Imaging Pearls ❯ Kidney ❯ Renal Stone Disease
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- Objectives To assess the accuracy of low-dose dual-energy computed tomography (DECT) to differentiate uric acid from non-uric acid kidney stones in two generations of dual-source DECT with stone composition analysis as the reference standard.
Methods Patients who received a low-dose unenhanced DECT for the detection or follow-up of urolithiasis and stone extraction with stone composition analysis between January 2020 and January 2022 were retrospectively included. Collected stones were characterized using X-ray diffraction. Size, volume, CT attenuation, and stone characterization were assessed using DECT post-processing software. Characterization as uric acid or non-uric acid stones was compared to stone composition analysis as the reference standard. Sensitivity, specificity, and accuracy of stone classification were computed. Dose length product (DLP) and effective dose served as radiation dose estimates
Dual-energy CT kidney stone characterization-can diagnostic accuracy be achieved at low radiation dose?
Euler A, Wullschleger S, Sartoretti T, Müller D, Keller EX, Lavrek D, Donati O.
Eur Radiol. 2023 Sep;33(9):6238-6244 - Results: A total of 227 stones in 203 patients were analyzed. Stone composition analysis identified 15 uric acid and 212 non-uric acid stones. Mean size and volume were 4.7 mm × 2.8 mm and 114 mm3, respectively. CT attenuation of uric acid stones was significantly lower as compared to non-uric acid stones (p < 0.001). Two hundred twenty-five of 227 kidney stones were correctly classified by DECT. Pooled sensitivity, specificity, and accuracy were 1.0 (95%CI: 0.97, 1.00), 0.93 (95%CI: 0.68, 1.00), and 0.99 (95%CI: 0.97, 1.00), respectively. Eighty-two of 84 stones with a diameter of ≤ 3 mm were correctly classified. Mean DLP was 162 ± 57 mGy*cm and effective dose was 2.43 ± 0.86 mSv.
Conclusions: Low-dose dual-source DECT demonstrated high accuracy to discriminate uric acid from non-uric acid stones even at small stone sizes.
Dual-energy CT kidney stone characterization-can diagnostic accuracy be achieved at low radiation dose?
Euler A, Wullschleger S, Sartoretti T, Müller D, Keller EX, Lavrek D, Donati O.
Eur Radiol. 2023 Sep;33(9):6238-6244 - Key points:
• Two hundred twenty-five of 227 stones were correctly classified as uric acid vs. non-uric acid stones by low-dose dual-energy CT with stone composition analysis as the reference standard.
• Pooled sensitivity, specificity, and accuracy for stone characterization were 1.0, 0.93, and 0.99, respectively.
• Low-dose dual-energy CT for stone characterization was feasible in the majority of small stones < 3 mm.
Dual-energy CT kidney stone characterization-can diagnostic accuracy be achieved at low radiation dose?
Euler A, Wullschleger S, Sartoretti T, Müller D, Keller EX, Lavrek D, Donati O.
Eur Radiol. 2023 Sep;33(9):6238-6244 - “In conclusion, low-dose DECT demonstrated high accuracy to discriminate uric acid from non-uric acid stones even at small stone sizes. Future studies could investigate if low dose DECT can replace low-dose SECT in a prospective randomized controlled non-inferiority trial.”
Dual-energy CT kidney stone characterization-can diagnostic accuracy be achieved at low radiation dose?
Euler A, Wullschleger S, Sartoretti T, Müller D, Keller EX, Lavrek D, Donati O.
Eur Radiol. 2023 Sep;33(9):6238-6244
- Renal Calcifications: Differential Diagnosis
- nephrocalcinosis
- nephrolithiasis
- milk of calcium
- failed renal transplant
- infection (eg, TB or Pneumocystis carinii)
- hematoma - Common Causes of Nephrocalcinosis
Medullary
- Hypercalcemia, such as from hyperparathyroidism
- Renal papillary necrosis
- Medullary sponge kidney
- Primary hyperoxaluria
- Renal tubular acidosis
- Infection and/or inflammation, such as tuberculosis or sarcoidosis
Cortical
- Chronic glomerulonephritis
- Acute cortical necrosis
- Alport syndrome
- Primary hyperoxaluria
- Failed renal transplant - “The term nephrocalcinosis is used to describe the deposition of calcium salts in the renal parenchyma as opposed to the more common nephrolithiasis, which refers to stones within the collecting system. On the basis of anatomic location, calcinosis can be medullary or cortical. Medullary nephrocalcinosis is 20 times more common than cortical nephrocalcinosis and can be identified at imaging when macroscopic. On radiographs and CT images, tiny foci of calcium are clustered in the renal pyramids and, when diffuse, can take the shape of the renal pyramids. At US, the pyramids are diffusely echogenic without posterior acoustic shadowing. When severe, the calcifications may erode into the calyces and become urinary stones, and patients can present with renal colic.”
