What tests should be ordered for a patient presenting with scrotal pain, particularly in a sexually active young male?

Diagnostic Testing for Scrotal Pain

Immediate First-Line Test

Duplex Doppler ultrasound of the scrotum is the mandatory first-line imaging study for any patient presenting with acute scrotal pain, as it can rapidly differentiate surgical emergencies like testicular torsion from medical conditions like epididymitis. 1, 2

Essential Components of the Ultrasound Examination

The ultrasound must include three critical elements to maximize diagnostic accuracy:

• Grayscale imaging to assess testicular homogeneity, identify the "whirlpool sign" of twisted spermatic cord (96% sensitivity), and detect scrotal wall thickening or hydrocele 1, 2

• Color Doppler assessment to evaluate testicular perfusion compared to the contralateral side, with reported sensitivity of 96-100% and specificity of 84-95% for detecting torsion 1, 2

• Power Doppler evaluation as it is more sensitive than color Doppler for detecting slow flow states, particularly crucial in prepubertal boys who normally have reduced intratesticular blood flow 1, 2

Additional Laboratory Testing

• Urinalysis should always be performed, though a normal result does not exclude either testicular torsion or epididymitis 2, 3

• Urine culture if epididymitis is suspected, particularly in sexually active males or those with urinary symptoms 4

Age-Specific Diagnostic Considerations

The differential diagnosis shifts dramatically by age, which should guide your clinical suspicion:

• Adolescents and young adults: Testicular torsion is the primary concern, with a bimodal peak in neonates and postpubertal boys 2

• Adults over 25 years: Epididymitis/epididymo-orchitis becomes the most common cause, representing approximately 600,000 cases annually in the United States 2

• Prepubertal boys: Torsion of testicular appendage is most common, though testicular torsion must still be excluded 2

Critical Timing Considerations

Time is testis—testicular viability is compromised if surgical intervention does not occur within 6-8 hours of symptom onset. 2 This means:

• Ultrasound should be performed emergently, not scheduled for later in the day 1

• If clinical suspicion for torsion is high (sudden onset, severe pain, negative Prehn sign), proceed directly to surgical exploration without waiting for imaging if ultrasound is not immediately available 2

• The TWIST score can be used for risk stratification: high scores (≥6) warrant immediate surgical exploration, while intermediate scores (1-5) require urgent ultrasound 2

Common Diagnostic Pitfalls

Be aware of these critical limitations that can lead to missed diagnoses:

• False-negative Doppler occurs in 30% or more of cases, particularly with partial torsion (<450 degrees), spontaneous detorsion, or very early presentation 2

• Partial torsion is the most challenging diagnosis because arterial flow may persist while venous obstruction occurs first, potentially showing diminished but present flow on Doppler 2

• Prepubertal boys normally have reduced intratesticular blood flow, which can lead to false-positive interpretations—always compare to the contralateral testis as an internal control 2

• Normal urinalysis does not exclude testicular torsion, as pyuria and bacteriuria are not expected findings in torsion 2

When Ultrasound is Equivocal or Unavailable

• If clinical suspicion remains high despite normal or equivocal Doppler findings, proceed immediately to surgical exploration—do not delay for additional imaging 2

• MRI can be used as a problem-solving tool when ultrasound is indeterminate, showing decreased perfusion on dynamic contrast-enhanced sequences and the "bell-clapper" deformity with 83% sensitivity 1, 2

• Nuclear scintigraphy is an alternative if Doppler is unavailable, showing central photon-deficient areas in torsion versus increased perfusion in epididymitis 4

Specific Ultrasound Findings by Diagnosis

Testicular torsion:

• Decreased or absent blood flow to the affected testis 1, 2
• "Whirlpool sign" of twisted spermatic cord on grayscale 1, 2
• Enlarged heterogeneous testis appearing hypoechoic 2
• Ipsilateral hydrocele and scrotal skin thickening 2

Epididymitis/epididymo-orchitis:

• Enlarged epididymis with increased blood flow on color Doppler (sensitivity near 100%) 2
• Scrotal wall thickening and reactive hydrocele 1
• Up to 20% concomitant orchitis rate 1

Torsion of testicular appendage:

• Normal testicular perfusion with localized hyperemia near the appendage 2
• The "blue dot sign" on physical exam is pathognomonic but only present in 21% of cases 2

Tests NOT to Order Initially

• Do not order CT scan as initial imaging for scrotal pain—it is only indicated after ultrasound confirms a testicular mass suspicious for malignancy 5

• Do not order MRI as the first-line test—it is reserved for problem-solving when ultrasound is equivocal 1, 5

• Serum tumor markers (AFP, β-hCG, LDH) are only indicated if a testicular mass is identified on ultrasound, not for acute scrotal pain evaluation 5