Pediatric Urology Are Stone Protocol Computed Tomography Scans Mandatory for Children With Suspected Urinary Calculi?

Transcription

1 Pediatric Urology Are Stone Protocol Computed Tomography Scans Mandatory for Children With Suspected Urinary Calculi? Emilie K. Johnson, Gary J. Faerber, William W. Roberts, J. Stuart Wolf, Jr., John M. Park, David A. Bloom, and Julian Wan OBJECTIVE METHODS RESULTS CONCLUSION To examine the clinical utility of noncontrast-enhanced computed tomography (NCCT) in pediatric patients with urolithiasis who progressed to surgery. Although NCCT is routine for the evaluation of adult patients with suspected urolithiasis, its routine use in the pediatric population is tempered by concern about radiation exposure. We conducted a retrospective chart review of all pediatric patients who had undergone surgery for urinary stones from 2003 to 2008 at our institution. The imaging modalities used, surgery type, stone composition, 24-hour urinalyses, and relevant predisposing conditions were characterized. A total of 42 pediatric patients (24 males and 18 females) were treated during the 6-year period. The average age was years (range ), and the most common treatment modalities were shock wave lithotripsy (28%) and ureteroscopy (22%). A discernible risk factor or cause of urolithiasis was absent in 21 patients (47%). A review of imaging studies found 38 with stones visible on ultrasonography and/or abdominal plain film. A total of 21 patients underwent NCCT, in addition to ultrasonography and/or abdominal plain film. Of these, only 5 patients required NCCT for the diagnosis or management of their stone. Nearly 90% of pediatric patients treated for symptomatic urolithiasis could have completed their evaluation and treatment without undergoing NCCT. For children who present with signs and symptoms suggesting urinary calculi, an initial evaluation and imaging with ultrasonography and abdominal plain film might suffice, avoiding the radiation of NCCT. UROLOGY 78: , Elsevier Inc. Although nephrolithiasis among children in the United States remains less common than in adults, its incidence appears to be increasing. 1 The 2007 Urologic Diseases in America survey found that the rate of hospital admissions for urolithiasis in adults was 62/ compared with 4.7/ in children. 2 It has now increased such that stone disease in children has become recognized as a significant medical problem, even by the lay press. 3 In addition to heritable metabolic conditions, such as cystinuria and primary oxaluria, important risk factors for pediatric nephrolithiasis include obesity, 4 male gender, 5 and, increasingly diet, in particular, the high salt load in the typical child s diet. Additionally, some children form stones as a side effect of medical therapy or surgical procedures. For example, the ketogenic diets used to help From the Department of Urology, University of Michigan Medical Center, Ann Arbor, Michigan Reprint requests: Emilie K. Johnson, M.D., Department of Urology, University of Michigan Medical Center, 3875 Taubman Center, 1500 East Medical Center Drive, Ann Arbor, MI emiliej@med.umich.edu Submitted: October 4, 2010, accepted (with revisions): February 7, 2011 control epileptic seizures and bladder enterocystoplasty have been associated with an increased risk of stones in children. 6,7 Pediatric nephrolithiasis is often a recurrent, chronic condition that will likely necessitate multiple imaging studies during the course of a lifetime for affected patients. Noncontrast-enhanced computed tomography (NCCT) is currently the standard imaging modality in the evaluation of adults with suspected urolithiasis owing to its high sensitivity and specificity for renal and ureteral calculi. 8 It has largely supplanted other methods, such as intravenous urography (IVU), renal ultrasonography (US), and plain abdominal radiography of the kidneys, ureters, and bladder (KUB). However, given the greater radiation dose (approximately 10 msv per scan), understandable concern exists about adopting this practice universally in the pediatric population. The concern is not simply that of total exposure. The younger the age of initial exposure to the radiation associated with a body CT scan, the greater the lifetime risk of radiation-induced cancer. 9 The published adult data have compared NCCT with the other imaging modalities in patients with suspected Elsevier Inc /11/$36.00 All Rights Reserved doi: /j.urology

