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CURRENT PRACTICE ISSUES |
Department of Radiology, Winthrop-University Hospital, Mineola, New York School of Medicine, State University of New York at Stony Brook
South Texas Radiology Group, San Antonio, Texas
Department of Emergency Medicine, North Shore University Hospital, Manhasset, New York
Any solution to a problem changes the problem.
Richard William Johnson
It isn’t that they can’t see the solution. It is that they can’t see the problem.
G. K. Chesterton
Acute pain due to an obstructing ureteral calculus is a very common problem, with a lifetime prevalence in the United States of up to 12%. Renal colic is therefore one of the most common conditions treated in emergency departments (1,2). An obstructing ureteral calculus may mimic, and be mimicked by, innumerable abdominal and pelvic conditions. Patient history, physical examination, and laboratory tests cannot help confirm or exclude the diagnosis with high enough accuracy (1,2). In particular, hematuria testing has a sensitivity of 81%–84% (3,4) and a specificity and negative predictive value of 48% and 65%, respectively (4), and numerous alternative conditions commonly produce hematuria as well.
First introduced in 1995 by Smith et al (5), unenhanced CT (followed by unenhanced helical CT and unenhanced multi–detector row CT) has become the imaging modality of choice for the evaluation of patients with flank pain. Unenhanced CT is faster, safer, and more accurate than excretory urography and does not carry the risk of a contrast material reaction. As a result, excretory urography is almost never performed for this indication nowadays. Other advantages of unenhanced helical CT include more precise sizing and localizing of stones, determination of overall stone burden, and a comparable or reduced radiation dose (1,2,5–7). The examination can also be used to guide subsequent patient treatment based on the size and location of a ureteral stone. The most important advantage of unenhanced helical CT may be its capacity to reveal alternative diagnoses, both within and outside the genitourinary tract. Many of these diagnoses would not be evident at radiography or excretory urography (8–10).
Rucker et al (11) beautifully document a broad spectrum of alternative diagnoses discovered at unenhanced helical CT over a 2-year period in patients who were initially suspected of having an obstructing ureteral stone. These alternative diagnoses include common disorders such as pyelonephritis, appendicitis, and ovarian lesions, uncommon diagnoses such as renal lymphoma and ascending colonic diverticulitis, and rare diagnoses such as acute spontaneous splenic rupture and hemorrhage due to a renal arteriovenous malformation. Some relatively recent cases from our practices in which unenhanced helical CT revealed both common and uncommon diagnoses other than a ureteral stone are demonstrated in Figures 1 –5. Rucker et al also very nicely and thoroughly review the recent CT literature on these entities and guide the reader through the decision-making process in the further evaluation of some of these patients, particularly with regard to the role of repeat CT with intravenously administered contrast material in selected circumstances (11). Unenhanced helical CT for suspected renal colic has become a major part of our practices and of the emergency radiology practices at many institutions; therefore, radiologists should pay particular attention to the various important points that are raised by Rucker et al.
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In our own series of 1,000 consecutive patients who underwent unenhanced helical CT for suspected renal colic, 10% were discovered to have an alternative or additional significant diagnosis, which could be confirmed in 87 patients at follow-up (9). Forty-five patients had significant diagnoses involving the genitourinary tract without a concurrent ureteral calculus (or evidence of a recently passed calculus), including adnexal masses, bladder outlet obstruction, complicated renal cyst, perinephric or renal hemorrhage, renal cell carcinoma, and arteriovenous malformation. Other emergent findings outside the genitourinary tract included cholecystitis, pancreatitis, rectus sheath hematoma, and aortic dissection. Some patients had findings in addition to a ureteral stone, including perinephric liposarcoma, porcelain gallbladder, and exacerbation of Crohn disease (9). Many of these entities are also discussed and illustrated by Rucker et al (11).
Because unenhanced helical CT for suspected renal colic is so frequently performed, it is a good situation in which to attempt radiation dose reduction (8,15–17). This is an ideal situation when a stone is present because (a) affected patients are often young and may require repeat unenhanced helical CT over time, and (b) there is high contrast between high-attenuation stones and the lower-attenuation soft tissues (8). There is concern, however, that the sensitivity for identification of alternative diagnoses may decrease on these lower-dose (and therefore noisier) images, especially in the absence of plentiful intraabdominal and intrapelvic fat (8). Approaches to date that have not compromised diagnostic accuracy for alternative diagnoses have included increasing the pitch (15) and lowering the milliamperage (16,17), but all of these series contained relatively small numbers of patients. In what is to our knowledge the largest such series to date, as reported by Tack et al (16), three radiologists working independently correctly identified 13 alternative diagnoses at very low dose (30 mAs) unenhanced helical CT.
As Rucker et al point out, although more recent research has shown that for earlier cases of acute appendicitis, both oral and intravenous contrast material administration yield higher accuracy rates for CT interpretation, radiologists need to be familiar with the unenhanced helical CT appearance of acute appendicitis because affected patients may present with suspected renal colic relatively often (and vice versa). Attention should be paid to the appendix in all patients with suspected right renal colic in whom a ureteral stone or evidence of a recently passed ureteral stone is not found at unenhanced helical CT. About 80% of patients with suspected renal colic who truly do not have appendicitis will have a normal appendix that is identifiable at unenhanced helical CT (18). Also, it is not surprising that in the setting of right lower quadrant pain, unenhanced helical CT has revealed numerous alternative diagnoses in about 20% of patients in several series (19–21).
