State of the art trends in imaging renal of colic

The role of serum and urinary markers in predicting obstructing ureteral stones and reducing unjustified non-contrast computerized tomographic scans in emergency departments

INTRODUCTION

The reported yield of non-contrast computed tomography (NCCT) in assessing flank pain and obstructive urolithiasis (OU) in emergency departments (EDs) is only ~ 50%. We investigated the potential capability of serum and urinary markers to predict OU and improve the yield of NCCT in EDs.

METHODS

All consecutive ED patients with acute flank pain suggestive of OU and assessed by NCCT between December 2019 and February 2020 were enrolled. Serum white blood cells (WBC), C-reactive protein (CRP) and creatinine (Cr) levels, and urine dipstick results were analyzed for association with OU, and unjustified NCCT scan rates were calculated.

RESULTS

NCCTs diagnosed OU in 108 of the 200 study patients (54%). The median WBC, CRP, and Cr values were 9,100/µL, 4.3 mg/L, and 1 mg/dL, respectively. Using ROC curves, WBC = 10,000/µL and Cr = 0.95 mg/dl were the most accurate thresholds to predict OU. Only WBC ≥ 10,000/µL (OR = 3.7, 95% CI 1.6-8.3, p = 0.002) and Cr ≥ 0.95 mg/dl (OR = 5, 95% CI 2.3-11, p < 0.001) were associated with OU. Positive predictive value and specificity for detecting OU among patients with combined WBC ≥ 10,000 and Cr ≥ 0.95 were 83% and 89%, respectively. Patients negative to the serum markers criteria underwent significantly more unjustified NCCTs (p = 0.03). The negative predictive value of the serum criteria for justified NCCT scanning was 81%.

CONCLUSIONS

WBC and Cr may be valuable serum markers in predicting OU among patients presenting to EDs with acute flank pain. They may potentially reduce the number of unjustified NCCT scans in the ED setting.

Comparison of ureteric stone size, on bone window versus standard soft-tissue window settings, on multi-detector non-contrast computed tomography

Objective

To compare the difference in mean stone size, as measured on bone window vs standard soft-tissue window setting using multi-detector computed tomography (MDCT) in patients with a solitary ureteric stone.

Patients and methods

In all, 60 patients presenting to the emergency and outpatient departments of a University Hospital from May 2015 to October 2015 and fulfilling the inclusion criteria were included in the study. A 64-slice MDCT was used to assess the locations and size of the ureteric stones. A consultant radiologist independently analysed the MDCT scans of all the patients. The mean difference in stone size was calculated between both window settings in axial and coronal planes.

Results

The mean (SD) age of the patients was 37.13 (11.9) years. Males constituted ∼68% of the cohort and 32% were female. In all, 85% of the patients had left ureteric stones and 15% had right ureteric stones. The mean (SD) stone size, as measured on the soft-tissue window setting was 6.68 (2.01) mm, and on the bone window setting was 4.8 (1.9) mm. The mean (SD) difference in stone size between the two window settings was +1.85 (0.55) mm. The two means were compared using Student’s t-test, and the difference was found to be statistically significant (P < 0.05).

Conclusion

The stone size measured using the soft-tissue window setting on a MDCT is significantly different from the measurement on the bone window setting.

Radiation Dose Reduction in Dual-Energy CT: Does It Affect the Accuracy of Urinary Stone Characterization?

OBJECTIVE

The purpose of this article is to assess the effect of radiation dose reduction in dual-energy CT (DECT) on the performance of renal stone characterization using a patient cohort.

MATERIALS AND METHODS

CT data from 39 unenhanced DECT examinations performed for stone characterization were retrospectively analyzed in this study. Reduced-dose images were simulated at 75%, 50%, and 25% of the routine dose using a previously validated noise-insertion algorithm. Differentiation between uric acid (UA) and non-UA stones was performed using a fixed cutoff value for the dual-energy ratio. ROC analysis was performed to determine optimal cutoff values and the associated sensitivity and specificity.

RESULTS

Of the 206 stones found, 43 were UA and 163 were non-UA. The mean (± SD) volume CT dose index (CTDIvol) was 16.0 ± 4.0 mGy at the 100% dose level. The mean noise in 100-kV images increased from 40.9 ± 6.8 HU at 100% dose to 46.8 ± 8.8 HU, 57.7 ± 12.5 HU, and 85.4 ± 22.9 HU at 75%, 50%, and 25% dose levels, respectively. Using the default cutoff value, for stones 10 mm(3) or larger, the sensitivity/specificity were 100.0%/98.8%, 82.8%/98.8%, and 89.3%/98.7%, at 75%, 50%, and 25% dose levels, respectively. ROC analysis showed varying optimal cutoff values at different dose levels. The sensitivity and specificity improved with use of these optimal cutoff values. Differentiation capability decreased for stones smaller than 10 mm(3).

