Dilated Renal Pelvis and Ureter Anechoic

Fig. 11.16 Pyelectasis resulting from an ampullary renal pelvis. L = liver; N = kidney.

aEnlarged, anechoic pyelocaliceal system (P), scan from

amore lateral angle shows a nondilated, normal-appear- ing ureter (arrow).

Fig. 11.18 Renal pelvic stone (arrow, acoustic shadow S) with radial anechoic streaks representing the dilated calices and infundibula. Here the renal pelvis is only minimally dilated. These stones are often missed at ultrasound, as are stones at the ureteropelvic junction (see also Fig. 11.22). N = kidney.

b High transverse scan of the right kidney (N). Posterior to the artery is the ectatic renal pelvis (P) with no dilatation of the proximal ureter. VC = inferior vena cava.

Fig. 11.19

a Obstructive pyelectasis. N = kidney; P = pelvis.

Continuing urinary stasis lasting hours or days constitutes an acute stasis, whereas a chronic stasis continues for month or years. Urinary stasis can be total or partial.

When the obstructing stone is not located at the ureteropelvic junction, ultrasound shows the features of pyelocaliectasis and ureteral dilatation. Stones tend to become impacted at three sites of physiological narrowing (Fig.11.3,

Fig.11.5):

●The ureteropelvic junction

●The point where the ureter crosses the iliac vessels

●The ureterovesical junction

Generally the ureter is not visualized by ultrasound unless it is filled with fluid as the result of an obstruction. It then appears as an anechoic band that can be traced distally from the renal pelvis, in some cases as far as its insertion in the bladder floor (Fig.11.3). Usually the impacted stone can be detected and local-

ized. This is not possible with partial obstructions, but in these cases it may be possible (with effort) to locate a constant, hyperechoic stony structure that casts an acoustic shadow.

Urinary stasis is present when:

●there is an anechoic dilatation of the renal pelvis of more than 2(–4) cm, measured in a transverse scan direction

●the neck of the calix is enlarged to more than 4 mm, and

●the ureter is enlarged to more than 5 mm.

Stasis is also indicated by

●a unilateral decrease or absence of the ureteral jet phenomenon (3–4 per minute is normal), and

●an elevated resistance index (RI): in the interlobar arteries RI exceeds 0.7 in the case of complete obstruction.

Sensitivity for stone detection in ultrasound is up to 81%, in CT 92–96%. Clinical examination

ing the degree of renal pelvic distension by fluid, the integrity of the renal sinus echo complex, and the loss of renal parenchyma (11.1).

Chronic urinary stasis can have a variety of causes, most of which can be demonstrated with ultrasound. Once urinary stasis has been detected sonographically, the cause can often

a Echo-free separation of the central renal sinus echogenicity; preservation of sinus echoes; intact parenchyma (N). This patient had metastatic colon cancer and postoperative ureteral occlusion by a suture ( 11.2f). PY = pelvis; U = ureter.

b Conspicuous, echo-free pyelocaliectasis

(C) with diminished sinus echoes and incipient parenchymal thinning. Postoperative ureteral occlusion by a suture as above, 6 months later. N = kidney.

c Conspicuous, echo-free pyelocaliectasis (K, P); loss of renal sinus echogenicity; thinned parenchyma, dilated ureter (U). Patient had a metastatic ovarian tumor. N= kidney.

d Calices (K) and renal pelvis (P) are combined to form an echo-free hydronephrotic sac with little or no evidence of any residual parenchyma.

be discovered by starting with a posterolateral scan of the ureteropelvic junction and then moving the scan anterolaterally and inferomedially, using color Doppler as needed, until the dilated, anechoic ureter appears to terminate. This site marks the point of the obstruction.

A special form of urinary stasis due to outflow obstruction is hydronephrosis. It is identical to the grade IV hydronephrotic sac described above, but there are several special features in addition to chronic urinary stasis:

the condition is usually detected incidentally and is based on an unnoticed, often congenital, cause. Its significance lies in the fact that when it is bilateral (usually due to an infravesical cause), it can lead to end-stage renal failure, infection, and pyonephrosis (see below).

The various causes of chronic urinary stasis are listed in Table 11.1 and illustrated in11.2.

Fibrosis arising from the region of the L 4 and L 5 vertebrae, with the formation of collagenous connective tissue fibers up to 2 cm thick, can lead to the extensive fibrous encasement of retroperitoneal structures including the psoas muscle, aorta, and vena cava along with the iliac vessels, mesentery, and ureters.

On ultrasound, the ureters are visibly ensheathed and obstructed, leading to chronic urinary stasis. In contrast to other occlusive diseases, a localized obstruction cannot be found. Instead there is a long, rigid, dilated ureteral segment with none of the tortuosity that is usually seen in association with chronic urinary stasis. The fibrosis itself is slightly echogenic and is poorly delineated from other retroperitoneal structures. The detection of fibrotic encasement on other retroperitoneal organs supports the ultrasound impression of fibrosis-induced urinary stasis.

Retroperitoneal fibrosis involving the ureters also occurs in inflammatory disorders

Reflux

Vesicoureteral and vesicorenal reflux also lead to dilatation of the ureter and renal pelvis. A distinction is drawn between primary congenital forms of reflux and secondary acquired forms.

Primary forms. Primary forms of reflux (ureterovesical junction obstruction, i. e., refluxing megaureter) are based on developmental abnormalities of the terminal ureter. These may consist of abnormal orifices, ectopic insertions, or an abnormal course of the ureter in the bladder wall. The results are partial or complete dilatation of the ureter and renal pelvis, with risk for developing progressive renal failure. Besides showing initial suggestive signs, ultrasound can furnish information on the degree of urinary obstruction. The detection of reflux is the domain of the excretory urogram and voiding cystogram. Although color Doppler can demonstrate the presence of a ureteral jet, Doppler ultrasound has not yet established itself as a standard study.5