Computerized Tomography Magnified Bone Windows Are Superior To Standard Soft Tissue Windows For Accurate Measurement Of Stone Size

Main Category: Urology / Nephrology
Article Date: 17 May 2009 - 1:00 PDT

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UroToday.com - Stone size is of key importance in making treatment decisions, especially for ureteral calculi. Earlier studies revealed that stone size on CT could at times be underestimated by as much as 1-2 mm; for ureteral calculi this could be the difference between initiating medical expulsive therapy versus an invasive ureteroscopic procedure. However, there are many ways to "view" a CT scan and by moving from the standard soft tissue view to a "bone" window view, different characteristics of tissue or foreign bodies can be appreciated. Such was first brought to the attention of many urologists when Dr. Stephen Dretler and colleagues reported the use of bone windows to distinguish ureteral stents from denser stone fragments.

In this study, both in vitro and in vivo analyses of stones using 5.13x and 4x bone windows, respectively provided more accurate stone measurements than the use of regular or magnified soft tissue windows. From a clinical standpoint, the take home message is that the use of standard soft tissue window can underestimate stone size by upwards of 2 mm, whereas the 4.0 magnified bone window view, underestimates stone size by only 0.3mm. This is highly useful clinical information and allows one to rely on the plain CT scan findings for developing an effective treatment plan.

Eisner BH, Kambadakone A, Monga M, Anderson JK, Thoreson AA, Lee H, Dretler SP, Sahani DV
J Urol. 2009 Apr;181(4):1710-5.
doi: 10.1016/j.juro.2008.11.116

Written by UroToday.com Medical Editor Ralph V. Clayman, MD

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