ACR Appropriateness Criteria®
Clinical Condition: Recurrent Lower Urinary Tract Infections in Women
Variant 1: With no underlying risk factors.
Radiologic Procedure |
Rating |
Comments |
RRL* |
CT abdomen and pelvis without and with contrast |
2 |
|
|
X-ray abdomen |
2 |
|
|
CT abdomen and pelvis without contrast |
2 |
|
|
CT abdomen and pelvis with contrast |
2 |
|
|
X-ray contrast enema |
2 |
|
|
X-ray cystography |
2 |
|
|
MRI pelvis without and with contrast |
2 |
MRI may be indicated if urethral diverticulum is suspected. |
O |
MRI pelvis without contrast |
2 |
|
O |
US kidneys and bladder retroperitoneal |
2 |
|
O |
US pelvis (bladder) |
2 |
|
O |
Tc-99m sulfur colloid cystography |
2 |
|
|
X-ray voiding cystourethrography |
2 |
|
|
X-ray intravenous urography |
1 |
Not cost-effective in this group. Has been supplanted by CT and MR urography. |
|
US pelvis (urethra) |
1 |
|
O |
Rating Scale: 1,2,3 Usually not appropriate; 4,5,6 May be appropriate; 7,8,9 Usually appropriate |
*Relative Radiation Level |
Note: Abbreviations used in the tables are listed at the end of the "Major Recommendations" field.
Variant 2: Patients who are nonresponders to conventional therapy, get frequent reinfections or relapses, and have known underlying risk factors.
Radiologic Procedure |
Rating |
Comments |
RRL* |
CT abdomen and pelvis without and with contrast |
7 |
|
|
MRI pelvis without and with contrast |
6 |
For suspected diverticulum or prolapse. Favored for patients who require repeated imaging examinations. See statement regarding contrast in text under "Anticipated Exceptions." |
O |
US pelvis (urethra) |
5 |
Favored for pregnant women. |
O |
MRI pelvis without contrast |
4 |
|
O |
X-ray voiding cystourethrography |
4 |
For reflux, bladder or urethral fistula, or prolapse. |
|
US kidneys and bladder retroperitoneal |
3 |
Less accurate for detection of pyelonephritis. |
O |
X-ray intravenous urography |
3 |
Limited use (or alternative) in young patients if MR is unavailable or not possible. |
|
CT abdomen and pelvis with contrast |
3 |
|
|
US pelvis (bladder) |
2 |
Also to evaluate for postvoid residual. |
O |
X-ray urethrography double balloon |
2 |
|
|
X-ray abdomen |
2 |
|
|
CT abdomen and pelvis without contrast |
2 |
|
|
X-ray contrast enema |
2 |
May be useful for vesicoenteric fistula. |
|
X-ray cystography |
2 |
May be useful for vesicoenteric fistula. |
|
Tc-99m sulfur colloid cystography |
2 |
|
|
Rating Scale: 1,2,3 Usually not appropriate; 4,5,6 May be appropriate; 7,8,9 Usually appropriate |
*Relative Radiation Level |
Note: Abbreviations used in the tables are listed at the end of the "Major Recommendations" field.
Summary of Literature Review
Urinary tract infections (UTI) are among the most common bacterial infections in women. Every year in the United States, about 15% of women are diagnosed with UTIs. Most occur in healthy, sexually active women with a normal urinary tract and normal renal function. These infections are usually limited to the lower urinary tract, are not recurrent, and respond to appropriate antimicrobial therapy. Lower UTIs are confined to the bladder and occasionally the urethra and result in irritative voiding symptoms such as frequency, dysuria, urgency, and hematuria in severe cases. There is usually no associated flank pain, fever, or other systemic symptoms. Complicated UTIs are those occurring in patients with underlying structural or medical problems. Uncomplicated UTI is classified as UTI without structural or functional abnormalities of the urinary tract and without relevant comorbidities.