Diagnostic Approach to Benign and Malignant Calcifications in the Abdomen and Pelvis
Maria Zulfiqar et al.
RadioGraphics 2020; 40:731–753 - “Up to 30% of renal cell carcinomas demon- strate calcification. Therefore, any calcified renal mass, regardless of the characteristics of the calcification, should raise the possibility of a malignant neoplasm. Rarely, macroscopic fat and calcification are seen concomitantly in renal cell carcinomas that arise due to osseous meta- plasia of the nonepithelial stromal component of the tumor.”
Diagnostic Approach to Benign and Malignant Calcifications in the Abdomen and Pelvis
Maria Zulfiqar et al.
RadioGraphics 2020; 40:731–753
- OBJECTIVE. The objective of our study was to determine the sensitivity of thin axial and coronal maximum-intensity-projection (MIP) images for the detection of renal stones on contrast-enhanced CT performed in the portal venous phase.
CONCLUSION. Thin axial images are highly sensitive for the detection of renal stones ≥ 2 mm on portal venous phase CT. Coronal MIP images do not improve renal stone detection over thin axial images.
Detection of Renal Stones on Portal Venous Phase CT: Comparison of Thin Axial and Coronal Maximum- Intensity-Projection Images Corwin MT et al. AJR 2016; 207:1200–1204 - “The results of our study show that thin images on portal venous phase CECT have a high sensitivity for the detection of renal stones ≥ 2 mm. Unenhanced CT is the recommended imaging test for patients pre- senting with acute flank pain and suspicion of renal stone disease . CECT has traditionally been thought to be limited in detecting renal stones and has not been recommended in this setting. In fact, the American College of Radiology appropriateness criteria give CT of the abdomen and pelvis with contrast material the lowest rating level (2, usually not appropriate) in this situation.”
Detection of Renal Stones on Portal Venous Phase CT: Comparison of Thin Axial and Coronal Maximum- Intensity-Projection Images Corwin MT et al. AJR 2016; 207:1200–1204 - “In our practice, we routinely evaluate thin axial reconstructed images or coronal MIP images to optimize renal stone detection on unenhanced CT. The results of our study show that thin axial images improve the sensitivity of stone detection during portal venous phase CECT to 83.1–89.9% for all stones.”
Detection of Renal Stones on Portal Venous Phase CT: Comparison of Thin Axial and Coronal Maximum- Intensity-Projection Images Corwin MT et al. AJR 2016; 207:1200–1204 - “Therefore, we conclude that thin axial images during portal venous phase CECT depict renal stones ≥ 2 mm with high sensitivity. If CECT is performed when there is some concern for renal stones, review of thin images should be performed to optimize stone detection.”
Detection of Renal Stones on Portal Venous Phase CT: Comparison of Thin Axial and Coronal Maximum- Intensity-Projection Images Corwin MT et al. AJR 2016; 207:1200–1204
- “Larger stone size, higher density, proximal location, and complaints of shivering, fever, and leukocytosis are the most important parameters for predicting invasive management of acute renal colic. Other clinical and radiologic information may be useful as supportive findings but do not predict the choice of patient management.”
Can Unenhanced CT Findings Predict Interventional Versus Conservative Treatment in Acute Renal Colic? Lotan E et al. AJR 2016; 207:1016–1021 - “The worldwide prevalence and incidence of urolithiasis have been increasing, with the number of new cases having nearly doubled in the United States over the past 3 decades. Acute urolithiasis is diagnosed in about 1% of all yearly ambulatory care visits in both U.S. and European emergency departments.”
Can Unenhanced CT Findings Predict Interventional Versus Conservative Treatment in Acute Renal Colic? Lotan E et al. AJR 2016; 207:1016–1021 - “Unenhanced CT is the diagnostic reference standard, with an accuracy that approaches 100%. Unenhanced CT can noninvasively identify, quantify, measure, and locate urinary stones and can reveal secondary signs of obstruction by the stone, including hydrone- phrosis, stranding of perinephric or periureteral fat, the tissue rim sign, decreased renal
attenuation, and nephromegaly.”
