Hydrocele is the most common cause of painless scrotal swelling. A hydrocele is a serous fluid collection between the parietal and visceral layers of the tunica vaginalis. The tunica vaginalis is a mesothelium-lined sac that results from closure of the superior portion of the processus vaginalis. This fascial structure normally covers the entire testis except the posterior border. It has a visceral layer and an outer parietal layer that lines the internal spermatic fascia of the scrotal wall. Hydroceles can be congenital or acquired. The congenital hydrocele or communicating hydrocele occurs when a patent processus vaginalis allows fluid to pass from the peritoneal space into the scrotum [33]. The acquired hydrocele may be idiopathic with no identifiable cause. The incidence of hydroceles is about 1 % of adult males. Hydroceles are usually anechoic on ultrasonography (Fig. 6.25). They may contain echogenic cholesterol crystals. The presence of septations is often associated with infection, trauma, or metastatic disease. Hydrocele may develop secondary to venous or lymphatic obstruction caused by infection, trauma, torsion, or tumor. About 10 % of testicular tumors are accompanied by a hydrocele; clinical suspicion increases with new onset of hydrocele in men in their 30s or 40s [34]. Scrotal ultrasound is essential to rule out testicular pathology in these patients. The testis is often posteriorly displaced by the hydrocele. A massive hydrocele exerts a pressure effect that may compromise blood flow within the testis. Vascular resistance in intratesticular arteries is increased, and color Doppler ultrasound may demonstrate an increase in the caliber of capsular arteries. Fluid aspiration and surgical excision of hydrocele sac has been shown to restore normal blood flow to the testis [35].

Pyocele is an accumulation of purulent material within the tunica vaginalis and is most often occurring because of untreated epididymo-orchitis. Pyoceles present with acute scrotal pain and symptoms of sepsis. A pyocele also appears heterogeneous on the ultrasonogram, and gas may be identified, causing hyperechoic reflections and shadowing [36] (Fig. 6.26).

Congenital inguinal hernia is due to failure of the processus vaginalis to obliterate and result in passage of intestinal loops or omentum or peritoneal fluid in the scrotal sac [12, 37, 38]. Right inguinal hernias are more common as the right processus vaginalis closes later. Scrotal ultrasound can be helpful for inconclusive physical examination. Clinically occult contralateral hernia can also be assessed with the ultrasound [39]. Patients with a scrotal hernia usually present with mesenteric fat and/or bowel loops seen superior to the testis. Real-time imaging can identify peristaltic activity or intestinal gas bubbles with their characteristic echogenic interfaces. Ultrasound of an omental hernia will demonstrate highly echogenic fat [40] (Figs. 6.27a, b and 6.28).

Spermatazoa are highly antigenic, and an intense inflammatory reaction occurs when they exit the vas difference [40]. Sperm granulomas occur in at least 40 % of men following a vasectomy [41] (Fig. 6.29). Sperm granulomas are rarely symptomatic. However, 2–3 % of vasectomy patients will have pain attributed to sperm granulomas, usually occurring 2–3 weeks postoperatively [42].

Lipomas of the spermatic cord are very common benign lesions of the spermatic card. They can be unilateral or bilateral, and often present as asymptomatic fullness of the spermatic cord. Ultrasound of a lipoma demonstrates homogeneous echogenicity similar to subcutaneous fat without internal color flow. The echogenicity of lipomas may be variable, and MRI may be helpful to confirm diagnosis, showing nonenhancing, fat saturated areas [43]. It is also important to differentiate a lipoma from an inguinal hernia by noting the intact external inguinal ring on physical examination and assessing for the presence of a hernia on ultrasound.

Rhabdomyosarcomas of the spermatic cord is a malignant lesion in children, and liposarcoma is the most common malignant tumor arising in the spermatic cord in adults, although both are rare. Leiomyosarcomas in the paratesticular space also have been reported. The ultrasound appearance of these lesions is an ill-defined solid mass with heterogeneous echotexture and increased vascular flow on Doppler color study (Fig. 6.30).

Epididymitis is the most common cause of subacute unilateral scrotal pain in preadolescent and adolescent boys and adult men. On physical exam the epididymis can often be identified as an enlarged and tender structure posterolateral to the testis. The pain is often relieved with elevation of the testis over the symphysis pubis, known as Prehn’s sign. Among sexually active men younger than 35 years old, epididymitis often results from sexually transmitted infections, particularly Chlamydia trachomatis and Neisseria gonorrhoeae. In older men, bacterial epididymitis can result from retrograde transit of bacteria from the vasa, and therefore the most common organisms are urinary pathogens: Escherichia coli and Proteus mirabilis. Rare infectious causes include brucellosis, tuberculosis, cryptococcus, syphilis, and mumps. Epididymitis in prepubertal boys normally has a benign course, and these boys commonly are found to have positive titers for enteroviruses and adenoviruses and M. pneumonia. Rare noninfectious causes include sarcoidosis and amiodarone. Blunt trauma as well as congestion following vasectomy is potential cause of epididymal inflammation [44, 45].

