It is a common diagnosis, mostly related to gram-negative enteric bacteria [10]. Urinalysis and urine culture are usually sufficient to confirm the diagnosis. Imaging is only necessary in the patients who do not demonstrate clinical improvement within 72 h of initiating antibiotic therapy. The purpose of imaging is to assess for an obstructing stone and rule out complications (such as abscess). US findings are usually normal in the setting of pyelonephritis; therefore, it is useful to exclude obstruction as a cause for the infection. US can be used to look for dilatation of the pelvicalyceal system, but, when present, echogenic mass is the most reliable sign of pyonephritis [11] (Fig. 58.3). In the case of renal abscess, US is able to show a hypoechoic mass that lacks internal flow on color Doppler flow images (Fig. 58.4). Less common findings are focal hypoechoic region with decreased vascular flow, renal enlargement, and loss of the sinus fat and/or corticomedullary differentiation [12]. Xanthogranulomatous pyelonephritis is a chronic destructive granulomatous process that is believed to result from an atypical, incomplete immune response to subacute bacterial infection. US typically demonstrates an enlarged kidney, with a large amorphous central echogenicity that corresponds to a renal pelvis staghorn calculus. The calculus is generally associated with acoustic shadowing. A loss of normal renal architecture is seen in most cases, but, because the disease is usually diffuse, a discrete inflammatory mass is uncommon. Although the US findings in diffuse xanthogranulomatous pyelonephritis are characteristic, US is usually followed by CT for definitive assessment [13].

The major and proper concern in the investigation of hematuria is the detection of bladder cancer. Other causes are renal stones, pyelonephritis, urinary tract and prostate cancer, and prostate hyperplasia. Anticoagulants could also be a cause for hematuria, although they should never be accepted as the cause without the exclusion of a urinary tract or prostate cancer [14]. US is mandatory in the clinical evaluation of hematuria to detect eventually bladder tumors because it is easy to perform and safe for the patient. At US, most tumors appear as non-mobile, papillary, hypoechoic masses or as an area of focal wall thickening (Fig. 58.5). Doppler imaging demonstrates flow within the mass, aiding differentiation between tumor and blood clot. Also moving the patient on his flank allows the differentiation with the clots. Transabdominal ultrasound cannot, however, provide useful information regarding tumor staging and depth invasion. CEUS is not usually present in the assessment of bladder cancer. Moreover, it can be useful to identify a bladder mass when the bladder is full of clots. Recently, three-dimensional US and CEUS have been proposed for the detection of bladder cancer. The ability of three-dimensional US has been demonstrated by several studies, but nowadays it remains not applied in the clinical practice [15].

Grayscale US together with color Doppler is the imaging modality of choice for evaluating patients who present with acute scrotal pain. Disease processes are mainly related to testicular torsion and epididymo-orchitis and less frequently may be due to intratesticular tumors with hemorrhagic complication. All these pathologies have the same symptom of pain at presentation, and US-CD evaluation helps in differentiating patients who require surgical from patients for whom can managed conservatively.

Acute epididymo-orchitis or epididymitis is the most common cause of acute scrotum in adolescent boys and adults. Epididymitis first affects the tail of the epididymis and then spreads to involve the body and head of the epididymis. Orchitis develops in 20–40 % of cases of epididymo-orchitis by direct spread of infection. At US, the epididymis is enlarged and hypoechoic; sometimes it can appear hyperechoic if hemorrhage is present [16]. Secondary signs are reactive hydrocele or pyocele and scrotal wall thickening. In the case of testicular involvement, US shows the enlargement and inhomogeneous testicular parenchyma. At CD examination, the epididymis and testis show clearly increased colored signals: this is the most important criterion for the diagnosis of epididymo-orchitis (Videos 58.1 and 58.2) [17]. Sometimes, it may be difficult to differentiate focal areas of heterogeneity from neoplastic lesions. In this case, the use of CEUS is able to achieve the differential diagnosis [18].

Torsion of the testis is the most important urological nontraumatic emergency. The ability to differentiate torsion from other causes of acute scrotal pain like epididymo-orchitis is crucial. Apart from clinical history and physical examination, US can usually suggest the proper diagnosis addressing the correct management of the patients. US findings depend on the duration of torsion and the degree of twisting of the spermatic cord. In the period immediately following torsion, the testes may appear normal on grayscale images. After 4–6 h, the testis becomes swollen, enlarged, and diffusely hypoechoic. Necrosis, vascular congestion, and hemorrhage occur after 24 h, producing a heterogeneous echotexture within the testes [19]. In the same time, the testis appears completely avascular. The absence of testicular flow at color and power Doppler is considered diagnostic of ischemia (Videos 58.3 and 58.4). For obtaining the correct diagnosis, the scanner must be optimized for detection of slow flow, using the contralateral testis adjusting the color gain for the lowest repetition frequency and the lowest possible threshold setting. According to Baker et al., color Doppler has a sensitivity of 88.9 % and specificity of 98.8 % [20]. In the setting of testicular torsion, normal testicular echogenicity is a strong predictor of testicular viability [21]. Another sign is the twisting of the spermatic cord. In the torsion of the testis, spermatic cord is twisted, changing in size and shape, and appears as a round or oval homogeneous extratesticular mass with or without blood flow.