AUTHOR AND EDITOR INFORMATION

Section 1 of 11  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT SCAN
• Mri
• Ultrasound
• Nuclear Medicine
• Intervention
• Multimedia
• References

INTRODUCTION

Section 2 of 11  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT SCAN
• Mri
• Ultrasound
• Nuclear Medicine
• Intervention
• Multimedia
• References

Background

Passage of a urinary stone is the most common cause of acute ureteral obstruction and affects as many as 12% of the population. The pain may be some of the most severe pain that humans experience, and complications of stone disease may result in severe infection; renal failure; or, in rare cases, death.

Pathophysiology

In patients with stone disease, more than 1 of 3 general mechanisms is likely to be active. These include the following: (1) the possible presence or abundance of substances that promote crystal and stone formation; (2) a possible relative lack of substances to inhibit crystal formation; and (3) a possible excessive excretion or concentration of salts in the urine, which leads to supersaturation of the crystallizing salt. The greater the degree of supersaturation, the greater the rate of growth of the calculi.

Stasis or anatomic factors can also contribute to the development of stone disease. These include ureteropelvic junction (UPJ) obstruction, horseshoe or ectopic kidney, autosomal dominant polycystic kidney disease, and vesicoureteral reflux. Calyceal diverticula, the result of anomalous budding of the calyceal system, is also associated with stone disease. In 10-40% of calyceal diverticula, stones are present. These range from a few large calculi to many tiny seed calculi and to the microscopic "milk of calcium."

Medullary sponge kidney is another common anatomic cause of renal calculi. The pathologic process in medullary sponge kidney is renal tubular ectasia. Calculi form in approximately 50% of patients. The calcifications form in the medulla but frequently pass into the collecting system. They are usually bilateral and diffuse, but they may also be unilateral or segmental. On intravenous urography (IVU), pyramidal clusters of calculi within the dilated tubules classically become obscured or appear enlarged after contrast material surrounds them in the dilated tubules.

Calcium stones account for 75-85% of urinary stones. Approximately one half of calcium stones are composed of a mixture of calcium oxalate and calcium phosphate. They demonstrate intermediate fragility to extracorporeal shock wave lithotripsy (ESWL). Approximately three eighths of calcium stones are formed of only calcium oxalate dihydrate. These may be spiculated, dotted, mulberry, or jackstone in appearance. Usually, these stones are fragile in response to ESWL. The remaining one eighth of stones are composed of calcium phosphate (apatite) or calcium monohydrate. These stones are the densest and, consequently, the least responsive to ESWL.

Calcium stones have numerous causes. Approximately 85% of calcium stones are idiopathic, or primary. Idiopathic hypercalciuria occurs in more than one half of patients with calcium oxalate stones. Most causes of hypercalciuria are absorptive. Increased absorption in individuals after a normal diet causes an elevation of serum calcium levels and a suppression of parathyroid function as an abnormal response to vitamin D. Approximately 10% of cases of primary hypercalciuria are renal in origin. The inability of the kidney to conserve calcium results in low serum calcium concentrations, which stimulate parathormone secretion.

The remaining 15% of calcium stones are secondary to some discernible etiology. Most commonly, they result from hyperparathyroidism, which is found in 5-10% of patients with stones. In this situation, hypercalcemia and increased absorption lead to hypercalciuria. Patients with the stones are treated with surgical removal of the parathyroid adenoma or hyperplasia. Calcium stones can also occur in approximately 15% of patients with sarcoidosis in whom the production of activated vitamin D by macrophages is abnormal.

Renal tubular acidosis (RTA) is an additional fairly common secondary cause of calcium stones. In type I (distal) RTA, kidneys have a decreased ability to lower urine pH levels, which may be primary or secondary to a variety of renal injuries. The injured distal tubule loses the ability to maintain the hydrogen-ion gradient. This, in turn, causes alkaline urine, hypercalciuria, and hyperphosphaturia. Nephrocalcinosis or urolithiasis is seen in as many as 70% of patients with type I RTA. Conversely, type II (proximal) RTA is associated with increased bicarbonate loss, which helps keep stones from forming. Type IV RTA commonly is seen in medical renal disease and does not predispose patients to stone formation.

Immobilization of an individual causes rapid mobilization of the calcium in bones, and this is an important mechanism in patients with spinal cord injury, who may develop stones within weeks to months of immobilization. Hyperoxaluria is another, less common, secondary cause of calcium stone formation and most often results from inflammatory bowel disease, bowel surgery, vitamin C overdose, or renal failure. Primary hyperoxaluria is a rare autosomal recessive disease. Other secondary causes include milk-alkali syndrome, use of steroids, Cushing syndrome, hypervitaminosis D, paraneoplastic phenomenon, and multiple myeloma.

