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Commentary |
1 Department of Radiology, Wake Forest University School of Medicine, Medical Center Blvd., Winston-Salem, NC 27157.
Received February 20, 2006; accepted after revision February 27, 2006.
Each month the American Journal of Roentgenology will republish
online one or more of the 100 most-cited articles from its first century. A
corresponding commentary in the print journal by a contemporary radiologist
will provide a current perspective. For a full list of these articles, see
page 3 of the January 2006 issue of AJR or
www.ajronline.org.
Keywords: abdomen • calculi • flank pain • helical CT • urinary tract
The profound effect of "Diagnosis of Acute Flank Pain: Value of Unenhanced Helical CT" [1] was likely underestimated at the time of its publication. The effect of this article gradually grew, like a tidal wave, eventually hitting clinical practices in such a way that they have been changed for the foreseeable future. Written by R. C. Smith and colleagues at the Yale University School of Medicine, this article expanded on an earlier article comparing unenhanced helical CT with excretory urography for the detection of ureteral calculi [2]. Both of these articles were an outgrowth of the development of helical CT coupled with the brilliant observation that virtually all urinary tract calculi are detectable with CT.
The advent of helical CT allowed the abdomen and pelvis to be scanned using thin collimation in a relatively short period of time during a single breath-hold. This avoided the problems with earlier incremental CT in which the patient's inability to exactly reproduce the depth of breath for each scan slice made misregistration of scans inevitable. The speed of older scanners also led radiologists to use thicker scan slices to obtain adequate anatomic coverage in a reasonable amount of time. These two factors made detection of small urinary tract calculi impractical.
Shortly after the introduction of helical CT scanners, Smith and his team suggested that helical CT was a better technique than excretory urography for diagnosing ureteral calculi. This seminal article in the AJR focused mainly on validating unenhanced helical CT as the best technique for diagnosing ureteral calculi. The article confirmed the accuracy of helical CT for diagnosis of ureteral stone disease, with sensitivity of 97%, specificity of 96%, and overall accuracy of 97%. It also showed that helical CT was extremely useful for diagnosing other causes of acute flank pain. The accuracy of helical CT far exceeded that of excretory urography, sonography, and abdominal radiography.
"Diagnosis of Acute Flank Pain" established helical CT as a better technique for diagnosing ureteral calculi than all previous imaging studies. In addition, it established helical CT as a solution that not only offered better accuracy for detection of ureteral calculi but also lowered the risks of making that diagnosis compared with the standard technique of excretory urography. Helical CT, as described by the authors, was to be performed without IV or oral contrast material. This eliminated the time required to administer oral contrast material for a standard CT scan, but more important, it eliminated the need for IV contrast material that posed a risk for patients undergoing excretory urography.
Helical CT also could be performed with approximately the same or reduced radiation compared with standard excretory urography [1]. Helical CT for the diagnosis of ureteral calculi could be performed rapidly, in 5 minutes or less, as described by the authors—much quicker than excretory urography or sonography examinations. Based on the win-win situation described, better accuracy, faster technique, and less patient risk, the helical CT examination rapidly eclipsed, and soon replaced, excretory urography as the standard technique used for diagnosis of ureteral calculi [3]. Certainly, this was an expected result after the publication of "Diagnosis of Acute Flank Pain" and the many subsequent articles [4-9] that confirmed the findings.
In addition, this article and later articles on this topic changed the way we think about urolithiasis. The standard mantra for radiologists before the introduction of helical CT was that approximately 90% of urinary tract calculi are radiopaque and visible on abdominal radiographs [10]. Later studies comparing helical CT and radiographs showed that only about half of urinary tract calculi are in fact visible using abdominal radiographs and excretory urography [11]. CT rapidly has become the gold standard for the detection of all urinary tract calculi, not just those in the ureters. Although the CT stone study was initially resisted by some urologists, it has been widely accepted as an improvement on excretory urography and abdominal radiography for the diagnosis of urolithiasis. In fact, many urologists are now replacing their in-office radiographic systems with in-office CT scanners for this purpose.
The effect of "Diagnosis of Acute Flank Pain" on the diagnosis of ureteral calculi was profound. Perhaps equally or more profound was the effect the article had on the evaluation algorithm for patients with acute abdominal pain. In this situation, it may be appropriate to take the view "The devil is in the details." The title of this article includes "diagnosis of acute flank pain." The word "flank" is a relatively subjective term describing a part of the body and is defined in the dictionary as "lateral part or side" [12], an imprecise area.
When Smith and colleagues reported that helical CT was extremely accurate in diagnosing the cause of flank pain [1], they clearly were expanding the use of helical CT beyond the diagnosis of ureteral calculi. Although unenhanced helical CT was promoted initially as a great technique for the diagnosis of ureteral calculi in patients with acute pain that was thought to be caused by a ureteral stone, indication creep soon set in [13]. Soon, many patients presenting to the emergency department with "flank pain," whether thought due to ureteral stones, diverticulitis, appendicitis, or an array of other potential intraabdominal diagnoses, were referred for helical CT of the abdomen and pelvis for evaluation.
The referring physicians rapidly recognized that helical CT was accurate for the diagnosis of the major disorders that caused not only flank pain but also acute abdominal pain. This led to increased use of abdominal and pelvic CT for patients seen in emergency departments with acute abdominal pain. In the years that followed publication of this article, helical CT, and more recently MDCT, has been established as an extremely accurate technique for diagnosing most common causes of acute abdominal pain.
Although unenhanced CT has been augmented in some situations with the addition of oral or IV contrast material or both, depending on the most likely cause of abdominal pain, this article on unenhanced helical CT set the stage for these applications. This broadening of applications for abdominal CT has sometimes been bemoaned by radiologists, but it has greatly increased the significance of radiology in making the diagnosis of acute intraabdominal disorders such as appendicitis and diverticulitis and has led to an increase in the number of abdominal CT scans requested by referring physicians. The emphasis on reducing slice thickness and scanning times to increase patient throughput in places such as busy emergency departments has helped push the industry to develop better scanning techniques including newer MDCT scanners.
As a caveat to the broadening of indications for CT for the symptoms of acute flank pain, radiologists have rapidly learned that solely diagnosing or excluding ureteral calculi is not adequate in evaluating these scans. It is critical to evaluate every detail on each scan because many diseases can mimic the symptoms of ureteral calculi. Evidence of many of these disorders will be detectable on abdominal CT. Missing an important diagnosis on one of these scans could have catastrophic results.
The effects of the Smith and colleagues article, describing the utility of unenhanced helical CT for disease diagnosis in patients with acute flank pain, have been unexpectedly large. Smith and his coauthors initially made an inspired observation that helical CT could be a more accurate way to detect ureteral calculi. The research reported in this now classic article confirmed their premise regarding the high accuracy of helical CT for diagnosis of ureteral calculi but also expanded the possible applications of CT to the diagnosis of an array of intraabdominal disorders.
The consequences of "Diagnosis of Acute Flank Pain" have led to improvements in our ability to diagnose not only ureteral calculi but also all urinary tract calculi, appendicitis, diverticulitis, and many other intraabdominal disease processes that cause symptoms that can mimic ureteral colic. This article and the work that built on it have helped fuel increased applications and innovations in CT of the abdomen. The authors should be applauded for their innovative thinking and for their methodical research confirming the utility of helical CT in the evaluation of patients with acute flank pain. The field of radiology has been dramatically changed for the better, largely based on this single article published in 1996 in the AJR.
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