Imaging in Renal Colic
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?
The Literature:
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. [1] 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. [2] 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?
The Literature:
An older
article in the British Journal of
Radiology published in 2001 [3] [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 [4]. 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.
Take home:
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.
References:
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.