You are working in the Emergency Department when a 30ish year-old female is wheeled by, clasping on to her right flank and clearly in pain. You head into the room and find out that she had the acute onset of right flank pain that has been coming and going for the last hour. She is otherwise healthy and denies any prior history of renal stones. Thinking that this is probably a kidney stone, you order some pain medication, a UA, and a urine pregnancy test. She is (thankfully) not pregnant and has 2+ blood in her UA.
You log back in to order your next diagnostic test of choice. You start to click on “renal stone protocol CT” but pause… and think to yourself: “Do I need to irradiate this woman to make the diagnosis? Will the results of the CT scan change my management in some way? What are the alternatives?”
Clinical Question #1:
Does a CT scan change management in cases of suspected uncomplicated renal colic?
There are several smaller studies that addressed whether a CT scan changes the clinical management in a patient where there is a high suspicion for renal stone.
Zwank et. al.  published a prospective observational study addressing this question. The study enrolled providers caring for 93 “clinically stable” patients > 18 yo with abdominal or flank pain, > 18 years of age and the “most likely diagnosis” of renal colic. Patients at higher risk of complication, i.e. those with a history of chronic kidney disease, nephrectomy, renal transplant, UTI, prior renal stones, were excluded from the study. Prior to the CT, providers were surveyed as to what their top 3 differential diagnoses were and whether they thought that the CT scan might change management. In the end, 62/93 patients who were scanned were diagnosed with renal colic (as a side note only 84% of these had hematuria on UA). Five (5.3%) patients received an alternative diagnosis after CT scan – two ovarian cysts, one ovarian tumor, diverticulitis, and mesenteric edema. Of the 16 patients where CT scan was obtained even though the provider thought it was very unlikely to change management, 10 had symptomatic renal stones and reportedly none had a change in management (unclear why the disparity if a diagnosis was not reach in 6/16 cases). On this small pool of data, the authors conclude that “This result indicates that providers who are confident with the diagnosis of renal colic and who do not anticipate benefit from a CT scan can trust their low pre-test probability or ‘gestalt’ of low likelihood of benefit and should strongly consider not ordering a CT scan.”
Another way of framing the question about whether CT scans change management in patients thought to have renal colic is to examine the incidence of alternative diagnoses that are found on CT in these patients. In their prospective study, Pernet et. al.  examined this question by following the CT diagnosis of 155 patients with suspected uncomplicated renal colic (i.e. exclusion of patients with compromised renal function, UTI, fever, suspected bilateral renal stones). 118/155 (77%) were found to have uncomplicated stones, while 10 (6%) of these patients were found to have alternative diagnoses after CT. These diagnoses included large calculi needing urology intervention, pyelonephritis, biliary colic, appendicitis, ileitis, small bowel obstruction and intra-renal hemorrhage. Though a similar proportion of alternative diagnoses were found in this study when compared with Zwank et. al. above, these authors argue that CT(low-dose radiation) should be performed in cases of predicted uncomplicated renal colic because of the proportion of alternative diagnoses that mandated other intervention or hospitalization. They further argue, that the population of patients which people would least want to irradiate (young women) are also the most likely to have some alternative diagnoses.
Clinical Question #2:
Given that stones requiring urologic intervention and alternative diagnoses are found on CT imaging, how does ultrasound measure up as an imaging modality?
An older article in the British Journal of Radiology published in 2001  [around the advent of use of CT and Ultrasound for diagnosis of renal calculi as opposed to intravenous urography (IVU)] prospectively evaluated the sensitivity and specificity of non-contrast CT and ultrasound for renal calculi. They prospectively enrolled 62 patients with suspected uncomplicated renal colic. These patients underwent both renal ultrasound and CT scan. The gold standard was stone recovery or urological intervention. 43 (69%) of patients with suspected renal colic were confirmed by the “gold standard”. Ultrasound showed 93% sensitivity and 95% specificity in the diagnosis of ureterolithiasis, while CT showed 91% and 95%. Alternative pathology was found in six patients (~ 10%). These alternative pathologies were cholelithiasis, cholecystitis, ovarian torsion, adnexal masses and appendicitis. Both CT and ultrasound detected these, with the exception of the case of appendicitis, which was detected by CT scan alone. Given advances in imaging technology, it is likely the sensitivity of CT has increased with time, but this is an impressive comparison.
Another study compared KUB + ultrasound versus CT scan for detection of clinically significant renal stones . This was a retrospective study of 300 patients evaluated with KUB, US, non-contrast CT or some combination of the above for renal colic. The study is overall very confusing because of the number of combinations of imaging modalities that patients had. Despite this, one interesting observation was that among 147 patients who underwent KUB and/or US and CT scan, 22 had a normal KUB or US (unclear what proportion had what) and a CT scan positive for stone. Of these, mean stone size was < 5 mm suggesting that this was a population of patients who was unlikely to need any type of urologic intervention.
Along the same lines of sensitivity of ultrasound for renal stones requiring urologic intervention, two separate studies examined the incidence of urologic intervention needed in patients with “normal” renal ultrasounds [5, 6]. In one of these studies (Yan et. al.) , they prospectively followed 341 patients with renal colic who were evaluated with ultrasound. Of the 105 (30.8%) patients were classified as “normal”, none had urologic intervention in the following 90 days. Alternative pelvic pathologies were identified on ultrasound (such as ovarian cysts and pregnancy) but there was no avenue for direct comparison with CT in this study. A similar study from Edmonds et. al. retrospectively reviewed the records of all patients undergoing renal ultrasound for suspected nephrolithiasis over the course of a year. Of a 352/817 (43%) that were classified as “normal”, only 2 patients (0.6%) required urologic intervention in the following 90 days. They did not comment on alternative diagnoses.
Renal ultrasound is a reasonable initially imaging modality for patients with suspected uncomplicated renal colic. While we are overall pretty good an predicting who has renal colic based on history and exam (~ 60- 70% of all patients with this as a suspected diagnosis had imaging confirming it in the above studies), we should keep in mind that anywhere between 5 – 10% of these patients will have an alternative diagnosis requiring alternative management. Ultrasound is good at picking up these alternative diagnoses as well.
1. Zwank et. al. “Does computed tomographic scan affect diagnosis and management of patients with suspected renal colic?” American Journal of Emergency Medicine 32 (2014) 367–370
2. Pernet et. al. “Prevalence of alternative diagnoses in patients with suspected uncomplicated renal colic undergoing computed tomography: a prospective study.” CJEM. 2014 Feb 1;16(0):8-14.
3. Patlas et. al. “Ultrasound vs CT for the detection of ureteric stones in
patients with renal colic”. The British Journal of Radiology, 74 (2001), 901–904
4. Ekici and Sinanoglu. “Comparison of conventional radiography combined
with ultrasonography versus nonenhanced helical computed
tomography in evaluation of patients.” Urol Res (2012) 40:543–547
5. Yan et. al. “Normal renal sonogram identifies renal colic patients at low risk for urologic intervention: a prospective cohort study” CJEM 2014:1-8.
6. Edmonds et. al. “The utility of renal ultrasonography in the diagnosis of renal colic in emergency department patients” CJEM 2010;12(3):201-6.
Kindly submitted by Maia Dorsett, PGY-3.