Findings of Non-enhanced Abdominal Computed Tomography for Pain Management of Acute Renal Colic Patients in the Emergency Department

1. Introduction

Urinary tract stones are a common condition. The incidence of symptomatic urolithiasis is 13% in men and 7% in women [1, 2]. Acute renal colic caused by urolithiasis is an increasing problem in patients who present to the emergency department (ED) [3]. Appropriate diagnosis and acute management are essential. Radiological imaging plays a primary role in the evaluation of the presence of urinary tract stones. Multiple modalities, including simple radiography, intravenous urography, ultrasonography and non-enhanced computed tomography (NECT), can be used to identify urinary tract stones. Currently, NECT is superior to other diagnostic modalities for diagnosis of urinary tract stones [4, 5, 6, 7]. Studies have reported a NECT specificity of nearly 100% and sensitivity ranging from 96% to 98% for identifying stones [8, 9, 10]. NECT can also provide information about the location and size of stones [10, 11].

In addition to faster and more accurate diagnosis of urinary tract stones, an appropriate disposition plan must be established in the ED [4], and methods of pain control, need for urologic consultation, hospitalization and a disposition plan must also be considered. NECT findings, such as the stone size and its locations, are known be related to spontaneous passage of renal stones. However, this information is not always determinable from other imaging modalities.

We hypothesized that radiological findings from NECT would be useful for establishing a pain management strategy and disposition plan in the ED. The aim of this study was to identify the NECT findings associated with the repeated administration of painkillers, hospitalization, and recurrent visits to the ED in patients with acute renal colic seen in the ED.

2. Methods

This was a retrospective, cross-sectional observational study. Subjects were recruited from October 2012 to October 2015 at an urban university medical centre. During the study period, all adult patients aged $>$ 18 years with an acute urinary stone diagnosed using NECT in the ED were enrolled. The exclusion criteria included patients with a known urinary tract anomaly, serious comorbidities (diabetes nephropathy or neuropathy, cardiovascular disease, underlying renal failure, liver failure or malignancy), combined urinary tract infection, acute kidney injury caused by obstruction, anuria or a diagnosis of recent urinary stone within the past 3 months.

The demographic, clinical data and NECT findings of the study subjects were collected from the electrical medical chart and included age and sex, clinical data (presence of costovertebral angle tenderness [CVAT]), length of stay in the ED, administration of painkillers, hospitalization, 5-day ED revisit after discharge. We summarized the CT data from the radiologist’s report and the NECT findings as follows: stone size, stone location, presence of the soft-tissue rim sign, perinephric infiltration (fluid collection or fat stranding) and hydronephroureter.

The stone location was categorized into three groups: 1) proximal (from the renal pelvis to the top edge of the sacrum), 2) mid (from the top edge to the lower edge of the sacrum) and 3) distal (from the lower edge of the sacrum to the urinary bladder) [12]. The soft-tissue rim sign was considered to be present when the ureteral stone had an obvious surrounding rim of soft tissue [13]. When the outer wall of the ureter could not be seen because of the absence of a clear fat plane at the level of the calcification on CT, the sign was categorized as ‘negative’. Perinephric infiltration was defined as an obvious fluid collection or fat stranding. Obvious fluid collection was defined as discrete, rounded areas of fluid collection within the perinephric space. More than 1 cm diameter of fluid collection was considered positive for a perinephric fluid collection and $<$ 1 cm diameter of fluid collection was considered as ‘negative’ [14]. Obvious perinephric fat stranding was defined as several thick or circumferential linear areas of soft-tissue attenuation in the perinephric space. Hydronephroureter was defined as obvious dilatation of the urinary collecting system of the kidney (the intra-renal pelvis or renal calyces) along with dilatation of the ureter compared with the contralateral side [15].

During the study period, the initial diagnostic workup and management were performed by the attending emergency physician. Pain control was achieved primarily using non-steroidal anti-inflammatory drugs and narcotics were added if pain was intractable. The need for hospitalization was determined after consultation with the urologist for those patients with intractable pain/vomiting or those stones with minimal possibility of spontaneous passage. Patients discharged from the ED were given discharge instructions and a follow-up outpatient appointment 5–7 days after discharge from the ED.

The study outcomes included: 1) the need for repeated administration of painkillers in the ED, 2) hospitalization from the ED and 3) revisiting the ED within 5 days after discharge. To identify associations between NECT findings and clinical outcomes, univariate and multivariate logistic regression testing were performed. Independent Student t tests were used to compare normally distributed data, which are presented as mean and standard deviation. Mann–Whitney U tests were used to compare non-normally distributed data, which are presented as median and interquartile range. Statistical analyses were performed using SPSS Statistics 17.0 (SPSS Inc., Chicago, IL). A two-sided p value of $<$ 0.05 was considered significant.

3. Results

4. Discussion

NECT is now used almost exclusively for the diagnosis of patients with acute renal colic. However, no trials have evaluated the relationships between NECT findings and clinical outcomes (need for repeated administration of painkiller, need for hospitalization and ER revisits after discharge) during the acute treatment phase. We studied the role of NECT findings beyond diagnosis to establish an emergency care plan for patients with urinary stones. Our results show that mid/large sized stones ($>$ 5 mm) and the presence of obvious hydronephroureter are independently associated with the need for hospitalization, and proximal/mid stone location and the soft tissue rim sign are independently associated with 5-day ED revisits. This information might be useful for emergency physicians when establishing the treatment and disposition plans for patients with urinary stones.

