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Genitourinary Imaging Tests

By

Paul H. Chung

, MD, Sidney Kimmel Medical College, Thomas Jefferson University

Last full review/revision May 2020| Content last modified May 2020
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Imaging tests are often used to evaluate patients with renal and urologic disorders.

Plain X-Rays Without Contrast

Abdominal x-rays without radiopaque contrast agents may be done to check for positioning of ureteral stents or to monitor position and growth of kidney stones. However, for initial diagnosis of urolithiasis Urinary Calculi Urinary calculi are solid particles in the urinary system. They may cause pain, nausea, vomiting, hematuria, and, possibly, chills and fever due to secondary infection. Diagnosis is based on... read more , plain x-rays are less sensitive than CT and lack anatomic detail, so they are not the study of choice.

X-Rays With Use of Contrast

Images taken after administration of water-soluble contrast 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 injury (contrast nephropathy Contrast nephropathy Radiopaque contrast agents are often used in radiography and fluoroscopy to help delineate borders between tissues with similar radiodensity. Most contrast agents are iodine based. Iodinated... read more ).

In urography, an x-ray is taken after IV, percutaneous antegrade or retrograde, or cystoscopic retrograde administration of a radiopaque contrast agent Radiographic Contrast Agents and Contrast Reactions Radiopaque contrast agents are often used in radiography and fluoroscopy to help delineate borders between tissues with similar radiodensity. Most contrast agents are iodine based. Iodinated... read more . Primary contraindications for all patients are iodine allergy and risk factors for contrast nephropathy.

IV urography (IVU)

IVU (sometimes called IVP, for intravenous pyelography) has been largely superseded by rapid multidimensional CT and MRI with or without a contrast agent. When IVU is done, abdominal compression may improve visualization of the renal pelvis and proximal ureters (with application) and distal ureters (after release). Additional x-rays at 12 and 24 hours after contrast administration may be indicated for detection of postrenal obstruction or hydronephrosis.

Percutaneous antegrade urography

For percutaneous antegrade urography, a radiopaque contrast agent Radiographic Contrast Agents and Contrast Reactions Radiopaque contrast agents are often used in radiography and fluoroscopy to help delineate borders between tissues with similar radiodensity. Most contrast agents are iodine based. Iodinated... read more 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. Antegrade urography is used in the following circumstances:

  • When retrograde urography is unsuccessful (eg, because of tumor obstruction at the bladder level)

  • When large kidney calculi requiring percutaneous surgery must be evaluated

  • When transitional cell carcinoma of the upper collecting system is suspected

  • When patients cannot tolerate general anesthesia or the degree of sedation required for retrograde urography

Complications relate to puncture and placement of the catheter in the genitourinary tract and include bleeding, infection, injury to the lungs or colon, hematuria Isolated Hematuria Hematuria is red blood cells (RBCs) in urine, specifically > 3 RBCs per high-power field on urine sediment examination. Urine may be red, bloody, or cola-colored (gross hematuria with oxidation... read more , pain, and prolonged urinary extravasation.

Retrograde urography

It is also useful for detailed examination of the pelvicaliceal collecting system and ureters to check for injury, stricture, or fistula. Overdistention and backflow from a kidney into the venous system may distort calyces and obscure details. Risk of infection is higher than that with other types of urography. Acute ureteral edema and secondary stricture formation are rare complications.

Cystourethrography

Voiding cystourethrography is done during urination and is primarily used to image the posterior urethra (eg, for strictures or valves). No patient preparation is necessary. Adverse effects include UTIs and urosepsis.

Angiography

Conventional catheter angiography has been largely replaced by noninvasive vascular imaging (eg, magnetic resonance angiography, CT angiography, ultrasonography, radionuclide scanning). Remaining indications include renal vein renin imaging and, among patients with renal artery stenosis, angioplasty and stent placement. 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 (spiral) CT is available.

Ultrasonography

Ultrasonography can provide useful images of many genitourinary structures without exposing patients to ionizing radiation. Images are interpreted as they are acquired, so the technician can focus on concerning areas and obtain additional information if necessary. Its main disadvantages are the need for a skilled operator and the time required. A full bladder helps provide better images of certain structures but no other preparation is needed.

