What are the disadvantages of CT scanning in the diagnosis of nephrolithiasis?

Updated: Jun 21, 2018
  • Author: Chirag N Dave, MD; Chief Editor: Bradley Fields Schwartz, DO, FACS  more...
  • Print
Answer

Disadvantages of CT scanning include the following:

  • It cannot be used to assess individual renal function or degree of obstruction.

  • It can fail to reveal some unusual radiolucent stones, such as those caused by indinavir and atazanavir, which are typically invisible on the CT scan (though some serve as a nidus for deposition of calcium oxalate or calcium phosphate deposition and thus become radiopaque). Because of this possibility, IVP with contrast should be used for patients taking indinavir or atazanavir. Sulfadiazine stones are also difficult to visualize on CT because of relatively low attenuation. [33]

  • It is relatively expensive.

  • It exposes the patient to a relatively high radiation dose (and thus should not be performed on pregnant women).

  • Precise identification of small distal stones is occasionally difficult.

  • Stone size as measured on CT KUB correlates poorly with actual size of the stone measured after spontaneous passage. [34] For this reason, caution should be used in counseling patients on the likelihood of spontaneous stone passage when stone size is determined using CT-based measurement.

  • Although CT scans can be used to estimate the overall size, width, and location of a stone, they can only approximate its shape. [35] Stone location can be described in anatomical terms, but the CT scan lacks the surgical orientation that most urologists prefer.

  • It is not suitable for tracking the progress of the stone over time, supporting the recommendation for KUB radiography along with the CT scan.

If a KUB or flat plate radiograph is performed at the same time as the CT scan, some of these objections and problems disappear. However, obtaining the extra films involves some additional delay, the patient is exposed to more ionizing radiation, and the total cost for the workup increases.

The "scout" reconstruction of the CT scan, formatted to look like a plain radiograph, is a reasonable substitute for a formal KUB radiograph in some cases. Stones 3 mm and larger can be observed routinely on these studies. If the findings from a noncontrast CT scan are positive for a stone and the findings from the scout CT radiograph are negative, a separate KUB radiograph should be performed.

A digital scout CT radiograph is not nearly as sensitive as a good plain radiograph in detecting calculi; however, if the stone is visible on the "scout" reconstruction, only plain radiography may be needed later to determine if the stone has moved or passed.


Did this answer your question?
Additional feedback? (Optional)
Thank you for your feedback!