The positive impact of unenhanced helical CT on diagnosis and treatment in patients with suspected renal colic in terms of revealing alternative diagnoses has been demonstrated in several studies (22,23), although there are dissenters (24). Abramson et al (23) prospectively studied 93 patients and discovered an alternative diagnosis in 17 (18%). The clinical management plan and the confidence in a specific diagnosis before and after unenhanced helical CT was recorded for each patient. Not unexpectedly, the subset of patients in whom CT revealed an alternative diagnosis was the group in which clinician confidence changed the most from before to after CT (23). Chen et al (22) compared the results of 100 unenhanced helical CT examinations performed in 1 year with those of 100 examinations performed the following year and demonstrated "indication creep"; that is, the percentage of cases with a ureteral stone decreased from 49% in the 1st year to 28% in the 2nd year, whereas the alternative diagnosis rate increased from 16% to 39%. The authors speculated that the indications for ordering unenhanced helical CT broadened because the emergency department physicians recognized over time that unenhanced helical CT is a rapid study that can be used to demonstrate not only ureteral stones but many alternative diagnoses (22).
The causes of abdominal and pelvic pain seen at unenhanced helical CT range from obvious to very subtle (9), and one must be especially careful when reviewing unenhanced helical CT scans on which there is limited fat within the abdomen and pelvis, or when no cause for the pain is discovered. The selective role of repeat CT with intravenous contrast material (eg, in cases of suspected renal abscess at initial unenhanced helical CT) is well shown in the figures provided by Rucker et al (11). We very much agree with the guidelines provided by the authors for the use of intravenous contrast material in specific situations and in general, including the recommendation that the decision to perform repeat CT be made on a case-by-case basis in consultation with the referring physician, who is usually working in the emergency department. We agree that caution is advisable with respect to particular vascular diagnoses, including (but not limited to) bowel ischemia, vascular thrombosis, aortic dissection, and renal infarction (2,9,14,22). If findings at initial CT are equivocal or negative in a patient with a strong pre-CT probability of a serious abdominal or acute pelvic disorder, or if further characterization of the findings would be beneficial, repeat CT with intravenous contrast material should be seriously considered as soon as possible—preferably with the patient still on the CT table—although in general the diagnostic yield is low if less strict guidelines are used. In a recent study by Miller et al (25), 1,236 patients with suspected renal colic underwent unenhanced helical CT over the course of 1 year. Of these patients, 735 also underwent repeat CT with intravenous contrast material. Only 8% of these 735 patients had an abnormality not seen at unenhanced CT, and in the majority of these cases (n = 32), pyelonephritis was diagnosed at repeat CT.
We strongly concur with the conclusion of Rucker et al that unenhanced helical CT is indispensable for accurate diagnosis in patients with clinically suspected ureterolithiasis, and that radiologists need to be aware of the numerous diseases that may be initially identified at such CT examinations.
Financial Interest: All authors have no financial relationships to disclose.
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Mallinckrodt Institute of Radiology, Washington University School of Medicine, St Louis, Missouri
We would like to thank Katz et al for their insightful commentary regarding the use of unenhanced helical CT for the diagnosis of renal colic, as well as for supplementing our work with additional case material. Clearly, the safety, speed, and accuracy of unenhanced helical CT and its ability to delineate alternative causes of flank pain have made it an indispensable diagnostic tool in the emergency setting.
Our experience with "indication creep" mirrors that of Chen et al (1), since we, too, have seen a decrease in recent years in the percentage of cases in which unenhanced helical CT is positive for urolithiasis. As Katz et al mentioned, many factors contribute to the increased use of unenhanced helical CT in the emergency department, including its speed compared with excretory urography, the lack of waiting time for oral contrast material administration, and the ability to proceed without determining the serum creatinine level. In emergency departments where throughput and waiting times are closely monitored, unenhanced helical CT can often be performed in less time than is required to perform standard admission laboratory tests.
We also agree with Katz et al that radiologists must be mindful of the radiation dose used with unenhanced helical CT. The increasing use of unenhanced helical CT in young patients, in many of whom multiple repeat scans are obtained over a short period of time, make this examination ideal for implementing dose-lowering strategies, such as decreased milliamperage or increased pitch (2). Recently, limited work has shown that the high contrast of urolithiasis allows accurate diagnosis even in the setting of a lower radiation dose (3,4). Further studies are needed to verify whether a lower-dose alternative will have an impact on making alternative diagnoses.
Increased use of unenhanced helical CT and "indication creep" result in an increased number of alternative diagnoses. Thus, radiologists must carefully evaluate the portion of the examination that does not involve the genitourinary system for potential causes of flank pain. Our goal in presenting these cases was to provide an atlas of causes of flank pain encountered at unenhanced helical CT performed for urolithiasis in a busy emergency department over a 2-year period. Although radiologists may be familiar with the appearance of many of these entities at CT performed with intravenous contrast material, it is the unenhanced CT appearance of these entities that will be encountered at CT performed for urolithiasis.
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