Pain management is important for management of acute renal colic during the ED stay. The repeated administration of painkillers is indicative of uncontrolled pain. In this study, we found that NECT findings related to uncontrolled pain was the presence of obvious hydronephroureter, not the size or location of the ureteral stone. Physicians caring for patients with obvious hydronephroureter may anticipate the possibility of intractable pain and the need for the administration of multiple painkillers.

For patients with urinary stones in the absence of complications, the need for hospitalization has been traditionally based on the severity of symptoms and the possibility of spontaneous passage [4]. The size of a ureteral calculus is a well-known factor for spontaneous passage [12, 14]. In a systematic review by the European Association of Urology Nephrolithiasis Guideline Panel, the stone-passage rate was estimated as 68% for stones measuring $\le$ 5 mm and 47% for stones measuring $>$ 5 and $\le$ 10 mm [16]. In this study, the stone size of $>$ 5 mm was independently associated with hospitalization. Physicians are more likely to recommend hospitalization for patients with larger stones.

Hydronephroureter is one of the most frequently observed CT findings of acute ureterolithiasis and is a sign of ureteral obstruction. In this study, 486 of 862 patients (56%) with NECT evidence of ureteral calculi showed hydronephroureter, similar to that in a previous report by Katz et al [17].In this study, obvious hydronephroureter was an independent finding associated with hospitalization. A previous study has reported that hydronephroureter was not significantly associated with spontaneous stone passage [14].Considering the relationship between hydronephroureter and repeated administration of painkiller in our study, the higher hospitalization rate in the presence of hydronephroureter may not be explained by delayed spontaneous stone passage but rather by intractable pain.

The NECT findings associated with 5-day ER revisits might suggest delayed stone passage. In our study, stone location and soft tissue rim sign were two NECT findings that were independently associated with 5-day ED revisits. Proximal or mid ureteral stone was highly associated with 5-day ED revisits, similar to a previous study that evaluated the 30-day revisit rate for patients with ureteral stones [18]. In addition, we found that the soft-tissue rim sign is significantly associated with 5-day ED revisits. The soft-tissue rim sign appears as a surrounding rim of soft tissue around a calcific density, representing ureteric wall edema [12].The soft-tissue rim sign is traditionally used to diagnose ureteric stones and distinguish a ureteric calculus from a phlebolith [19]. Previous studies reported that the prevalence of the soft-tissue rim sign did not differ between patients with spontaneous stone passage and those who failed conservative management [14],and was not associated with the stone location or degree of obstruction [13, 20].However, recent research on ureteral wall thickness (UWT) suggests that the soft tissue rim sign may be associated with delayed stone passage. Yoshida et al. reported that higher UWT ( $>$ 2.7 mm) is associated with failed 4-week spontaneous stone passage [21]. In our study, we considered the soft tissue rim sign as positive when there is an obviously visible rim of soft tissue surrounding the ureteral stone, suggesting that only ureteral stones with a higher UWT were categorized as having a soft tissue rim sign. The soft tissue rim sign may indicate stone impaction and delayed spontaneous stone passage, and therefore can explain the association between the soft tissue rim sign and more frequent 5-day revisits.

In addition to the NECT findings, we found that women required significantly more hospitalizations and more frequently revisited the ED than men. We could not determine the exact cause in this retrospective study, but it may be that women have a greater ability to discriminate painful sensations, higher pain ratings, and a lower tolerance for pain than men [22]. Although the incidence of ureteral stones is higher in men, women seem to be more symptomatic.

This study has several limitations. First, physician preferences regarding hospital admissions for patients with renal colic might have affected the outcomes of this study. Second, our study results cannot be generalized since it reflects a single ED experience. No international standard guidelines have been established for pain control and hospitalization for patients with renal colic. Even if patients present with similar clinical symptoms, decisions may differ between medical institutions and between nations because of differences in culture or medical systems. In addition, our ED had a basic policy of short-term outpatient follow-up of 5–7 days, which we used to define the time for the revisit. Other hospitals have used a different follow-up time after ED discharge [18].Therefore, the revisit results of our study may have limited applicability to other institutions.

5. Conclusion

NECT findings are useful for predicting clinical outcomes in the ED in patients with renal colic. Hydronephroureter and large/mid-size stones were independently associated with the need of hospitalization, and proximal/mid stone location and the soft tissue rim sign were independently associated with 5-day ED revisits.

Acknowledgements

The authors would like to express our gratitude to institutional support from the clinical research supporting department of Konkuk University Medical Centre for sharing and analyzing its clinical data. Thanks to all the peer reviewers for their opinions and suggestions.

Conflict of Interest

All authors declare that they have no conflict of interest.

Ethics Approval

This study protocol was reviewed and approved by the institutional review board of the Konkuk University Medical Centre (KUH1260028). All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.

Funding information

This work was supported by the Soonchunhyang University Research Fund.