Background
Urinary tract stones 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 60 years of age. For example, it is estimated that 19% of men and 9% of women will be diagnosed with a kidney stone by 70 years of age.
Stones also tend to be recurrent, with recurrence rates shown to be higher in those with 2 or more previous stone episodes.
Symptoms:
Owing to ureteral hyperperistalsis in the setting of a stone,
- Flank pain is a common presenting symptom of urolithiasis, although nonspecific and associated with a variety of other entities.
- Hematuria, secondary to irritation of and trauma to the ureter may also result.
- Hydronephrosis: ureteral obstruction is a potential serious complication of stones.
Treatment:
- Conservative with supportive and medical therapy.
- Invasive therapies are required in some instances, commonly via percutaneous nephrolithotomy, rigid and flexible ureteroscopy, or shock wave lithotripsy.
Stone size and location have been shown to be important determinants in stone passage and the need for invasive management, with larger and more proximally located stones being associated with lower rates of spontaneous passage.
Given the often nonspecific presentation, imaging allows for the diagnosis of stones. Furthermore, imaging plays a larger role in assessment of alternative diagnoses, complications, and appropriateness of potential therapies.
Special Imaging Considerations
CT urography (CTU)
Imaging study that is tailored to improve visualization of both the upper and lower urinary tracts. There is variability in the specific parameters, but it usually involves unenhanced images followed by intravenous (IV) contrast-enhanced images, including nephrographic and excretory phases acquired at least 5 minutes after contrast injection.
CTU should use thin-slice acquisition with Reconstruction methods, including maximum intensity projection or 3-D volume rendering. Dual-energy CT allows for the characterization of stone composition (ie, uric acid, cystine, and calcium) and the generation of virtual unenhanced images simulating noncontrast CT images.
MR urography (MRU)
Is tailored to improve visualization of the urinary system. Unenhanced MRU relies upon the intrinsic high signal intensity from urine on heavily T2-weighted imaging for the evaluation of the urinary tract. IV contrast is administered to provide additional information regarding obstruction, urothelial thickening, focal lesions, and stones. Contrast-enhanced T1-weighted series should include corticomedullary, nephrographic, and excretory phases. Thin-slice acquisition and multiplanar imaging should be obtained.
Ultrasound (US) Kidneys and Bladder Retroperitoneal
US demonstrates variable performance in the detection of renal calculi depending on the clinical scenario and associated complications.
Compared with noncontrast CT, initial studies evaluating grayscale US demonstrated an overall sensitivity of 24% to 57% for stone detection with decreased sensitivity for smaller stones. Detection of ureteral calculi is also reduced compared with CT, demonstrating sensitivity up to 61% with a specificity of 100%, although sensitivity is improved if there are associated signs of obstruction. Stone size estimation at US is also limited compared with CT, particularly with smaller (≤5 mm) stones, with a tendency of US to overestimate stone size.
US has been found to be up to 100% sensitive and 90% specific for the diagnosis of ureteral obstruction (hydronephrosis, ureterectasis, and perinephric fluid) in patients presenting with acute flank pain [37]. However, within the first 2 hours of presentation, these findings are less sensitive because secondary signs of obstruction may not have had time to develop. Furthermore, although hydronephrosis on US does not accurately predict the presence or absence of a ureteral stone on computerized tomography in up to 25% of patients, it has been shown that in an US-first approach, the lack of hydronephrosis on US makes the presence of a larger ureteral stone (>5 mm) less likely.
Summary of Recommendations
Variant 1:
CT abdomen and pelvis without IV contrast is usually appropriate for the initial imaging of acute onset flank pain and suspicion for urolithiasis and with no history or remote history of stone disease. Although the panel did not agree on recommending US color Doppler kidneys and bladder retroperitoneal or US kidneys and bladder retroperitoneal because there is insufficient medical literature to conclude whether these patients would benefit from the procedure, its use may be appropriate.
Variant 2:
In the setting of acute onset flank pain with known current stone disease that was diagnosed on recent imaging, CT abdomen and pelvis without IV contrast is usually appropriate as the follow-up imaging for recurrent symptoms of stone disease. Although the panel did not agree on recommending US color Doppler kidneys and bladder retroperitoneal because there is insufficient medical literature to conclude whether these patients would benefit from the procedure, its use and the use of CT abdomen and pelvis with IV contrast may be appropriate.
Variant 3:
US kidneys and bladder retroperitoneal is usually appropriate for the initial or follow-up imaging of pregnant patients with acute onset flank pain and suspicion of stone disease. Although the panel did not agree on recommending US color Doppler kidneys and bladder retroperitoneal because there is insufficient medical literature to conclude whether these patients would benefit from the procedure, its use as well as the use of MRU without IV contrast or CT abdomen and pelvis without IV contrast may be appropriate.
Variant 4:
In the setting of acute onset flank pain and suspicion of stone disease, MRU without and with IV contrast or CT abdomen and pelvis with IV contrast or CTU without and with IV contrast may be appropriate as the next imaging study when CT without IV contrast is inconclusive for the presence of stones.
Supporting Documents
The evidence table, literature search, and appendix for this topic are available at https://acsearch.acr.org/list. The appendix includes the strength of evidence assessment and the final rating round tabulations for each recommendation. For additional information on the Appropriateness Criteria methodology and other supporting documents go to www.acr.org/ac.
Sources / Credits:
- Header Image: Image by wayhomestudio via Freepik
