How does CT scanning compare to IV pyelography (IVP) 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

CT has largely supplanted IVP in a number of settings. However, a comparison of the pros and cons of the two modalities suggests IVP retains some advantages (see Table, below).

Table. Intravenous Pyelography Versus CT Scanning: Which Is Better? (Open Table in a new window)

Imaging Study (Pro/Con)

Details

CT scan

Pro

  • Fast

  • No IV contrast necessary, so no risk of nephrotoxicity or acute allergic reactions

  • With only rare exceptions, shows all stones clearly

  • May demonstrate other pathology

  • Can be performed in patients with significant azotemia and severe contrast allergies who cannot tolerate IV contrast studies

  • Clearly shows uric acid stones

  • Shows perinephric stranding or streaking not visible on IVP and can be used as an indirect or secondary sign of ureteral obstruction

  • No radiologist needs to be physically present

  • Preferred imaging modality for acute renal colic in most EDs

Con

  • Without hydronephrosis, cannot reliably distinguish between distal ureteral stones and pelvic calcifications or phleboliths

  • Cannot assess renal function

  • No nephrogram effect study to help identify obstruction

  • Size and shape of stone only estimated

  • Lacks surgical orientation*

  • Unable to identify ureteral kinks, strictures, or tortuousities

  • May be hard to differentiate an extrarenal pelvis from true hydronephrosis

  • Gonadal vein sometimes can be confused with the ureter

  • Does not indicate likelihood of fluoroscopic visualization of the stone, which is essential information in planning possible surgical interventions

  • May require addition of KUB radiograph

  • Cannot be performed during pregnancy because of high dose of ionizing radiation exposure

  • Usually more costly than an IVP in most institutions

  • Higher radiation dose than IVP

IVP

Pro

  • Clear outline of complete urinary system without any gaps

  • Clearly shows all stones either directly or indirectly as an obstruction

  • Nephrogram effect film indicates obstruction and ureteral blockage in most cases, even if the stone itself might not be visible

  • Shows relative kidney function

  • Definitive diagnosis of MSK

  • Ureteral kinks, strictures, and tortuousities often visible

  • Can modify study with extra views (eg, posterior oblique positions, prone views) to better visualize questionable areas

  • Stone size, shape, surgical orientation, and relative position more clearly defined

  • Orientation similar to urologists’ surgical approach

  • Limited IVP study can be considered in selected cases during pregnancy, although plain ultrasonography is preferred initially

  • Lower cost than CT scan in most institutions

  • Includes KUB film automatically

Con

  • Relatively slow; may need multiple delay films, which can take hours

  • Cannot be used in azotemia, pregnancy, or known significant allergy to intravenous contrast agents

  • Risk of potentially dangerous reactions to IV contrast material

  • Cannot detect perinephric stranding or streaking, which is visible only on CT scans

  • Harder to visualize radiolucent stones (eg, uric acid), although indirect signs of obstruction are apparent

  • Presence of a radiologist generally necessary, which can cause extra delay

  • Cannot be used to reliably evaluate other potential pathologies

*Many urologists find CT scans inadequate to help plan surgery, predict stone passage, or monitor patients. This causes a delay, which may be significant in some institutions, and adds additional patient radiograph exposure and cost. These include significant allergic responses and renal failure.

The noncontrast or renal colic-type CT scan is good for the initial diagnosis of a stone, especially in unusual or atypical cases or when patients are unable to tolerate intravenous contrast because of allergy or azotemia. Without definite hydronephrosis, a CT scan may not be able to isolate a specific stone, although secondary signs, such as perinephric streaking and nephromegaly, may be present.

The CT scan can be performed quickly in most institutions, even with an additional KUB radiograph, but it usually costs more than the IVP. In one series of 397 consecutive emergency urolithiasis patients from several university centers, the average fee for a CT scan was $1407, compared with $445 for an IVP.

CT scans are generally preferred by most ED physicians for the initial evaluation of patients with acute flank pain, except for HIV-positive patients who may be on protease inhibitors, who require an IVP, and pregnant women, who require ultrasonography for their initial imaging modality.

The IVP is better for clearly outlining the entire urinary tract and determining relative renal function. This test clearly shows stones causing blockage, whether the stones are radiolucent or opaque. While an IVP can reliably help in the diagnosis of an MSK, the clinical importance of this diagnosis is limited. The IVP is sometimes preferred by urologists in certain situations because of its better orientation and superior value in predicting possible stone passage, although these advantages are mostly negated if a KUB radiograph routinely accompanies the CT scan.


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