Magnesium ammonium phosphate (struvite) stones account for approximately 10-20% of urinary stones. These stones are lucent but complex with calcium phosphate. On occasion, they enlarge and branch (staghorn). Although they fragment easily, patients with these stones usually are treated with percutaneous fragmentation and extraction because of the large size of the stones and, usually, the presence of infection. Struvite stones are caused by urea-splitting bacteria such as Proteus, Klebsiella, and Pseudomonas species. However, as many as one half of patients have an underlying metabolic cause for stone disease; therefore, metabolic evaluation is indicated. Combined obstruction and infection frequently cause renal destruction and, potentially, renal failure if both kidneys are affected.

Uric acid stones account for 5-10% of urinary stones. These small smooth stones usually appear radiolucent on conventional radiographs but opaque on CT scans. Predisposing factors include acidic concentrated urine, excess urinary uric acid, small-bowel disease or resection, gout, and cell lysis (eg, resulting from treatment of leukemia or from starvation). Treatment and prevention for these stones is alkalinization and dilution of the urine.

Cystine stones account for only approximately 1% of urinary stones. These ground-glass stones, which result from cystinuria (a rare autosomal recessive metabolic disorder), are homogeneous; less opaque; and less fragile than other stones, especially if they are smooth.

Several other less common forms of urolithiasis may produce stones that appear relatively lucent, even on CT scans. Inspissation of indinavir, an antiretroviral protease inhibitor used to treat HIV infection, may cause stones that appear lucent on CT scans. Matrix stones formed from inspissated mucoproteins in patients with a chronic Proteus infection may demonstrate soft tissue attenuation on CT scans. Stones can also be caused by metabolic byproducts and drugs (eg, sulfa drugs, salicylates, triamterene ephedrine).

Frequency

United States

Renal calculi occur in 5-12% of the American population, and they are bilateral in 10-15% of patients. The prevalence of urinary lithiasis is as high as 2-3% in the general population.

International

A slightly lower prevalence of urinary stones is found in less developed countries, possibly because of diets lower in protein.

Mortality/Morbidity

• Passage of a renal stone is the most common cause of acute ureteral obstruction. When this occurs, pressure in the collecting system and renal blood flow acutely increase, followed by decreased blood flow after 1-2 hours. Hematuria usually occurs. This can be intermittent or persistent and microscopic or gross. However, as many as 10% of patients with acute stones may not have hematuria.
• Acute ureteral obstruction by stone causes severe, colicky (intermittent) flank pain that can radiate throughout the groin, testicles, back, or periumbilical region. Some patients with renal calculi may have no symptoms at all. Stones smaller than 4 mm pass spontaneously in approximately 80% of patients. Stones that are 4-6 mm pass in approximately 50% of patients, whereas stones larger than 8 mm pass in only approximately 20% of patients.
• Occasionally, recurrent infection may result in pyelonephritis or abscess. Stones can cause renal scarring, damage, or even renal failure if they are bilateral. In 10% of patients, stones recur within 1 year. This percentage increases to 50% within 10 years.

Race

Urinary stones occur more often in white populations than in black populations. They are also more prevalent in highly developed countries, possibly as a result of a higher protein diet.

Sex

Males are at a greater risk than females, with a male-to-female ratio of 3:1 (except for struvite stones and in black populations).

Age

Stones are uncommon but not unknown in children. The peak age for development is in persons aged 40-60 years.

Clinical Details

Acute ureteral obstruction by stone causes severe colicky (intermittent) flank pain that can radiate throughout the groin, testicles, back, and periumbilical region. Some patients with renal calculi may have no symptoms at all.

Hematuria usually occurs. It can be intermittent or persistent and microscopic or gross. However, as many as 10% of patients with acute stones may not have hematuria.

Occasionally, recurrent infection may result in pyelonephritis or abscess. Stones can result in renal scarring, damage, and renal failure.

Preferred Examination

The goals of imaging are to determine the presence of stones within the urinary tract, evaluate for complications, estimate the likelihood of stone passage, confirm stone passage, assess the stone burden, and evaluate disease activity.

When acute flank pain suggests the passage of a urinary stone, many methods of examination can be used. Often, conventional radiography is initially used to screen for stones, bowel abnormalities, or free intra-abdominal air. Radiographs can also be used to monitor the passage of visible stones.

IVU (excretory urography) provides important physiologic information regarding the degree of obstruction. Ultrasonography (US) is useful in young or pregnant patients and in patients allergic to iodinated contrast material. US is also helpful in problem solving.

