usually begins in the epididymal tail and spreads to the epididymal body and head. approximately 20% to 40% of cases are associated with orchitis due to direct spread of infection into the testis. at ultrasound, the findings of acute epididymitis include an enlarged hypoechoic or hyperechoic (presumably secondary to hemorrhage) epididymis . other signs of inflammation such as increased vascularity, reactive hydrocele, pyocele and scrotal wall thickening may also be present. testicular involvement is confirmed by the presence of testicular enlargement and an inhomogeneous echotexture. hypervascularity on color doppler images is a well-established diagnostic criterion and may be the only imaging finding of epididymo-orchitis in some men. doppler ultrasound of epididymitis, seen as a substantial increase in blood flow in the left epididymis (top image), while it is normal in the right (bottom image). the thickness of the epididymis (between yellow crosses) is only slightly increased (7 mm). doppler ultrasound of the scrotum of the same case, in the axial plane, showing orchitis (as part of epididymo-orchitis) as hypoechogenic and slightly heterogenic left testicular tissue (right in image), with an increased blood flow. there is also swelling of peritesticular tissue. tuberculous epididymo-orchitis fig. 21. tuberculous epididymo-orchitis. (a) transverse sonography of a surgically proved tuberculous epididymitis shows an enlarged epididymis containing calcification and necrosis. (b) composite image: transverse sonography of the same patient shows multiple hypoechoic nodules in the left testis associated with surrounding reactive hydrocele. although the genitourinary tract is the most common site of extra-pulmonary involvement by tuberculosis, tuberculous infection of the scrotum is rare and occurs in approximately 7% of patients with tuberculosis. at the initial stage of infection, the epididymis alone is involved. however, if appropriate antituberculous treatment is not administered promptly, the infection will spread to the ipsilateral testis. the occurrence of isolated testicular tuberculosis is rare. clinically patients with tuberculous epididymo-orchitis may present with painful or painless enlargement of the scrotum, hence they cannot be distinguished from lesions such as testicular tumor, testicular infarction and may mimic testicular torsion. at ultrasound, tuberculous epididymitis is characterized by an enlarged epididymis with variable echogenicity. the presence of calcification, caseation necrosis, granulomas and fibrosis can result in heterogeneous echogenicity . the ultrasound findings of tuberculous orchitis are as follow: (a) diffusely enlarged heterogeneously hypoechoic testis (b) diffusely enlarged homogeneously hypoechoic testis (c) nodular enlarged heterogeneously hypoechoic testis and (d) presence of multiple small hypoechoic nodules in an enlarged testis . although both bacterial and tuberculous infections may involve both the epididymis and the testes, an enlarged epididymis with heterogeneously hypoechoic pattern favors a diagnosis of tuberculosis (muttarak and peh, 2006, as cited in kim et al., 1993 and chung et al., 1997). with color doppler ultrasound, a diffuse increased blood flow pattern is seen in bacterial epididymitis, whereas focal linear or spotty blood flow signals are seen in the peripheral zone of the affected epididymis in patients with tuberculosis. fournier gangrene fournier gangrene. (a) transverse sonography image shows echogenic areas with dirty shadowing representing air in the perineum. (b) gas presented as numerous, discrete, hyperechoic foci with reverberation artifacts is seen at scrotal wall. fournier gangrene is a polymicrobial necrotizing fasciitis involving the perineal, perianal, or genital regions and constitutes a true surgical emergency with a potentially high mortality rate. it usually develops from a perineal or genitourinary infection but can arise following local trauma with secondary infection of the wound. 