2 nephrolithiasis. Compared with NCCT, US is less sensitive and specific However, the stones missed on US are most often of a size ( 5 mm) that does not require procedural intervention and should pass spontaneously. 10 Additionally, patients with signs and symptoms of urolithiasis presenting to the emergency room are much less likely to require urologic intervention if the renal US scan is negative (0.6%) compared with those for whom the US findings suggest urolithiasis (6.8%). 13 A simple KUB is also less sensitive and specific compared with NCCT but is more accurate in determining the actual size of the urinary tract calculi. 14 The published data in the pediatric population is less extensive and clear than for the adults. Previous studies have demonstrated that a large proportion of pediatric renal and ureteral calculi can be identified without using NCCT. For example, 1 series of 29 pediatric patients showed that 78% of calculi seen on NCCT were also detected on US. 15 The overlapping concerns about limiting radiation exposure and maintaining effective stone detection led us to question whether NCCT should have the same prominence in imaging pediatric patients with stones as it does in adults. Our study reports on the clinical utility of NCCT in pediatric patients with stones who progress to surgical intervention to determine how often NCCT is useful in this patient population. MATERIAL AND METHODS We conducted a chart review of all pediatric patients with urinary tract calculi who progressed to procedural treatment from 2003 to 2008 at our institution. We defined a pediatric patient as any patient aged 18 years or any patient seen by a pediatric urologist because of an underlying condition being treated by that provider. The types and number of imaging studies required were assessed for each patient. When a NCCT scan was required, the specific indication for the study was ascertained. We excluded patients whose diagnostic workup did not include at least a single KUB (including those conducted as a specific study, as well as those obtained as component of IVU or voiding cystourethrogram) or US scan. The other clinical characteristics evaluated included procedure type and total number of procedures performed, stone composition, 24-hour urinalysis findings, and relevant predisposing conditions or comorbidities. The University of Michigan institutional review board approved the present study. RESULTS We identified 45 pediatric patients who underwent procedures for urolithiasis during the 6-year study period. The intervention was most commonly indicated because of pain or ureteral obstruction. Of the 45 patients, 3 were excluded because they had not undergone 1 KUB or US scan. Of these 3 patients, 2 had undergone NCCT as their initial and only mode of diagnostic imaging, and 1, with a neurogenic bladder, had a stone identified on routine cystoscopy. The demographic characteristics of the 42 patients included in the analysis are listed in Table 1. Of the 42 Table 1. Patient characteristics (n 42) Characteristic Value Sex Male 24 (57.1) Female 18 (42.9) Mean age (y) Average number of procedures Procedures (n) 1 20 (47.6) 2 14 (33.3) 3 8 (19.0) Stone location Renal 24 (57.1) Ureteral 13 (31.0) Bladder 5 (11.9) Predisposing conditions Neurogenic bladder 9 (21.4) Ureteropelvic junction obstruction 3 (7.1) Urogenital sinus 1 (2.4) Cystinuria 1 (2.4) Other metabolic abnormality 8 (19.0) None 20 (47.6) Stone composition* Homogeneous stone 8 (30.8) 100% CaOx dihydrate 3 100% CaPO % Uric acid 1 100% cystine 1 Matrix stone 2 Mixed stone composition 18 (69.2) CaOx/CaPO 4 11 CaOx dihydrate/caox monohydrate 3 CaOx/CaCO 3 3 CaOx/urate 1 24-h Urinalysis findings Low volume 7 (31.8) Multiple abnormalities 14 (63.6) Normal 1 (4.5) CaOx, calcium oxalate; CaPO 4, calcium phosphate; CaCO 3, calcium carbonate. * Data available for 26 patients. Data available for 22 patients. patients, 24 were 24 male and 18 were female. The procedures were performed for 24 renal, 13 ureteral, and 5 bladder calculi. The average age at surgery was years (range ). Of the 75 procedures performed (average procedure number per patient ), the most common were extracorporeal shock wave lithotripsy (29%) and ureteroscopy (23%). A neurogenic