CONCLUSION

At 75% of the 16-mGy routine dose, the sensitivity and specificity for differentiating UA from non-UA stones were minimally affected for stones 10 mm(3) or larger. The use of optimal cutoff values for dual-energy ratio as dose decreased (and noise increased) provided improved performance.

Acute Urinary Tract Disorders

Acute urinary tract disorders often manifest as flank pain and are a common complaint of patients who present to the emergency department. The pain is often a vague, poorly localized sensation that may have a variety of causes. Laboratory and clinical findings, such as hematuria, are neither sensitive nor specific for determining the cause of the flank pain. Accordingly, imaging is an important tool in determining a diagnosis and management plan. Patients with acute urinary tract disorders who present with pain include those with calculi as well as renal infection, vascular disorders, and hemorrhage.

Is CTKUB the gold standard in assessing flank pain with diagnostic uncertainty? A one-year review of 228 cases

The use of computed tomography of the kidneys, ureters and bladder (CTKUB) in a "renal colic pathway" has been reported to yield high diagnosis rates and also identifies other non-urological pathology accounting for patients’ symptoms. Our study explores the diagnostic yield of CTKUB as the first-line investigation for suspected renal colic with regard to urolithiasis and additional findings. All CTKUB performed in cases of suspected renal colic were extracted from our radiology database from 1 April 2010 to 1 April 2011. Extracted information included: demographics, the department ordering the investigation, presence of ureteric calculi, presence of renal calculi and any additional findings that could account for patients’ symptoms, or otherwise. During the study 228 CTKUB were performed. The diagnosis rate of ureteric calculi was 33.7%. In the absence of a ureteric stone, additional findings as well as alternative diagnoses were higher (additional finding 49.7% ( n=75) vs. 35% ( n=27); alternative diagnosis 33.1% ( n=50) vs. 15.6% ( n=12) p < 0.05). In patients with ureteric calculi, the alternative diagnosis yield of 15.6% falls within the range of that previously documented. This study illustrates that when diagnostic clarity is not reached, CTKUB is being overused. This leads to unnecessary radiation exposure and resource wastage.

Assessment of referral patterns for CT KUB in a tertiary setting

The purpose of this study was to assess the referral patterns and the use of unenhanced renal tract CT (CT KUB) for investigating patients presenting with clinically suspected renal colic. We retrospectively reviewed 500 consecutive CT KUB studies requested for suspected renal colic carried out at a single institution between December 2006 and July 2007. Follow-up radiology reports and discharge summaries on the hospital clinical Intranet were also reviewed. Studies were analysed for characteristics including patient demographics, referring clinical team, time of referral, final diagnosis and requirement for further imaging. The majority of requests were from Emergency (ED) or Urology Departments (49%, 245 out of 500, and 37%, 186 out of 500, respectively). The positive rate for urolithiasis was 67% (337 out of 500), the negative rate was 25% (123 out of 500), and 8% (40 out of 500) of patients had alternative significant findings. Female patients were more likely to have a negative study than male patients (35 versus 20%, P < 0.0001) and more likely to have alternative significant pathology (12 versus 6%, P < 0.0001). Patients referred by specialities other than Urology and ED were more likely to be female and have a negative or alternative finding (P < 0.0001). CT KUB is a widely used first method of investigation for patients with suspected renal colic with a high positive predictive value allowing rapid diagnosis and intervention. However, given the high rate of negative or alternative findings on CT KUB in young women, especially those referred by specialities other than ED or Urology, ultrasound should be considered as an alternative imaging method to minimise unnecessary radiation exposure.

Noncontrast multidetector CT of the kidneys: utility of 2D MPR and 3D rendering to elucidate genitourinary pathology

To encourage routine use of 2D multiplanar reconstructions (MRPs) and 3D renderings when interpreting noncontrast computed tomography (CT) of the kidney, as this practice can unveil findings related to the kidney or its vasculature that are not apparent on axial sections. Inspecting the kidneys or characterizing CT findings with both axial sections and MPRs may facilitate identification of vascular and neoplastic pathology.