Can Unenhanced CT Findings Predict Interventional Versus Conservative Treatment in Acute Renal Colic? Lotan E et al. AJR 2016; 207:1016–1021 - “The relationship between shivering, fever, and leukocytosis and interventional treat- ment revealed low sensitivity (29%, 26% and 16%, respectively) but very high specificity (98%, 95% and 98%, respectively) and positive predictive value (PPV) (92%, 83% and 86%, respectively) (p < 0.05). No other clinical factors reached a level of statistical significance. .”
Can Unenhanced CT Findings Predict Interventional Versus Conservative Treatment in Acute Renal Colic? Lotan E et al. AJR 2016; 207:1016–1021 - “Stone size and stone density were statistically significantly different between patients who were treated conservatively and patients who underwent an interventional procedure (stone size, 4.6 ± 1.9 vs 6.7 ± 3.9 mm [p < 0.001]; stone density, 730 ± 296 vs 910 ± 329 HU [p < 0.01]; Table 3). Stones located in the proximal ureter were significantly more likely to undergo interventional treatment in comparison with other stone locations.”
Can Unenhanced CT Findings Predict Interventional Versus Conservative Treatment in Acute Renal Colic? Lotan E et al. AJR 2016; 207:1016–1021 - “ROC curves that were constructed for stone size and attenuation revealed that stones larger than 6.5 mm and stones with an attenuation value greater than 1100 HU were more likely to require interventional treatment, with an AUC of 0.74 and 0.68, respectively.”
Can Unenhanced CT Findings Predict Interventional Versus Conservative Treatment in Acute Renal Colic? Lotan E et al. AJR 2016; 207:1016–1021 - “Because higher stone attenuation corresponds to calcium-based stones and because stone attenuation in our study ranged quite uniformly between 200 and 1444 HU, our results imply that calcium-based stones tend to require more interventional procedures than other kinds of stones (i.e., uric acid, struvite, or cyste- ine stones).”
Can Unenhanced CT Findings Predict Interventional Versus Conservative Treatment in Acute Renal Colic? Lotan E et al. AJR 2016; 207:1016–1021 - “In our study, 86% (12/14) of patients who had a stone larger than 6.5 mm with an attenuation value higher than 1100 HU underwent interventional treatment. On the other hand, conservative treatment was successful in 67% (8/12) of patients with a stone larger than 6.5 mm but with an attenuation value less than 1100 HU.”
Can Unenhanced CT Findings Predict Interventional Versus Conservative Treatment in Acute Renal Colic? Lotan E et al. AJR 2016; 207:1016–1021 - “Our results showed that larger stone size, higher density, and proximal location are significantly associated with the selection of interventional over conservative management for patients with acute renal colic. Complaints of shivering, fever, and leukocytosis also strongly correlate with the selection for interventional treatment. Other clinical and radiologic information may be useful as supportive findings, but they were not predictive for the purposes of choosing suitable patient management.”
Can Unenhanced CT Findings Predict Interventional Versus Conservative Treatment in Acute Renal Colic? Lotan E et al. AJR 2016; 207:1016–1021
- “Passage of a ureteral calculus depends on size and location, with a spontaneous passage rate of 48% for proximal versus 75% for distal ureteral calculi and 76%, 60%, 48%, and 25% for 2 to 4, 5 to 7, 7 to 9, and greater than 9 mm diameter, respectively.”
Acute Urinary Tract Disorders Goel RH et al. Radiol Clin N Am 53 (2015) 1273–1292
- “The lifetime risk for a urinary calculus disease is 12% for men and 6% for women Risk factors include a personal or family history of stones, urinary tract anatomic abnormality, obesity, and metabolic disorders. The incidence for stone disease is highest in warm regions and during the summer months because of an increased rate of dehydration.” Acute Urinary Tract Disorders Goel RH, Unnikrishnan R, Remer EM Radiol Clin N Am 53 (2015) 1273–1292
- CT of Renal Stone Disease
• When is imaging needed in the evaluation of suspected renal stone disease?
• What is the scan protocol for suspected renal calculi?
• What are the key facts that the CT scan can provide?
• When are contrast enhanced scans necessary? - “The American Urological Association and the American College of Radiology (ACR) recommend low-dose (for body mass index [BMI] <30) noncontrast CT for the initial presentation of flank pain.” Acute Urinary Tract Disorders Goel RH, Unnikrishnan R, Remer EM Radiol Clin N Am 53 (2015) 1273–1292
- When will a stone pass?
