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 and less specific 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 kidney 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IVU (sometimes called IVP, for intravenous pyelography) has been largely superseded by rapid multidimensional CT and MRI with or without a contrast agent.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 uses cystoscopy and ureteral catheterization to introduce 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 directly into the ureters and renal collecting system. Sedation or general anesthesia is required. This technique can be used when CT and MRI with IV contrast agents are contraindicated (eg, in chronic kidney disease Chronic Kidney Disease Chronic kidney disease (CKD) is long-standing, progressive deterioration of renal function. Symptoms develop slowly and in advanced stages include anorexia, nausea, vomiting, stomatitis, dysgeusia... read more ) or unavailable or when results are equivocal (eg, in renal insufficiency).
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.
For cystourethrography, 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 directly into the urethra and bladder. This technique provides more details than other imaging studies for evaluation of the following:
Suspected urethral or bladder trauma (eg, perforation)
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.
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 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:
Bladder: For bladder volumes (eg, postvoid volume, assessed immediately after voiding; in suspected urinary retention due to bladder outlet obstruction), diverticula, and stones
Scrotum: For hydroceles, spermatoceles, testicular tumors, varicoceles, and (with Doppler blood flow measurement) for testicular 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
Prostate: To measure prostate volume (eg, to help assess benign prostatic hyperplasia Benign Prostatic Hyperplasia (BPH) Benign prostatic hyperplasia (BPH) is nonmalignant adenomatous overgrowth of the periurethral prostate gland. Symptoms are those of bladder outlet obstruction—weak stream, hesitancy, urinary... read more or interpret prostate-specific antigen results) and to guide needle biopsy
Penis: To help evaluate Peyronie disease Peyronie Disease Peyronie disease is fibrosis of the cavernous sheaths leading to contracture of the investing fascia of the corpora, resulting in a deviated and sometimes painful erection. Peyronie disease... read more ; with Doppler, to assess blood flow (when evaluating erectile dysfunction Erectile Dysfunction Erectile dysfunction is the inability to attain or sustain an erection satisfactory for sexual intercourse. Most erectile dysfunction is related to vascular, neurologic, psychologic, and hormonal... read more )
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 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.
Urologic application of MRI includes the evaluation of renal cysts and small renal masses. MRI is also helpful in imaging blood vessels (eg, for renal artery stenosis Renal Artery Stenosis and Occlusion Renal artery stenosis is a decrease in blood flow through one or both of the main renal arteries or their branches. Renal artery occlusion is a complete blockage of blood flow through one or... read more and renal vein thrombosis Renal Vein Thrombosis Renal vein thrombosis is thrombotic occlusion of one or both main renal veins, resulting in acute kidney injury or chronic kidney disease. Common causes include nephrotic syndrome, primary hypercoagulability... read more ), and its use is increasing as MRI becomes more widely available.
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.
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. It also has the benefit of not requiring IV contrast and may be used safely in patients at risk for 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 . Radionuclide scanning also provides more information than does IV urography or cross-sectional imaging about the following:
Segmental renal emboli
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 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. Routine FDG PET scans are not very useful for most cases of prostate cancer but can be useful for other genitourinary tumors such as kidney or testicular cancer. Newer PET imaging includes targeting PSMA (prostate-specific membrane antigen) on the surface of prostate cancer cells.