All of these methods have become less useful with the advent of more sensitive and specific nonenhanced CT scanning. When CT is available, it is now considered the examination of choice for the detection and localization of urinary stones. Almost all studies conducted to date show that IVU provides no additional clinically important information after nonenhanced CT is performed. As a result of the higher radiation dose of CT, conventional or digital radiography should be used to monitor the passage of stones if radiographic follow-up studies are indicated and if the stone is visible on conventional radiographs.

Limitations of Techniques

Because of the higher radiation dose with CT, conventional or digital radiography should be used to monitor the passage of stones if radiographic follow-up is believed to be indicated and if the stone is visible on conventional radiographs. Pregnant or pediatric patients may be imaged with US first to avoid radiation exposure. The rare false-negative finding is usually due to reader error or a protease-inhibitor CT-lucent stone. False-positive results are usually due to phleboliths adjacent to the ureter. In some cases, intravenous contrast material may be needed to opacify the ureter.

US has limited sensitivity for smaller stones, and does not depict the ureters well. It should be used mainly in patients who are young, those who are pregnant, or those undergoing multiple examinations (eg, patients with spine injury).

IVU is the traditional examination for the assessment of urinary stone disease, and it does provide physiologic information related to the degree of obstruction. The radiation dose is generally smaller than that of CT, but it is of the same order of magnitude. Intravenous contrast is required, with resultant risks of an allergic reaction or nephrotoxicity. IVU is less sensitive than CT, especially for small or nonobstructing stones.

DIFFERENTIALS

Section 3 of 11  

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• Introduction
• Differentials
• Radiograph
• CT SCAN
• Mri
• Ultrasound
• Nuclear Medicine
• Intervention
• Multimedia
• References

Other Problems to be Considered

Blood clot
Fungus ball
Calcifications in tumors such as renal cell carcinoma
Complicated renal cysts
Infection
Abscess
Infarcts
Hematoma
Malakoplakia
Atherosclerotic calcification
Biliary colic
Ulcer disease
Diverticulitis

RADIOGRAPH

Section 4 of 11  

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Findings

Conventional radiography

Conventional radiography is often performed as a preliminary examination in patients with abdominal pain possibly resulting from urinary calculi. These images should be obtained before contrast material is administered to prevent obscuring calcifications within the collecting system or calyceal diverticula. Conventional radiographs should include the entire urinary tract, and, often, 2 images are required.

• Stones are often found at key points of narrowing such as the UPJ, the ureterovesical junction (UVJ), and the point at which the ureter crossing the iliac vessels. An addition site is on the right side where the ureter passes through the root of the mesentery.
• Calcium stones as small as 1-2 mm can be seen. Cystine stones as small as 3-4 mm may be depicted, but uric acid stones are usually not seen unless they have become calcified.
• An erect or posterior oblique radiograph obtained on the side of the calcification may help in distinguishing urinary stones from extraurinary calcifications. This view can also depict calcifications that are projected over the sacrum or transverse processes on the frontal view.
• Preinjection renal tomography may depict additional stones, and it can be used to confirm the relationship of stones to the kidneys.
• Because stones are more visible with a lower peak kilovoltage (kVp), maintaining a maximum of 60-80 kVp is best, if possible. Larger patients may require a higher peak kilovoltage for acceptable exposure and scatter. In this situation, compression of the abdomen and collimation is critical.
• Mild bowel preparation may be helpful for increasing the sensitivity of conventional radiography for small stones in patients undergoing screening or follow-up observation for stones.
• Typically, phleboliths are round or oval, and they may demonstrate a central lucency. However, they are often difficult to distinguish from ureteral calculi. Phleboliths in the pelvis are usually located lower than and lateral to the ureter, but they overlap with the ureter. Because gonadal veins parallel the upper ureters, contrast enhancement may be needed to opacify the ureter and demonstrate the extraurinary location of phleboliths in the gonadal veins.

Intravenous urography

IVU is useful for confirming the exact location of a stone within the urinary tract. IVU depicts anatomic abnormalities such as dilated calyces, calyceal diverticula, duplication, UPJ obstruction, retrocaval ureter, and others that may predispose patients to stone formation or alter therapy. Because contrast agents can obscure stones in the collecting system, scouting the entire urinary tract prior to their administration is critical.

When an acute urinary stone is the primary consideration, compression may not be used to increase sensitivity for detection of low-grade obstruction. A caveat is that the contralateral kidney may have an abnormality that requires ureteric compression for adequate examination. In rare cases, the use of compression has been associated with forniceal rupture.

