IMAGING

Coronal imaging to assess urinary tract stone size
Nadler RB, Stern JA, Kimm S, Hoff F, Rademaker AW
Department of Urology, Northwestern University Feinberg School of Medicine, Chicago, Illinois, USA
J Urol. 2004: 172: 962-4

• Purpose: Urinary tract stones are typically measured using axial images from computerized tomography (CT). Such images provide a precise measurement of stone length and width. However, cephalocaudad dimensions can be difficult to determine from axial images. Coronal reconstructions, which can more accurately measure cephalocaudad dimensions, are seldom used to measure stones. We determined if coronal reconstructions could aid in more precisely determining stone size.
• Materials and Methods: CT in patients who had undergone CT to evaluate urolithiasis at our institution during the 9-month period of January 2001 to September 2001 were reviewed. Length and width were measured using axial images, and cephalocaudad length and width were measured using coronal reconstructions. Cephalocaudad length was also estimated from axial images. Total area was calculated from axial and coronal reconstructions. The paired t test was used to assess statistical significance.
• Results: The CT images of 102 patients with a total of 151 stones had undergone coronal reconstructions and, thus, were included in the study. Mean area in the axial and coronal reconstruction groups was 22.23 and 31.29 mm3, respectively. Mean greatest axial dimension (length or width) was 4.87 mm and mean greatest coronal dimension (cephalocaudad length) was 6.51 mm. Cephalocaudad length estimated from axial images was 8.8 mm. Differences for all 3 of these comparisons (axial vs. coronal area, greatest axial vs. coronal dimension and estimated vs. actual cephalocaudad length) proved to be statistically significant (p <0.0001).
• Conclusions: While urinary tract stones have typically been measured using axial images, coronal images provide a different impression of stone size. These data demonstrate that examining only axial images provides an inaccurate measure of stone size. We suggest that coronal images should also be used to measure more accurately stone size, which is critical for clinical decision making.
  
  
• Editorial Comment
  The authors describe the impact on the estimation of the size of ureteral stone when this measurement is done also on coronal images. This is an important contribution since several studies has shown the accuracy of non-enhanced CT estimation of stone size using only the transverse plane (axial images). Size measurement and location of the stone in the ureter, are the most important determinants of therapy. The authors has shown that size measurement is precisely evaluated by non-enhanced CT, particularly when the coronal images are additionally used for obtaining an accurate volumetric measurement of the urinary calculi (greatest axial and craniocaudal length). An accurate determination of the size of the stone in the ureter is important since about 90% of stones 1 mm in diameter does pass, but less than 50% of stones larger than 7 mm pass. Urinary calculi located in the upper ureter and measuring 5 mm or more, usually do not pass spontaneously, whereas distal stones even if fairly large most often do pass. In general, stones larger than 6 mm commonly require intervention. In conclusion, radiologist should use both planes (axial and coronal) in order to obtain adequate measurement of stone size.

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