OBJECTIVE. The purpose of this study is to describe the prevalence and the characteristics of clinically important incidental extraurinary findings detected at MDCT urography performed for hematuria.
MATERIALS AND METHODS. A computer search of CT reports using the term “hematuria” identified 1209 reports of patients who had undergone MDCT urography. The results were retrospectively reviewed to determine unsuspected extraurinary findings that are clinically important or potentially important, warranting further imaging studies or medical or surgical intervention. We further categorized these important findings as acute (i.e., requiring immediate medical attention) or nonacute (i.e., requiring further evaluation in a nonurgent manner). By use of our electronic medical records, these findings were correlated to histologic diagnosis, further imaging evaluation, and clinical information.
RESULTS. In 82 of 1209 patients (6.8%), 85 clinically important incidental extraurinary findings were identified. Follow-up evaluation was available for 43 of 85 (50.6%) findings by histologic diagnosis (n = 9), imaging evaluation (n = 31), or clinical information (n = 3). There were 11 (0.9%) examinations with acute findings, of which acute inflammation of the gastrointestinal tract and pancreaticobiliary system were the most common. Seventy-two (5.9%) examinations revealed 74 nonacute but important findings. Lung nodules were the most prevalent, followed by intraabdominal aneurysms and cystic ovarian masses. There were five (0.4%) histologically proven malignant neoplasms.
CONCLUSION. The prevalence of clinically important incidental extraurinary findings at MDCT urography performed for hematuria was 6.8%.
Hematuria is a common clinical manifestation of a wide spectrum of urologic diseases. MDCT urography allows comprehensive evaluation of the upper urinary tract and has become the standard imaging examination in the evaluation of hematuria in most adults [1–3]. Because the organs outside the urinary tract are also included in the image FOV, MDCT urography can reveal unanticipated findings unrelated to urinary disease. Incidental findings at cross-sectional imaging are a well-recognized phenomenon . Although early detection of treatable disease would be desirable, incidental findings can also lead to a clinical dilemma in which the decision to pursue the workup must be weighed against the potential additional tests, expenses, and patient anxiety for the findings, many of which may ultimately prove to be inconsequential to patient care. A growing number of studies in recent literature have addressed the prevalence of incidental findings at CT [5–7].
CT colonography literature has many reports on incidental findings [8–13], and we know of three renal calculi CT studies that reported incidental findings [14–16]. However, there are few data in the imaging literature and, to our knowledge, only one published study  about incidental findings at CT urography. Unlike CT colonography or renal calculi CT, which are performed without IV contrast agent typically at a low dose, MDCT urography is performed without and with IV contrast agent, with initial unenhanced series to detect urinary tract calculi followed by contrast-enhanced series optimized to evaluate neoplasms of the urinary tract. Thus, the prevalence of clinically important incidental findings in MDCT urography may be different than that in CT colonography or renal calculi CT. It is plausible that some small lesions may be more conspicuous with added enhanced series, whereas other lesions may be adequately characterized at MDCT urography and are not considered incidental findings that require further workup.
The purpose of this study was to determine the prevalence and the characteristics of clinically important extraurinary findings found at MDCT urography obtained for hematuria evaluation.
Materials and Methods
This HIPAA-compliant retrospective study was approved by our institutional review board, and the requirement for informed consent was waived. The reports of abdominal and pelvis CT examinations performed without and with IV contrast agent administration at our academic institution from March 2004 to September 2008 were queried for the word “hematuria” in the examination history. The search yielded the records of 1221 MDCT urography examinations performed on 1209 patients. For the 12 patients who underwent two examinations, only the first MDCT urogram was included in this study. The study population consisted of 1209 patients (654 men and 555 women). The mean age of the study group was 59 years (range, 20–94 years).
MDCT Urography Technique
CT urography was performed at our academic institution using 4-, 16-, or 64-MDCT scanners (4- and 16-MDCT LightSpeed, 16-MDCT Brightspeed, and 64-MDCT VCT, all from GE Healthcare; 4-MDCT Asteion and 16-MDCT Aquilion, both from Toshiba Medical Systems; 16-MDCT Sensations, Siemens Healthcare). Our MDCT urography technique evolved from a three-phase scan to a two-phase split-bolus technique in March 2006 during the study period. There were 112 (9.3%) MDCT urography examinations performed using the three-phase technique and 1097 (90.7%) examinations with the split-bolus technique as described later in this article.