When a stone causes acute obstruction, an obstructive nephrogram may be present. This may be prolonged and hyperopaque, with increasing opacity over time. The nephrogram of acute obstruction is usually homogeneous, but may also be striated or occasionally not visible on radiographs.

Other signs include delayed excretion, dilatation to the point of obstruction, or blunting of the calyceal fornices. Immediately after the passage of a stone, residual mild obstruction or edema can be detected at the UVJ. Delayed images may be needed to opacify to the point of the obstruction, but using gravity to position the more opaque and more distal contrast material–laden-urine is also possible by placing the patient in a prone or erect position.

Extravasation of urine at the fornices may result in pyelosinus or pyelolymphatic extravasation, which is often first indicated by blurring of the calyceal fornices. Greater extravasation may outline the collecting system, and the contrast may dissect into the perinephric space; however, if the urine is not infected, this is usually clinically insignificant.

Degree of Confidence

Although 90% of urinary calculi are opaque on abdominal radiographs, the sensitivity for the prospective identification of individual stones is only 50-60%, and the specificity is only approximately 70%. Approximately 10% of stones are radiolucent on conventional radiographs.

False Positives/Negatives

Occasionally, false-positive findings result from extrarenal calcification, but these are usually correctly identified with IVU. Lucent stones appear as filling defects on IVU, but they are not distinguished from non–stone-filling defects such as transitional cell carcinomas or blood clots. US and CT are effective tools in making this distinction; however, much of the ureter cannot be visualized with US.

CT SCAN

Section 5 of 11  

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• CT SCAN
• Mri
• Ultrasound
• Nuclear Medicine
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• References

Findings

With a sensitivity of 94-97% and a specificity of 96-100%, helical CT is the most sensitive radiologic examination for the detection, localization, and characterization of urinary calcifications; therefore, helical CT is considerably more effective than IVU. Helical CT scans frequently depict non-obstructing stones that are missed on IVU. CT is faster and no contrast agent is needed in most patients. CT easily differentiates between non-opaque stones and blood clots or tumors (compared with IVU, which may depict only a filling defect). In addition, helical CT is better than US or IVU in detecting other causes of abdominal pain. In fact, in most studies, IVU added little or no information.

Rarely, pure matrix stones may demonstrate soft-tissue opacity on CT scans, and indinavir stones appear lucent. However, all other stones appear opaque on CT scans.

Technique

Because stones in the collecting system may be obscured by contrast material, nonenhanced CT is usually performed. Helical CT is important to avoid missing stones because of section misregistration. A 5-mm helical technique with a pitch of 1.5:1 or less is preferred, although some radiologists choose to use a pitch of as much as 2:1. The kidneys and, if possible, the entire abdomen should be scanned during a single breath hold to prevent section misregistration.

Because patients with stones are often young and because stone disease may recur, minimizing the radiation dose is critical. A fairly high level of noise as a result of the inherently high contrast levels is tolerable in most patients. Reported radiation doses for CT are 2.8-4.5 mSv compared with 1.3-1.5 mSv for a 3-image IVU. However, the uterine dose is approximately 0.006 Gy for 4-image IVU compared with 0.0046 Gy for nonenhanced CT.

At the authors' institution, approximately 12% (10-20%) of patients who undergo nonenhanced CT for possible urinary stones receive intravenous contrast material for further evaluation. To discern between phleboliths and urinary stones, 50 mL of low-osmolar contrast agent should be administered. After 3-5 minutes, a 5-mm helical scan is obtained through the area of concern. Fewer contrast-enhanced studies are needed with increasing experience. Soft tissue around the rim of a calculus can differentiate it from a phlebolith. A phlebolith may have a comet tail of soft tissue extending from it; this finding differentiates it from a calculus. On CT scans, phleboliths do not have radiolucent centers, as often seen on plain radiographs.

When contrast-enhanced scans are required to evaluate pain not related to stones, routine abdominal and/or pelvic CT should be performed. In this situation, 100-150 mL of a low-osmolar oral and rectal contrast agent is used, and a 5-mm helical CT scan is obtained with a pitch of 1.5:1. Patient selection determines the number of examinations needed.

Stones at the UVJ may be difficult to distinguish from stones that have already passed into the bladder. If the distinction changes therapy, a repeat scan through the UVJ in the prone position may be helpful. Stones that have already passed into the bladder will drop into a dependent location.