• Passage of a ureteral calculus depends on size and location, with a spontaneous passage rate of 48% for proximal versus 75% for distal ureteral calculi and 76%, 60%, 48%, and 25% for 2 to 4, 5 to 7, 7 to 9, and greater than 9 mm diameter, respectively.
• Acute Urinary Tract Disorders Goel RH, Unnikrishnan R, Remer EM Radiol Clin N Am 53 (2015) 1273–1292 - Renal Stone Composition
• calcium based (75%)
• struvite (15%)
• uric acid (UA) (8%)
• cysteine (3%)
- “Important IF occurred in 12.7% of non-enhanced CT scans performed for suspected renal colic in the emergency department and are more common in older individuals. Prospective studies that use radiographic recommendations to characterize IF and examine the outcome and cost of their workup are encouraged.”
Incidental Findings on CT for Suspected Renal Colic in Emergency Department Patients: Prevalence and Types in 5,383 Consecutive Examinations.
Samim M et al.
J Am Coll Radiol. 2015 Jan;12(1):63-9. - “PURPOSE:
This study aimed to determine the prevalence, importance, and types of incidental findings (IF) in non-enhanced CT scans performed for suspected renal colic, based on ACR white papers and other accepted radiographic recommendations.
METHODS:
Retrospective review of 5,383 consecutive finalized reports of nonenhanced CT using renal colic protocol performed on adult patients at 2 emergency departments over a 5.5-year period. IF were defined as those unrelated to symptoms (as opposed to alternate causes of symptoms) and were categorized as "important" if follow-up was recommended based on recently published consensus recommendations.”
Incidental Findings on CT for Suspected Renal Colic in Emergency Department Patients: Prevalence and Types in 5,383 Consecutive Examinations.
Samim M et al.
J Am Coll Radiol. 2015 Jan;12(1):63-9. - “Important IF were identified in 12.7% (95% confidence interval [CI]: 11.8%-13.6%) of scans. Prevalence of important IF increased with age: important IF in individuals age >80 years were 4 times more common than for those aged 18-30 years: 28.9% (95% CI: 22.4%-36.4%) versus 6.9% (95% CI: 5.5%-8.6%), respectively, P ≤ .05. Women had a higher prevalence of important IF compared with men: 13.4% (95% CI: 12.2%-14.7%) versus 11.9% (95% CI: 10.7%-13.2%), but the difference was not statically significant (P = .09).”
Incidental Findings on CT for Suspected Renal Colic in Emergency Department Patients: Prevalence and Types in 5,383 Consecutive Examinations.
Samim M et al.
J Am Coll Radiol. 2015 Jan;12(1):63-9.
- “ Determination of the maximum axial area may improve the accuracy in predicting spontaneous passage of ureteral stones, particularly those between 5 and 10 mm.”
CT-Based Determination of Maximum Ureteral Stone Area: A Predictor of Spontaneous Passage
Demehri S et al.
AJR 2012: 198:603-608
- Nephrolithiasis: Imaging Studies
- Ultrasound
- CT scanning
- Excretory Urography
- MR Nephrourography - Nephrolithiasis: What does the referring clinician need to know?
- Presence or absence of calculus
- Location of calculus (kidney, ureter, bladder)
- Number of stones
- Stone diameter
- Presence of additional findings (i.e. acute pyelonephritis)
Nephrolithiasis: What Surgeons Need to Know
Eisner BH et al.=
AJR 2011; 196:1274-1278 - Can renal calculi be missed on CT?
- 99 percent of stones can be detected ranging from calcium based stones to radiolucent stones like uric acid, xanthine, or cystine.
- The one percent of stones that can be missed are pure matrix stones or stones composed of protease inhibitor, indinavir - “ Not only does this study enable the detection of stones of all sizes, but in its area of examination from above the kidneys to below the bladder base, it enables the evaluation of other urinary and extraurinary abnormalities that may be contributing to symptoms of acute flank pain.”
Nephrolithiasis: What Surgeons Need to Know
Eisner BH et al.
AJR 2011; 196:1274-1278 "In patients with known calculi greater than 3 mm being evaluated for recurrent pain or when calculi 3 mm or smaller are viewed as not clinically important due to their spontaneous passage, a protocol with up to 75% reduction in dose should be considered."
Urinary Calculi: Radiation Dose Reduction of 50% and 75% at CT-Effect on Sensitivity
Ciaschini MW et al.
