| Problem | Does the patient have a renal stone |
| Protocol | This is a non contrast protocol which focuses on the kidney but the scan extends thru the bladder. Therefore the study requires no oral or IV contrast although it is helpful to have the patient drink 500-1000cc of water prior to the study. The scans should be done with thin section CT and use a lower dose protocol. Images should be reviewed in axial and coronal plane. |
| Pearls | The accuracy for detecting stones likely approaches 100% but there are certain pitfalls involved. Some of the things to remember are;- Stones that are not opaque can be missed. Fortunately non opaque stones are rare
- Stone size and stone density help predict whether a stone will pass
- Coronal views are helpful in not missing a stone which at times can be overlooked on the axial CT
- Although we focus on the kidney we need to make certain that there is no stone in the ureter or bladder. Water as an oral agent distends the bladder making it easier to detect bladder stones
- It may be a challenge to always distinguish between a stone in the distal ureter and a phlebolith. In these cases following the ureter downward is helpful. (is it dilated?)
- Widened soft tissue windows may be helpful in these cases
- In a patient with hematuria (especially macroscopic hematuria) a negative stone study does not mean a normal CT scan. A followup study with IV contrast will be necessary.
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