IMAGING

Clinical characteristics of ureteral calculi detected by nonenhanced computerized tomography after unclear results of plain radiography and ultrasonography
Kobayashi T, Nishizawa K, Watanabe J, Ogura K
From the Department of Urology, Hamamatsu Rosai Hospital, Hamamatsu, Japan
J Urol. 2003; 170: 799-802

• Purpose: Prospective nonenhanced computerized tomography (CT) was performed for patients presenting with renal colic and showing negative or equivocal results on plain x-ray of the kidneys, ureters and bladder (KUB) as well as ultrasonography (US) to evaluate the usefulness of plain CT. We also evaluated the clinical characteristics of urinary calculi detected under such conditions.
• Materials and Methods: Between January 2000 and June 2002, 560 patients presented with acute unilateral renal colic. Of these patients 238 negative or equivocal for ureteral calculus on KUB and US underwent nonenhanced CT. The diagnostic value of plain CT in patients with negative or equivocal KUB and US was determined, and results and other clinical findings were compared. Clinical characteristics of ureteral stones detected by plain CT were compared with those of stones diagnosed by KUB and US.
• Results: By plain CT 143 (60.1%) and 6 (2.5%) cases of pain were determined to have been caused by ureteral stones and other pathogeneses, respectively. No definitive diagnosis was obtained in 89 (37.4%). Stone size detected by plain CT was significantly smaller than controls (3.77 vs 6.37 mm, p < 0.0001) and tended to be located in the middle or lower ureter (76.2% or 109 of 143 vs 52.2% or 168 of 322, p < 0.0001). Symptoms spontaneously improved in 137 (95.8%) after conservative therapy while 6 underwent intervention, a rate significantly lower (p < 0.0001) than controls (32.9% or 106 f 322).
• Conclusions: Nonenhanced CT is a useful modality for diagnosis of patients presenting with acute renal colic but whose results are negative or equivocal on KUB and US. Excretory urography is rarely needed because stones undetected on KUB and US tend to be small and in the middle or lower ureter, and spontaneous passage is expected.
  
  
• Editorial Comment
  Since its introduction, nonenhanced computed tomography (NECT) has become a very important diagnostic tool for detection and characterization of urolithiasis with unprecedented sensitivity, specificity and accuracy. NECT provides also useful information regarding treatment planning (location and size of the calculus) and etiology of several diseases that simulates renal colic. This technology has been shown to have sensitivity of 96% - 100%, specificity of 95.5% - 100%, and accuracy of 96% - 98%. In this study, the authors used NECT for renal colic evaluation only when plain film of the abdomen (KUB) and urinary tract ultrasound were negative or equivocal. Studying a population of 560 patients, they found ureteral stones in 322. Of the remaining 238 patients (42.5%) a definitive diagnosis of ureteral stones by NECT was possible in only 60 % of patients. Although the sensitivity and specificity could not be calculated, it is clear that this rate is too low when compared to previous reports. As already pointed out by the authors, the main reason for their low sensitivity in diagnosing ureteral stone could be explained by different technology employed. In previous report showing higher accuracy, images were obtained at a section thickness of 3 - 5 mm and pitch of 1.0 - 1.8. By using 10 mm slice thickness the authors had lower accuracy rate and also detected larger stones. Another fact that could explain the low yield of NECT in this population is because KUB and US previously detected the majority of larger calculus (mean stone size detected by KUB = 6.37 mm; mean stone size detected by CT 3.77 mm). It is obvious that when NECT is done as the initial diagnostic modality, it will show higher sensitivity and specificity because all sizes of stone will be available for its detection. In other words, the stones will not be previously “filtered” by KUB and US evaluation leaving only the small ones for the CT detection. Although the authors used different technical protocol and presented lower sensitivity rate, this paper is very important because is the first one to show the value of NECT as a complimentary modality for patients with negative or equivocal screening tests (KUB and US).
  In many important medical centers around the world, including some in Brazil, spiral NECT has becoming more and more accepted as the primary modality for screening patients with renal colic. Although this procedure has important drawbacks as high dose radiation exposure and for this reason should not be used in children and pregnant patients, it is of great value. In our institution, similarly to many others, NECT for renal colic has the same cost of an IVP, but economical consideration is still a very important issue. New protocols using less radiation have been already developed. It is expected that in the near future NECT will completely replace IVP for the evaluation of renal colic.

Dr. Adilson Prando
Department of Radiology
Vera Cruz Hospital
Campinas, São Paulo, Brazil