What causes testicular pain with a normal Doppler (duplex) ultrasound?

Testicular Pain with Normal Doppler Ultrasound: Differential Diagnosis

When Doppler ultrasound shows normal testicular blood flow in a patient with acute testicular pain, the most common diagnoses are epididymitis/epididymo-orchitis in adults, torsion of testicular appendage in prepubertal boys, or early/intermittent testicular torsion that has spontaneously detorsed. 1

Critical Clinical Context: Understanding Doppler Limitations

While Doppler ultrasound is highly sensitive for testicular torsion, false-negative evaluations occur in up to 30% of cases, particularly with partial torsion, spontaneous detorsion, or early presentation within the first few hours. 2 Color Doppler sensitivity ranges from 69-96.8%, meaning a normal study does not completely exclude torsion. 2

Key Scenarios Where Doppler Appears Normal Despite Pathology:

• Partial/incomplete torsion (<360-450 degrees): Arterial flow may persist because venous obstruction occurs first due to thinner vessel walls and lower pressure, while arterial flow continues. 2 This can show diminished arterial velocity and decreased diastolic flow on spectral Doppler, but may appear "normal" on color Doppler. 2

• Intermittent torsion with spontaneous detorsion: The testis may have normal flow at the time of imaging despite recent ischemic episodes. 2, 3

• Very early torsion: Within the first few hours, the testis may still appear normal before complete vascular compromise develops. 2

Age-Stratified Differential Diagnosis

Adults (>25 years):

Epididymitis/epididymo-orchitis is overwhelmingly the most common cause of testicular pain in adults, representing approximately 600,000 cases annually in the United States. 2, 4

• Characterized by gradual onset of pain (versus abrupt onset in torsion) 2
• Ultrasound shows enlarged epididymis with increased flow on color Doppler 1, 4
• May have abnormal urinalysis, though normal urinalysis does not exclude epididymitis 2
• Scrotal wall thickening and hydrocele are common 1
• Up to 20% concomitant rate for orchitis 1

Prepubertal Boys:

Torsion of testicular appendage is the most common cause of testicular pain in prepubertal boys. 2

• The "blue dot sign" is pathognomonic but only seen in 21% of cases 2
• Doppler shows normal testicular perfusion with localized hyperemia near the appendage 1
• Usually managed conservatively with rest and analgesics 1

Adolescents:

• Bimodal risk for both testicular torsion and epididymitis 2
• Testicular torsion has peak incidence in postpubertal boys 2
• Clinical suspicion must remain high despite normal Doppler 2

Additional Diagnostic Considerations with Normal Flow

Segmental Testicular Infarction:

• Classic wedge-shaped avascular focal area on ultrasound 1, 4
• May also present as round lesions with variable Doppler flow 1
• If ultrasound is equivocal, MRI can be helpful 1, 4

Acute Idiopathic Scrotal Edema:

• Rare, self-limiting condition primarily affecting prepubertal boys but can occur in adults 1
• Usually painless or minimally painful 1
• Marked scrotal wall thickening with heterogeneous striated appearance 1
• Increased peritesticular blood flow but normal testicular vascularity 1
• Diagnosis of exclusion 1

Critical Management Algorithm

When Clinical Suspicion for Torsion Remains High Despite Normal Doppler:

Immediate urological consultation and surgical exploration should proceed regardless of imaging findings when clinical suspicion is high, as testicular viability is compromised if not treated within 6-8 hours. 2

1. Assess clinical risk using TWIST score or clinical features: 2

   • Abrupt onset of severe pain suggests torsion 2
   • Gradual onset suggests epididymitis 2
   • Normal urinalysis does not exclude torsion 2

2. Review ultrasound technique and findings carefully: 2

   • Ensure power Doppler was used (more sensitive for low-flow states) 1
   • Look for grayscale findings: "whirlpool sign" of twisted cord (96% sensitivity), enlarged heterogeneous testis, ipsilateral hydrocele 1, 2
   • Compare spectral Doppler waveforms to contralateral testis 2

3. Consider repeat imaging in 6-8 weeks for indeterminate findings with normal tumor markers 1, 2

Common Pitfalls to Avoid

• Never delay surgical exploration based solely on normal Doppler when clinical suspicion is high - the 6-8 hour window for testicular salvage is critical. 2

• Prepubertal boys normally have reduced intratesticular blood flow, which can lead to false-positive interpretations of torsion; always compare to the contralateral side. 1, 2

• Subacute torsion (>8 hours) can show misleading inhomogeneous testicular appearance that may be misdiagnosed as tumor or epididymitis on grayscale imaging. 5

• Significant overlap exists in clinical presentation between different causes of acute scrotal pain, making diagnosis challenging. 2

• In rare cases of severe epididymo-orchitis with venous infarction, absent or reversed diastolic flow can occur, but complete absence of all arterial flow is uncommon. 2