Hypoechoic

Urinary Tract

Malformations

Dilated Renal Pelvis and Ureter Anechoic

Hypoechoic

Renal Pelvic Mass, Ureteral Mass Changes in Bladder Size or Shape Intracavitary Mass

Wall Changes

Hemorrhage (Traumatic, Clot)

Infected Obstruction

Suppurative Pyelitis

Pyonephrosis

If a patient with renal stone colic becomes febrile, an infected obstruction should be suspected. Urinalysis will show signs of a urinary tract infection. Not every infected obstruction is preceded by stone colic, but an obstructive, septic urinary tract infection should be considered in patients who present with unexplained fever. This is especially likely in older patients with impaired host resistance and in patients with poorly controlled diabetes.

Ultrasound often shows only a hypoechoic or largely anechoic dilatation of the pyelocaliceal system. A stone is frequently but not always detectable. If the obstruction can be visualized, it may appear as a hyperechoic mass in the renal pelvis (staghorn calculus), in the ureter (ureteral stone), or at the vesical or infravesical level (tumor, reflux, or prostatic hyperplasia, which is bilateral). For this reason, the sonographic investigation of fever should always include a detailed inspection of the kidneys, ureters, and bladder (Figs. 11.31, 11.32, 11.33).

Fig. 11.31 Infected obstruction in association with a prevesical stone; septic temperatures.

a Grade I urinary stasis. The renal pelvis (P) and ureter (U) are not entirely anechoic. N = kidney.

Even if a stone is not detected and there is no ureteral dilatation, the mere suspicion of an infected obstruction warrants intervention in order to prevent urosepsis.

b Prevesical obstructing stone (arrow, acoustic shadow S). HB = bladder.

b Radiograph: ureteropelvic junction obstruction?, probably due to an aberrant vessel.

struction or a dilated renal pelvis with internal echoes to circumscribed round, oval, or bandlike hypoechoic or anechoic masses. Inflammatory swelling (to > 2 mm) of the renal pelvic walls, which appear as smooth, thin, hypoechoic bands, is virtually pathognomonic of this condition ( 11.3, Fig.11.1).

Urinary Tract

Malformations

Dilated Renal Pelvis and Ureter Renal Pelvic Mass, Ureteral Mass

Hypoechoic

Hyperechoic

Changes in Bladder Size or Shape Intracavitary Mass

Wall Changes

Urothelial Carcinoma

Ureteral Clots

Classification. The majority of urinary tract tumors are urothelial carcinomas. They arise as malignant tumors from the transitional epithelium (urothelium) and therefore occur in the renal pelvis, ureter, and bladder. The following tumor types are named in the 2004 WHO classification of renal pelvic tumors:8

Urothelial tumors

●Infiltrating urothelial carcinoma

●Non-invasive urothelial neoplasias (carcinoma in situ, high grade, low grade)

–Non-invasive papillary urothelial neoplasm of low malignant potential

–Urothelial papilloma

Squamous neoplasms

Glandular neoplasms

●Adenocarcinoma

●Villous adenoma

Neuroendocrine tumors Melanocytic tumors Mesenchymal tumors

Hematopoietic and lymphoid tumors Miscellaneous tumors

Actual urothelial carcinomas—transitional cell carcinomas—are less common than renal cell carcinomas. They occur grossly in papillary or solid forms.

Ultrasound. The ultrasound appearance varies with tumor location. Tumors in the renal pelvis usually assume the shape of the pyelocaliceal system and may extend into the upper ureter as well as the renal parenchyma. They are somewhat more reflective than the renal parenchyma, but they may also be less echogenic.

A long-standing tumor may contain foci of liquefaction, giving it a cystic or abscess-like appearance.

A hemorrhagic cyst should be excluded, because a tumor may also be stemmed and mobile. Their high vascularization also helps in differentiating a tumor from sinus lipomatosis or an abscess.

The differential diagnosis includes metastases, and extension of renal cell carcinoma into the renal pelvis. Tuberculosis involves exclusively the ureter and is nonifiltrating (Figs. 11.34, 11.35, 11.36, 11.37; 11.2 d, see also Chapter 9, p. 354).

Urothelial carcinoma in the ureter appears as a hypoechoic mass with associated obstruction to urine outflow ( 11.2 d).

Ureteral clots appear as hypoechoic or heterogeneous tumor-like masses in the ureters with associated obstruction to urine outflow. They may occur in the setting of a generalized hemorrhagic diathesis, after surgical procedures, or in association with a renal tumor or urolithiasis. They are difficult or impossible to distinguish from primary tumors by ultrasound. The correct diagnosis is usually made from the history, the clinical course, or endoscopic inspection (Fig.11.38).

Fig. 11.38 Ureteral clot, caused by renal cell carcinoma bleeding into the ureter. Patient presented clinically with renal colic. Hypoechoic mass in the prevesical ureter (U). Arrows = echogenic ureteral ridge; HB = urinary bladder; SB = seminal vesicles.

Hyperechoic

Caliceal Stones

Renal Pelvic Stone

Staghorn Calculus

Ureteral Stone

require a relatively static precipitation medium in order to grow, they tend to form at sites where a high salt concentration is combined with fluid stasis and a favorable pH. Stones therefore most commonly form in the renal pelvis and bladder.

Sonographic criteria. Regardless of the stone composition—urate or cystine/xanthine stones, calcium oxalate/calcium phosphate stones, or infection stones (struvite/carbonate apatite)

—ultrasound shows an intensely echogenic focus with distal acoustic shadowing. Because a stone surface echo is very difficult to discern within the high-level echoes of the renal sinus

Caliceal Stones

A renal caliceal stone is characterized by a stone echo with an acoustic shadow and by caliectasis, which occurs proximal to the site of the stone. Concomitant ectasia of the caliceal neck suggests a calculus located distal to the infundibulum, whereas a caliceal stone echo

not associated with caliectasis is difficult or impossible to distinguish from papillary calcification. The history and clinical presentation in these cases will suggest the correct diagnosis (Figs. 11.39, 11.40, 11.41).

Fig. 11.44 a and b Partial staghorn calculus.

a High-amplitude echo, shadowing, in the lower pole of the left kidney: supported nonobstructive stone.

Fig. 11.45 Staghorn calculus: multiple high-level stone echoes with acoustic shadows (S) throughout the pyelocaliceal system. Depending on the scan plane, ultrasound may demonstrate multiple isolated stone echoes as shown here or a broad linear echo (Fig. 11.46). N = kidney.

The differential diagnosis of hyperechoic masses in the renal sinus echo complex is reviewed in Table 11.2.