bladder was present in 9 patients (21%), and 21 patients (48%) had no identifiable predisposing condition. Stone analysis data were available for 28 patients, of whom 21 had calcium oxalate as the primary stone component. Only 1 pure cystine and 1 pure uric acid stone were found. In 16 patients, radiopaque stones were not recoverable for analysis. The 24-hour urinalysis data were available for 22 patients. Of these, only 1 was completely normal; all other patients had a low urine volume, often in association with other abnormalities. In all, 36 US scans, 26 KUBs, and 21 NCCT scans were performed for the evaluation of urolithiasis, with most patients undergoing evaluation with 2 imaging modalities. These studies revealed that 38 (90%) of the UROLOGY 78 (3),

3 Table 2. Clinical situations necessitating NCCT Pt. No. Stone Location Reason for NCCT Other Studies Performed 1 Proximal ureteral To further delineate anatomy before endoscopic US intervention 2 Renal To guide percutaneous treatment KUB (large renal stone visualized) 3 Distal ureteral US findings nondiagnostic; distal ureteral stone US 4 Distal ureteral US findings nondiagnostic; distal ureteral stone US 5 Distal ureteral US findings nondiagnostic; distal ureteral stone US NCCT, noncontrast-enhanced computed tomography; Pt. No., patient number; US, ultrasonography; KUB, abdominal plain film. 42 patients had visible stones on US and/or KUB. The US findings were falsely negative in 4 (11%) of 36 patients, 3 of whom underwent NCCT for a definitive diagnosis of a distal ureteral calculus. None of these patients received a KUB before proceeding to NCCT. KUB failed to demonstrate a stone in 5 (19%) of 26 patients, however, all 5 stones were seen on US. NCCT was used for the definitive diagnosis in 4 patients and for treatment planning in 1 patient. A total of 16 (76%) of 21 patients underwent NCCT, along with another imaging modality, when the evaluation and treatment did not necessarily require it clinically. The indication for NCCT for each patient for whom it was required is listed in Table 2. Additionally, none the patients who had false-negative US findings had undergone a KUB before proceeding to NCCT; thus, the proportion of patients who could have had a stone diagnosed without NCCT might actually have been 90%. COMMENT The management of urolithiasis has evolved and advanced with new diagnostic and therapeutic technologies. The earliest diagnostic approaches consisted of uroscopy and urethral sounding. Physicians since Hippocrates have recognized the necessity of cutting for stone as a treatment modality. 16 Cystoscopy, litholopaxy, and cystolithotomy became practicalities in the late 19th century. Within 1 century, extracorporeal shock wave lithotripsy, electrohydraulic and laser lithotripsy, ureteroscopy, and percutaneous nephrolithotomy have expanded the armamentarium. It is now possible to reach stones in children as young as 3 years old with the latest small scopes. 17 Although these technologies have improved therapy, our data suggest that older, simpler, and less-advanced imaging techniques might be as effective, with far less radiation risk. Clear indications for NCCT include nonvisualization of a stone on US and/or KUB and the necessity for treatment planning. In our patient population, we found that 90% of the patients had a stone visible on KUB and/or US. Moreover, 76% of the NCCT studies did not significantly add to the diagnosis or treatment planning for these children with symptomatic urolithiasis who progressed to surgery. Additionally, just over one half of our pediatric patients with urolithiasis underwent a 24-hour urine test to evaluate for metabolic abnormalities; this low rate of metabolic evaluation is a clear target for improvement in our population of symptomatic children with stone disease. Although a slim majority (53%) of our patients had some underlying risk factor for their stone formation, a low urine volume was a nearly universal finding for those patients with 24-hour urine collection data. Thus, although increased daily fluid intake would be expected to help decrease future stone formation risk, our patients are likely to be at risk of multiple stones during their lifetime. Judicious use of imaging remains a paramount concern, in particular, for in our selected population whose stones were symptomatic and/or