The differential diagnosis in a patient presenting with acute scrotum may pose a diagnostic dilemma, and ultrasound can play a key role in effectively narrowing down the differentials, confirming the presumptive clinical diagnosis and providing additional relevant information. Although the scrotum is a superficial structure,clinical examination is frequently not enough for making a specific diagnosis. The main aim of ultrasonography in a patient presenting with acute painful scrotum is to distinguish testicular torsion from acute epidiymo-orchitis, as the former warrants emergent surgery to prevent permanent damage.
Two forms of acute epididymitis have been described. The first occurs in young males, is transmitted sexually, and is usually due to chlamydia or gonococci. The other kind occurs in older males, is non- sexually transmitted, and is caused by organisms such as E.coli or pseudomonas. These patients may have prostatic hypertrophy or urinary tract infection as predisposing factors. Systemic infections and trauma are uncommon causes of epididymitis. In 20 –40% patients, the testis also gets inflamed, producing the picture of epidiymo-orchitis. A few drugs such as amiodarone can produce chemical epididymitis. Complications of acute epididymitis include contiguous spread to the testis, chronic pain, infarction, abscess, gangrene, infertility, atrophy, and pyocele.
The epididymis is comprised of the head, body and tail. The normal epididymal head is seen above the superior pole of the testis, measuring 5-12 mm in length. The normal body is usually not identified discretely from the surrounding para-testicular tissues. The tail is seen near the inferior pole of testis, and measures 2-5 mm in diameter. In epididymitis, the epididymis may be significantly enlarged and shows altered echotexture, usually hypoechoic, but may sometimes be hyperechoic. A normal epididymis is almost always iso-echoic to the testis, and may have a slightly coarser echotexture as compared to the testis. A reactive hydrocele or secondary complications such as pyocele may be present. Orchitis, if present, usually presents as an enlarged testis, with altered echogenicity and texture.
Power Doppler usually shows increased blood flow through the affected organ. Increased blood flow through the involved testis and epididymis is an established criterion for the diagnosis of epididymo-orchitis. The sensitivity of color Doppler in diagnosing inflammation is almost 100%. In acute epididymitis, the epididymis demonstrates increased number of vessels, which show low resistance and high velocity flow. Studies have shown that in 20% of cases of epididymitis and 40% of cases of orchitis, hyperemia may be the only diagnostic color Doppler finding because gray-scale ultrasound findings are normal. Therefore, in all cases of suspected epididymitis, it is a good idea to image the scrotum in both gray scale and color Doppler modes.