Recurrent lower UTIs are usually defined as at least three episodes of infection within the preceding 12 months. Antibiotic prophylaxis is the most effective way to reduce recurrent UTIs. In most cases, such infections are the result of sexual habits and hygiene (e.g., women who are sexually active, especially those using diaphragms and/or spermatocides). In fact, such lower UTIs are commonly referred to as "honeymoon cystitis." A clean-catch or catheterized specimen for culture typically reveals >100,000 organisms per milliliter of urine. The typical infecting organism is Escherichia coli. The route of infection is ascending from the perianal area and vagina via the urethra and into the bladder. It is not at all uncommon for such infections to be severe enough to result in gross hematuria. Postmenopausal women are at increased risk for recurrent UTI in the presence of urinary incontinence, cystocele, or high postvoid residuals of urine.
Three-day antimicrobial regimens are effective in at least 90% of women. Women who have three or more symptomatic infections over a 12-month period may benefit from prophylaxis. In patients without underlying risk factors (see Appendix 1 of the original guideline document) and with lower UTIs as defined above that do not exceed two episodes per year on average, and that respond promptly to appropriate therapy, imaging is usually not cost-effective.
"Relapses" of recurrent lower UTIs in women must be differentiated from "reinfection," which may indicate causes such as a vesicovaginal or vesicoenteric fistula or a paravesical abscess with fistula to the bladder. Recurrent and chronic infections with the same organism are termed "relapses" or "persistent" infections. If infection develops more than 2 weeks after a symptomatic cure, or if it is caused by a second pathogen, it is termed a "reinfection." Causes of bacterial persistence include calculi, foreign bodies, urethral or bladder diverticula, infected urachal cyst, and postoperative changes such as a remaining ureteral stump that retains urine and results in stasis. In such patients with frequent relapses or reinfections, imaging is indicated to detect a treatable condition and monitor its progress.
Imaging Options
In support of the premise that imaging has little efficacy in uncomplicated lower UTIs in women, several studies evaluating women with recurrent UTIs with intravenous urography (IVU) revealed no findings that altered the medical or surgical management. In an additional study, the 6% of patients with recurrent UTIs that demonstrated "major structural urologic abnormalities requiring further therapy" all had risk factors (to be defined subsequently).
Therefore, imaging studies should be reserved for women who do not respond promptly to appropriate antimicrobial therapy, those who suffer frequent reinfections or relapses, and those with known risk factors. Other documented risk factors include: childhood UTIs, flank pain, fever >38.5° C, history of urinary calculi or urinary tract obstruction, obstructive voiding symptoms (straining to urinate, feeling of incomplete bladder emptying, etc.), infection with a urea-splitting organism, abnormal renal function studies, pelvic floor dysfunction, neurogenic bladder dysfunction, history of genitourinary surgery, asymptomatic bacteriuria, diabetes mellitus or other immunocompromised states, and analgesic abuse.
The following paragraphs discuss the various imaging examinations that may be useful in evaluating women with recurrent UTIs.
Radiography
Radiography of the abdomen has long been an important examination for detecting calculi, bladder wall calcifications, gas in the wall or lumen of the urinary bladder, and/or foreign bodies that may be the etiology of a UTI. Use of digital tomosynthesis of the abdomen results in improved detection of urinary stones in general over digital radiography, with only a slight increase in effective dose.
When calcifications are seen in the bladder wall, it is often possible to make a correct clinical diagnosis if these findings are viewed in the context of the clinical history, physical examination, appropriate laboratory studies, and further imaging of the remainder of the urinary tract. Bladder wall calcification is typically due to prior infection with schistosomiasis (uncommon in the United States, but very common in other parts of the world), tuberculosis, cytoxan cystitis, or radiation cystitis.
Intravenous Urography
Historically, IVU was the imaging study of choice to evaluate the urinary tract. However, computed tomography (CT) and magnetic resonance urography have supplanted the use of IVU in many institutions. IVU optimally includes thin-section nephrotomography, which may show renal scarring to indicate prior episodes of pyelonephritis. Although ill-defined renal margins may suggest a perirenal inflammatory process, complications of suspected pyelonephritis are best evaluated by CT. However, for evaluation of the collecting system, IVU may detect the changes caused by reflux nephropathy, papillary necrosis, and subtle urothelial neoplasms, as well as other changes associated with infections such as pyelitis cystica and leukoplakia. IVU is also useful for detecting or excluding congenital anomalies or obstruction of the urinary tract. The bladder phase of the IVU can usually identify contour abnormalities suggestive of inflammation or neoplasm. Further, the ability of the bladder to empty on voiding can be reasonably assessed. Cystoscopy is the best method to evaluate bladder wall pathology suspected on imaging studies. In patients with recurrent UTIs, investigators have found that 9 of 118 (8%) patients had abnormalities on cystoscopy. Additionally, patients with no underlying risk factors demonstrate a very high negative predictive value for cystoscopy.
