Computed Tomography for suspected renal colic in a regional stone unit: Are we diagnosing effectively and appropriately?
BAUS ePoster online library. Tien T. Jun 26, 2018; 217794
Mr. Tony Tien
Mr. Tony Tien
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Abstract
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Introduction
The lifetime incidence of urolithiasis is estimated to be 12% and occurs three times more frequently in males (Trinchieri, 2008). Patients typically present with severe colicky flank pain radiating to the groin with or without haematuria. Patients can develop complications such as obstruction, pyelonephritis, sepsis and renal failure without appropriate management (Al-Mamari, 2017).
At our regional centre, the first line investigation for suspected renal colic is non-contrast computed tomography of the kidneys, ureters and bladder (CT KUB). Alternative diagnoses such as abdominal aortic aneurysm, ectopic pregnancy, acute surgical abdomen and pyelonephritis are excluded prior to scanning. If urinalysis is positive for blood, they are managed with hydration, analgesia and a CT KUB within 24 hours of presentation (figure 1).

CT KUB was first proposed by Smith et al. (1995) as an investigation for ureteric colic in 1995. It is now increasingly being used in suspected renal colic due to its increased accuracy. A meta-analysis of prospective studies in low dose CT KUB has a pooled sensitivity of 96.6% and specificity of 94.9% (Niemann et al., 2008). The British Association of Urological Surgeons (BAUS) and The European Association of Urology (EAU) have now stated that CT KUB is the investigation of choice for suspected ureteric colic (Tsiotras et al., 2018; Türk et al., 2016).
Advantages of CT KUB include high sensitivity and specificity, operator independence, availability, low radiation dose, no contrast requirement and the detection of alternative abdominal pathology (Hoppe et al., 2006; Nadeem et al., 2012). However, with the high recurrence rate of ureteric colic, repeat CT KUB increases radiation exposure. Other imaging modalities include ultrasound scan of the kidneys, ureters and bladder (US KUB) and intravenous urogram (IVU). US KUB benefits in producing no radiation, though it has a lower sensitivity than CT KUB and is operator dependent (Ekici and Sinanoglu, 2012). IVU provides structural and functional information on the kidneys, ureters and bladder as well as the location and degree of obstruction. However, patients are exposed to intravenous contrast with the risk of an adverse reaction (Pfister et al., 2003).
Aims
We aimed to establish our positive pick up rate for urinary tract calculi, and investigate the suitability in patients imaged.
Methods
A retrospective audit of all CT KUBs performed during a 3-month period (June - August 2017) at a single regional hospital was carried out. All CT KUB examinations were carried out on a Toshiba Aquilon ONE 320 slice or Toshiba Aquilon PRIME 80 slice CT scanner (Toshiba Corporation, Tokyo, Japan). They are scanned with 120kV, low mA, which is modulated to patient size, in 0.5mm thickness and reconstructed to 1mm thickness with 1mm spacing. Coronal reformats at 3mm are also provided. All scans were reported by a consultant radiologist.
Data was obtained from discharge summaries, imaging reports and clinic letters from Integrated Clinical Environment (ICE) (Sunquest, Tucson, Arizona) and Insight PACS (Insignia Medical Systems, Basingstoke, United Kingdom). Information on patient demographics, clinical indication, stone presence, location and size and admissions were recorded. Ethical approval was not required due to the retrospective nature of this study.
Patients with known stones and those being scanned for follow up were excluded from analysis. Subgroup analysis was carried out to compare results based on patients' gender, age group (≤30 or >30) and the requesting clinical team.
Statistical analysis was performed using IBM® SPSS® Statistics v.25 for Windows.
Categorical variables were presented using absolute and relative frequencies, and continuous variables as mean (± standard deviation) for symmetrical and median (minimum-maximum) for asymmetrical distribution. Chi-square and Fisher tests were used to compare these variables, the latter for expected values below 5. The independent t test was used when distribution was symmetrical and the Mann-Whitney U test for asymmetrical distribution.
Results
A total of 379 CT KUB scans were performed during the 3 month period (1st June - 31st August) with 212 (55.94%) on male patients and 167 (44.06%) on female patients. The median age was 55 (17-101) years.
Suspected renal colic was the indication for 258 (68.07%) of the scans completed. The accident and emergency (A&E) department, urology department and other specialties requested 202 (78.29%), 36 (13.95%) and 20 (7.75%) scans respectively. Presence of a urinary tract stone was detected in 120 (46.51%) of the scans. The urology department had the highest positive stone rate with 52.78%, followed by A&E with 46.04% and then other specialties with 40%. Out of the scans positive for urinary tract stone, A&E had the highest rate for ureteric stone (30.69%) followed by other specialties (25.00%) and then the urology department (13.89%). More patients were being admitted from A&E for emergency treatment (73.21%) compared to the urology department (12.50%). 41.67% of CT scans arranged by the urology department were on an outpatient basis following clinic review. All positive CT KUB requested by other specialties were already inpatients (table 1).

