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1
Department of Radiology, MC 0024, Denver Health Medical Center, 777 Bannock
St., Denver, CO 80204.
2
Department of Radiology, University of Washington Medical, Center, 1959 N.E.
Pacific St., Seattle, WA 98195.
Received February 9, 2000;
accepted after revision March 8, 2000.
Presented at the annual meeting of the American Roentgen Ray Society, New
Orleans, May 1999.
Abstract
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SUBJECTS AND METHODS. We prospectively evaluated helical abdominal CT scans for hepatic and splenic injuries in 300 consecutive patients with blunt abdominal trauma over a 4-month period. There were 204 males and 96 females with a mean age of 34 years (age range, 1-87 years). For each patient, initial CT diagnosis of hepatic or splenic injury was made from images obtained with standard abdominal window settings. CT scans were then immediately reinterpreted using additional images obtained at narrow window width (liver windows). Changes in conspicuity and characterization of injury were recorded. All CT examinations were performed with helical 7-mm collimation at a pitch of 1.5 after oral ingestion of diluted barium and during bolus IV administration of 125 mL of ioversol at a rate of 2-3 mL/sec.
RESULTS. We detected hepatic or splenic injuries in 34 patients (11.3%). There were 19 hepatic injuries and 18 splenic injuries. Three patients had injuries to both liver and spleen. Conspicuity of hepatic or splenic injuries was mildly increased (+1 H) on liver windows in 16 patients, whereas the injury was equally conspicuous on both liver window and standard window images in 19 cases. In no case did review of the liver windows result in a change in grade of injury or reveal an injury that was not seen on standard abdominal window images. The total increased cost for printing liver windows was $5748.
CONCLUSION. Routine use of liver window settings for abdominal CT in trauma patients has little clinical usefulness and is not cost-effective.
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Many institutions routinely obtain dedicated CT liver windows in addition to images obtained at standard abdominal window settings for all their abdominal CT examinations; however, printing liver window scans adds cost to the CT examination, including film and processing costs, costs for the time of technologists and radiologists, and costs incurred for alternator space and film storage [7].
The purpose of this study was to evaluate prospectively the usefulness of liver window scans, viewed in conjunction with CT scans obtained at standard abdominal window settings, for the detection and characterization of hepatic and splenic injuries in a subset of patients with blunt abdominal trauma.
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At our institution, patients are considered for CT examination if they exhibit normal hemodynamic status and any of a number of clinical signs and symptoms, including gross hematuria, decreased hematocrit (<35%), evidence of free intraperitoneal fluid on trauma sonography, or altered mental status or confounding injury that might limit the sensitivity of the abdominal physical examination. Occasionally patients with a significant mechanism for injury but without specific signs and symptoms also will be sent for CT examination. Patients who are not stable hemodynamically or those who show evidence of diffuse peritoneal irritation proceed immediately to laparotomy.
All CT examinations were performed using a helical CT scanner (HiSpeed; General Electric Medical Systems, Milwaukee, WI) with a pitch of 1.5 and 7-mm collimation reconstructed at 7-mm intervals, extending from the dome of the diaphragm to the superior margin of the iliosacral joint. Additional 10-mm-thick collimated scans were obtained through the pelvis. Per protocol, patients ingested 750-1000 mL of diluted barium sulfate suspension (Readicat; Mallinckrodt, St. Louis, MO) approximately 1 hr before scanning and an additional 500 mL of enteric contrast agent or water immediately before scanning. All patients received 125 mL of ioversol (Optiray 320; Mallinckrodt, St. Louis, MO) by bolus IV injection at a rate of 2-3 mL/sec with the CT scanning initiated either after a timed 70-sec delay or after a delay determined by a computerized bolus-tracking method (SmartPrep; General Electric Medical Systems).
Experienced CT technologists obtained the images from each examination at the operator's console using standard abdominal window settings (mean window width, 395 H [range, 336-472 H]; mean window level, 60 H [range, 39-88 H]). The CT technologists then obtained the images through the upper abdomen, encompassing liver and spleen again, using narrow window width (liver window) settings (mean window width, 195 H [range, 144-260 H]; mean window level, 94 H [range, 63-119 H]).
