Imaging Urolithiasis and Their Complications

Fig. 19.1

US of a typical lithiasis. Sagittal scan of the left kidney demonstrating a hyperechoic lithiasis in the lower calices with acoustic shadowing (arrow). The pyelocaliceal system is dilated due to the migration of another lithiasis

Fig. 19.2

US of a lithiasis without acoustic shadowing and the twinkle sign. (a) Sagittal scan of the kidney; there is a hyperechoic focus without shadowing (arrow). (b) Sagittal scan applying the color Doppler, the typical artifact is obvious

US is able to demonstrate dilatation of the urinary tract secondary to obstruction (Fig. 19.1). The technique is highly accurate in demonstrating pyelo-ureteral junction obstructive stones or lithiasis obstructing the uretero-vesical junction (with a sufficiently full bladder) (Fig. 19.3). One should not hesitate to examine the patient both supine and prone in order to increase the detection of renal stones. In case of acute obstruction, the renal parenchyma may appear hyperechoic and swollen and on duplex Doppler analysis, the resistive index may rise close to 1. US may also demonstrate perirenal fluid indicating fornix rupture. Intrarenal staghorn calculus may be underdiagnosed in the absence of calyceal dilatation as they may appear linear with little acoustic shadowing (Fig. 19.4a). Lithiasis within the lumbar ureter may also be harder to demonstrate. Combining an abdominal radiograph (Fig. 19.4b) and US increases the sensitivity for detecting the stone. Lithiasis within the bladder is usually large and causes acoustic shadowing (Fig. 19.5); it should not be overlooked due to an empty bladder or due to the shadowing. Overall the sensitivity of US for detecting urolithiasis is estimated around 75% and its specificity around 100% compared to 95% and 98%, respectively, for CT.

Fig. 19.3

Lithiasis at the UV junction. Case of a 10-year-old boy under chemotherapy for Hodgkin disease. US of the right UV junction demonstrating the lithiasis (between the crosses) B Bladder

Fig. 19.4

Staghorn lithiasis—case of congenital cystinuria. (a) Sagittal scan of the left kidney. The staghorn urolithiasis appears as a long thick line with limited shadowing (arrows). (b) Plain radiograph of the abdomen demonstrating the calcified staghorn urolithiasis

Fig. 19.5

Vesical lithiasis—case of 5-year-old disabled girl. (a) US demonstrating a large intravesical lithiasis (between the crosses) with acoustic shadowing. (b) Plain radiograph confirms the presence of a calcified lithiasis

Another important role for US will be to demonstrate an underlying metabolic disease. For this purpose, the liver should be examined as metabolic diseases may affect both the kidneys and the liver (e.g., tyrosinemia). In the kidneys, a metabolic disease should be suggested in case of recurrent (multiple) lithiasis or in case of nephrocalcinosis (Fig. 19.6) (see below). The latter is defined as calcium deposits within the renal medulla, cortex or both. In typical cases, the nephrocalcinosis will be located within the pyramids (Fig. 19.6) and induce a reversed cortico-medullary differentiation (hyperechoic medulla). In less typical cases, the nephrocalcinosis will be more subtle. Less usually, it will be diffused to both the renal cortex and medulla (e.g., oxalosis—see below) [5–8].

Fig. 19.6

Idiopathic hypercalciuria in a 3-year-old boy. (a) Dilatation of right kidney due to urolithiasis with hyperechoic medulla. (b) Left kidney with typical appearance of nephrocalcinosis due to the hypercalciuria

The use of US will also be important for the follow-up of any treatment (see below).

19.2.2 Conventional Radiology (KUB: Intravenous Urography) [7]

19.2.2.1 Kidney-Ureter-Bladder (Plain Radiograph of the Abdomen)

The KUB film can reveal radio-opaque stones (>90% of lithiasis in children) (Figs. 19.4b and 19.5b). Its specificity is 69%, its sensitivity is 82%. Calculi containing uric acid, cysteine, xanthine, or indinavir tend to be radiolucent. Another interest of KUB would be the visibility of some parts of the skeleton; the detection of some specific skeletal anomalies (signs of secondary hyperparathyroidism, osteoporosis, etc.) would orient towards metabolic diseases.

19.2.2.2 Intravenous Urography (IVU)

The use of IVU has greatly diminished. Nowadays, IVU will be used when a CT scan is not available and before therapeutic planning like lithotripsy in order to precisely localize the lithiasis especially in case of low density, poorly opaque stones. For this purpose, only a few films (1, 2, or) are sufficient at 10 or 15′ post injection of contrast. IVU is contraindicated in acute ureteral obstruction (risk of fornix rupture) and in case of renal failure.

19.2.3 CT

Nonenhanced CT (NE-CT) is the method with the highest sensitivity (91–100%) and specificity (91–100%) for the demonstration of urolithiasis. Density measurements of the lithiasis facilitate estimation of stone composition. The disadvantage of the method is the radiation burden (2.8–5.0 mSv) much higher than with a plain film of the abdomen. The use of CT scan has expanded during the last years especially in emergency departments and therefore one of the main issues will be to reduce this irradiation either by reducing the number of CTs or by optimizing the settings used for the examination. CT seems helpful in case of multiple locations or urolithiasis blocked in the lumbar segment of the ureter (Fig. 19.7a, b). Noteworthy, the couple “US + plain film of the abdomen” have somewhat lower success but usually provide sufficient information in comparison to NECT.

Fig. 19.7

Multiple left urolithiasis with obstructing left ureter lithiasis—Unenhanced CT work-up. (a) Axial view of the kidneys. The left pyelocaliceal system appears dilated with two lithiases in the dependent calices. (b) Axial view of the lower abdomen a large lithiasis is obvious

As mentioned, whenever a CT is performed, the settings should be optimized in order to maximize diagnostic sensitivity and minimize the dose by increasing the pitch and decreasing mA. The latter should be decreased around 80–100 mA. Even at such low mA, the sensitivity of CT for detecting urolithiasis is as high as 96% and its specificity around 95%. The mA settings should not be reduced further as the diagnostic accuracy might be decreased. Iterative reconstruction techniques should be favored since they produce images of similar diagnosis yield at lower doses. Further technical improvements will help to reduce the doses. To be noted, the use of dual energy CT improves the characterization of urolithiasis. The higher the Hounsfield units score on CT, the less likely the success of extracorporeal shock wave lithotripsy [6–10].

19.3 Urolithiasis and UTI [1, 2]

Urinary tract infections (UTI) are associated with an increased risk of developing urolithiasis especially when the UTI is due to Proteus, Klebsiella, pseudomonas, and enterococcus. These microorganisms induce a biochemical cascade that creates conditions to struvite stone formation. Struvite stones start small but may grow as staghorn calculi filling the entire pelvicalyceal system.

On imaging, the stone may be isolated without dilatation (Fig. 19.8). Still, more commonly, the infected urine (pyonephrosis) mixed with sludge and stones will provoke obstruction and dilatation of the urinary tract leading to acute symptoms [5].

Fig. 19.8

Obstructing urolithiasis with APN. Sagittal scan of the left kidney (between the crosses); there are multiple lithiasis within the renal hilum; the renal parenchyma appears swollen and without CMD

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