Overall, male patients had a higher rate of CT KUB positive for urinary tract stone, 61.07% vs 31.50% (p<0.001). Patients in the >30 age group had a higher positive rate for urinary tract stone compared to the ≤30 age group, 50.23% vs 26.83% (p<0.05) (table 2a). In the >30 years age group, males again had a higher rate of CT KUB positive for stone, 64.96% vs 33.0% (p<0.001) (table 2b). Alternative diagnoses found on CT KUB included appendicitis, diverticulitis, cholecystitis, pyelonephritis and renal tumour (table 3).

Discussion
CT KUB has become the investigation of choice at most institutions in the United Kingdom and is recommended in the BAUS and EAU guidelines for suspected urolithiasis. Previous studies reported a positive stone rate of 29.00%-66.00% and ureteric stone rate of 35.12%-49.49% (table 4). Our data showed a positive stone rate of 46.5%, which is comparable to the established rates in the literature but our ureteric stone rate (27.90%) is lower than expected. This may be because a proportion of the scans were deliberately delayed in known stone formers who chose to have their scan as an outpatient (41.67%). It is plausible therefore, that the reduced ureteric stone pick up rate seen in our series reflects the passage of stone in these patients prior to their scan.

The literature has shown a two fold increase in radiation for CT KUB compared to IVU (Pfister et al., 2003). However, our centre has moved onto using ultra low dose CT KUB reducing radiation exposure to 1.1mSv. The radiation exposure for ultra low dose CT KUB has been proposed as <1.9mSv and low dose as <3.5mSv (Rob et al., 2017) compared to 4.5-5mSv produced by standard dose CT KUB (Türk et al., 2016). Low dose CT KUB has comparable sensitivity and specificity to standard CT KUB except in patients with stones <3mm or a body mass index of >30kg/m2 where it may not be as effective (Rob et al., 2017).
IVU dose is on average is 2.2mSv. CT KUB though, gives additional information on all stones present and may show signs of ureteric obstruction such as hydronephrosis, hydroureter, perinephric stranding and 'tissue rim sign' even after a stone passage (Pfister et al., 2003). In addition, CT demonstrates superiority over IVU as it is faster, less expensive, less risky and has the ability to detect other pathologies (Pfister et al., 2003). A possible disadvantage of CT KUB is the loss of functional information provided by IVU (Pfister et al., 2003).
There is debate on whether the merit of diagnostic accuracy for CT KUB outweighs the risk of radiation, particularly to the younger population. In our series, CT was more likely to detect a stone in patients over the age of 30. Our study also showed a reduced pick up rate of urinary tract stones in female patients compared to male patients, It is often difficult clinically to exclude differential diagnoses. Nonetheless, it is important to take a thorough history, examination and request basic investigations to identify patients who may reasonably avoid CT in favour of ultrasound, thus avoiding radiation.
The limitations of this study include its retrospective nature. Data collected for this study was from a single regional centre and therefore not representative of other hospitals in the country.
Conclusion
CT KUB has high sensitivity and specificity for most patients. We have successfully established our positive stone pick up rate in patients attending with suspected renal colic and found that the rate is comparable with that published in the literature. The ureteric stone pick up rate is slightly lower than expected. The CT KUB radiation dose at our centre is lower than that in many published series. Young female patients should be considered for alternative initial imaging such as ultrasound, which would reduce radiation exposure.
Recommendations
1) Presentation of findings at Stone Multidisciplinary Team Clinical Governance Quarterly meeting.
2) Ensure trust protocol for ureteric colic is printed and clearly visible in A&E.
3) Dynamic prospective review of positive stone pick up rate in patients presenting with suspected renal colic.































