In patients with acute epididymitis, the epididymis is enlarged with increased vascularity. Epididymitis may lead to focally or global enlargement and thickening of the epididymis. Gray scale ultrasound demonstrates a hypoechoic or heterogeneous enlarged epididymis (Fig. 6.31). The color flow Doppler shows increased vascularity with high-flow, low-resistance pattern (Fig. 6.32). A reactive hydrocele is often present. Complications of epididymitis include infectious spread to the testis resulting in epididymo-orchitis, testicular abscess formation, and testicular infarction due to obstruction of venous flow which may result in testicular atrophy. Patients with chronic epididymitis often present with persistent pain. In these men, ultrasound examination reveals an enlarged epididymis with increased echogenicity and possible areas of calcifications (Fig. 6.33).

Torsion of the appendix testis is important to differentiate from torsion of the spermatic cord (testicular torsion), as this condition is self-limiting and does not threaten testicular viability. Clinically, the cremasteric reflex is preserved and a palpable nodule with bluish discoloration (blue dot) is often detected [46]. Ultrasound shows a hyperechoic mass with central hypoechoic area adjacent to the testis or epididymis. Other associated findings include scrotal wall edema and epididymal enlargement. Blood flow in the peritesticular structures may be increased. Doppler ultrasound is helpful as blood flow within the testis is normal in torsion of the appendix testis.

An epidydimal cyst is a nonpainful cystic structure that, when large, displaces the testis inferiorly. Cysts of the epididymis occur in up to 40 % of the men and contain lymphatic fluid. They are typically thin walled and well defined, usually with strong posterior acoustic enhancement and no internal echoes. These men will often have multiple cysts occurring present throughout the length of the epididymis.

Spermatoceles are benign cystic lesions, which contain spermatozoa, lymphocytes, and debris. Spermatoceles form as a result of efferent duct obstruction and usually located in the head of the epididymis. Ultrasonography cannot differentiate between epididymal cysts and spermatocele, but the spermatocele often has septations (Fig. 6.34).

Adenomatoid tumors are the most common tumors of the paratesticular tissues, accounting 30 % of these lesions and up to 77 % of the benign tumors arising from the epididymis. They are most commonly identified in men in their 20s to 40s. It has been suggested that they derive from vascular endothelium, the mesonephros, or müllerian epithelium, although most recent reports consider them to be mesothelial in origin [47]. They are round, firm, smooth, discrete masses measuring 0.5–5 cm in diameter that are usually asymptomatic and slow growing. Ultrasonography can confirm the extratesticular nature of these masses. Ultrasound of adenomatoid tumors reveals an isoechoic mass with increased vascularity (Fig. 6.35).

Papillary cystadenoma is a rare benign tumor of epithelial origin believed to arise from the efferent ductules of the head of the epididymis [48]. Papillary cystadenoma presents clinically as a firm, nontender palpable mass in the epididymis. Two-thirds of papillary cystadenomas occur in patients with von Hippel-Lindau (VHL) syndrome and are frequently bilateral [49]. Unilateral presentation is seen very rarely in sporadic cases. Sonographically, small papillary cystadenoma are usually solid and echogenic, but when large may appear vascular and cystic [49].

Leiomyomas are benign epididymal solid tumors. These lesions are most commonly seen in men over the age of 50. The ultrasound appearance is a well-defined solid mass with heterogeneous echotexture located in paratesticular space separate from the epididymis [50].

Malignant tumors arising from the epididymis are very rare, with the exact incidence of malignant tumors of the epididymis uncertain because of the small number of reported cases. Sarcoma of the epididymis comprises of more than half of the reported malignant neoplasms of the epididymis [51]. Fibrosarcoma of the epididymis has been reported in isolated case reports. Dowling et al. reported fibrosarcoma in a 60-year-old male confined to the epididymis on final pathology [52]. Leiomyosarcoma of the epididymis on ultrasound appears as a large hypoechoic mass (Fig. 6.36). Clear Cell carcinoma of the Epididymis is very rare and has been reported in individual case reports [53]. Ultrasound findings may include large cysts, necrosis, and invasive margins.

Patients who are diabetic or immunocompromised are more susceptible to infection and scrotal wall cellulitis or abscess. Ultrasonography demonstrates thickening of the subcutaneous tissue and heterogeneity with increased blood flow on color Doppler study. The scrotal wall abscess appears on ultrasound as a well-defined hypoechoic lesion within the scrotal wall and no Doppler flow within the lesion [5].