CT findings

CT may depict the following:

• Stones in the ureter
• Enlarged kidneys
• Hydronephrosis (83% sensitive, 94% specific)
• Perinephric fluid (82% sensitive, 93% specific)
• Ureteral dilatation (90% sensitive, 93% specific)
• Soft-tissue rim sign (good positive predictive value with a positive odds ratio of 31:1)

The amount of perinephric fluid is correlated with the degree of obstruction seen on IVU, and as with the obstruction, the amount of fluid is correlated with the likelihood of stone passage. Normal hyperattenuating renal pyramids sometimes are seen. These indicate that significant obstruction is not present. However, this finding has been seen with proven ureteral calculi and is often absent in patients without stones. For this reason, the usefulness of IVU is limited. If contrast material is administered, a delayed or hyperattenuating nephrogram may also be visible on CT scans if the ureter has an obstruction.

Conventional radiography may be helpful in visualizing larger stones, once they are identified on CT scans, to provide a baseline to follow passage of the stone. If kidney, ureter, and bladder radiographs fail to depict the stone, CT may be needed to follow its passage. Approximately 40-55% of stones are not visible on abdominal radiographs. Almost no stones with attenuation values of less than 200 HU are visible, and repeat CT scans are usually required if passage of the stone is to be followed. Cystine and urate stones have an attenuation of 100-500 HU; calcium stones usually demonstrate attenuation higher than 700 HU. Considerable overlap exists in the CT attenuation values of calcium stones.

Degree of Confidence

Individual CT signs are associated with varying degrees of confidence, as noted in CT findings above.

False Positives/Negatives

False-positive results are almost exclusively the result of a phlebolith adjacent to the ureter. False-negative results are primarily due to indinavir radiolucent stones and error. CT scans often suggest an alternative or additional diagnosis when renal stone disease is clinically suspected.

MRI

Section 6 of 11  

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• Mri
• Ultrasound
• Nuclear Medicine
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Findings

Stones are not directly visible on MRIs because they produce no signal. However, they may be indirectly visualized as a filling defect in the ureter or collecting system on heavily T2-weighted images or on gadolinium-enhanced T1-weighted images. MRI can be useful as a problem-solving tool if the use of iodinated contrast material or radiation is contraindicated (eg, during pregnancy).

Gadolinium-based contrast agents (gadopentetate dimeglumine [Magnevist], gadobenate dimeglumine [MultiHance], gadodiamide [Omniscan], gadoversetamide [OptiMARK], gadoteridol [ProHance]) have recently been linked to the development of nephrogenic systemic fibrosis (NSF) or nephrogenic fibrosing dermopathy (NFD). For more information, see the eMedicine topic Nephrogenic Fibrosing Dermopathy. The disease has occurred in patients with moderate to end-stage renal disease after being given a gadolinium-based contrast agent to enhance MRI or MRA scans.

As of late December 2006, the FDA had received reports of 90 such cases. Worldwide, over 200 cases have been reported, according to the FDA. NSF/NFD is a debilitating and sometimes fatal disease. Characteristics include red or dark patches on the skin; burning, itching, swelling, hardening, and tightening of the skin; yellow spots on the whites of the eyes; joint stiffness with trouble moving or straightening the arms, hands, legs, or feet; pain deep in the hip bones or ribs; and muscle weakness. For more information, see the FDA Public Health Advisory or Medscape.

Degree of Confidence

The degree of confidence remains to be determined.

False Positives/Negatives

False-positive and false-negative findings remain to be described.

ULTRASOUND

Section 7 of 11  

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Findings

On sonograms, stones are demonstrated as bright echogenic foci with posterior acoustic shadowing. Stones are visualized fairly well with US in the kidneys and the distal ureter at or near the UVJ, especially if dilatation is present. US is good for the visualization of complications such as hydronephrosis (or other signs of obstruction); however, some patients with acute obstruction have little or no dilation.

In particular, US is helpful in evaluating those with renal insufficiency or contraindications for the use of contrast media; however, US is often skipped in favor of nonenhanced CT.

In addition, US is good for characterizing lucent filling defects that are visualized as stones on IVU. However, US does not provide direct physiologic information regarding the degree of obstruction. Doppler imaging may demonstrate a high resistive index in acute obstruction, but this may not occur immediately or after forniceal rupture. Absence of the ureteral jet, as visualized with color Doppler on the symptomatic side, is presumptive evidence for a high-grade obstruction in a well-hydrated patient.

Degree of Confidence

US is very insensitive for stones, especially stones smaller than 2 mm, stones at the UPJ, or stones in the mid ureter. Fowler et al suggest that US has a sensitivity as low as 24%, compared with nonenhanced CT. Furthermore, estimations of stone size may not be accurate. Compared with nonenhanced CT, US is more dependent on the operator's ability and more time consuming.

