ACR Appropriateness Criteria®
Clinical Condition: Acute Onset Flank Pain
Variant 1: Suspicion of stone disease.
| Radiologic Procedure |
Rating |
Comments |
RRL* |
| CT abdomen and pelvis without contrast |
8 |
Reduced-dose techniques preferred. |
High |
| X-ray intravenous urography |
7 |
|
Low |
| US kidney with Doppler and KUB |
6 |
Preferred exam in pregnancy, in patients who are allergic to iodinated contrast, and if NCT is not available. |
Low |
| MRI abdomen and pelvis |
4 |
MR urography technique should be performed. See comments regarding contrast in text under "Anticipated Expectations." |
None |
| X-ray abdomen |
1 |
Most useful in patients with known stone disease. |
Low |
| Rating Scale: 1=Least appropriate, 9=Most appropriate |
*Relative Radiation Level |
Note: Abbreviations used in the tables are listed at the end of the "Major Recommendations" field.
Variant 2: Recurrent symptoms of stone disease.
| Radiologic Procedure |
Rating |
Comments |
RRL* |
| CT abdomen and pelvis without contrast |
7 |
Reduced dose techniques preferred. |
High |
| US kidney with Doppler and KUB |
7 |
|
Low |
| X-ray abdomen |
6 |
Good for baseline and follow-up post treatment. |
Low |
| X-ray intravenous urography |
2 |
|
Low |
| MRI abdomen and pelvis |
2 |
|
None |
| Rating Scale: 1=Least appropriate, 9=Most appropriate |
*Relative Radiation Level |
Note: Abbreviations used in the tables are listed at the end of the "Major Recommendations" field.
Summary of Literature Review
Urinary tract stones (calculi) are thought to result from either excessive excretion or precipitation of salts in the urine or a relative lack of inhibiting substances. Men are more commonly affected than women, and the incidence increases with age until age 60. Blacks and children are affected less frequently. Renal calculi tend to be recurrent, and flank pain is a nonspecific symptom that may be associated with other entities; therefore, evaluation with imaging is recommended at the initial presentation.
A renal calculus small enough to pass into the ureter may cause blockage of urine flow with distension of the upper urinary tract. Ureteral hyperperistalsis occurs, resulting in acute onset of sharp, spasmodic flank pain and hematuria. The ureter contains several areas where calculi commonly become lodged, (e.g., at the ureteropelvic junction), the iliac vessels, and the ureterovesical junction. The probability of spontaneous passage of a ureteral calculus measuring 5 mm in axial diameter or less is very high. A 10 mm calculus, however, is very unlikely to pass spontaneously. Therefore, the treating physician wants to know the size of the calculus as well as its location and its effect on renal function.
Patients with a suspected diagnosis of renal colic have traditionally been evaluated with urinalysis, plain abdominal radiography (KUB), or excretory urography, commonly referred to as intravenous pyelogram (IVP). More recently, ultrasonography (US), computerized tomography (CT), and magnetic resonance imaging (MRI) have been used.
Radiography
The plain-film of the abdomen may be sufficient to diagnose ureterolithiasis in patients with known stone disease and previous KUBs. The sensitivity of the KUB for ureterolithiasis in other patients is poor. Studies by some researchers found sensitivities of 62% and 58% when the radiographs were interpreted retrospectively. One study correlated the KUB with noncontrast CT (NCT) retrospectively, so that an exact correlation was made between stones on the CT scan and the calcific density on the KUB. A sensitivity of only 59% was found for detecting ureteral calculi on the KUB. Another study used the KUB as a guide for US evaluation of flank pain. They found 64% sensitivity for detecting ureteral calculi and had 6 false positive cases among the 66 patients evaluated. While the KUB may be a valuable part of the IVP or US evaluation of flank pain, it has a very limited role when used alone, and it should not be used to triage which patient should receive NCT.
Computed Tomography
Since the introduction of the use of helical (spiral) NCT as the initial study in evaluating flank pain numerous investigations have confirmed it to be the study with the highest sensitivity (95%-96%) and specificity (98%) for ureterolithiasis. Virtually all stones are radio-opaque, and stone size can be measured accurately in cross section, aiding in predicting outcome. Stone location, accurately depicted by NCT, has also been associated with spontaneous stone passage rates, with the more proximal stones having a higher need for intervention. Recently, coronal reconstruction of axial CT scans have been shown to more accurately predict stone size in the craniocaudad direction, although this dimension is not critical to estimating the likelihood of stone passage. The degree of perinephric stranding present on the affected side on NCT has also been shown to correlate inversely with the likelihood of stone passage, giving additional prognostic information, but this finding has been disputed in other studies.