The weaknesses of IVU include the lack of parenchymal detail and the inability to characterize filling defects. CT of the abdomen and pelvis without and with contrast and including high resolution imaging during the excretory phase (CT urography) has superseded IVU.
Computed Tomography
CT without and with intravenous contrast has been described as the "examination of choice" in evaluating complicated UTIs for detecting underlying structural problems or complications. CT is the modality of choice for evaluating acute bacterial nephritis. This is especially true in patients with known underlying risk factors, repeated episodes of reinfection, or persistent infection despite adequate therapy. CT can not only define the extent of disease but also identify complications such as renal and perirenal abscess which may be associated with these infections.
Although abdominal radiography is considered the most cost-effective imaging modality for detecting radio-opaque calculi associated with recurrent UTI, it may prove inadequate in some cases (e.g., poor definition due to moderate overlying bowel, radiolucent calculi). Its benefits include increased accuracy in detecting calculi (contrast resolution and lack of overlying bowel and bone), increased speed of examination, and increased abdominal detail, allowing, in some cases, an alternate diagnosis to explain patients' signs, symptoms, and laboratory findings. As a result, unenhanced CT has been used predominantly for the emergency patient with "renal colic" and/or hematuria. It has also been used to define the severity and extent of upper-tract calculi, which are sometimes associated with recurrent UTIs. Reduced-radiation protocols for CT are being developed, which result in similar detection of renal stones while reducing patient radiation exposure.
Ultrasound (US)
Some investigators have advocated the use of renal and pelvic US combined with radiographs as a replacement for IVU. They conclude that young women with recurrent UTIs should have this combination of examinations (i.e., US and radiographs) as the investigation of choice because it is cost-effective, "non-invasive, inexpensive and acceptable to the patient." US has the advantage of no ionizing radiation. US can efficiently measure postvoid residuals within the bladder and detect some bladder diverticula. However, it is less accurate in the detection of pyelonephritis when compared with other imaging modalities, including CT and magnetic resonance imaging (MRI).
Magnetic Resonance Imaging
MRI has been shown to be useful in evaluating UTI. It does not use ionizing radiation and therefore is favored in patient populations such as pregnant women, children, and patients who require repeated imaging examinations. MRI is effective at diagnosing pelvic organ prolapse. The resultant cystoceles and urinary incontinence associated with pelvic organ prolapse are significant risk factors for recurrent UTIs in postmenopausal women. MRI best assesses the structure and complexity of urethral diverticula, allowing for accurate diagnosis and improved surgical planning. Given the excellent soft-tissue contrast on MR imaging, this modality is also effective for evaluating vesicovaginal and enterovesicular fistulae.
MRI is less sensitive than CT for detecting urinary tract calculi. In a study of 149 patients, MR urography demonstrated 69% sensitivity for detecting calculi versus (vs) 100% for CT. MRI may be of greatest value in documenting active upper tract infection vs scar formation to determine whether therapy has been effective in the high-risk patient and in differentiating active infection from other complications post renal transplant.
Diverticula
Patients with suspected bladder diverticula may be imaged with cystography, US, or CT. Bladder diverticula are unusual in women and are associated with neurogenic, or postoperative bladder, or rarely are congenital. When a bladder diverticulum is at or near a ureteral orifice, voiding cystourethrography should be considered to evaluate the possibility of vesicoureteral reflux. Although used commonly in children to reduce the dose of radiation, nuclear cystography has not been used widely in adults.
