Plain x‐ray misses many ureteric calculi: Time to challenge the old dogma?

Department of Urology, Royal Brisbane and Women’s Hospital, Brisbane, Queensland, Australia Faculty of Medicine, University of Queensland, Brisbane, Queensland, Australia Emergency and Trauma Centre, Royal Brisbane and Women’s Hospital, Brisbane, Queensland, Australia Department of Medical Imaging, Royal Brisbane and Women’s Hospital, Brisbane, Queensland, Australia Faculty of Medicine, University of Queensland Centre for Clinical Research, Brisbane, Queensland, Australia


| INTRODUCTION
Ureteric colic is a common emergency department (ED) presentation and usually diagnosed with noncontrast computed tomography (CT).
Plain abdominal x-ray (AXR) was historically used for diagnosis and may help to monitor position of radio-opaque calculi during conservative management in contemporary practice. Despite being fast, convenient and having low ionising radiation exposure compared with CT, the clinical usefulness of AXR in contemporary practice is unclear.
Investigations with little clinical value may unnecessarily impede patient flow and increase ED wait-times and length of stay (LOS). The aim of this study was to determine the clinical benefits of AXR in ED patients with ureteric calculi for follow-up purposes and the impacts of AXR on ED LOS.
Information about patients with ureteric colic who presented to the Royal Brisbane and Women's Hospital ED between October 2019 and September 2020 was retrieved from the Emergency Department Information System and matched with information from radiology departmental archives for patients who underwent CT and AXR. Ureteric colic presentations were identified by diagnosis codes for 'renal colic' and 'urinary calculus'. Patients who did not have ureteric calculi on CT were excluded. The visibility of ureteric calculi on AXR was determined by radiologist interpretation and review by the authors.
Over half of ureteric calculi detected with CT were not identified on AXR (48.6% identified, n = 52/107) despite CT images being available to the AXR reporting radiologist. Review of AXR by the authors identified fewer calculi (41.1%, n = 44/107) with disagreement for 12 AXR, of which 10 was the inability to identify calculi, so the greater figure was used to represent the best-case scenario. Calculi visible on AXR tended to be larger (mean size 4.61 vs. 3.76 mm, p = 0.003) and located in the proximal ureter (60.7%, n = 17/28) rather than mid or AXR. There was comparatively greater yield for AXR in identifying proximal calculi of any size (60.7%, n = 17/28, p = 0.04) and any calculi that were 6 mm or larger (78.9%, n = 15/19, p < 0.01) compared with distal calculi ≤4 mm. As such, AXR has limited utility for followup of small distal ureteric calculi but may be considered in larger or proximal ureteric calculi.
Detection of calculi on AXR also depends on radio-opacity due to calcium content. Analysis of calculi from 2009 to 2011 in Australia found that 16% of upper tract calculi are uric acid composition, which would be radiolucent, and this has remained largely static since the 1970s. 1 In a study of patients with a history of calcium-containing calculi requiring urological intervention, 75% of calculi were detectable with AXR, although there was a higher calculi size (median 7 mm, IQR 5-10 mm) than our results and there were at least two reviewers of each AXR. 2 As such, there may be more of a role for AXR in patients with an established history of recurrent calcium-based calculi. There may also be local resource constraints mandating use of AXR, such as in remote areas. One study reported that AXR can be useful in deciding between endoscopic management or extracorporeal shockwave lithotripsy using fluoroscopy guidance, although the availability of lithotripters with ultrasound guidance may reduce this utility. 3,4 While AXR has lower ionising radiation exposure than standard dose CT, ultralow dose CT (ULD CT) achieves comparable exposure while reliably identifying ureteric calculi, including smaller distal ureteric calculi. Ultralow dose CT has a mean effective dose of 1.02-1.04 mSv in contemporary series (<1.9 mSv by definition) while maintaining diagnostic accuracy of 95.5%. [5][6][7] The effective dose of AXR can be 0.5-1 mSv, and one retrospective series reported that 34% of AXR exposed patients to higher effective doses than their concurrent CT. 6,8 As such, a pathway incorporating ULD CT where available, in place of AXR, for ureteric calculi follow-up purposes may result in similar levels of ionising radiation exposure. Recurrent stone formers may also have multiple CT scans, so this must still be used judiciously.
In conclusion, we found that the use of AXR in ureteric colic increased total ED LOS, and rates and lengths of admission to the ED short stay unit yet failed to identify many ureteric calculi even with F I G U R E 1 Percentage of ureteric calculi visible on abdominal x-ray (AXR) in 107 emergency department patients investigated for ureteric colic, according to axial diameter and location