Is ultrasound (US) of the scrotum the best initial imaging modality for a patient suspected of having epididymitis?

Ultrasound is the Best Initial Imaging for Epididymitis

Yes, ultrasound with Doppler of the scrotum is definitively the best and recommended initial imaging modality for suspected epididymitis. 1, 2

Primary Recommendation

Duplex Doppler ultrasound (grayscale combined with color-power Doppler) should be performed as the first-line imaging study for all patients with suspected epididymitis. 1, 2 The American College of Radiology explicitly designates this as the imaging modality of choice for evaluating scrotal infections, including epididymitis, orchitis, and testicular abscesses. 2

Why Ultrasound is Superior

Diagnostic Accuracy

• The combination of grayscale and color-power Doppler US significantly improves diagnostic accuracy for focal inflammatory processes like epididymitis. 1, 2
• Sensitivity approaches 100% for detecting scrotal inflammation, with characteristic findings of enlarged epididymis and markedly increased blood flow on color Doppler. 2
• Ultrasound can accurately depict and characterize infectious processes, showing heterogeneous, hypoechoic echotexture of involved tissue. 1

Clinical Context

• Epididymitis is the single most common cause of acute scrotal pain, representing approximately 600,000 cases annually in the United States. 1, 2
• In patients over 25 years of age, infection overwhelmingly accounts for acute scrotal symptoms. 1
• The more gradual onset of pain in epididymitis (versus abrupt onset in torsion) makes imaging crucial for differentiation. 1

Proper Ultrasound Protocol

When ordering or performing ultrasound for suspected epididymitis, ensure the following components are included: 2

• Grayscale examination to assess testicular homogeneity, size, and echotexture
• Color/Power Doppler assessment to evaluate perfusion patterns (Power Doppler is particularly useful for detecting low-flow states)
• Comparison to the contralateral testis as an internal control
• Spectral Doppler analysis when indicated to characterize flow patterns

Alternative Imaging Modalities Are Not Appropriate

CT, MRI, and nuclear medicine scans are NOT routinely used as initial imaging for suspected epididymitis. 1 There is no relevant literature supporting their use in this clinical scenario. 1

• MRI may only serve as a problem-solving tool when ultrasound findings are unclear, but this is not for initial evaluation. 1
• CT of the abdomen/pelvis and nuclear scans have no role in the initial workup of scrotal infection. 1

Critical Diagnostic Pitfalls to Avoid

Do Not Rely on Urinalysis Alone

Normal urinalysis does NOT exclude epididymitis—infection can be present despite normal urine studies. 1, 2 This is a common clinical trap that can lead to delayed diagnosis.

Beware of Torsion Mimics

• Severe epididymitis with venous infarction can occasionally show absent or reversed diastolic flow, potentially mimicking torsion. 2
• However, complete absence of all arterial flow is uncommon in epididymitis. 2
• In the acute setting with high clinical suspicion for torsion, do not delay surgical consultation while waiting for imaging, as testicular viability is compromised after 6-8 hours. 2

Limitations in Differentiating Malignancy

Duplex US cannot definitively differentiate malignancies from certain inflammatory conditions (orchitis, granuloma, focal fibrosis), which can mimic cancer and lower specificity. 1, 2 If a solid mass is identified, further evaluation may be warranted despite inflammatory findings.

Advanced Technique Consideration

Contrast-enhanced ultrasound (CEUS) has been demonstrated to be particularly useful in patients with acute scrotal pain in the setting of infection, improving early diagnosis and detection of postinfectious complications. 2 CEUS can unequivocally differentiate between hypervascular, hypovascular, and avascular scrotal lesions. 2