The three-phase protocol consisted of an unenhanced phase, either a corticomedullary or nephrographic phase, and an excretory phase. The unenhanced phase was obtained through the abdomen and pelvis at 0.6–2.5-mm collimation, depending on the scanner type. After IV administration of 100 mL of low-osmolar contrast agent (iohexol, Omnipaque 300, GE Healthcare; or iopromide, Ultravist 300, Bayer HealthCare) at a rate of 3 mL/s, either corticomedullary or nephrographic phase scans (0.6–2.5-mm collimation) were obtained at 60 or 100 seconds, respectively, after injection. The excretory phase scans (0.6–2.5-mm collimation) were obtained at 5 minutes after the contrast injection.
The two-phase split-bolus technique consisted of an unenhanced phase and a synchronous nephrographic and excretory phase using dual injection of contrast medium, a variant of the protocol described by Chai et al. . After acquisition of unenhanced scans of the abdomen and pelvis (0.6–2.5-mm collimation), an initial dose of 40 mL of low-osmolar contrast agent (iohexol, Omnipaque 350, GE Healthcare) was administered and followed by 120 mL of normal saline, both at a rate of 2 mL/s. After a 10-minute delay, a second dose of 90 mL of iohexol was administered at a rate of 4 mL/s. The enhanced phase scans were obtained at 0.6–2.5-mm collimation 140 seconds after the administration of the second dose of contrast material. Both unenhanced and enhanced phase images were reconstructed in the axial and coronal plane at 5-mm thickness. Additional bilateral coronal oblique projections of ureters were created using maximum intensity projection at 10 mm.
Data Review and Analysis
The finalized radiology reports of 1209 MDCT urography examinations were retrospectively reviewed to determine previously unknown unsuspected findings outside the urinary tract, specifically excluding the kidney, collecting system, ureter, and the bladder. Before reviewing the reports, we defined important incidental extraurinary findings as those that were clinically important or potentially important—that is, warranting further surgical or medical intervention or imaging evaluation—parallel to the E4 category of incidental finding classifications from the CT Colonography Reporting System . The E4 category of incidental extracolonic findings is defined as “findings that, if left untreated, have greater potential to adversely affect the patient’s health” . Our list of important findings also include some of the “findings of high importance,” “clinically important findings,” and “findings of high clinical significance” from previous CT colonoscopy and CT urography studies [8, 11, 17]. We further categorized these important findings as acute (i.e., requiring immediate medical attention) or nonacute (i.e., requiring further evaluation in a nonurgent manner). For the lung nodules, we included those larger than 4 mm from Fleischner Society recommendations for low-risk patients . For indeterminate masses of solid organs, our size criterion was at least 1 cm, including the adrenal nodules . For cystic adnexal masses, we adopted the ultrasound size criteria from the Society of Radiologists in Ultrasound Consensus statement  for follow-up because there is no current guideline for CT, and used a 1-cm threshold for postmenopausal women and at least 3 cm for premenopausal women, assuming age greater than 50 years to be postmenopausal . We also included clinically important incidental bone lesions. In patients with multiple aneurysms, the findings were counted as one entity. These incidental findings were correlated to subsequent histologic diagnosis (if pathology examination was obtained), follow-up imaging evaluation, or clinical follow-up (e.g., operative notes and discharge notes), according to our electronic medical records. For findings with multiple methods of follow-up, the histologic diagnosis was considered the reference standard. For imaging follow-up, we considered more than 1 year of stability as an indicator of a benign process for solid organ lesions when there were no specific imaging diagnoses. For lung nodules, we used the stability criteria for benign lesions based on Fleischner society recommendations for low-risk patients . The examinations with incidental findings were then reviewed by two fellowship-trained radiologists with subspecialty expertise in abdominal imaging to determine whether the reported incidental findings were visible on the unenhanced series. The unenhanced images were reviewed separately and before the contrast-enhanced series.
We compared the patient age and sex distribution between the groups with and without clinically important incidental findings by independent samples Student t test and chi-square test using Stata (version 10 StataCorp). p values of less than 0.05 were considered statistically significant.
There were 85 clinically important incidental findings outside the urinary tract identified at MDCT urography in 82 of the 1209 patients (6.8%). Three patients had two important findings. The demographics of the patients with important findings compared with the patients without such findings are presented in Table 1. There was a significant difference in patient age between the two groups (p < 0.001). Eleven of the 82 (13.4%) patients with important findings had an acute finding requiring immediate medical attention, and 72 (87.8%) patients had nonacute important findings. One patient had both acute and nonacute important findings. Follow-up evaluation was available on 43 findings in 41 patients (50.6% of 85 findings) by histologic diagnosis (n = 9), imaging evaluation (n = 31), or clinical follow-up (n = 3). For imaging follow-up, the mean interval between MDCT urography and the last imaging was 294 days (range, 2–949 days). Forty-two of the 85 (49.4%) clinically important incidental findings had no further imaging or clinical follow-up on our hospital network electronic medical record and were considered lost to follow-up.
