What is the differential diagnosis for a male patient presenting with sudden scrotal swelling and pain?

Differential Diagnosis for Sudden Scrotal Swelling and Pain

The three most common causes of acute scrotal pain and swelling are testicular torsion (a surgical emergency), epididymitis/epididymo-orchitis, and torsion of testicular appendage, with age being the critical factor in determining likelihood. 1

Age-Stratified Differential Diagnosis

Prepubertal Boys

• Torsion of testicular appendage is the most common cause in this age group 1
• Testicular torsion has a bimodal peak, with neonates and postpubertal boys at highest risk 1, 2
• The "blue dot sign" is pathognomonic for appendage torsion but only visible in 21% of cases 1

Adolescents and Young Adults

• Testicular torsion is the primary concern and must be ruled out first, as it represents a surgical emergency requiring intervention within 6-8 hours 1, 2
• Epididymitis remains common in this age group, particularly in sexually active males 1
• In heterosexual young men with epididymitis, N. gonorrhoeae and C. trachomatis are the most likely organisms 3

Adults Over 25 Years

• Epididymitis/epididymo-orchitis is overwhelmingly the most common cause, representing approximately 600,000 cases annually in the United States 1
• Testicular torsion is rare in patients over 35 years of age 1
• In older men, E. coli, Pseudomonas species, and gram-positive cocci are the most common pathogens 3

Critical Distinguishing Clinical Features

Testicular Torsion (Surgical Emergency)

• Abrupt onset of severe scrotal pain developing within minutes 1, 2
• Pain is not relieved when the testicle is elevated (negative Prehn sign) 1, 2
• Nausea and vomiting are common 2, 4
• Normal urinalysis does not exclude testicular torsion 1
• Red, swollen scrotum often in the absence of trauma 4

Epididymitis/Epididymo-orchitis

• Gradual onset of pain over hours to days 1
• May have abnormal urinalysis, though normal urinalysis does not exclude epididymitis 1
• Pain may be relieved with testicular elevation (positive Prehn sign) 1
• Scrotal wall thickening and possible hydrocele 1

Torsion of Testicular Appendage

• Most common in prepubertal boys 1
• Normal testicular perfusion with localized hyperemia near the appendage 1
• "Blue dot sign" when visible is diagnostic 1

Additional Differential Considerations

• Segmental testicular infarction: Classic wedge-shaped avascular area on ultrasound, median age 37-38 years 1
• Acute idiopathic scrotal edema: Rare, self-limiting condition with marked scrotal wall thickening, usually painless or minimally painful, primarily affecting prepubertal boys but can occur in adults 1
• Testicular tumor: Rarely presents as acute pain but should not be overlooked, as it can occasionally mimic torsion 5
• Traumatic hematoma or testicular rupture: History of trauma is key 6, 7
• Strangulated inguinal hernia: Consider in differential, particularly with palpable inguinal mass 4
• Varicocele or hydrocele: Generally painless but can cause discomfort 7

Diagnostic Algorithm

Step 1: Risk Stratification

• Use the TWIST score (Testicular Workup for Ischemia and Suspected Torsion) for risk stratification in pediatric patients 1, 2
• High clinical suspicion (TWIST score >5) warrants immediate surgical exploration without imaging 2

Step 2: Imaging for Intermediate Suspicion (TWIST 1-5)

• Duplex Doppler ultrasound is the first-line imaging modality with sensitivity 69-96.8% and specificity 87-100% 1, 3, 6, 4
• Key ultrasound findings for testicular torsion: 1
  • Decreased or absent blood flow to affected testicle
  • "Whirlpool sign" of twisted spermatic cord (96% sensitivity)
  • Enlarged heterogeneous testis appearing hypoechoic
  • Ipsilateral hydrocele and scrotal skin thickening
• Key ultrasound findings for epididymitis: 1
  • Enlarged epididymis with increased blood flow on color Doppler
  • Scrotal wall thickening
  • Up to 20% concomitant orchitis rate
• Power Doppler is particularly useful for prepubertal testes with slow flow 1
• Use the contralateral asymptomatic testicle as an internal control 1

Step 3: Management Based on Diagnosis

• If testicular torsion confirmed or highly suspected: Immediate urological consultation and surgical exploration within 6-8 hours 1, 2
• If epididymitis diagnosed: Bed rest, scrotal elevation, analgesics, and appropriate antibiotic therapy based on age and risk factors 1, 3
• If torsion of appendage: Conservative management with analgesics and observation 1

Critical Clinical Pitfalls

• False-negative Doppler evaluations occur in 30% or more of cases, particularly with partial torsion, spontaneous detorsion, or early presentation 1, 2
• Partial torsion may show diminished arterial velocity and decreased diastolic flow rather than complete absence of flow 1
• Significant overlap exists in clinical presentation between different causes of acute scrotal pain 1
• Infants and young boys often have normally reduced intratesticular blood flow, potentially leading to false-positive evaluations 1
• When clinical suspicion for torsion remains high despite normal Doppler, proceed immediately to surgical exploration 1
• Complete torsion >450 degrees results in absent arterial and venous flow, but partial torsion presents the greatest diagnostic challenge 1
• Any delay in surgical intervention beyond 6-8 hours significantly increases risk of testicular loss 1, 2