- Author: Vikram S Dogra, MD; Chief Editor: Eugene C Lin, MD more...
Acute epididymitis is the most common condition that causes acute scrotal pain, although acute epididymitis, testicular torsion, and testicular tumors can have a common presentation of pain. Distinguishing between acute epididymitis and testicular torsion is important because their treatments differ significantly.[1, 2, 3]
Normal testes develop in the celom and begin to descend into the scrotum at 36 weeks' gestation, guided by the contractile, cordlike structure called the gubernaculum testis. The epididymis and ductus deferens develop from the wolffian ducts.
At sonography, a normal adult testis has medium-level echoes and measures 5 x 3 x 2 cm. Septa extend from the tunica albuginea into the testicle, dividing the testes into lobules. The posterior surface of the tunica albuginea is reflected into the interior of the gland to form the incomplete septum known as the mediastinum of the testis. Each lobule is composed of many seminiferous tubules that open, via tubules (tubuli recti), into dilated spaces called the rete testes in the mediastinum. These, in turn, communicate via efferent ductules in the epididymal head.
The epididymis is composed of a head, body, and tail, the ducts of which continue as the vas deferens in the spermatic cord. The epididymis lies superior and lateral, along the posterior aspect of the testis; the head of epididymis is the most cephalic part.
Four testicular appendages have been described; however, only 2 are clinically relevant: the appendix of the testis (müllerian duct remnant) and the appendix of the epididymis, a wolffian duct remnant. Sonographically, the head of the epididymis is better depicted in the longitudinal view than in others. It is an isoechoic or slightly hypoechoic structure with medium-level echoes. Usually, the body of the epididymis is not identified at sonography in healthy adults. Sometimes, the epididymal tail is seen.
Radiography has no role in the evaluation of epididymitis. The preferred imaging examination is ultrasonography, which is very useful in the detection of the epididymitis and/or epididymo-orchitis (see the following images). Ultrasonography is helpful in excluding testicular torsion.[4, 5, 6, 7, 8, 9, 10, 11]
Ultrasonographic findings considered diagnostic of acute epididymitis include an enlarged (>17 mm) epididymis with a hypoechoic, hyperechoic, or heterogeneous echotexture (gray-scale ultrasonography) and increased blood flow (color or power Doppler ultrasonography) (see the images below).[12, 13, 14, 15, 16, 17, 18, 19, 20, 9] Associated reactive hydrocele and scrotal wall thickening may be present. Blood flow can be seen in a normal epididymis; therefore, the mere presence of blood flow should not be considered the sine qua non of epididymitis. It is the asymmetrical increase (more in the affected epididymis) that is important.
The epididymis is primarily involved in epididymo-orchitis, with orchitis developing in about 20-40% of cases by means of direct spread. Diffuse testicular involvement is confirmed with testicular enlargement and an inhomogeneous echotexture. These findings are nonspecific, but acute epididymo-orchitis is the most common disease with this pattern. This pattern of heterogeneous echotexture can also occur in patients with tumors, metastasis, and infarction. Therefore, patients with these conditions should be followed up with ultrasonography to demonstrate complete resolution.
The readily detectable intratesticular venous flow is highly suggestive of orchitis. Analysis of the spectral waveform also can provide useful information. In the testes of a healthy volunteer, the resistive index (RI) is rarely less than 0.5, but more than half of the patients with epididymo-orchitis have an RI of less than 0.5.
Degree of confidence
Ultrasonography is the first-line imaging modality for evaluating a patient with suspected acute epididymo-orchitis. The sensitivity of color Doppler ultrasonography in detecting scrotal inflammation is almost 100%.
Usually, no false-positive or false-negative findings occur. However, the epididymis may be involved in some patients with testicular torsion. Hence, in every case of epididymitis, intratesticular blood flow should be carefully evaluated to exclude the possibility of acute testicular torsion.
Nuclear medicine study is an alternative method for evaluating epididymitis. However, because of the improved capability of color and power Doppler ultrasonography in the evaluation of testicular perfusion, this modality is no longer favored. The most common scenario in which epididymitis appears on scintigrams is in patients who undergo imaging for suspected torsion.
The radionuclide angiogram obtained with technetium-99m (99m Tc) pertechnetate reveals increased spermatic cord blood flow. Static images reveal increased radiotracer uptake, which may be focal (as in epididymitis) or diffuse (as in epididymo-orchitis), in the involved hemiscrotum. These findings should easily differentiate epididymitis from acute torsion. However, if an abscess or hydrocele formation is present, a photopenic area with a hypervascular rim (halo sign) can be apparent. This finding could potentially mimic late, missed torsion.
Nuclear medicine studies help in the differentiation of epididymo-orchitis from acute torsion. Increased radionuclide uptake may be present in the setting of trauma.
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