False Positives/Negatives

US is fairly specific when stones are seen, with a specificity as high as 90%. With US, matrix or indinavir stones may have soft tissue echogenicity without shadowing. False-positive findings may result from renal vascular calcifications. False-positive diagnoses of hydronephrosis also result from dilated vascular structures in the renal hilum. Doppler imaging is helpful in distinguishing dilated vascular structures from hydronephrosis.

NUCLEAR MEDICINE

Section 8 of 11  

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• Nuclear Medicine
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• References

Findings

Nuclear medicine studies may demonstrate the retention of activity in the cortex or collecting system when the obstruction is ongoing. Nuclear medicine tests are useful in determining differential renal function for treatment planning and for assessing how much renal function might return after the obstruction is relieved. For example, a kidney with very little function might be removed if very little function persists after a trial of drainage. Occasionally, confirming the obstruction with nuclear medicine studies is useful if the administration of iodinated contrast material is contraindicated.

False Positives/Negatives

Renal function evaluation is not reliable in the presence of ongoing obstruction. Conversely, imaging findings may be normal with low-grade obstruction.

INTERVENTION

Section 9 of 11  

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• Multimedia
• References

Retrograde or antegrade pyeloureterography may be indicated if the collecting system cannot be opacified otherwise. This becomes much less useful as a diagnostic examination when CT is available. Retrograde stent placement is indicated if obstruction is present with proximal infection (pyonephrosis). Stent placement is performed to prevent sepsis and irreversible renal damage. If retrograde stent placement is unsuccessful, nephrostomy or antegrade stent placement serves as a reliable backup.

Patient Education: For excellent patient education resources, visit eMedicine's Kidneys and Urinary System Center. Also, see eMedicine's patient education articles Kidney Stones and Intravenous Pyelogram.

Medical/Legal Pitfalls

• Medical/legal issues related to urinary lithiasis are similar to other areas of radiology. A missed diagnosis may progress to renal damage, or the renal infection may worsen. Untreated urinary obstruction with infection may progress rapidly to renal damage and possibly sepsis and subsequent multi-organ failure. Other unrelated findings on radiologic examinations may also be overlooked. Renal colic is extremely painful and if the diagnosis is missed, the patient does not receive adequate pain control.
• If contrast material is used for IVU or for problem solving with CT, nephrotoxicity and allergy-like reactions are possible. Patients may potentially sue for contrast material–related injuries if nonenhanced CT was available but not used.
• Radiation exposure should be minimized in pregnant women, and female patients should be questioned carefully. If needed, a pregnancy test should be performed prior to CT scanning or radiography. US may be used initially in pregnant or pediatric patients, but CT may be indicated to confirm or diagnose urinary stone disease and exclude other pelvic pathology in pregnant women.

Special Concerns

• In the diagnosis and treatment of kidney stones, special concerns exist in patients who are pregnant, in those who have contraindications to the use of contrast media, and in those with renal insufficiency.
• • Pregnancy does not predispose patients to stone formation; however, stone formation is a complication in as many as 0.05% of pregnancies, and the diagnosis may be difficult to establish with imaging because of the displacement and obscuration of organs by the enlarged uterus and fetus. Consider using US first in a pregnant patient, especially in the first trimester. IVU can be used, but the views should be limited to scout and 10- to 30-minute images if possible. CT can also be useful, and the radiation dose may be justified (especially if the clinical picture is confusing), because any fetal damage is unlikely at the typical radiation doses. Minimize the dose by increasing the pitch and decreasing the milliamperage. MRI may be a useful tool for problem solving.
  • Nonenhanced CT results are usually diagnostic, but if contrast material is needed, actions can be taken to decrease the risk of an adverse reaction in patients. The patient can be premedicated with steroids and histamine blockers. Use of low-osmolar contrast agent also helps. Use of iodinated contrast agents should be avoided in patients who have had previous life-threatening reactions. Nonenhanced CT is usually sufficient with the aid of US and MRI as problem-solving tools. Nuclear scintigraphy may also be helpful in confirming obstruction.
  • Usually, in patients with renal insufficiency, nonenhanced CT is sufficient. Very poor renal function results in a failure to opacify the collecting system. As in pregnant patients, US, MRI, and scintigraphy can be useful as problem-solving tools.

