What is the role of plain renal tomography in the diagnosis of nephrolithiasis?

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

Plain renal tomography requires moving the radiograph projector and film in such a way that a zone of photographic clarity is positioned at the stationary focus point of the radiograph beam. All other overlying material is eliminated. The focal point is adjusted along the anteroposterior axis a distance of 1 cm, and the radiograph procedure is repeated. Usually, a series of 4-6 films is needed to completely image both kidneys. If such a series of films is needed, it should be obtained before any IV contrast is administered; contrast obscures any stones present.

Although largely replaced by CT scanning without contrast, plain renal tomography has some uses and advantages. It does not require extensive preparation and can be performed quickly. In addition, the cost and radiation dosage to the patient are less than with CT scanning.

Plain renal tomography can be useful for monitoring a difficult-to-observe stone after therapy. Observing even a relatively large radiopaque stone located in the kidney or renal pelvis on a standard abdominal flat plate radiograph can be difficult or impossible if the patient has abundant gas or stool overlying the area, and plain renal tomography can often overcome this difficulty.

Plain renal tomography may be helpful for clarification of stones not clearly detected or identified with other studies (eg, differentiating intrarenal calcifications that are likely to be stones from extrarenal opacities that are clearly not renal calculi). It is often helpful in finding small stones in the kidneys, especially in patients who are large or obese whose bowel contents complicate observation of any renal calcifications.

Plain renal tomography is also useful for determining the number of stones present in the kidneys before a stone-prevention program is instituted. This information is used to better differentiate stones formed before therapy began from those formed later.


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