Radiology 2009; 251:105-111"There was no statistically significant difference in sensitivity with a 50% or 75% dose reduction for the detection of calculi greater than 3 mm in diameter."
Urinary Calculi: Radiation Dose Reduction of 50% and 75% at CT-Effect on Sensitivity
Ciaschini MW et al.
Radiology 2009; 251:105-111"There was no significant differences between the 100% examinations and the 50% and 25% examinations for the detection of calculi greater than 3 mm."
Urinary Calculi: Radiation Dose Reduction of 50% and 75% at CT-Effect on Sensitivity
Ciaschini MW et al.
Radiology 2009; 251:105-111"For all stones, stone size estimation is improved in the coronal plane, and the difference is significantly more pronounced for vertically oriented stones, which may be underestimated in the axial plane by more than 20%."
Assesment of Urinary Tract Calculi With 64-MDCT: The Axial Versus Coronal Plane
Metser U et al.
AJR 2009; 192:1509-1513"The detection of stones and estimation of maximal stone diameter were improved using coronal reformations. The conspicuity of stones and diagnostic confidence in identifying stones smaller than 5 mm in diameter were also improved on the coronal plane."
Assesment of Urinary Tract Calculi With 64-MDCT: The Axial Versus Coronal Plane
Metser U et al.
AJR 2009; 192:1509-1513"On arterial phase scans, 75% of the renal calculi and all renal calculi larger than 5 mm were detected; the attenuation of the calculi had a significant correlation to detectability."
Detection of Renal Calculi on Late Arterial Phase Computed Tomography Images: Are Noncontrast Scans Always Needed to Detect Renal Calculi?
Kawamoto S, Horton KM, Fishman EK
J Comput Assist Tomogr 2008;32:859-864"The reduced radiation CT protocol (30 mAs) resulted in similar detection of renal stones 3.0 mm or larger compared with the standard radiation protocol (100 mAs) while reducing patient exposure by as much as 70%."
Effect of Reduced Radiation CT Protocols on the Detection of Renal Calculi
Jin DH et al
Radiology 2010; 255;100-107"Detection of 2.0 mm stones is difficult, even with standard CT protocols by using 5 mm section reconstruction; this may lead to a significant overestimation of sensitivity in clinical studies where a conventional CT scan is used as a reference standard."
Effect of Reduced Radiation CT Protocols on the Detection of Renal Calculi
Jin DH et al
Radiology 2010; 255;100-107"In patients with known calculi greater than 3 mm being evaluated for recurrent pain or when calculi 3 mm or smaller are viewed as not clinically important due to their spontaneous passage, a protocol with up to 75% reduction in dose should be considered.”
Urinary Calculi: Radiation Dose Reduction of 50% and 75% at CT-Effect on Sensitivity
Ciaschini MW et al.
Radiology 2009; 251:105-111"There was no statistically significant difference in sensitivity with a 50% or 75% dose reduction for the detection of calculi greater than 3 mm in diameter."
Urinary Calculi: Radiation Dose Reduction of 50% and 75% at CT-Effect on Sensitivity
Ciaschini MW et al.
Radiology 2009; 251:105-111"There was no significant differences between the 100% examinations and the 50% and 25% examinations for the detection of calculi greater than 3 mm."
Urinary Calculi: Radiation Dose Reduction of 50% and 75% at CT-Effect on Sensitivity
Ciaschini MW et al.
Radiology 2009; 251:105-111- "Coronal reformations from MDCT do not improve urinary stone detection but may reduce evaluation time; however, there is a danger of missing additional findings. Coronal reformations from thick (i.e. 3-5mm) axial sections may result in reduced detection of small stones and should therefore be avoided."
Unenhanced MDCT in Patients with Suspected Urinary Tract Stone Disease: Do Coronal Reformations Improve Diagnostic Performance Memarsadeghi M et al.
AJR:189, August 2007,329
- Urolithiasis
Very common:
- 12% of the population - Of those, 50% will have recurrence within 5 years
- Accounts for up to 1/100 hospital admissions
- Incidence increasing
Who is affected?:
- Males more than females
- More common in caucasians
- Usually present between 20-40 years of age
- "Multidetector computed tomography has become the imaging study of choice for the diagnosis of urinary tract calculi, investigation of hematuria, and the characterization of renal masses."
Imaging for Renal Colic and Hematuria
Miller JC et al.
JACR 2006:814-817.