Eleven acute findings requiring immediate medical attention were found in 11 of 1209 (0.9%) total patients (Table 2). There were two patients each with unsuspected diverticulitis, pancreatitis, and retroperitoneal bleed. There was one patient each with cholecystitis, ileitis, colitis, sigmoid volvulus, and a splenic hematoma (Fig. 1). Four of the patients with acute findings had further imaging or clinical follow-up noted in the hospital medical record. One patient with acute ileitis and adjacent abscess underwent MR enterography 6 days later, which confirmed MDCT urography findings and diagnosed active Crohn disease. One patient with an incidental sigmoid volvulus required sigmoid colectomy after the diagnosis was confirmed intraoperatively. One patient with incidental cholecystitis underwent cholecystectomy with the diagnosis confirmed intraoperatively. One of the two patients with acute diverticulitis had a diverticular abscess and subsequently underwent CT-guided abscess drainage. The remaining seven patients with acute unsuspected findings (two with pancreatitis, two with retroperitoneal bleeds, and one each with diverticulitis, colitis, and a splenic hematoma) did not have further imaging or available clinical follow-up.
There were 74 nonacute but clinically important extraurinary findings in 72 of 1209 (5.9%) patients (Table 3). Fifty-six of the 74 nonacute findings were indeterminate masses, including endometrial thickening, and 18 were nonmass findings. The most common unsuspected findings were lung nodules (n = 22), aortoiliac aneurysms (n = 16), ovarian cysts (n = 14), pancreatic cysts (n = 6), liver lesions (n = 4), and postmenopausal endometrial thickening (n = 4). The lung nodules ranged from 5 to 39 mm in diameter (Table 4). Twelve ovarian cysts (1.3–7.6 cm) were detected in postmenopausal women, and two were seen in premenopausal women. Of the six pancreatic masses, five were cystic lesions smaller than 2 cm, and one was a 3.8-cm complex cystic mass. Thirty-eight of 56 (67.9%) masses had further follow-up by histologic diagnosis (n = 9) or imaging evaluation (n = 29). Eighteen of 56 (32.1%) indeterminate masses had no further follow-up. Of the 29 masses with further imaging evaluation, nine masses underwent diagnostic imaging studies (three MRI, three ultrasound, two CT, and one PET/CT), 12 masses were stable for at least 1 year (mean, 1.8 years; range, 1–2.6 years), and eight masses had less than 1 year of follow-up. Of the 18 nonmass findings, other than one case of avascular necrosis of femoral head confirmed by MRI, the remaining 16 aneurysms and one case of avascular necrosis had no further follow-up.
There were five histologically proven incidental extraurinary malignant neoplasms diagnosed, constituting 0.4% of the study group. There were four bronchogenic carcinomas ranging from 14 to 39 mm (Fig. 2). Three of these patients were diagnosed with stage I disease (two patients were subsequently treated by lobectomy and one patient was treated with radiofrequency ablation because of patient comorbidities), and one patient was diagnosed with metastatic disease. There was one patient with follicular lymphoma diagnosed at surgical excision of an enlarged inguinal lymph node.
Twenty-five of 56 (44.6%) masses were confirmed to be benign on follow-up evaluation by histology (n = 4), imaging diagnosis (n = 9), or imaging stability (n = 12). The confirmed benign masses were benign lung nodules (n = 9); ovarian cysts (n = 5); pancreatic cysts and a benign cystic neoplasm (n = 5); hepatic hemangioma, cysts, and nonspecific inflammatory lesion (n = 4); adrenal adenoma (n = 1); and a hyperplastic lymph node (n = 1). The diagnoses of 26 masses (46.4%) remained indeterminate because of insufficient (n = 8) or missing (n = 18) follow-up.
When unenhanced and contrast-enhanced series of 82 examinations with incidental findings were compared, 83 of 85 (97.6%) findings were detected on both series. Of these, a liver mass and postmenopausal thickening, although visible on both series, were better characterized on the contrast-enhanced series. In two examinations (2.4%), postmenopausal endometrial thickening were visible only on the contrast-enhanced series.
