KEY FACTS
Terminology
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Inflammation of epididymis &/or testis
Imaging
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Grayscale US
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Epididymis enlarged and hypoechoic
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Testes mildly heterogeneous
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Color Doppler US
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Diffuse or focal hyperemia in body and tail of epididymis ± increased vascularity of testis
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In severe cases can cause vascular compromise and ischemia or infarction
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Reversal of arterial diastolic flow of testis is ominous finding associated with testicular infarction
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Orchitis is usually secondary, occurring in 20-40% of epididymitis due to contiguous spread of infection
Top Differential Diagnoses
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Testicular torsion
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Testicular lymphoma
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Testicular trauma
Pathology
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Starts within tail of epididymis → body → testis
Clinical Issues
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Commonest cause of acute scrotal pain in adolescent boys and adults (15-35 years)
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Males 14-35 years of age: Most commonly caused by Neisseria gonorrhoeae and Chlamydia trachomatis
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Scrotal swelling, erythema; fever; dysuria
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Scrotal pain due to epididymitis is usually relieved after elevation of testes (scrotum) over symphysis pubis (Prehn sign)
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Associated lower urinary tract infection and its symptoms, urethral discharge
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Prognosis excellent if treated early with antibiotics; follow-up scans to exclude abscess if no improvement
Scanning Tips
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Compare side by side with contralateral asymptomatic side with both color and power Doppler in single image
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Avoid using dual image for side-by-side comparison
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Suggested setting for color Doppler: 5 cm/s
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Head, body, and tail of epididymis should be carefully evaluated
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Use high-frequency transducers (9-15 MHz)
enveloping the testis posteriorly. Note that the testis 
appears normal in size and configuration.
compared to the left, and there is a small right hydrocele 
.
.
of the epididymis consistent with acute epididymitis.
in appearance compared to the left, consistent with right-sided orchitis. In addition, there are associated findings of scrotal wall thickening 
and a small hydrocele 
.
in a patient with a history of epididymo-orchitis. The findings are consistent with a pyocele.
