Introduction

Prevalence of nephrolithiasis in the developed world is estimated at 13% [1, 2], suspected ureteric colic is a common reason for presentation to the emergency department [3]. A renal ultrasound has a pooled sensitivity of 45% and specificity of 94% for detection of symptomatic ureteral calculi [4, 5]. The European Association of Urologists guidelines on urolithiasis advise renal ultrasound as the first-line imaging for patients with suspected ureteral calculi, however acknowledge that in practice CT KUB is now more frequently performed [6]. Unenhanced low-dose computed tomography in the assessment of suspected reno-ureteral colic is a highly sensitive imaging modality for the diagnosis of obstructing nephroureteral calculi [7,8,9], and has been showed to have a sensitivity and specificity of 97% and 96% respectively in the diagnosis of urolithiasis regardless of their size, location or composition [10]. The effective dose of a CT KUB can be as low as 1.3 millisieverts (mSv) [11]. In comparison, the mean effective radiation dose of a standard contrast-enhanced CT abdomen and pelvis can be as high as 8 mSv [12].

As the radiation dose is not negligible, it is important to monitor the diagnostic yield of CT KUBs. The aim of this study is to evaluate the diagnostic yield of CT KUB studies performed for suspected ureteral stones in patients presenting to the emergency department.

Methods

Study design

A retrospective review was performed of 500 patients who underwent CT KUB from the Emergency Department over a seven month period. CT KUB referrals and their reports were reviewed on the national picture archiving and communication system (PACS). Patient notes from the emergency department were also reviewed for the purposes of collecting data regarding haematuria. For the purposes of this study, we defined proximal ureter as extending from the renal pelvis to the upper border of the sacrum, mid ureter as extending from the upper to the lower border of the sacrum and distal ureter from the lower border of the sacrum to the urinary bladder [13].

Eligibility criteria

An institutional review board approved the study to retrospectively evaluate CT KUBs performed which had been requested by the emergency department physicians on adult patients. Patients presenting with urological devices in situ such as nephrostomy tubes and internal ureteral stents were excluded (n = 18). One patient was excluded as they were transferred from another hospital with a known ureteral calculus and they underwent repeat imaging (n = 1).

Statistical analysis

Numerical data are presented as mean standard ± differentiation. Categorical data are given as numbers and percentages. To compare patient groups the chi-square test was used. Statistical analysis was performed using GraphPad Prism 8 (GraphPad Software, San Diego, CA, USA). A P value of less than 0.05 was considered statistically significant.

Results

Urolithiasis

There were 500 patients included in the analysis. The mean age was 44.66 ± 15.62. Gender distribution was equal, 49% female (n = 248) and 51% male (n = 252). The was no significant difference between male and female patients age (Fig. 1). Of the total CTs performed, 34% (168/500) were positive for obstructing nephroureteral calculus. In three cases, although no calculus was seen, based on radiological findings including hydroureteronephrosis and periureteral fat stranding, it was inferred that a ureteral calculus had recently passed. These cases were excluded from the analysis due to the diagnostic uncertainty. In 5% (27/500) of cases, no localising side of discomfort was provided by the requesting clinician, limiting evaluation.

Fig. 1
figure 1

Age distribution of patients included in this study. There was no significant difference between male and female patients (female 44.14 vs male 45.18, p = 0.4583). Legend: ns = not significant

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CTKUB demonstrated obstructing ureteric calculi in 48% (120/252) of males and 19% (48/248) in females (p < 0.0001) (Fig. 2). There was no significant difference across genders in terms of ureteric stone size (Fig. 3). In the 200 female patients who were negative for obstructing urolithiasis, the mean age was 43. No underlying cause for symptoms was found for 61% (152/248) of females in this study (Table 1). Of those, 69% (105/153) were below the age of 50 (age range 16–49). In men by comparison, in only 37% (94/252) was no cause identified for the presenting symptoms.

Fig. 2
figure 2

A significantly greater number of negative CTKUB studies are performed on female patients

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Fig. 3
figure 3

There was no significant difference across genders in terms of ureteric calculus size (female 4.405 vs male 4.378, p = 0.9491). Legend: ns = not significant

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Table 1 Distribution of CTKUB findings across genders
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A slight majority of obstructing ureteral stones were on the left side (55%, 93/168), and unusually, in one case there were bilateral concurrent obstructing ureteral calculi. Calculus size ranged from 2 mm – 24 mm. Over half of the ureteral calculi identified were in the distal ureter (61%, 102/168), with 25% in the proximal ureter (42/168) and 14% identified in the mid ureter (24/168). In patients with obstructing ureteral calculi 37% (62/168) were found to also have non-obstructing renal calculi.

Alternative diagnoses

Alternative diagnoses were also reviewed (Table 1). In women, the most common alternative diagnosis was of ovarian pathology which was seen in 7.6% (19/248). These included ovarian dermoid tumour (3/248), haemorrhagic or ruptured ovarian cyst (3/248), enlarged heterogenous uterus suggestive of uterine leiomyomas (3/248) and ovarian cysts (10/248). The most common alternative diagnosis in men was a urological diagnosis such as pelviureteric obstruction (1.2%, 3/252), ureteric stricture (0.4%, 1/252), urological infection (2%, 5/252), renal mass (1.2%, 3/252) and a malignant extrinsic ureteric obstruction from lymphoma (0.4%, 1/252). Alternative urological diagnoses in women included infection (1.2%, 3/248), pelviureteric junction obstruction (0.4%, 1/248) and renal mass (0.8%, 2/248). Men were significantly more likely to be diagnosed with acute cholecystitis than women (1.6% in men versus 0% in women; p = 0.0457).