large enough to require procedural intervention. Smith et al, 18 in 1995, was the first to describe NCCT as superior to IVU in the diagnosis of ureteral calculi. Since then, NCCT has become the de facto reference standard to evaluate flank and abdominal pain in adults. Previous studies in the adult published data comparing NCCT with other modalities have found that, in general, NCCT is more sensitive and specific for the detection of renal and ureteral calculi compared with US with or without KUB ,19-21 Ripolles et al 19 showed that NCCT was more sensitive and specific than the combination of KUB and US. However, importantly, they noted that all stones not detected on US passed spontaneously without requiring surgical intervention. 19 Catalano et al 20 presented similar findings from a cohort of patients who had undergone an initial evaluation with KUB and US, with the addition of NCCT only in equivocal cases. Despite the increased sensitivity and specificity of NCCT compared with KUB and US in adults, it is not so clear that NCCT should be the first imaging study when a child presents with flank pain or other signs and symptoms suggestive of urolithiasis. NCCT is unquestionably effective for the diagnosis of urolithiasis in children; 664 UROLOGY 78 (3), 2011

4 Figure 1. Renal US scan showing left lower pole stone with twinkle artifact. however, there has been an historical lack of attention to radiation dosing protocols in this patient population. 22,23 The vast majority of stones that require intervention in children can be detected by less-expensive, less radiationintense tools than NCCT. Oner et al 15 examined pediatric patients with equivocal KUB findings and showed that NCCT is more sensitive, in particular for small stones. However, US was able to detect 78% of calculi without exposing children to the radiation of CT. 15 Another investigation by Passerotti et al 24 demonstrated a 76% sensitivity and 100% specificity for US compared with NCCT in detecting urolithiasis in children. In the cases in which a discrepancy occurred, the US scan yielded enough information to dictate additional study, such as NCCT. 24 Although the combination of KUB and US is a reasonable first step in the child with suspected urolithiasis, in some children the diagnosis can remain equivocal or detailed cross-sectional imaging could be necessary for treatment planning. Physicians, especially those who work in emergency rooms or who are not familiar with the patient and who are evaluating pediatric patients with urolithiasis, should appreciate that conventional NCCT delivers a radiation dose approximately 10 times that of a KUB. The average person in the United States receives an effective does of about 3 msv annually owing to naturally encountered sources of background radiation, such as cosmic rays and household radon. A CT scan of the abdomen and pelvis is about 10 msv or approximately 3 years of exposure. For perspective, an IVU is about 3 msv, a chest radiograph is 0.1 msv, and a voiding cystourethrogram is msv. Variations will occur, depending on institutional protocols, but these relative proportions should help frame any discussion of risk. 25 More recent low-dose protocols have reduced the exposure; however, the radiation dose is still approximately twice that of KUB under the most ideal circumstances. 26 Many centers do not routinely reduce the dosages for children undergoing NCCT despite published protocols and strategies to limit exposure. 23,27,28 These low-dose protocols moreover do not appear to lower the efficacy in making the diagnosis of pediatric urolithiasis compared with the more traditional NCCT protocols. 29 At present, the combination of KUB and US delivers the lowest radiation dose while still detecting the vast majority of stones requiring surgical intervention. US is quite dependent on the quality of the equipment, hydration status of the patient, and skill of the operator; with these factors optimized, it can be a very effective study for identifying urinary tract stones (Fig. 1). Our study had several limitations. First, we were limited by the relatively small sample size and retrospective nature of the study. For example, we are unaware of any patients who might have initially undergone imaging for stones at our facility but who later underwent surgical intervention at another