MULTIMEDIA

Section 10 of 11  

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• Radiograph
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• Mri
• Ultrasound
• Nuclear Medicine
• Intervention
• Multimedia
• References

Media file 1:  Magnified scout intravenous urogram shows a large, relatively lucent calculus in the lower pole of the right kidney.
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Media file 2:  Scout intravenous urogram shows a smooth, dense, round calculus in the left kidney (same patient as in Image 3).
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Media file 3:  Intravenous urogram. After the intravenous injection, contrast material in the collecting system obscures the calculus (same patient as in Image 2).
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Media file 4:  Scout intravenous urogram shows a smooth stone in the right kidney (same patient as in Images 5-8).
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Media file 5:  Intravenous urogram obtained 5 minutes after the intravenous injection. Contrast material in the collecting system obscures the stone (same patient as in Images 4 and 6-8).
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Media file 6:  This intravenous urogram was obtained 10 minutes after the intravenous injection of contrast medium. Additional contrast material is present in the collecting system, and the stone is seen as a relatively lucent filling defect (same patient as in Images 4-5 and 7-8).
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Media file 7:  Renal sonogram demonstrates an echogenic shadowing calculus in the renal collecting system with hydronephrosis (same patient as in Images 4-6 and 8).
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Media file 8:  Contrast-enhanced CT section reveals a dense calculus in the right kidney, but the hydronephrosis has resolved (same patient as in Images 4-7).
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Media file 9:  Abdominal radiograph shows calcification filling the left collecting system. This finding is consistent with a staghorn calculus. For its size, the stone is relatively lucent (same patient as in Image 10).
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Media file 10:  Contrast-enhanced CT scan demonstrates an opaque staghorn calculus filling the left renal collecting system (same patient as in Image 9).
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Media file 11:  Scout intravenous urogram shows innumerable small calcifications in the region of the renal pyramids in a patient with nephrocalcinosis.
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Media file 12:  Scout intravenous urogram demonstrates innumerable calcifications over the medullary region of the left kidney in a patient with nephrocalcinosis (same patient as in Image 13).
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Media file 13:  Renal longitudinal sonogram in a patient with nephrocalcinosis shows diffuse echogenic shadowing calcifications in the renal pyramids (same patient as in Image 12).
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Media file 14:  Intravenous urogram. Prospectively, no stone was seen on the scout radiograph (same patient as in Images 15-16). In retrospect, a stone in the distal left ureter is projected over the lateral edge of the mid sacrum.
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Media file 15:  This intravenous urogram was obtained 5 minutes after the intravenous injection of contrast agent (same patient as in Images 14 and 16). A prolonged hyperintense left nephrogram demonstrates delayed contrast material excretion into the left collecting system due to ureteral obstruction.
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Media file 16:  This intravenous urogram was obtained 10 minutes after the intravenous injection of contrast material (same patient as in Images 14-15). Mild left hydronephrosis and hydroureter extend to the level of the stone in the true pelvis.
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Media file 17:  Scout intravenous urogram demonstrates a small, focal, almost triangular, radiopaque calculus on the left side of the pelvis (same patient as in Images 18-19). Another pelvic calcification with central lucency is a typical phlebolith.
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Media file 18:  Scout intravenous urogram was obtained 5 minutes after the intravenous injection of contrast agent (same patient as in Images 17 and 19). A prolonged hyperintense nephrogram and moderate hydronephrosis are present in the left kidney. The right kidney and collecting system are normal.
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Media file 19:  Intravenous urogram was obtained 10 minutes after the intravenous injection of contrast agent (same patient as in Images 17-18). A column of contrast material in the left ureter extends down to the calculus noted on the scout radiograph. The small phlebolith can barely be seen projecting slightly off the ureter.
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Media file 20:  Intravenous urogram (30-minute delay image) of the right kidney shows a moderately hydronephrotic collecting system to the level of a proximal ureteral stone (arrow) (same patient as in Image 21).
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Media file 21:  Axial nonenhanced CT section at the level of the kidney demonstrates an attenuating proximal ureteral calculus (arrow) (same patient as in Image 20). No significant hydronephrosis is identified. CT can be performed much more rapidly than urography and without the use of intravenous contrast material.
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Media file 22:  Scout intravenous urogram demonstrates several calcifications in the left hemipelvis (same patient as in Images 23-25).
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Media file 23:  Intravenous urogram was obtained 10 minutes after the intravenous injection of contrast agent (same patient as in Images 22 and 24-25). A prolonged hyperintense nephrogram and mild hydronephrosis are present.
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Media file 24:  Intravenous urogram, delayed radiograph, reveals a large amount of contrast material extravasation (likely a fornix rupture with pyelosinus backflow) in the region of the left renal pelvis (same patient as in Images 22-23 and 25). Contrast agent fills the distal ureter.
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Media file 25:  Intravenous urogram, magnified view, shows extravasated contrast agent from a fornix rupture and pyelosinus backflow (same patient as in Images 22-24).
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Media file 26:  Axial nonenhanced CT image at the level of the kidneys shows bilateral renal calculi, right hydronephrosis, and moderate perinephric fluid (same patient as in Images 27-28).
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Media file 27:  Axial nonenhanced CT image of the urinary bladder demonstrates an attenuating calculus at the right ureteropelvic junction (same patient as in Images 26 and 28).
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Media type:  CT

