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X-rays:
Abdominal x-rays without radiocontrast are virtually useless in evaluation of renal and urologic disorders; these x-rays show only about 15% of renal calculi (Ca oxalate calculi and rarely staghorn calculi). However, x-rays taken after administration of water-soluble radiocontrast agents highlight the kidneys and urinary collecting system. Nonionic iso-osmolal agents (eg, iohexol, iopamidol) are now widely used; they have fewer adverse effects than older hyperosmolal agents but still pose a risk of acute renal insufficiency or failure (contrast nephropathy—see Tubulointerstitial Diseases: Contrast Nephropathy; see Principles of Radiologic Imaging: Radiographic Contrast Agents and Contrast Reactions).
In urography, an x-ray is taken after IV, percutaneous antegrade or retrograde, or cystoscopic retrograde administration of radiopaque contrast. Primary contraindications for all are iodine allergy and risk factors for contrast nephropathy.
IVU (IV urography or pyelography) has been largely superseded by rapid multidimensional CT and MRI with or without a contrast agent. Abdominal compression during IVU may improve visualization of the renal pelvis and proximal ureters (with application) and distal ureters (after release). Additional x-rays at 12 and 24 h may be indicated for postrenal obstruction or hydronephrosis.
For percutaneous
anterograde urography, radiopaque contrast is introduced through an existing nephrostomy tube or, less commonly, through percutaneous puncture of the renal pelvis guided by fluoroscopy. Occasionally, a ureterostomy or an ileal conduit can be used. This technique is used when existing percutaneous access makes it practical or when IVU, CT, or MRI is unsuccessful or unsatisfactory because of impaired renal function or proximal obstruction. Anterograde urography is indicated when retrograde urography is unsuccessful (eg, because of tumor obstruction at bladder level), when large kidney stones requiring percutaneous surgery must be evaluated, when transitional cell carcinoma of the upper collecting system is suspected, or when patients cannot tolerate general anesthesia for retrograde urography. Complications relate to placement of the nephrostomy tube and include bleeding, sepsis, and injury to adjacent organs; microscopic hematuria, pain, and urinary extravasation are less serious.
Retrograde
urography uses cystoscopy and ureteral catheterization to introduce radiocontrast directly into the ureters and renal collecting system. Sedation or general anesthesia is required. This technique is used when CT or MRI is unsuccessful; when the degree, type, cause, and length of ureteral obstruction must be defined; or when patients are allergic to radiopaque contrast. It is useful for detailed examination of the pelvicaliceal collecting system, ureters (eg, to check for ureterovaginal fistulas), and bladder. However, overdistention and backflow may distort calyces and obscure detail. Risk of infection is higher than that with other types of urography; acute ureteral edema and secondary stricture formation are rare.
For cystourethrography, radiopaque contrast is introduced directly into the urethra and bladder. This technique is more precise than IVU for evaluation of vesicoureteral reflux, urinary incontinence, recurrent UTIs, urethral strictures, and suspected urethral or bladder trauma. Voiding cystourethrograms are taken during urination and used to identify posterior urethral valves. No patient preparation is necessary. Adverse effects include UTIs and urosepsis; severe urethral strictures are a relative contraindication.
Angiography:
Angiography has been largely replaced by noninvasive vascular imaging (eg, ultrasonography, CT, MRI, radionuclide scanning). Remaining indications include renal vein renin testing and angioplasty and stenting in patients with renal artery stenosis. Arteriography is also rarely used for evaluation and treatment of renal hemorrhage and before kidney-sparing surgery. Digital subtraction angiography is no longer used when rapid-sequence multidimensional CT or helical CT is available.
Ultrasonography:
Doppler ultrasonography is widely used to image the kidneys, bladder, prostate, testes, and penis. The test is safe but provides no information about renal function, and renal images may be difficult to obtain in overweight or obese patients. Also, there is no means to improve distinction between types of tissues, and test quality is operator-dependent. No patient preparation is necessary, but a full bladder facilitates its imaging. Ultrasonography can show urine volume after micturition (postvoiding residual). Doppler ultrasonography in patients with testicular pain helps distinguish torsion from other causes.
CT:
CT provides a broad view of renal, urologic, and surrounding structures. Conventional or helical scanners are used for most purposes with or without IV radiocontrast agents. Helical (spiral) CT without radiocontrast is used mainly to evaluate calculi. Use of radiocontrast with either technique resembles IVU but provides additional detail of urologic and surrounding structures. CT without radiocontrast is best for evaluation of trauma and other disorders that may involve acute hemorrhage (which appears bright white and can be confused with contrast agents) or urine extravasation.
MRI:
MRI is safer than CT for patients at risk of contrast nephropathy. Magnetic resonance angiography, used to enhance blood vessels, has virtually replaced angiography for evaluating renal artery stenosis and renal vein thrombosis. Other uses include distinction between hemorrhage and infection within renal cysts; determination of extent of tumor invasion within the bladder wall; and precise imaging of the pelvis and genitals using a pelvic or endorectal coil. MRI with IV lymphotropic superparamagnetic nanoparticles (eg, monocrystalline iron oxide) can identify lymph node metastases in prostate cancer but is not widely available. MRI poorly defines intrarenal calcifications because they have few mobile protons.
Radionuclide
scanning:
Cortical tracers that bind to proximal tubular cells (eg, technetium-99m dimercaptosuccinic acid [99mTc DMSA]) are used to image the renal parenchyma; excretory tracers that are rapidly filtered and secreted into urine (eg, 99mTc diethylenetriamine pentaacetic acid [DTPA], 99mTc mercaptoacetyltriglycine-3 [MAG3]) are used to assess and quantify excretory function. Radionuclide scanning provides more information about segmental renal emboli, renal parenchymal scarring due to vesicoureteral reflux, functional significance of renal artery stenosis, and renal transplant function than does IVU or cross-sectional imaging. 99mTc pertechnetate can be used to image blood flow to the testes and to distinguish torsion from epididymitis in patients with acute testicular pain, although Doppler ultrasonography is used more commonly because it is quicker. No patient preparation is necessary, but patients should be asked about known allergies to the tracer.
Last full review/revision November 2005
Content last modified November 2005
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