Video Clips on DVD
- 2-1
MRI Demonstrating a Transverse Vaginal Septum
- 2-2
CT Urogram Demonstrating a Complex Vesicovaginal Fistula
- 2-3
MRI Demonstrating a Periurethral Abscess
- 2-4
CT Demonstrating a Retropubic Hematoma
- 2-5
CT Urogram Demonstrating a Urethrovaginal Fistula
- 2-6
MRI Demonstrating Vaginal Cysts
- 2-7
CT Urogram Demonstrating a Vesicovaginal Fistula
- 2-8
CT Scan Demonstrating an Obstructing Stone
- 2-9
CT Urogram Demonstrating a 3D Rotating Image
- 2-10
CT Urogram Demonstrating Construction of 3D Images
- 2-11
Dynamic MRI Demonstrating a Cystocele and Rectocele
Introduction
For the urinary tract, many conventional radiographic studies have been used, including plain radiography, conventional tomography, intravenous urography (IVU), antegrade or retrograde pyelography (AGP or RGP), and voiding cystourethrography (VCUG). These techniques are still commonly performed to evaluate various urologic abnormalities, including stone diseases, urinary tract obstruction, vesicoureteral reflux, hematuria, and urothelial abnormalities.
Recently, the use of cross-sectional imaging modalities (e.g., ultrasonography [US], computed tomography [CT], and magnetic resonance imaging [MRI]) has increased. Compared with conventional imaging techniques, these cross-sectional imaging techniques have several advantages, including the ability to directly visualize renal or other urinary tumors and to obtain images in multiple planes.
The most notable recent advances in uroradiology include the introduction of noncontrast CT for evaluating patients with flank pain, and CT urography (CTU) and MR urography (MRU) for the evaluation of urothelial abnormalities. These techniques are increasingly used and have been found useful in many conditions, including hematuria workup and evaluation of stone disease or urothelial tumors. CTU also has reported accuracy in evaluating patients with postoperative urinary diversion. In many instances, CTU is replacing conventional studies such as plain radiography and IVU. MRU can be used as an alternative modality in patients with contraindications to iodinated contrast media.
This chapter describes the advantages and disadvantages as well as indications and contraindications of different imaging modalities commonly used to evaluate the female urinary tract, along with examples of characteristic imaging findings of urologic abnormalities.
Imaging Studies: Indications and Techniques
Plain Radiography
Indications and Contraindications
More than 85% to 90% of urinary calculi are radiopaque. Plain radiography, which is also referred to as KUB (radiograph of the kidney, ureter, and bladder), is used commonly in the evaluation or follow-up of radiopaque calcium calculi. KUB can also be used in evaluating the position of urinary stents. For pregnant women, even though most standard abdominal radiographs are not likely to pose serious risks to the fetus, KUB should be used only when the benefits outweigh the risk of harm. Every potential childbearing female patient should be screened for possible pregnancy before the examination.
Techniques
Overlying bowel gas and fecal material may obscure the urinary calculi. However, bowel preparation is not needed. Tomography of the kidneys is often more helpful in revealing small renal calculi than plain KUB. Less opaque or nonopaque urinary calculi such as uric acid or cystine stones may not be visible on KUB or even on tomography. However, on noncontrast CT these calculi are visible as high attenuation and thus can be easily depicted. Bladder or urethral calculi can be seen on KUB, but small calculi in urethral diverticula may only be seen on CT.
Intravenous Urography
Indications and Contraindications
IVU has been used as the primary imaging modality for various urologic abnormalities because it is inexpensive and widely available. IVU is limited, however, in depicting small renal masses or radiolucent stones. Common indications include hematuria workup, stone disease, urinary tract obstruction, and renal mass, as well as upper urinary tract abnormalities such as stricture, inflammation, fistula, and urothelial tumors. It is also used to assess the integrity of the upper urinary tract following urologic surgery or stent placement. Recently, IVU has been replaced by CTU in many of these conditions. Common contraindications to IVU include allergic reaction to iodinated contrast media and renal insufficiency. Patients with a history of severe iodinated contrast reaction, including respiratory distress, should be evaluated with other imaging modalities such as US or MRI. In patients with a history of minor reaction, iodinated contrast media can be used with steroid premedication.
