Is Coronal CT Imaging a More Accurate Method of Measuring the Size of Urinary Tract Stones?

Nagaraja Rao

Disclosures

Nat Clin Pract Urol. 2005;2(2):72-73. 

In This Article

Synopsis

There are several options for the management of patients with urinary tract calculi. The clinician's choice between conservative therapy , ureteroscopy, percutaneous nephrolithotomy and extracorporeal shock wave lithotripsy is informed by assessment of the size of the obstruction(s). Axial images of stones obtained by CT allow more precise estimation of length and width than the standard of plain abdominal X-ray. Could coronal CT reconstructions, incorporating measurement of craniocaudal dimensions, further enhance precision, thereby optimizing treatment outcomes?

To determine if coronal CT imaging, incorporating measurement of craniocaudal length and width, generates a more accurate estimation of stone size than axial CT imaging.

This study was a single-institution retrospective review of CT images of urinary tract calculi collected using a LightSpeed multidetector scanner (GE Medical Systems, Milwaukee, WI) according to standard protocols. Images were obtained during the 9 months to September 2001. Contiguous coronal images (3 mm) were reconstructed from the raw data. These coronal reconstructions and axial images (5 mm) were processed by the PathSpeed Picture Archiving and Communications System (GE Medical Systems), which electronically measured stone dimensions. Estimations of axial length and width, plus craniocaudal length, were derived from axial images. Craniocaudal length and width were measured from coronal reconstructions. Total stone area was calculated from both types of image.

Differences between stone dimensions (length, width and area) measured from axial and coronal CT images.

CT images of 151 stones in 102 patients were analyzed. The location of calculi varied; most were located in the renal pelvis (47) and lower pole (44), followed by the upper pole (18) and distal (20) and proximal (13) ureters, then the mid ureter (5) and ureteropelvic junction (4). The average craniocaudal length of stones estimated from axial images was significantly greater than that measured on coronal reconstructions (8.8 mm vs 6.5 mm, P <0.0001; range 2.0 mm to 39.4 mm). The greatest dimension estimated from axial images was length/width (mean 4.9 mm). This was significantly less than the largest dimension (craniocaudal length) measured from coronal images (mean 6.5 mm, P <0.0001). This discrepancy was reflected by the average calculated area of stones; 22.2 mm3 from axial images and 31.3 mm3 from coronal reconstructions ( P <0.0001).

Compared with axial CT imaging, coronal CT reconstructions yield more accurate estimates of the dimensions of urinary tract stones. Measurements from axial images are overestimates of craniocaudal length and underestimates of stone area. On the basis of these data, the authors assert that coronal images should be routinely obtained to optimize management of patients with calculi.

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