Is epididymitis always detected on Ultrasound Scan (USS)?

Is Epididymitis Always Detected on Ultrasound?

No, epididymitis is not always detected on ultrasound, though it has very high sensitivity approaching 100% when classic findings are present. The diagnosis can be missed in early presentations, atypical cases, or when technical factors limit image quality.

Typical Ultrasound Findings in Epididymitis

The classic sonographic appearance includes:

• Enlarged epididymis with variable echogenicity (can be increased, decreased, or mixed compared to normal tissue) 1, 2
• Increased blood flow (hyperemia) on color Doppler imaging, which is the hallmark finding with sensitivity approaching 100% for detecting scrotal inflammation 2
• Scrotal wall thickening is commonly present 1, 2
• Reactive hydrocele (fluid collection around the testis) frequently accompanies epididymitis 2

High Sensitivity Finding: Funiculitis

• Spermatic cord inflammation (funiculitis) is present in 96% of acute epididymitis cases, appearing as increased echogenicity of the spermatic cord fat with mass-like cord thickening 3
• Funiculitis has 95.9% sensitivity and 81.6% specificity for diagnosing acute epididymitis, making it a valuable secondary finding when present 3

When Ultrasound May Miss Epididymitis

Early or Mild Disease

• In very early presentations, inflammation may not yet be severe enough to produce detectable hyperemia or epididymal enlargement, though this is not explicitly quantified in the guidelines 1, 2

Atypical Presentations

• Tuberculous epididymitis can show variable echogenicity (hypoechoic in 59%, hyperechoic in 9%, mixed in 32% of cases) with heterogeneous echotexture in 77% of cases, making diagnosis more challenging 4
• The heterogeneous appearance may be confused with other pathology 4

Technical Limitations

• Power Doppler is more sensitive than color Doppler for detecting slow flow states, particularly in prepubertal boys who normally have reduced intratesticular blood flow 1
• Operator experience and equipment quality affect detection of subtle hyperemia 5

Critical Diagnostic Considerations

The primary clinical imperative is distinguishing epididymitis from testicular torsion, as torsion is a surgical emergency requiring intervention within 6-8 hours 2:

• Epididymitis shows increased blood flow on Doppler imaging 2
• Testicular torsion shows decreased or absent blood flow, the opposite pattern 2
• Color Doppler sensitivity for detecting torsion ranges from 96-100%, but false-negatives occur in up to 30% of cases, particularly with partial torsion 1, 6

Concomitant Orchitis

• Up to 20% of epididymitis cases develop concomitant orchitis (epididymo-orchitis), which shows increased testicular blood flow on Doppler 1, 2
• Rarely, severe epididymo-orchitis can be complicated by global testicular infarction, which appears as absent flow and requires surgical management 1, 5

Clinical Algorithm When Ultrasound is Equivocal

When ultrasound findings are unclear or normal despite clinical suspicion:

• Review for funiculitis (present in 96% of cases) as a secondary diagnostic marker 3
• Assess for gradual onset of pain (typical of epididymitis) versus abrupt onset (typical of torsion) 6
• Check urinalysis, though normal urinalysis does not exclude either epididymitis or torsion 6
• When clinical suspicion for torsion remains high despite normal or equivocal Doppler, proceed immediately to urological consultation and surgical exploration rather than relying solely on imaging 6

Common Pitfalls

• Do not assume normal ultrasound excludes epididymitis in early disease or when clinical presentation is compelling 7
• A large portion of epididymitis cases remain idiopathic despite advances in imaging and pathogen detection 7
• False-negative Doppler evaluations occur, particularly in partial torsion or early presentations, emphasizing the importance of clinical judgment over imaging alone 6