MDCT urography has become a commonly performed study for the evaluation of hematuria, and it can reveal unanticipated extraurinary findings. Incidental findings are common at MDCT because of its high spatial resolution and increased utilization for various clinical indications; however, not all incidental findings are clinically important or merit further workup. In our study of 1209 MDCT urography examinations, 6.8% of patients had clinically important or potentially important incidental findings requiring further investigation. Of these, clinically significant results proved uncommon with acute findings diagnosed in 0.9% of patients and extraurinary malignancy confirmed in 0.4%.
Although there are several studies reporting the diagnostic yield and validity of CT urography in identifying the source of hematuria, with several studies showing promising results of diagnosing upper tract urothelial neoplasm [23–28], we are aware of only one published study addressing the incidental findings detected outside the urinary tract at CT urography: in a study of 344 patients, Liu et al.  reported 18.0% prevalence of highly clinically significant extraurinary findings at MDCT urography in patients with hematuria, compared with 6.8% prevalence in our study. The reason for the different prevalences between the two studies is unclear. The age distributions of the two studies are similar, with our mean age of 59 years (range, 20–94 years) versus theirs of 56 years (range, 17–95 years). One source of our lower prevalence may be the stricter size criteria we applied for lung nodules and adrenal masses, which accounted for 2.1% (25/1209) of our total prevalence compared with 5.5% (19/344) in their study. Lung nodules were still the most common incidental finding in both studies. Incidental lung nodules are common at CT of the abdomen, with up to 39.1% prevalence reported in one retrospective study, although only 8.4% were prospectively reported . The majority of these incidental nodules were reported to be small (< 4 mm). Clinically important acute findings were similar, at 0.9% in our study population and 1.4% (diverticulitis, appendicitis, and common femoral artery pseudoaneurysm) in the study by Liu et al.
Our results can be compared with the data from the CT colonography literature, which encompasses the largest number of studies on incidental findings at CT of the abdomen and pelvis targeted for a specific indication. Our 6.8% prevalence of clinically important or potentially important incidental findings is at the lower range of CT colonography prevalence, which is approximately 7–13% [8–13]. The difference in the overall prevalence could be attributed to several factors. First, by definition, an incidental finding of urinary tract, such as a renal mass at CT colonography, is not considered incidental at MDCT urography. Renal mass is one of the most common highly important incidental findings at CT colonography [8–11, 13], and in one study, Veerappan et al.  reported 41% of E4 findings to be renal masses. Thus, excluding renal masses would decrease the overall prevalence of incidental finding at MDCT urography compared with CT colonography. Conversely, although a colonic polyp or mass would be considered an important incidental finding at MDCT urography, these lesions are unlikely to be detected without luminal distention, and none were found in our study.
Second, the criteria used for clinically important incidental findings in CT colonography have been variable. We considered only previously unknown important findings to be incidental in our study and also applied more stringent size criteria for some lesions on the basis of current imaging guidelines and recommendations, which may have further reduced the number of important incidental findings. Third, the presence of contrast agent at MDCT urography may also have reduced the number of indeterminate lesions requiring further imaging evaluation, such as hepatic hemangioma, which may appear indeterminate at CT colonography but may be adequately characterized at MDCT urography. Although small indeterminate lesions of a solid organ may be more conspicuous on the contrast-enhanced phase of MDCT urography, these are unlikely to have added to our prevalence of important findings because we have included only lesions larger than 1 cm to warrant further evaluation. In our study, most important findings did not require contrast agent for their detection because 97.6% of these findings were visible on unenhanced images. This is largely a result of the composition of our important findings, because the more prevalent lesions, such as lung nodules and aneurysm, are easily seen on unenhanced CT. In a study comparing the importance of extracolonic findings at IV contrast-enhanced versus unenhanced CT colonography in different cohorts of 72 and 30 patients, Spreng et al.  reported that a substantially greater proportion of findings on IV contrast-enhanced CT colonography led to further workup and treatment. However, the authors acknowledged that findings such as aortic aneurysm, mass lesion, enlarged lymph nodes, and cholecystitis would probably have been diagnosed even with unenhanced CT.
