram-negative enteric organisms. 1

Diagnostic Approach

Clinical Assessment

• Look for signs of systemic toxicity, tissue necrosis, crepitation, and pain disproportionate to examination—these indicate necrotizing infection requiring emergency surgery. 2
• Assess for history of vascular surgery, diabetes, immunosuppression, recent trauma, or IV drug use. 1, 2, 5
• Examine for draining sinus tracts, skin changes, pulsatile masses, or distal ischemia. 1

Laboratory Evaluation

• Obtain complete blood count, inflammatory markers (CRP, procalcitonin), and lactate levels. 2
• Elevated lactate indicates tissue hypoperfusion and suggests necrotizing infection. 2
• Blood cultures should be obtained before antibiotics. 1
• Consider LRINEC score for early diagnosis of necrotizing infections. 2

Imaging Strategy

• Ultrasound is the preferred initial imaging modality, especially in unstable patients, with 94% specificity for detecting subcutaneous gas in necrotizing infections. 2, 5
• Ultrasound can distinguish abscesses (distinct masses) from cellulitis (soft-tissue swelling), though overlap exists. 5
• CT with contrast should be obtained in hemodynamically stable patients with equivocal findings (90% sensitivity, 93.3% specificity for necrotizing infections). 2
• Critical warning: In unstable patients or those with high clinical suspicion for Fournier gangrene, proceed directly to surgery without imaging. 2

Special Considerations

SGLT2 Inhibitor Users

• Patients on SGLT2 inhibitors have increased risk of genital mycotic infections (6% vs 1% with placebo). 6
• While Fournier gangrene risk is extremely low, consequences are catastrophic. 6
• If Fournier gangrene is suspected in SGLT2 inhibitor users, immediately discontinue the medication and proceed with emergency evaluation. 6

Non-Infectious Mimics

• Incarcerated/strangulated inguinal or femoral hernias can present with groin swelling and systemic symptoms. 7
• Vascular conditions including false aneurysms and hematomas may present similarly. 8
• These typically lack the severe systemic toxicity and rapid progression of necrotizing infections. 2