The amount of stranding is related to the time after onset of pain and is usually not seen in the first 2 hours following the onset of flank pain. It may take up to 8 hours after the onset of pain to become maximal. Secondary signs such as ureteral dilatation and perinephric stranding allow CT to make a diagnosis of a recently passed stone.
NCT has been directly compared with the IVP in three series. NCT was equal to the IVP in diagnosing obstruction and more reliable in diagnosing the presence of nephrolithiasis. NCT is also reliable for diagnosing flank pain due to causes other than ureterolithiasis such as appendicitis, diverticulitis, and torsed ovarian masses. NCT is safer than the IVP since it uses no contrast media, is rapid (with the entire study taking minutes), and does not require the technical expertise that US does. When CT is available, it is the best first study in the nonpregnant adult presenting with flank pain likely to be due to stone disease and has been shown to be more cost effective.
Concerns over radiation exposure, especially in young stone patients, have led to the development and evaluation of reduced dose regimens. Other recent technique refinement has included evaluation of the effect of slice width and overlapping image reconstruction on stone detection.
Intravenous Pyelography
The IVP is the previous standard study for ureterolithiasis and is still the best investigation if NCT is not available. It provides information regarding site and degree of obstruction, size of stone, and effect of obstruction on renal excretion. This examination has a number of relative contraindications, including renal insufficiency, dehydration, past reaction to iodinated contrast agents, and pregnancy. The availability of nonionic iodinated contrast material has reduced the risk of reaction. It may take several hours for excretion to occur in the presence of acute obstruction, in which case it is more time consuming than the alternative techniques. Another disadvantage is the inability of the IVP to identify alternative diagnoses.
Ultrasound
US is a safe, noninvasive imaging modality that can be used to study the urinary tract effectively. The diagnosis of obstructive urinary tract calculi depends on identification of the offending calculus and concomitant pelvicaliectasis and ureterectasis extending to the obstructing site. Because it may take many hours for pelvicaliectasis and ureterectasis to develop, US reportedly will miss over 30% of acute obstructions caused by an uretheral stone in patients who are not specifically hydrated for the study. Two studies detected hydronephrosis in 7 of 20 patients (35%) and 16 of 22 patients (73%), respectively, nonhydrated patients with uretheral calculi. More recently, US has been found to be 100% sensitive for signs of obstruction (hydronephrosis, ureteral dilatation, and/or perirenal fluid) perhaps indicating improvement in US equipment. The use of intrarenal Doppler US improves the detection of early obstruction by evaluating for elevated resistive index (RI) in kidneys with nondilated collecting systems.
Since KUB is superior to US in detecting ureteral calculi, one study recommended a combination of KUB and US. US in these cases is used to detect ureteropyelocaliectasis and then to trace the dilated ureter to a shadowing stone. US can also evaluate the presence and type of ureteral jet (with obstruction the jets are absent, diminished significantly in frequency or a constant slow trickle). In a series of 180 patients, the authors showed a 95% negative predictive value of the KUB/US combination, indicating that IVP was not likely to be helpful if the KUB/US tests are negative. However, IVP was indicated if the KUB/US combination was equivocal or if interventional treatment was anticipated.
One group of researchers also performed a comparison of KUB, US, combination of KUB/US, and IVP in 49 patients. The accuracies of KUB (61%) and US (69%) were lower than that of IVP (92%). The accuracy of the combination of KUB/US was 71%, still lower than that of IVP. In an effort to reduce the number of IVP examinations needed, a model was tested in which only patients with negative US results went on to have an IVP. This algorithm showed 93% sensitivity and 79% specificity. The KUB/US combination has also been compared to NCT. In this prospective study of 66 patients, the KUB/US combination had a sensitivity of 79% (vs. 93% for NCT) for detecting ureteral stones. All missed cases had spontaneous stone passage, leading the authors to conclude that after a negative KUB/US combination, NCT would not add useful information. They suggest use of NCT in those who fail to respond to conservative management or in those in whom surgery is anticipated. The advantage of US is its lack of ionizing radiation and its ability to show some calculi. For this reason it has been suggested for evaluating stones in pregnant women. Its disadvantages include the need for skilled personnel, its inability to accurately measure the size of the calculus, the need to observe the ureteral jet phenomenon at the ureterovesical junction, and its inability to differentiate dilatation without obstruction from true obstruction.