Finally, the difference in patient age may also have contributed to the difference in the prevalence of important incidental findings. The patients in CT colonography studies are often slightly older, with mean or median ages of 60–69 years [8–11, 13], compared with our mean age of 59. Incidental findings are, in general, more prevalent in older patients. In our study, the patients with clinically important incidental findings were significantly older than those without incidental findings. Excluding the urinary findings of CT colonography, the characteristics of our incidental findings were similar to those of CT colonography studies, and lung nodules and aortoiliac aneurysms were the most common [8, 9, 11, 13]. Incidental adnexal masses were also relatively common, as reported by Pickhardt and Hanson .
We found incidental extraurinary malignant neoplasms (lung cancer and non-Hodgkin lymphoma) in 0.4% of our patient cohort. Malignant neoplasm is uncommon among incidental findings. In patients undergoing CT colonography, malignant extracolonic neoplasms were diagnosed in 0.3–0.8% of patients, and renal cell carcinoma was the most common type in several studies [8, 11, 13, 31]. In a study of 10,286 asymptomatic patients, Pickhardt et al.  reported extracolonic cancer in 36 patients, and renal cell carcinoma was the most common, accounting for 11 cases, followed by lung cancer and non-Hodgkin lymphoma. Lymphoma and lung cancer were also responsible for the 0.9% malignant extraurinary neoplasms diagnosed at MDCT urography in the study by Liu et al. .
Our study confirms that recommendations by radiologists are often not followed by referring clinicians. Our patient populations, in general, tend to have their follow-up care and imaging studies within the network of our hospitals and outpatient centers because of local practice patterns. However, 49.4% of important findings, of which 42.9% were indeterminate masses, had no further follow-up. Lack of follow-up for incidental findings has been reported in previous studies [6, 8, 14, 15, 17, 32]. Adherence to appropriate follow-up recommendations may improve as the standardized guidelines for imaging findings become more widely used by radiologists and accepted by referring clinicians.
There are several limitations to our study. The lack of follow-up has been discussed already, and the nature of 46.4% of indeterminate masses remained indeterminate. In some acute settings, the lack of follow-up likely reflects the current acceptance of CT diagnoses as the reference standard, frequently with no further diagnostic workup if the patient’s clinical condition improves. Among the nonacute findings, 16 aneurysms and one case of avascular necrosis did not have follow-up as defined by our study design; however, these findings are diagnostic at CT, not requiring additional study for confirmation.
Our second limitation is that in this retrospective study, we used finalized reports of the MDCT urography examinations to identify important incidental findings and did not confirm the diagnoses by image review, other than in the 82 examinations where images were reviewed to compare the unenhanced and enhanced series in detecting the reported incidental findings. However, there is no reason to think that the prevalence and the characteristics of incidental findings would be different had all studies been blindly reviewed.
Finally, although we tried to define and categorize important findings on the basis of current literature, we recognize that in clinical practice these findings have to be considered in the context of individual patients’ overall clinical status. For example, a 10-mm nodule in a 50-year-old healthy patient may have a different implication than if it were found in an octogenarian with multiple comorbidities.
In conclusion, the prevalence of clinically important incidental extraurinary findings at MDCT urography performed for hematuria was 6.8%. Lung nodules were the most common incidental finding, and malignant extraurinary neoplasm was found in 0.4% of cases.
APPENDIX 1: AJR Journal Club
Incidental Clinically Important Extraurinary Findings at MDCT Urography for Hematuria Evaluation: Prevalence in 1209 Consecutive Examinations
1. Does the study accomplish its stated objective?
2. Is the research question clinically relevant?
3. How does the article define clinically important extraurinary findings? Is this definition adequate? What resources are available for providing appropriate follow-up recommendations of clinically important findings?
4. How were patients selected for inclusion in this study? What were the exclusion criteria?
5. How did the study determine whether appropriate follow-up of clinically important incidental findings had been performed?
6. What are the limitations to this study? Does the study adequately address these limitations?
7. What explanation does the article provide for the variation in prevalence of clinically important findings between this study and the referenced study conducted by Liu, Mortelé, and Silverman at Harvard? How does the prevalence determined in this study compare to the prevalence of clinically important findings on studies of CT colonography?
8. What are the current criteria for recommending follow-up of lung nodules, adrenal masses, and adnexal masses?
9. The study describes three-phase and two-phase, split-bolus techniques for MDCT urography. What are the relative advantages of each technique? How do the techniques vary with respect to patient dose? How is MDCT urography performed at your institution?
10. How do you manage incidental findings at imaging and appropriate management of these findings at your institution?
11. Is there a mechanism in place at your institution to track communication and follow-up of clinically relevant incidental findings? What responsibility, if any, does a radiologist have to ensure appropriate follow-up or management is accomplished?
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