Contrast-induced nephropathy (CIN) may occur following intravenous administration of iodinated contrast media for urographic or CT examinations. It is defined as an increase of serum creatinine value greater than 25% to 50% from baseline or an absolute increase in serum creatinine of 0.5 to 1.0 mg/dL following intravenous contrast administration. The prevalence is dose related and, although controversial, nonionic contrast material is associated with lower prevalence of CIN compared with ionic contrast material. Preexisting renal insufficiency, diabetes, dehydration, cardiovascular disease, advanced age, multiple myeloma, and nephrotoxic drugs are known risk factors for developing CIN. Although the serum creatinine level gives only a crude estimate of renal function, most institutions use this value as a reference. The threshold value for the use of iodinated contrast media varies from institution to institution, but the majority adopt a threshold value of 1.5 mg/dL for selecting high-risk patients for CIN. Prophylactic measures for high-risk patients include adequate hydration and use of a minimum required dose of nonionic contrast media. Oral N -acetylcysteine and sodium bicarbonate infusion can be used, but their effects have not been investigated fully.
A bowel preparation with a mild oral laxative can be used before IVU. Stimulating a bowel movement can reduce gas and fecal material in the colon and may improve visualization of the kidneys and ureters.
Techniques
Intravenous iodinated contrast material is given most commonly by hand injection. The dose of contrast depends on the patient size and radiologist’s or institution’s preference. Typically, a total volume of 50 to 100 mL of contrast medium is administered. Timed, sequential films are obtained before and after contrast administration. Nephrotomography increases sensitivity for depicting renal calculi or masses. Prone, upright, or oblique images can be added for suspicious renal and ureteral lesions. Postvoid bladder imaging is helpful in evaluating bladder contractility, postvoid residual, and urethral diverticula.
Voiding Cystourethrography
Indications and Contraindications
Voiding cystourethrography is commonly used for the evaluation of vesicoureteral reflux but can also be helpful in evaluating various bladder and urethral abnormalities. This study should be avoided in patients with acute or active urinary tract infection. Although intravesical contrast is normally not absorbed into the bloodstream, sporadic cases of anaphylactic reaction during VCUG or RGP have been reported.
Techniques
Diluted iodinated contrast material is given through a transurethral Foley catheter to fill the bladder. Spot radiographs of the bladder and kidneys are obtained after fully filling the bladder and during micturition.
Retrograde Pyelography
Indications and Contraindications
RGP is often indicated for patients with nonvisualization on the IVU or a suspicious filling defect or obstructing lesion in the upper urinary tract on IVU or CT. It can also be used when IVU or CT cannot be performed due to the patient’s impaired renal function. Although RGP may accurately demonstrate urothelial details, it is more invasive and requires catheterization and sedation or anesthesia.
Ultrasonography
Indications and Contraindications
US is commonly used as a screening modality for urinary tract obstruction or renal masses and can be used in pregnant patients owing to a lack of ionizing radiation and wide availability. US can depict hydronephrosis easily and can differentiate solid from cystic renal masses. Despite its high sensitivity in depicting hydronephrosis, the ureters are difficult to image on US and the evaluation of stone disease or obstructing lesion can be limited. Because of this limitation, it has been suggested that US should be used in combination with KUB for the evaluation of obstructing stone disease and with IVU for hematuria workup when CT cannot be used.
Noncontrast CT
Indications and Contraindications
Noncontrast CT (NCT) has been commonly used in evaluating patients with acute flank pain in the United States. NCT has been reported to be superior to IVU, with reported sensitivities ranging from 94% to 99% compared with that of IVU ranging from 63% to 75%. NCT has also been reported to be cost effective in evaluating patients with acute flank pain. Owing to recent technical advances, the total scan time is less than 5 minutes and multiplanar reconstruction can be generated ( Fig. 2-1 ). Compared with KUB, the radiation dose of NCT examination is higher. The mean effective dose of single abdominopelvic CT is typically more than 10 times that of KUB. However, when compared with standard IVU, CT can be performed with similar or reduced radiation.
) CT Urography
Indications and Contraindications
With recent technical advances of multidetector CT, CTU has become the major diagnostic imaging tool for urinary tract abnormalities and has rapidly replaced IVU in many instances. The most common indications for CTU include hematuria workup ( Fig. 2-2 ) and postoperative follow-up for patients with urothelial carcinoma; however, it can be used for most IVU indications. CTU is commonly used to evaluate the ureters and lower urinary tract for injury or obstruction. It has been reported to be superior to IVU in determining the cause of hematuria and in depicting nephrolithiasis and renal masses. Although IVU has been most commonly used for evaluating urothelial tumors, the role of CTU is increasing. Reported accuracies for CTU in depicting urothelial tumors range from 89% to 94%. Because iodinated contrast material is used as for IVU, CTU is contraindicated in patients with a history of severe iodinated contrast allergy or severe renal impairment.