One of two trauma body imaging attending radiologists (with a combined total of 12 years of experience after fellowship) prospectively evaluated the images for hepatic or splenic injuries or both. In all cases, the hard-copy images obtained at standard abdominal window settings were reviewed first, and the liver and spleen were scrutinized closely for the presence of injury. Injuries detected in the liver or spleen were graded according to standardized grading systems [8], with hepatic injuries graded on a scale of I to VI and splenic injuries graded on a scale of I-V. If no injury was detected, the liver or spleen was graded as zero. Immediately after this review was performed, the radiologist reviewed the narrow-window-width images through the upper abdomen. These images were viewed in conjunction with the initial images and were evaluated for the following: detection of new injury, differences in conspicuity of previously identified injury, and change in CT grade of injury. Differences in conspicuity of injuries were assessed on a 7-point scale: +3, marked improvement in conspicuity or new injury identified; +2, moderate improvement in conspicuity; +1, mild improvement in conspicuity; 0, no change in conspicuity; -1, mild decrease in conspicuity; -2, moderate decrease in conspicuity; or -3, marked decrease in conspicuity or inability to identify previously seen injury.
All CT examinations subsequently were reviewed by the second radiologist independently and were evaluated and scored according to the methodology already described. Data were analyzed and differences between the two radiologists were resolved by consensus during a joint review of all cases in which discrepancies were present.
At the end of the study period, we retrospectively reviewed the medical records of all patients to assess outcome and to determine whether any injuries had been missed. We used the kappa statistic for multiple observers to measure the degree of disagreement between the two reviewers [9]. The degree of disagreement was not factored into the calculation. A kappa value of less than 0.20 was considered poor agreement; 0.21-0.40, fair; 0.41-0.60, moderate; 0.61-0.80, good; and 0.81-1.00, excellent.
Finally, we performed a cost analysis estimating the added expenses incurred from the practice of routinely filming liver windows in cases of abdominal trauma.
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Conspicuity of hepatic or splenic injuries was judged to be mildly increased (+1) on liver windows in 16 cases (eight cases of hepatic injury and eight cases of splenic injury) (Fig. 1A,1B), whereas the injury was judged to be equally conspicuous on both liver window and standard window images in 19 cases (10 cases of hepatic injury and nine cases of splenic injury) (Fig. 2A,2B). In one patient with injury to both the liver and spleen, streak artifacts from metal in the posterior spine caused mild (-1) obscuration of a hepatic laceration and moderate (-2) decreased conspicuity of the splenic laceration (Fig. 3A,3B). In no case did review of the liver window images reveal a hepatic or splenic injury that was not seen on the standard abdominal window images. Liver windows never completely obscured visualization of an injury previously identified. The mean conspicuity score for liver injuries (excluding those judged to be normal) was +0.3, whereas the mean conspicuity score for splenic injuries was +0.4.
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The radiologists disagreed with each other regarding the CT grading of
injury in 12 cases (seven cases of hepatic injury and five cases of splenic
injury) but agreed completely on all cases in which no injury was detected.
Level of agreement between radiologists was good for both grading and
conspicuity of injuries (
= 0.80 and = 0.77, respectively).
When we retrospectively reviewed medical records and outcomes, we did not identify any patients in whom significant hepatic or splenic injury had been missed. Of the 34 patients with hepatic or splenic injury on CT, injuries were confirmed at surgery or autopsy in 23. The remaining patients were treated conservatively, and no confirmation of CT findings was available in these patients. Of the 266 patients without hepatic or splenic injury on CT, no hepatic or splenic injury was seen in the five patients who underwent exploratory laparotomy or in the two patients who died. Outpatient follow-up records were available in 92 patients (follow-up range, 1 week-16 months; mean, 14.5 weeks), and no missed hepatic or splenic injuries were found. One-hundred forty-four patients had no follow-up visits. Sixty-four of these patients were treated in the emergency department and released. Of the 80 patients who were admitted, no missed hepatic or splenic injuries were detected during their hospital stay (stay range, 2-32 days; mean, 7 days). Medical records of the remaining 23 patients were unavailable for review.