Fournier’s gangrene is a polymicrobial rapidly progressing necrotizing fasciitis commonly involves perineum and genital regions. Fournier’s gangrene is a urologic emergency with mortality up to 50 % [54, 55]. Computer tomography remains the imaging modality of choice [56]. However, ultrasonography can provide valuable clues at the time of initial presentation. Ultrasonography shows marked thickening of the scrotal skin with multiple hyperechogenic foci associated with shadowing, which are consistent with the presence of subcutaneous gas, pathognomonic of Fournier’s gangrene [57].

Ultrasound is often used to assess boys and adolescents with acute scrotal pain when the urologist is concerned for testicular torsion. Testicular torsion can be classified as extravaginal or intravaginal. The extravaginal form of torsion is found exclusively in newborn infants. Intravaginal torsion is more common and is due to a bell-and-clapper deformity in which the tunica vaginalis has an abnormally high insertion on the spermatic cord and completely encircles the testis, leaving the testis free to rotate within the tunica vaginalis. The deformity is bilateral in most cases. Intravaginal testicular torsion occurs most frequently in adolescent boys, with two-thirds of cases occurring between 12 and 18 years of age. Intravaginal torsion may occur in testes that are retractile or are not fully descended. Blunt trauma, sudden forceful rotation of the body, or sudden exertion also predispose to testicular torsion.

Ultrasound is very effective in differentiating testicular torsion from other causes of acute scrotal pain. The severity of torsion of the testis can range from 180° to 720°, but complete occlusion of blood flow is thought to occur after 450° of torsion [12]. Transient or intermittent torsion with spontaneous resolution sometimes occurs. Venous congestion or occlusion progresses to arterial occlusion, testicular ischemia, and infarction. The collateral blood flow is typically not adequate to provide viability to the testicle if the testicular artery is occluded. There is a 90 % chance of salvaging the testicle when ischemia has been present for less than 6 h, which decreases to 50 % at 12 h and 10 % at 24 h [67]. While irreversible testicular damage is presumed after 4 h of torsion, only 50 % of men who were detorsed less than 4 h after their symptoms began were noted to have normal semen quality [68].

On gray scale ultrasound, the affected testis usually appears hypoechoic (Fig. 6.38a) and Doppler color flow study shows decreased or no flow in the affected testis (Fig. 6.38b). Testicular size can vary from increased to decreased when compared to its counterpart depends upon the duration of the torsion. The sonographer should always compare the affected testis with the contralateral side using longitudinal, transverse, and coronal views. When the sonographer attempts to align the transducer parallel to flow, apical views can be particularly informative. In patients with acute torsion, the epididymis may appear hypoechoic and enlarged, similar to epididymitis. With testicular torsion ultrasound may also demonstrate that the spermatic cord immediately cranial to the testis and epididymis is twisted, which gives it a characteristic ‘torsion knot’ or ‘whirlpool appearance ’ (Fig. 6.39a, b).

Acute unilateral scrotal pain may be of a nonemergent etiology, due to epididymitis or torsion of a testicular or epididymal appendage. Waldert et al. retrospectively reviewed the charts of 298 boys who presented with an acute scrotum and underwent color Doppler ultrasonography followed by exploratory surgery, regardless of the sonographic findings. Twenty percent were diagnosed with testicular torsion, 56 % with torsion of an appendage, 8 % with epididymitis, and 11 % with no definite diagnosis. Color Doppler sonography sensitivity, specificity, positive predictive value, and negative predictive value for testicular torsion were 96.8 %, 97.9 %, 92.1 %, and 99.1 %, respectively. The two boys in this study misdiagnosed as epididymo-orchitis were both found to have 90° of torsion and no venous drainage but with residual arterial flow [69].

Despite the findings that color Doppler sonography has a high sensitivity and specificity, it is our feeling that torsion remains a clinical diagnosis proven only at surgery. Ultrasound should only be used to document findings. Many conditions including torsion–detorsion, intermittent torsion, persistent capsular flow, and color flow artifacts can suggest apparent flow in cases where none exists. Therefore, ultrasound does not diagnose or “rule out” torsion, only surgical exploration is indicated when the diagnosis of testicular torsion is suspected.

The ultrasound findings of patients with orchitis are often an enlarged testis with homogenous appearance. Orchitis may be diffuse or focal, with focal orchitis appearing as multiple hypoechoic lesions with increased testicular blood flow (Fig. 6.40a, b). Additionally, the RI of the epididymal and testicular artery has been shown to be significantly lower in patients with epididymo-orchitis than in control subjects [70]. If inflammation progresses, the pressure of intratesticular edema may compromise blood flow leading to infarction; the ultrasound will demonstrate absence of blood flow and surrounding reactive hyperemia [71].