Magnetic Resonance Imaging
One study applied magnetic resonance urography (MRU) to the evaluation of 23 patients with acutely obstructed kidneys. They found 100% sensitivity for diagnosing obstruction, with perirenal fluid seen in 21 of 23 obstructed kidneys (87%) and in no normal kidneys. The site of the obstruction was seen in 80% of these obstructed kidneys. Round signal voids corresponding to the location of stones on correlative IVPs were seen in 12 of 18 patients with ureteric obstruction caused by a stone. These appearances were nonspecific and were also seen secondary to blood clot or tumor. Another study examined 60 patients with obstructive uropathy. In the 13 patients with ureteric stones, MRU correctly identified the site of obstruction in 12 (1 stone moved between the MRU and confirmatory imaging). Forty-six percent of the stones were seen as signal voids against a background of bright urine on T2-weighted images. MRU has been successfully used in pregnant patients with flank pain.
Recurrent Symptoms of Stone Disease
In addition to pregnant patients, the patient with known stone disease and recurrent symptoms also presents a challenge. In this setting, the likelihood of stone disease as the cause of flank pain is higher, but repeated NCTs raise a concern about excessive radiation exposure. One group of researchers examined the issue of radiation exposure associated with repetitive NCT in this setting. In a 6-year period, 5,564 NCTs were performed for renal colic. While the vast majority of patients (96%) underwent 1 or 2 NCTs with an estimated effective dose of 6.5-17 mSv, 176 patients had three or more NCTs with an estimated dose of 20-154 mSv. One patient had 18 NCTs over the 6- years! In this setting, every effort should be made to use low-dose NCT. A recent study found excellent sensitivity (95%) and specificity (97%) for detecting stones with a low-dose protocol (30 mA) compared to a standard-dose protocol (180 mA) in patients with a body mass index (BMI) of <30. Further, if the patient has persistence of symptoms from a documented stone and repeat imaging is contemplated, a limited NCT of the area of the stone through the bladder could be considered if stone passage is the main question. Alternatively, if the stone can be seen by KUB, a repeat KUB might provide useful information at a much lower dose.
Anticipated Exceptions
NCT is the most rapid and accurate technique for evaluating flank pain. If there is uncertainty about whether a calcific density represents a ureteral calculus or a phlebolith, contrast medium can be injected and the scan repeated for definitive diagnosis. The IVP, which is readily available and is familiar to nonradiologic physicians, is the technique of choice if CT is not available. In pregnant patients with flank pain, US is the best initial study. While a limited IVP has been used to evaluate flank pain in pregnancy when the US study is not diagnostic, MRU has potential utility in diagnosing acute urinary tract obstruction without the use of ionizing radiation. NCT using an ultra-low-dose protocol could also be considered.
Nephrogenic systemic fibrosis (NSF, also known as nephrogenic fibrosing dermopathy) was first identified in 1997 and has recently generated substantial concern among radiologists, referring doctors and lay people. Until the last few years, gadolinium-based MR contrast agents were widely believed to be almost universally well tolerated, extremely safe and non-nephrotoxic, even when used in patients with impaired renal function. All available experience suggests that these agents remain generally very safe, but recently some patients with renal failure who have been exposed to gadolinium contrast agents (the percentage is unclear) have developed NSF, a syndrome that can be fatal. Further studies are necessary to determine what the exact relationships are between gadolinium-containing contrast agents, their specific components and stoichiometry, patient renal function and NSF. Current theory links the development of NSF to the administration of relatively high doses (e.g., >0.2 mM/kg) and to agents in which the gadolinium is least strongly chelated. The FDA has recently issued a "black box" warning concerning these contrast agents (http://www.fda.gov/cder/drug/InfoSheets/HCP/gcca_200705HCP.pdf).
This warning recommends that, until further information is available, gadolinium contrast agents should not be administered to patients with either acute or significant chronic kidney disease (estimated GFR <30 mL/min/1.73m2), recent liver or kidney transplant or hepato-renal syndrome, unless a risk-benefit assessment suggests that the benefit of administration in the particular patient clearly outweighs the potential risk(s).
Abbreviations
- CT, computed tomography
- KUB, kidneys, ureters, bladder
- MR, magnetic resonance
- MRI, magnetic resonance imaging
- NCT, noncontrast computed tomography
- US, ultrasound