institution. Also, ideally, all patients would have undergone NCCT and a KUB or US scan, as well as a 24-hour urine collection and stone analysis. However, by selecting patients who ultimately progressed to surgical intervention, we hoped to identify the most symptomatic patients with recurrent stone formation and, theoretically, selected for the patients most likely to require additional imaging in the future. Additionally, although we had some level of internal control within our study with multiple patients undergoing NCCT, combined with US and/or KUB, this was a nonrandomized investigation that sought to evaluate the existing practices. From the results of the present analysis, we suggest any pediatric patient presenting with signs and symptoms of urolithiasis should be first evaluated with US, then KUB, and then only with NCCT, if the index of suspicion for stone disease remains high and the US and KUB findings were equivocal or negative. We have several plans for additional study at our institution. First, we are developing a protocol to examine NCCT use in our emergency department before and after instituting recommendations determined by the findings of the present investigation. Additionally, we plan to continuously evaluate the protocols for NCCT for pediatric patients who do require cross-sectional imaging for urolithiasis to ensure we are striving toward the use of the lowest necessary radiation dose in those patients who still require NCCT. CONCLUSIONS NCCT is necessary only in a few children with urolithiasis before intervention. The initial imaging modalities in children with urolithiasis should be renal US and/or KUB. Although NCCT imaging protocols have improved during the past decade, the radiation dose is still significantly larger than for a KUB. NCCT should be reserved for select situations in which the diagnosis is unclear or additional imaging is required for treatment planning. UROLOGY 78 (3),

5 References 1. VanDervoort K, Wiesen J, Frank R, et al. Urolithiasis in pediatric patients: a single center study of incidence, clinical presentation and outcome. J Urol. 2007;177: Pearle MS, Calhoun E, Curhan GC. Urolithiasis. In: Litwin MS, Saigal CS, eds. Urologic Diseases in America. Washington, DC: US Government Printing Office; 2007: Tarkan L, Woo SB, Pavlakis M, et al. A Rise in Kidney Stones Is Seen in US Children. New York Times, Sarica K, Eryildirim B, Yencilek F, et al. Role of overweight status on stone-forming risk factors in children: a prospective study. Urology. 2009;73: Novak TE, Lakshmanan Y, Trock BJ, et al. Sex prevalence of pediatric kidney stone disease in the United States: an epidemiologic investigation. Urology. 2009;74: Blyth B, Ewalt DH, Duckett JW, et al. Lithogenic properties of enterocystoplasty. J Urol. 1992;148: Kossoff EH, Pyzik PL, Furth SL, et al. Kidney stones, carbonic anhydrase inhibitors, and the ketogenic diet. Epilepsia. 2002;43: Smith RC, Verga M, McCarthy S, et al. Diagnosis of acute flank pain: value of unenhanced helical CT. AJR Am J Roentgenol. 1996;166: Brenner D, Elliston C, Hall E, et al. Estimated risks of radiationinduced fatal cancer from pediatric CT. AJR Am J Roentgenol. 2001;176: Fowler KA, Locken JA, Duchesne JH, et al. US for detecting renal calculi with nonenhanced CT as a reference standard. Radiology. 2002;222: Ulusan S, Koc Z, Tokmak N. Accuracy of sonography for detecting renal stone: comparison with CT. J Clin Ultrasound. 2007;35: Palmer JS, Donaher ER, O Riordan MA, et al. Diagnosis of pediatric urolithiasis: role of ultrasound and computerized tomography. J Urol. 2005;174: Edmonds ML, Yan JW, Sedran RJ, et al. The utility of renal ultrasonography in the diagnosis of renal colic in emergency department patients. CJEM. 2010;12: Narepalem N, Sundaram CP, Boridy IC, et al. Comparison of helical computerized tomography and plain radiography for estimating urinary stone size. J Urol. 2002;167: Oner S, Oto A, Tekgul S, et al. Comparison of spiral CT and US in the evaluation of pediatric urolithiasis. JBR-BTR. 2004;87: National Institutes of Health. The Hippocratic oath. Available from: Accessed November 28, Schuster TG, Russell KY, Bloom DA, et al. Ureteroscopy for the treatment of urolithiasis in children. J Urol. 2002;167:1813, Smith RC, Rosenfield AT, Choe KA, et al. Acute flank pain: comparison of non-contrast-enhanced CT and intravenous urography. Radiology. 