) Techniques
CTU techniques are still being developed and refined and the detailed protocols are different from institution to institution. Typically, a total of two or three abdominopelvic acquisitions are obtained before and after contrast administration, which includes an unenhanced scan, an early nephrographic phase scan (70 to 120 seconds following contrast administration), and an excretory phase scan (3 to 15 minutes following contrast administration). Renal parenchymal lesions such as cysts or tumors are best seen on nephrographic phase images and renal collecting systems, ureters, and bladder can be best evaluated on excretory phase images. The acquisition of thin-slice CT scans of an optimally distended urinary tract obtained during the excretory phase of enhancement is essential for CTU (see Fig. 2-2 ). Additional delayed imaging may be required in patients with urinary tract obstruction as well as those with urinary tract injury or suspicious fistula following pelvic surgery.
Because the use of CTU is increasing, the radiation dose to patients is of growing concern. The mean effective dose of a typical CTU examination is more than 2 times that of a single-acquisition abdominopelvic CT. Because of this higher radiation dose, precautions should be taken when imaging children or young patients. In this case, the examination should be avoided when possible and low-dose techniques can be applied.
MR Imaging and Urography
Indications and Contraindications
Although the spatial resolution of MRI is inferior to that of CT, it can be used in patients with iodinated contrast allergy or renal impairment, or in children or pregnant women. MRI can be helpful in staging renal tumors and in characterizing cystic renal masses. MRI is limited, however, in evaluating urinary calculi. Although small caliceal abnormalities or urothelial tumors may be difficult to depict on MRU, recent advances in techniques seem to be promising. MRU can be used as an alternative to CTU when CTU is contraindicated ( Fig. 2-3 ).
) Whereas iodinated contrast medium is used for CT, gadolinium chelates are used for MRI. Recently, exposure to gadolinium in patients with renal failure and those maintained on dialysis has been linked with the development of nephrogenic systemic fibrosis. This disease may involve the skin, skeletal muscles, heart, lungs, and other organs, and can be fatal. The majority of affected patients are on dialysis or have stage 4 or 5 chronic renal disease. Because of the risks for this devastating disease, it is recommended that all patients scheduled for MRI should be screened for a history of renal disease or dialysis. In patients with severe renal disease or renal failure, the estimated glomerular filtration rate should be obtained before the MRI examination. Gadolinium contrast agents should be avoided in patients with estimated glomerular filtration rate equal to or less than 30 mL/min/1.73 m 2 or those already on dialysis.
Techniques
In addition to the common sequences of noncontrast T1- and T2-weighted imaging of the abdomen and pelvis, typical MRU protocol includes noncontrast coronal heavily T2-weighted hydrographic sequences and contrast-enhanced coronal and/or axial T1-weighted, three-dimensional-spoiled, gradient-recalled echo sequences in nephrographic and excretory phase (see Fig. 2-3 ). Commonly, 10 to 20 mg of furosemide is given intravenously to achieve maximal distention of the urinary tract.
Specific Use of Imaging Studies
To help referring physicians make decisions on the most appropriate imaging modality for a specific condition, the American College of Radiology (ACR) developed the ACR Appropriateness Criteria. ACR rated each modality for over 160 topics, on a scale from 1 (least appropriate) to 9 (most appropriate). The complete tables are available in the ACR website ( http://acr.org/SecondaryMainMenuCategories/quality_safety/app_criteria.aspx ) and are revised periodically. Some commonly used radiologic studies for conditions often encountered in gynecologic urology are discussed here.
Acute Flank Pain or Suspicious Urinary Stone Disease
Noncontrast CT is most useful for acute flank pain. Alternatively, IVU or a combination of US and KUB can be used. For recurrent stone symptoms, noncontrast CT, US with KUB, or KUB alone can be used instead of IVU.
Recurrent Lower Urinary Tract Infection
In patients with recurrent lower urinary tract infection, imaging may be indicated to detect or exclude urinary tract abnormalities. Noncontrast and contrast-enhanced CT and IVU are among the most useful modalities, although other modalities such as KUB, NCT, VCUG, and US can also be used. If urethral diverticulum is suspected, MRI or VCUG can be performed.