Structures that can be imaged and common indications include the following:

Computed Tomography

Computed tomography provides a broad view of the urinary tract and surrounding structures. Conventional or helical scanners are used for most purposes with or without IV contrast agents Radiographic Contrast Agents and Contrast Reactions Radiopaque contrast agents are often used in radiography and fluoroscopy to help delineate borders between tissues with similar radiodensity. Most contrast agents are iodine based. Iodinated... read more . Use of contrast agents with either technique resembles IV urography (IVU) but provides additional detail. Previously, in trauma patients, there was concern that use of contrast would make it difficult to distinguish abdominal hemorrhage from urinary tract disruption, but with modern imaging techniques and protocols, this distinction can be made. Helical CT without a contrast agent is the study of choice for imaging of calculi; dual-energy scanners may provide additional information that can help determine stone composition.

The main disadvantage of CT is that it exposes patients to a relatively large dose of ionizing radiation. CT angiography CT angiography CT shows a focal area of osteolysis (arrows) involving the right acetabulum that is consistent with particle disease. In CT, an x-ray source and x-ray detector housed in a doughnut-shaped assembly... read more CT angiography is a less invasive alternative to conventional angiography.

Magnetic Resonance Imaging

Compared with CT, MRI is safer for patients at risk of contrast nephropathy Contrast Nephropathy Contrast nephropathy is worsening of renal function after IV administration of radiocontrast and is usually temporary. Diagnosis is based on a progressive rise in serum creatinine 24 to 48 hours... read more , does not expose patients to ionizing radiation, and provides superior soft-tissue detail (but images bones and calculi poorly). Magnetic resonance imaging is contraindicated in patients with ferromagnetic metal (ie, containing iron) implants and magnetically activated or electronically controlled devices (eg, cardiac pacemakers). See also the MRI safety web site.

Also, due to the risk of nephrogenic systemic fibrosis, MRI with gadolinium contrast is contraindicated in patients with glomerular filtration rate (GFR) < 30 mL/min.

Multiparametric MRI is now the imaging study of choice for staging prostate cancer Prostate Cancer Prostate cancer is usually adenocarcinoma. Symptoms are typically absent until tumor growth causes hematuria and/or obstruction with pain. Diagnosis is suggested by digital rectal examination... read more and for serial imaging of patients with prostate cancer on active surveillance. A multiparametric MRI examination includes paramagnetic contrast and consists of 3 separate imaging techniques (parameters): T2-weighted imaging, diffusion-weighted imaging, and dynamic contrast-enhanced imaging. A technique known as MRI fusion biopsy is sometimes used during a prostate biopsy Prostate biopsy Biopsy of the urinary tract requires a trained specialist (nephrologist, urologist, or interventional radiologist). Indications for diagnostic biopsy include unexplained nephritic or nephrotic... read more . An MRI of the prostate is obtained prior to ultrasound-guided prostate biopsy, during which the MRI image is digitally combined (fused) with the ultrasound image to better identify lesions that need to be biopsied.

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 excreted into urine (eg, iodine-125 iothalmate, 99mTc diethylenetriamine pentaacetic acid [DTPA], 99mTc mercaptoacetyltriglycine-3 [MAG3]) are used to assess glomerular filtration rate (GFR) and overall renal perfusion. Radionuclide scanning can be used to evaluate renal function when use of IV contrast is undesirable. Radionuclide scanning also provides more information than does IV urography or cross-sectional imaging about the following:

99mTc pertechnetate can be used to image blood flow to the testes and to distinguish torsion Testicular Torsion Testicular torsion is an emergency condition due to rotation of the testis and consequent strangulation of its blood supply. Symptoms are acute scrotal pain and swelling, nausea, and vomiting... read more from epididymitis Epididymitis Epididymitis is inflammation of the epididymis, occasionally accompanied by inflammation of the testis (epididymo-orchitis). Scrotal pain and swelling usually occur unilaterally. Diagnosis is... read more Epididymitis in patients with acute testicular pain, although Doppler ultrasonography is used more commonly because it is quicker. No patient preparation is necessary for radionuclide scanning, but patients should be asked about known allergies to the tracer.

Newly available nuclear positron emission tomographic (PET) agents can detect metastatic prostate cancer.

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Several metabolic disturbances can cause tubulointerstitial nephritis. Acute urate nephropathy is not a true form of acute tubulointerstitial nephritis but rather an intraluminal obstructive uropathy. The most common cause of this type of nephropathy is which of the following?
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