1995;194: Ripolles T, Agramunt M, Errando J, et al. Suspected ureteral colic: plain film and sonography vs unenhanced helical CT: a prospective study in 66 patients. Eur Radiol. 2004;14: Catalano O, Nunziata A, Altei F, et al. Suspected ureteral colic: primary helical CT versus selective helical CT after unenhanced radiography and sonography. AJR Am J Roentgenol. 2002;178: Persaud AC, Stevenson MD, McMahon DR, et al. Pediatric urolithiasis: clinical predictors in the emergency department. Pediatrics. 2009;124: Strouse PJ, Bates DG, Bloom DA, et al. Non-contrast thin-section helical CT of urinary tract calculi in children. Pediatr Radiol. 2002;32: Paterson A, Frush DP, Donnelly LF. Helical CT of the body: are settings adjusted for pediatric patients? AJR Am J Roentgenol. 2001; 176: Passerotti C, Chow JS, Silva A, et al. Ultrasound versus computerized tomography for evaluating urolithiasis. J Urol. 2009;182: Radiological Society of North America (RSNA) and American College of Radiology (ACR). Patient Safety. Radiation exposure in X-ray and CT examinations. Available from: radiologyinfo.org/en/safety/index.cfm?pg sfty_xray. Accessed January 23, Katz SI, Saluja S, Brink JA, et al. Radiation dose associated with unenhanced CT for suspected renal colic: impact of repetitive studies. AJR Am J Roentgenol. 2006;186: Hamm M, Knopfle E, Wartenberg S, et al. Low dose unenhanced helical computerized tomography for the evaluation of acute flank pain. J Urol. 2002;167: Spielmann AL, Heneghan JP, Lee LJ, et al. Decreasing the radiation dose for renal stone CT: a feasibility study of single- and multidetector CT. AJR Am J Roentgenol. 2002;178: Karmazyn B, Frush DP, Applegate KE, et al. CT with a computersimulated dose reduction technique for detection of pediatric nephroureterolithiasis: comparison of standard and reduced radiation doses. AJR Am J Roentgenol. 2009;192: EDITORIAL COMMENT Ultrasonography (US) has emerged as the modality of choice for the diagnosis and follow-up of a wide gamut of diagnostic dilemmas in the pediatric age range. I applaud the authors for confirming the efficacy of US for the diagnosis of urinary tract stones in the pediatric population. Although noncontrast-enhanced computed tomography (NCCT) has been accepted as the reference standard for the evaluation of flank and abdominal pain in adults, this guideline should not be extrapolated to children, because their body habitus is generally ideal for evaluation with US. To increase the sensitivity and accuracy of US, state-of-the-art US equipment and proper probe technology must be used to optimize the demonstration of urinary tract stones and their complications. To maximize the identification of stones, patients should be well hydrated so the collecting systems are maximally distended and the bladder can provide a sonic window for evaluation of the distal ureters and ureterovesical junctions. The US evaluation of the urinary tract in both the pre- and the postvoid states is useful in the presence of hydroureteronephrosis. It is acknowledged that it is extremely difficult to demonstrate stones in nondilated ureters with US. However, when the computed tomography findings of whether a stone is within a distal ureter, at the ureterovesical junction, in the bladder, or is a phlebolith are unclear, US is useful for differentiation. Although at times, small brightly echoic foci identified on US can be inconclusive for the diagnosis of stones, the demonstration of shadowing of the US beam, as well as the US twinkle artifact, can help to confirm that such foci are stones. In addition, one can examine the entire urinary tract with US, including the urethra, which can be visualized in girls using a suprapubic or perineal approach or the perineum and in boys with a combination of a suprapubic approach and a highresolution linear probe directly on the penis. It can be helpful to have the child void during real-time US observation so the urethra is distended with fluid (hydrosonourethrography). It is impressive that the authors report that 76% of the NCCT studies performed in their patients did not significantly add to the diagnosis or treatment planning for these children with symptomatic urolithiasis. Although plain abdominal radiography can add information when the US findings are nega- 666 UROLOGY 78 (3), 2011