Acute Pyelonephritis
For a patient with uncomplicated pyelonephritis, imaging is often not needed. In contrast, imaging is usually needed for diabetic or immunocompromised patients. In these patients, CT, US with KUB, IVU, MRI, and dimercaptosuccinic acid (DMSA) scan can be used. For children, DMSA scan is often used. When vesicoureteral reflux is suspected, VCUG is commonly used.
Hematuria Workup
For hematuria workup, IVP and CTU are used most commonly, along with cystoscopy. US can be used but may miss ureteral or urothelial lesions. RGP, MRU, or noncontrast and contrast-enhanced CT can also be used.
Indeterminate Renal Masses
Either CT or MRI is most appropriate for indeterminate renal masses. Intravenous contrast is essential for both CT and MRI. US can be helpful in differentiating lesions seen on IVU or further evaluating indeterminate lesions seen on CT. Biopsy is indicated when imaging findings are equivocal or lymphoma or metastasis is suspected.
Urinary Tract Obstruction
US can easily depict hydronephrosis, and CT is useful in evaluating the obstructing lesion. When contrast-enhanced CT is contraindicated, MRI can be used. US or NCT may not be sensitive in diagnosing very early urinary obstruction because dilation of the renal collecting system may not be present or can be minimal. Contrast-enhanced CT, IVU, or nuclear renogram may be preferred. For renogram, both tubular agents such as technetium-99m mercaptoacetyltriglycine (MAG3) and glomerular agents such as technetium-99m diethylenetriaminepenta-acetic acid (DTPA) can be used. However, Tc 99m–MAG3 is preferred because it can be used in patients with impaired renal function. To assess presence or absence of obstruction, half-time value ( 
) can be calculated from clearance curves. A 
of less than 10 to 15 minutes from the time of diuretic effect is considered normal. Relative function of each kidney can also be assessed. For ureteral obstruction, RGP or AGP can also be helpful for elucidating the nature of ureteral obstruction. If offending ureteral calculi are suspected clinically, NCT, KUB, or IVU can be obtained for further evaluation.
Blunt Trauma
When multiorgan injury is suspected in a patient with hematuria, contrast-enhanced CT is most helpful. Other imaging modalities, including IVU, angiography, renal scan, and US, can be used. For patients with suspicious bladder rupture, conventional or CT cystography is most appropriate, but contrast-enhanced CT, angiography, or IVU can also be used. For IVU or CT, delayed imaging is often needed to evaluate the presence or absence of urinoma or fistula.
Postoperative Complications
For evaluating the integrity of the urinary tract or urinary tract obstruction following pelvic surgery, IVU or CTU can be used. Delayed imaging is often needed. If ureteral injury is suspected on these studies, RGP or AGP can be performed. For patients with suspected urinary tract fistula, IVU, CTU, or MRU may be helpful. Conventional or CT cystography, RGP, AGP, or colon study may be needed to visualize the fistulous tract. CT cystography consists of CT imaging of the bladder before and after instillation of diluted contrast media into the bladder via a Foley transurethral catheter or an indwelling suprapubic catheter.
Imaging Findings
Congenital Anomalies
Duplicated renal collecting system and ureter may be well demonstrated on IVU or CTU ( Figs. 2-4 and 2-5 ). The upper moiety of a duplicated system is often associated with obstruction. The obstructed upper renal moiety may not be well visualized on IVU, whereas the dilated upper renal collecting system can be seen on US, CT, or MRI. The distal portion of the dilated system may be associated with ureterocele or ectopic ureter, which may be demonstrated on CT or MRI ( Fig. 2-6 ). The lower renal moiety is often associated with vesicoureteral reflux, which may result in caliceal dilation and associated renal cortical scarring. For anomalies of the lower urinary tract, MRI can be helpful ( Fig. 2-7 ).
Stone Disease
Most urinary calculi are calcium stones and radiopaque on plain radiography with or without tomography, although tiny stones or stones obscured by overlying bowel gas and fecal material may not be visible on radiographs. For patients with acute flank pain, noncontrast CT or IVU can be used ( Fig. 2-8 ). Not only can noncontrast CT depict the stone but it may also demonstrate proximal urinary tract dilatation and perinephric or periureteral inflammatory stranding in cases of acute obstruction ( Fig. 2-9 ). On occasion, intravenous contrast injection may be necessary to differentiate ureteral stones from extraurinary calcification such as a pelvic phlebolith.
