What does unilateral swelling and erythema on the scrotum indicate?

Unilateral Scrotal Swelling and Erythema: Differential Diagnosis

Unilateral scrotal swelling and erythema most commonly indicates epididymitis in adults, but testicular torsion must be immediately excluded first as it is a surgical emergency requiring intervention within 6-8 hours to prevent permanent testicular loss. 1, 2

Critical First Priority: Rule Out Testicular Torsion

Any acute scrotal swelling with erythema must be treated as testicular torsion until proven otherwise, particularly in adolescents and young adults. 2, 3

Key Clinical Features Distinguishing Torsion from Epididymitis

Testicular Torsion (Surgical Emergency):

• Sudden onset of severe pain developing within minutes (not gradual) 1, 2
• Negative Prehn sign (pain NOT relieved with testicular elevation) 1, 2
• Absence of urinary symptoms or urethral discharge 3
• Nausea and vomiting commonly present 2
• High-riding, firm, swollen testis on examination 4
• More common in adolescents and postpubertal boys (bimodal distribution: neonates and postpubertal males) 1, 3

Epididymitis (Most Common in Adults):

• Gradual onset of pain over hours to days 2, 3
• Unilateral testicular pain with palpable epididymal swelling 3
• May have urinary symptoms or urethral discharge 3
• Positive Prehn sign (pain relief with elevation) 2
• Overwhelmingly the most common cause in adults (approximately 600,000 cases annually in the United States) 1

Immediate Diagnostic Algorithm

Step 1: Assess Clinical Suspicion Based on Onset and Features

• High suspicion (sudden severe pain, negative Prehn sign, adolescent/young adult): Proceed directly to immediate urological consultation and surgical exploration WITHOUT delay for imaging or analgesia 2, 3
• Intermediate suspicion: Urgent Duplex Doppler ultrasound with grayscale and color Doppler assessment 1, 2
• Low suspicion with gradual onset and infectious symptoms: Diagnostic workup for epididymitis 2

Step 2: Ultrasound Findings (If Performed)

Testicular Torsion:

• Decreased or absent blood flow to affected testicle on color Doppler 1
• "Whirlpool sign" of twisted spermatic cord (96% sensitivity) 1
• Enlarged heterogeneous testis appearing hypoechoic 1
• Ipsilateral hydrocele and scrotal skin thickening 1

Epididymitis:

• Enlarged epididymis with increased blood flow on color Doppler 1, 2
• Scrotal wall thickening 1
• Up to 20% concomitant orchitis rate 1

Step 3: Laboratory Testing

• Urinalysis (evaluate for infection) 2
• Gram-stained smear of urethral exudate or intraurethral swab (>5 PMNs per oil immersion field indicates urethritis) 3
• NAAT for N. gonorrhoeae and C. trachomatis on intraurethral swab or first-void urine 3

Treatment Based on Diagnosis

If Testicular Torsion Confirmed or Highly Suspected:

Immediate surgical exploration and detorsion within 6-8 hours of symptom onset 1, 2

• Bilateral orchiopexy performed to prevent contralateral torsion (82% have Bell-clapper deformity) 1
• Testicular salvage rates decline significantly after 6-8 hours 1, 3

If Epididymitis Diagnosed:

Start empiric antibiotic therapy immediately before culture results: 3

For sexually active men <35 years (likely STI-related):

• Ceftriaxone 250 mg IM single dose PLUS
• Doxycycline 100 mg orally twice daily for 10 days 2, 3

For men >35 years or homosexual men (likely enteric organisms):

• Ofloxacin 300 mg PO BID for 10 days 2

Adjunctive measures:

• Bed rest, scrotal elevation, and analgesics (including ketorolac) until inflammation subsides 2
• Reevaluate within 3 days if no improvement 3

Critical Pitfalls to Avoid

• Never delay surgical consultation for analgesia when torsion is suspected - pain relief may mask worsening ischemia 2
• Normal urinalysis does NOT exclude testicular torsion or epididymitis 1, 2, 3
• Do not assume epididymitis without considering torsion first, especially in adolescents and young adults - significant overlap in clinical presentation exists 2, 3
• False-negative Doppler evaluations occur in 30% or more of cases, particularly with partial torsion or early presentation 1
• Color Doppler sensitivity ranges from 69-96.8% - clinical judgment supersedes imaging when suspicion is high 1, 2
• Starting antibiotics empirically without ruling out torsion delays correct diagnosis and treatment 2

Age-Specific Considerations

Prepubertal boys: Torsion of testicular appendage is most common cause of testicular pain, but torsion must still be excluded 1

Adolescents/young adults: Testicular torsion is more common in this age group - maintain high index of suspicion 1, 3

Adults >35 years: Epididymitis is overwhelmingly most common, but torsion still possible 1, 5