Incidental findings

Incidental findings requiring radiological follow-up imaging were detected in 12% (60/500). The commonest findings were renal lesions (2.8%, 14/500), liver lesions (1.8%, 9/500) and ovarian lesions (1.8%, 9/500). Other findings included lung nodules, gallbladder thickening, uncomplicated cholelithiasis, uterine lesions, lymphadenopathy, bowel thickening, pleural thickening, adrenal hyperplasia, bone lesions, splenic lesions, breast lesions and pancreas lesions.

Haematuria

In patients found to have ureteral calculi, 81% had non-visible haematuria (microscopic or dipstick), 7% had visible haematuria (macroscopic or gross), 4% did not have haematuria and 8% were not documented whether they did or did not have haematuria.

Haematuria was noted in 73% (145/200) of female patients without urinary tract calculi. A possible underlying aetiology for haematuria was noted on imaging in just 1.4% (2/145) of these cases.

Discussion

This study is the largest series from Ireland to evaluate the appropriateness of CT KUB utilization for suspected ureteral calculi among patients presenting to the emergency department. The CTKUB positivity rate is 34% and is significantly greater for male patients (48% in males versus 19% in females). We a notably higher rate of non-diagnostic scans in female patients compared to male patients (61% versus 37%). Ovarian pathology is the commonest alternate diagnosis made among patients with suspected ureteral calculi. Thirty seven percent of patients with ureteral calculi will also have non-obstructing renal calculi requiring further follow-up by Urology [14]. Incidental findings were identified in 12% of patients presenting to the emergency department with renal colic.

In our study 34% of patients who underwent CT KUB for suspected ureteric colic were positive. The American Urological Association and European Association of Urology guidelines, as well as the Royal College of Radiologists, suggest that CT KUB studies performed should detect calculi in at least 44% of patients, with alternate diagnoses identified in a further 6–18% [6, 15, 16]. In our study, 17% of cases had an alternative diagnosis (86/500), which was slightly higher in comparison to prior studies which have reported alternative diagnoses made in 12% of patients [7, 17]. Patatas et al. described this phenomenon as the “indication creep” whereby there is a danger that CT KUB might be over-used as these respectively lower dose, non-contrast studies are perhaps more readily accessible [17].

Concerningly, there was a significantly lower positivity rate in females compared to males (19% versus 48%; p < 0.0001) which raises the issue of radiation exposure to this cohort. Further, the disparity in these two groups was not explained by an alternative diagnosis with 61% of females having no cause for symptoms identified. This is particularly of concern as all pelvic CT causes direct gonadal radiation in female patients [10], and in our study, 69% of the female patients with non-diagnostic scans were below the age of 50. Previous studies have demonstrated a higher detection rate of CT KUB for obstructing urolithiasis in men compared to women, and that as in our study, this difference is not accounted for by the detection of alternative diagnoses in the female cohort [17, 18].

We identified incidental findings in 12% of patients in our study. The commonest findings were renal lesions (2.8%, 14/500), liver lesions (1.8%, 9/500) and ovarian lesions (1.8%, 9/500). This volume of incidental findings is similar in a contemporary large series[19]. This can be a source of significant psychological distress for patients who are being discharged from the emergency department.

Haematuria is a known predictor of urological malignancy [20]. Haematuria was detected in 88% of patients with obstructing urolithiasis and this finding is similar to multiple other similar studies [21, 22]. Haematuria was noted in 73% (145/200) of female patients without urinary tract calculi. A possible underlying aetiology for haematuria was noted on imaging in just 1.4% (2/145) of these cases. The remaining 143 patients all had haematuria and abdominal pain of unknown aetiology, necessitating follow-up urinalysis and referral to a urologist for haematuria of unknown aetiology.

The limitations of this study include that is it a retrospective, single centre case series. In gathering data via the radiology information system, we were heavily reliant on the clinical information provided by the ordering clinician at the time of scan request. This study also did not include data on point-of-care ultrasound which is increasingly utilised by the emergency physicians in this institution. This study does not include follow-up data regarding the incidental findings noted on CT KUB. Future studies should include this information to evaluate clinical outcomes, workload burden and the economic impact these incidental findings cause.

It is clear that there is a potential for over-use of the CT KUB as a diagnostic tool for pain that may not conform to the classical history of ureteric colic. It is the duty of the requesting physician and of the radiologist to ensure that only appropriate scans are being performed. Teaching of urology at undergraduate level plays a large role in this as regardless of future career intentions, most if not all clinicians will encounter patients with urological problems during their work, especially those who choose a career in Emergency medicine [23]. Despite having a relatively low dose, CT KUB still delivers a dose of ionising radiation and as we have demonstrated, the majority of our female patients who did not have an obstructing urolithiasis were young. Based on the findings in this study we propose that clinicians consider ultrasound kidneys as an initial diagnostic tool in female patients with suspected renal colic and if hydronephrosis is identified then proceed to a CT KUB. This intervention would reduce harmful radiation exposure in this cohort.

Conclusion

Women are less likely than men to have obstructing urolithiasis on CT KUB for suspected renal colic. This difference is not accounted for by a higher rate of alternative diagnoses among female patients and therefore raises concerns regarding radiation exposure. Ovarian pathology was the most common alternative diagnosis in female patients. Thirty seven percent of patients with ureteral calculi will also have non-obstructing renal calculi requiring further follow-up. incidental findings are found in 12% of renal colic emergency department presentations. The findings of this study should prompt clinicians to exercise caution when considering this imaging modality in this patient cohort and entertain alternative diagnoses, particularly in female patients.