40–60% of patients are being diabetic. although the diagnosis of fournier gangrene is often made clinically, diagnostic imaging is useful in ambiguous cases. the sonographic hallmark of fournier gangrene is presence of subcutaneous gas within the thickened scrotal wall. at ultrasound, the gas appears as numerous, discrete, hyperechoic foci with reverberation artifacts . evidence of gas within the scrotal wall may be seen prior to clinical crepitus. the only other condition manifesting with gas at sonographic examination is an inguinoscrotal hernia. this can be differentiated from fournier gangrene by the presence of gas within the protruding bowel lumen and away from the scrotal wall. (levenson et al., 2008). other benign lesions of the scrotum tubular ectasia fig. 23. tubular ectasia of the testis. honey-comb shaped cystic lesion at mediastinum testis. fig. 24. tubular ectasia of the testis. lesion in the testis mimicking testicular tumor, but the microcystic appearance of this lesion is suggestive of tubular ectasia. the normal testis consists of several hundred lobules, with each lobule containing several seminiferous tubules. the seminiferous tubules of each lobule merge to form the straight tubes, which in turn converge to form the rete testis. the rete testis tubules, which lie within the mediastinum testis, are an anastomosing network of irregular channels with a broad lumen, which then empties into the efferent ductules to give rise to the head of the epididymis. obstruction in the epididymis or efferent ductules may lead to cystic dilatation of the efferent ductules, which usually presents as an epididymal cyst on ultrasound. however, in the more proximal portion this could lead to the formation of an intratesticular cyst or dilatation of the tubules, so-called tubular ectasia. factors contributing to the development of tubular ectasia include epididymitis, testicular biopsy, vasectomy or an aging process. clinically this lesion is usually asymptomatic. the ultrasound appearance of a microcystic or multiple tubular-like lesions located at the mediastinal testis and associated with an epididymal cyst in a middle-aged or elderly patient should alert the sonographer to the possibility of tubular ectasia. the differential diagnosis of a multicystic lesion in testis should include a cystic tumor, especially a cystic teratoma. a cystic teratoma is usually a palpable lesion containing both solid and cystic components; and the cysts are normally larger than that of tubular ectasia, which appear microcystic . furthermore, the location of tubular ectasia in the mediastinum testis is also helpful in making the differential diagnosis. testicular microlithiasis histologically, testicular microlithiasis refers to the scattered laminated calcium deposits in the lumina of the seminiferous tubules. these calcifications arise from degeneration of the cells lining the seminiferous tubules. at ultrasonography, microliths appear as tiny punctate echogenic foci, which typically do not shadow. although minor microcalcification within a testis is considered normal, the typical us appearance of testicular microlithiasis is of multiple nonshadowing echogenic foci measuring 2–3 mm and randomly scattered throughout the testicular parenchyma (dogra et al., 2003, as cited in janzen et al., 1992). the clinical significance of testicular microlithiasis is that it is associated with increased risk of testicular malignancy, thus follow up of affected individuals with scrotal sonography is necessary to ensure that a testicular tumor does not develop. fig. 25. testicular microlithiasis. multiple hyperechoic foci without acoustic shadow presenting as a starry sky appearance is seen in the testis. testicular torsion fig. 26. testicular torsion of the right testis. absence of vascular flow and ill-defined hypoechoic lesions are seen in the testis. the normal testis and epididymis are anchored to the scrotal wall. if there is a lack of development of these attachments, the testis is free to twist on its vascular pedicle. this will result in torsion of the spermatic cord and interruption of testicular blood flow. testicular torsion occurs most commonly at 12 to 18 years but can occur at any age. torsion results in swelling and edema of the testis, and as the edema increases, testicular perfusion is further altered. the extent of testicular ischemia depends on the degree of torsion, which ranges from 180° to 720° or greater. the testicular salvage rate depends on the degree of torsion and the duration of ischemia. a nearly 100% salvage rate exists within the first 6 hours after the onset of symptoms; a 70% rate, within 6–12 hours; and a 20% rate, within 12–24 hours. therefore, testicular torsion is a surgical emergency and the role of ultrasound is to differentiate it from epididymitis as both disease presents with acute testicular pain clinically. there are two types of testicular torsion: extravaginal and intravaginal. extravaginal torsion occurs exclusively in newborns. ultrasound findings include an enlarged heterogeneous testis, ipsilateral hydrocele, thickened scrotal wall and