Media file 28:  Axial contrast-enhanced CT scan. The excretory phase image through the kidneys shows extravasation of contrast material in and near the renal pelvis and surrounding the proximal ureter, which is opacified. The finding is consistent with fornix rupture (same patient as in Images 26-27).
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Media file 29:  Scout intravenous urogram demonstrates radiopaque left renal calculi in the mid kidney and lower pole (same patient as in Images 30-32).
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Media file 30:  Scout intravenous urogram obtained after lithotripsy (same patient as in Images 29 and 31-32) shows absence of the previously seen calcification over the mid kidney and linear group of calcifications in the path of the distal left ureter (steinstrasse, from the German, meaning "stone street").
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Media file 31:  Intravenous urogram, magnified view of the scout image in Image 30, was obtained after lithotripsy and shows a steinstrasse appearance (same patient as in Images 29-30 and 32).
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Media file 32:  Intravenous urogram, 10-minute delay image, demonstrates delayed excretion and a slightly hyperopaque left nephrogram due to obstruction by distal ureteral stone fragments (same patient as in Images 29-31). Stents are often placed to prevent obstruction after lithotripsy.
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Media file 33:  Intravenous urogram, scout radiograph. Large radiopaque calculus overlies the left hemipelvis near the expected location of the ureterovesical junction (same patient as in Images 34-37). Two adjacent phleboliths are noted lateral and caudal to the stone.
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Media file 34:  Intravenous urogram. Magnified view of the scout radiograph in Image 33 reveals faintly lamellated pelvic calcification at the expected location of the left ureterovesical junction (same patient as in Images 33 and 35-37).
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Media file 35:  Intravenous urogram (10-min delay). Contrast-enhanced study demonstrates the left ureterocele as a slightly lucent halo around the previously noted pelvic calcification (same patient as in Images 33-34 and 36-37).
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Media file 36:  Intravenous urogram (10-min delay) Magnified view of the left ureterocele (see Image 35) with a large stone in it (same patient as in Images 33-35 and 37).
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Media file 37:  Axial contrast-enhanced CT image through the ureterovesical junction confirms the stone within a left ureterocele (same patient as in Images 33-36). A Foley catheter balloon is visible in the bladder.
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Media file 38:  Intravenous urogram (tomogram) shows enlarged relatively lucent right kidney with no excretion of contrast material (same patient as in Images 39-41).
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Media file 39:  Intravenous urogram (5-min renal view) shows enlarged relatively lucent right kidney with no excretion of contrast (same patient as in Images 38 and 40-41).
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Media file 40:  Longitudinal sonogram of the right kidney demonstrates marked dilatation of the calyces. No calculi are apparent (same patient as in Images 38-39 and 41).
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Media file 41:  Sonogram shows marked dilatation of the calyces and communication with the renal pelvis, which confirms severe hydronephrosis (same patient as in Images 38-40).
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Media file 42:  Nonenhanced CT image of the kidneys demonstrates left hydronephrosis and strands of perinephric fluid but no dense calculus (same patient as in Images 43-44).
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Media type:  CT

Media file 43:  Nonenhanced CT image of the pelvis shows dilatation of the distal left ureter and mild periureteral fluid near the left ureterovesical junction (same patient as in Images 42 and 44).
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Media type:  CT

Media file 44:  Nonenhanced CT image of the pelvis shows a small attenuating stone at the left ureterovesical junction (same patient as in Images 42-43).
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Media file 45:  Nonenhanced CT image shows slightly hyperattenuating renal pyramids, most notably on the left. This is a secondary sign and indicates a lack of obstruction of the collecting system (same patient as in Image 46).
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Media file 46:  Nonenhanced CT image shows a nonobstructing calculus just above the left ureterovesical junction (same patient as in Image 45).
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Media file 47:  Contrast-enhanced CT image of the kidneys shows mild hydronephrosis, perinephric fluid, and delayed enhancement. The perinephric fluid indicates obstruction and correlates with the likelihood of the passage of the stone (same patient as in Image 48).
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Media type:  CT

Media file 48:  Contrast-enhanced CT image of the lower abdomen shows a tiny, obstructing, left ureteral calculus (same patient as in Image 47).
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Media type:  CT

Media file 49:  Magnified nonenhanced CT image of the right kidney shows slightly hyperattenuating renal pyramids in the right kidney despite the mild hydronephrosis (same patient as in Image 50).