A history of recurrent UTI is seen in 30% to 50% of patients with urethral diverticula. Diverticula of the urethra can be evaluated with high sensitivity and specificity by double balloon urethrography, voiding CT urethrography, and MRI. MRI best assesses the structure and complexity of urethral diverticula, allowing for accurate diagnosis and improved surgical planning. In at least one report, MRI altered the surgical management in 15% of patients. Double balloon urethrography can be technically difficult and may be uncomfortable for the patient. CT urethrography requires imaging postprocessing on a workstation.
When performing cystography and urethrography for evaluating the lower urinary tract, the use of digital radiography has been shown to decrease radiation dose by approximately 90% while maintaining diagnostic accuracy. This is particularly important in reducing the gonadal radiation dose during the examination of young women.
Enterovesical Fistulae
Enterovesical fistulae are usually caused by diverticulitis (cancer is the second most common cause). Clinical suspicion is frequently raised by the presence of UTI with pneumaturia and/or fecaluria. CT is the primary imaging modality for suspected cases of enterovesical fistulas. A group of researchers found that CT diagnosed 20 of 20 cases of enterovesical fistula. Another group found that CT revealed fistulas in 12 of 15 patients (80%). Cystoscopy was performed in 16 patients with 87.5% positive and barium enema in eight with 50% positive. The authors concluded that CT is the optimum imaging modality for diagnosis as it can also identify the underlying etiology. The multiplanar imaging capability, lack of radiation, and high soft-tissue resolution inherent to MRI also makes this modality suitable for imaging suspected fistulae, particularly when repeat imaging and radiation doses are of issue. IVU, colonoscopy US, upper gastrointestinal/small-bowel follow-through, sigmoidoscopy, and nuclear imaging have very low yields, making them even less cost-effective.
Summary
- Women with recurrent UTIs should have one or more additional risk factors to justify urologic or radiologic investigation.
- The basis for radiologic or urologic investigation of women with recurrent UTI is to detect abnormalities that could result in future morbidity. In such cases, cystoscopy may provide a cost-effective diagnosis.
- CT is a mainstream investigational modality for evaluating UTIs, especially in patients with underlying or known risk factors, episodes of reinfection or infection resistant to conventional therapy.
- Abnormalities of the bladder and the urethra have traditionally been demonstrated with cystography and urethrography, respectively, with MRI now playing a more central role in evaluation of the urethra as well as for diagnosing bladder prolapse.
- For the detection of fistulae, CT is the optimum imaging technique and may also provide an etiology.
Anticipated Exceptions
Nephrogenic systemic fibrosis (NSF) is a disorder with a scleroderma-like presentation and a spectrum of manifestations that can range from limited clinical sequelae to fatality. It appears to be related to both underlying severe renal dysfunction and the administration of gadolinium-based contrast agents. It has occurred primarily in patients on dialysis, rarely in patients with very limited glomerular filtration rate (GFR) (i.e., <30 mL/min/1.73 m2), and almost never in other patients. There is growing literature regarding NSF. Although some controversy and lack of clarity remain, there is a consensus that it is advisable to avoid all gadolinium-based contrast agents in dialysis-dependent patients unless the possible benefits clearly outweigh the risk, and to limit the type and amount in patients with estimated GFR rates <30 mL/min/1.73 m2. For more information, please see the American College of Radiology (ACR) Manual on Contrast Media (see the "Availability of Companion Documents" field).
Abbreviations
- CT, computed tomography
- MRI, magnetic resonance imaging
- Tc-99m, technetium-99 metastable
- US, ultrasound
Relative Radiation Level Designations
Relative Radiation Level* |
Adult Effective Dose Estimate Range |
Pediatric Effective Dose Estimate Range |
O |
0 mSv |
0 mSv |
|
<0.1 mSv |
<0.03 mSv |
|
0.1-1 mSv |
0.03-0.3 mSv |
|
1-10 mSv |
0.3-3 mSv |
|
10-30 mSv |
3-10 mSv |
|
30-100 mSv |
10-30 mSv |
*RRL assignments for some of the examinations cannot be made, because the actual patient doses in these procedures vary as a function of a number of factors (e.g., region of the body exposed to ionizing radiation, the imaging guidance that is used). The RRLs for these examinations are designated as "Varies". |