absence of vascular flow in the testis and spermatic cord. the ultrasound findings of intravaginal torsion vary with the duration and the degree of rotation of the spermatic cord. gray scale ultrasound may appear normal if the torsion just occurs. at 4–6 hours after onset of torsion, enlarged testis with decreased echogenicity is seen. at 24 hours after onset, the testis appears heterogeneous due to vascular congestion, hemorrhage and infarction. as gray scale ultrasound is often normal during early onset of torsion, doppler sonography is considered essential in early diagnosis of testicular torsion. the absence of testicular flow at color and power doppler ultrasound is considered diagnostic of ischemia, provided that the scanner is set for detection of slow flow, the sampling box is small and the scanner is adjusted for the lowest repetition frequency and the lowest possible threshold setting. varicocele fig. 27. varicocele. (a) multiple tortuous tubular like structure are seen in the left scrotum. (b) color doppler sonography shows vascular reflux during valsalva's maneuver. fig. 28. intratesticular varicocele. (a) dilated tubular structures are seen within the testis. (b) presence of vascular reflux is noted during valsalva's maneuver. varicocele refers to abnormal dilatation of the veins of the spermatic cord due to incompetence of valve in the spermatic vein. this results in impaired blood drainage into the spermatic vein when the patient assumes a standing position or during valsalva's maneuver. varicoceles are more common on the left side due to the following reasons (a) the left testicular vein is longer; (b) the left testicular vein enters the left renal vein at a right angle; (c) the left testicular artery in some men arches over the left renal vein, thereby compressing it; and (d) the descending colon distended with feces may compress the left testicular vein. the us appearance of varicocele consists of multiple, hypoechoic, serpiginous, tubular like structures of varying sizes larger than 2 mm in diameter that is usually best visualized superior or lateral to the testis . color flow and duplex doppler us optimized for low-flow velocities help confirm the venous flow pattern, with phasic variation and retrograde filling during a valsalva's maneuver . intratesticular varicocele may appear as a vague hypoechoic area in the testis or mimics tubular ectasia. with color doppler, this intratesticular hypoechoic area also showed reflux of vascular flow during valsalva's maneuver . undescended testis normally the testes begin its descent through the inguinal canal to the scrotum at 36 weeks’ of gestation and completed at birth. failure in the course of testes descent will result in undescended testes (cryptorchidism). undescended testis is found in 4% of full-term infants but only 0.8% of males at the age of 1 year have true cryptorchidism. although an undescended testis can be found anywhere along the pathway of descent from the retroperitoneum to the scrotum, the inguinal canal is the most common site for an undescended testis. deviation of testis from the normal pathway of descent will result in ectopic testis that is commonly seen in pubopenile, femoral triangle and perineal regions. besides infertility, undescended testes carry an increased risk of malignancy even for the normally located contralateral testis. the risk of malignancy is estimated to be as high as 10 times the normal individual with seminoma being the most common malignancy. the incidence of infertility is decreased if surgical orchiopexy is carried out before the 1–3 years but the risk of malignancy does not change. because of the superficial location of the inguinal canal in children, sonography of undescended testes should be performed with a high frequency transducer. at ultrasound, the undescended testis usually appears small, less echogenic than the contralateral normal testis and usually located in the inguinal region . with color doppler, the vascularity of the undescended testis is poor. fig. 29. undescended testis. (a) normal testis in the scrotum. (b) atrophic and decreased echogenicity of the contralateral testis of the same patient seen in the inguinal region. testicular appendiceal torsion fig. 30. testicular appendiceal torsion. a hyperechoic lesion with surrounding vascularity is seen in the groove between the testis and epididymis. at sonography, the appendix testis usually appears as a 5 mm ovoid structure located in the groove between the testis and the epididymis. normally it is isoechoic to the testis but at times