At our institution, the cost per conventional film including the film itself, chemicals, and technologist time is $9.58. Costs for increased physician time to view the additional images and for alternator space and film storage are difficult to quantify. Twelve images are printed on each sheet, and the printing of liver windows for depiction of the upper abdomen required an average of two sheets per examination. Printing the additional liver window images costs an additional $19.16 per case. For the 300 patients in our study, the total increased cost for printing liver windows was $5748. Annual cost to the institution was estimated to be $17,244.
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Pomerantz et al. [1] reviewed organ-specific windows on a soft-copy workstation and found significant clinical benefit from review of liver and bone window settings in 203 randomly selected abdominal and thoracic CT examinations. Those researchers found improvement in conspicuity and characterization of lesions in 67% of 121 abnormal findings, and the specific window settings had substantial effect on final diagnoses in 18%. In their study design, which included a time estimate based on a random sample of 15 cases per radiologist, evaluation of the images at additional window and level settings required only an additional 40 sec per case. There was a high prevalence of disease in their study subjects, and they did not specifically study patients with abdominal trauma.
In contrast, Mayo-Smith et al. [7], working in a film-based environment, found limited added usefulness in routine liver-window scans for detection of hepatic disease in 1175 consecutive abdominal CT scans. Only 36 patients (3.1%) had new lesions seen with the addition of liver windows, and diagnosis or recommendation for follow-up was altered in only 1.7% and 0.85% of their patients, respectively. Although they performed abdominal CT for a number of different indications and did not focus on a trauma population, they noted that none of their patients with a history of trauma had additional benefit with liver windows [7].
In our study, we evaluated the routine use of liver windows to evaluate scans in a subset of patients with a clinical history of blunt abdominal trauma. We found the use of narrow-window, high-contrast images to have little effect in the detection of hepatic and splenic injuries and to have no effect in characterization of extent or grade of injury. No new injuries were detected on liver window images, and patient treatment was not altered in any case. Although the cost of printing additional liver windows for an individual case was relatively small, when such liver windows are printed routinely for all cases, the cumulative costs can be substantial.
Our study had notable limitations. First, although we studied a relatively large number of patients who presented for abdominal CT after blunt abdominal trauma, the number of patients who actually had hepatic or splenic injury was relatively small, and the low prevalence of injury in our population may have reduced the benefit of obtaining CT scans with liver window settings. However, this relatively low prevalence of injury among our CT patients accurately reflects our clinical practice as well as that of other major trauma centers where screening abdominal CT and a high rate of negative findings have become more commonplace. Second, we did not dictate to our technologists that they use strict window and level settings for filming standard abdominal or liver window images, relying instead on their experienced eye to film standard soft-tissue and high-contrast images at the operator's console. Although this decision resulted in a range of window and level settings for both standard abdominal and liver window scans, this variability may make our results more applicable to other sites because specific window and level settings may vary from institution to institution. Third, the study design relied on a determination of conspicuity of traumatic findings, a necessarily subjective criterion. Nevertheless, a strict scoring system was defined at the outset, and agreement between the reviewers was good. Fourth, the two radiologists viewed the standard abdominal window scans first and then the liver window scans immediately after that review. Although this protocol was intended to identify true changes in perception of abnormalities between the two scans, it may have introduced a bias in favor of the liver window images because the reviewers were reinterpreting the same levels and concentrating on finding differences. Alternatively, because the radiologists knew that they were specifically evaluating hepatic and splenic injuries, they may have been more diligent initially on review of the standard abdominal window scans, thereby creating bias in favor of the scans first reviewed. Finally, the scope of this study was limited to CT of trauma patients, and the reported results cannot necessarily be extrapolated to other indications for CT, such as tumor detection.
Despite these limitations, we believe that our study provides compelling evidence that the routine practice of obtaining liver window settings for CT in trauma patients has little clinical usefulness. Although the mild increase in conspicuity of injury provided by liver windows occasionally may be beneficial in an individual patient, we do not believe that this minimal benefit justifies the extra cost of routinely filming liver windows for all patients presenting for trauma CT. In a department in which conventional scanning is still used extensively, more selective use of liver windows for patients with identifiable but subtle injury may result in substantial cost savings over time.
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