Discussion
CT KUB has become the investigation of choice at most institutions in the United Kingdom and is recommended in the BAUS and EAU guidelines for suspected urolithiasis. Previous studies reported a positive stone rate of 29.00%-66.00% and ureteric stone rate of 35.12%-49.49% (table 4). Our data showed a positive stone rate of 46.5%, which is comparable to the established rates in the literature but our ureteric stone rate (27.90%) is lower than expected. This may be because a proportion of the scans were deliberately delayed in known stone formers who chose to have their scan as an outpatient (41.67%). It is plausible therefore, that the reduced ureteric stone pick up rate seen in our series reflects the passage of stone in these patients prior to their scan.








































































The literature has shown a two fold increase in radiation for CT KUB compared to IVU (Pfister et al., 2003). However, our centre has moved onto using ultra low dose CT KUB reducing radiation exposure to 1.1mSv. The radiation exposure for ultra low dose CT KUB has been proposed as <1.9mSv and low dose as <3.5mSv (Rob et al., 2017) compared to 4.5-5mSv produced by standard dose CT KUB (Türk et al., 2016). Low dose CT KUB has comparable sensitivity and specificity to standard CT KUB except in patients with stones <3mm or a body mass index of >30kg/m2 where it may not be as effective (Rob et al., 2017).
IVU dose is on average is 2.2mSv. CT KUB though, gives additional information on all stones present and may show signs of ureteric obstruction such as hydronephrosis, hydroureter, perinephric stranding and 'tissue rim sign' even after a stone passage (Pfister et al., 2003). In addition, CT demonstrates superiority over IVU as it is faster, less expensive, less risky and has the ability to detect other pathologies (Pfister et al., 2003). A possible disadvantage of CT KUB is the loss of functional information provided by IVU (Pfister et al., 2003).
There is debate on whether the merit of diagnostic accuracy for CT KUB outweighs the risk of radiation, particularly to the younger population. In our series, CT was more likely to detect a stone in patients over the age of 30. Our study also showed a reduced pick up rate of urinary tract stones in female patients compared to male patients, It is often difficult clinically to exclude differential diagnoses. Nonetheless, it is important to take a thorough history, examination and request basic investigations to identify patients who may reasonably avoid CT in favour of ultrasound, thus avoiding radiation.
The limitations of this study include its retrospective nature. Data collected for this study was from a single regional centre and therefore not representative of other hospitals in the country.
Conclusion
CT KUB has high sensitivity and specificity for most patients. We have successfully established our positive stone pick up rate in patients attending with suspected renal colic and found that the rate is comparable with that published in the literature. The ureteric stone pick up rate is slightly lower than expected. The CT KUB radiation dose at our centre is lower than that in many published series. Young female patients should be considered for alternative initial imaging such as ultrasound, which would reduce radiation exposure.
Recommendations
1) Presentation of findings at Stone Multidisciplinary Team Clinical Governance Quarterly meeting.
2) Ensure trust protocol for ureteric colic is printed and clearly visible in A&E.
3) Dynamic prospective review of positive stone pick up rate in patients presenting with suspected renal colic.
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