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Emergency Radiology |
1 From the Department of Radiology, Boston Medical Center, One Boston Medical Center Place, Boston, MA 02118. From the 2004 RSNA Annual Meeting. Received December 10, 2004; revision requested February 2, 2005; revision received March 25; final version accepted April 18. Address correspondence to J.A.S. (e-mail: jorge.soto{at}bmc.org).
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ABSTRACT |
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Materials and Methods: Institutional review board consent was obtained, and written informed consent was waived. The study was HIPAA compliant. A total of 662 patients (497 men, 165 women; mean age, 40.5 years; range, 18–94 years) were identified who were evaluated with CT after blunt abdominal trauma during a 1-year period. Delayed CT scans were acquired 5 minutes after intravenous contrast material injection by using a decreased tube current of 100 mAs. Injury was identified in 106 patients. Two radiologists blinded to initial CT scan interpretation reviewed these cases to determine the quality and utility of delayed scans. Disagreement was settled by consensus. Delayed scans were considered useful when they aided in (a) characterizing initial CT findings, (b) identifying findings not present at initial CT, (c) excluding injury suggested at initial CT, and (d) increasing reader confidence with regard to initial CT findings.
Results: All delayed scans were diagnostic. Delayed scans were useful in 27% (12 of 44) of patients with solid organ injury, 5.9% (one of 17) of patients with bowel or mesenteric injury, 4.5% (one of 22) of patients with pelvic fractures, and in none of the patients with free fluid only. Overall, delayed CT was useful in 2.1% (14 of 662) of all patients (95% confidence interval: 1.0, 3.2) referred for evaluation following blunt abdominal trauma. Utility increased to 13.2% (14 of 106) (95% confidence interval: 6.8, 19.7) in the group of patients with injury or suspected of having injury after initial CT.
Conclusion: If delayed CT scans are acquired when patients with blunt abdominal trauma are evaluated, selective, rather than routine, acquisition is recommended and a reduced radiation dose seems adequate.
© RSNA, 2006
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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Delayed CT can be performed routinely in all patients with trauma or selectively on a case-by-case basis. To be selective, the radiologist has to be present to review the initial intravenous contrast material–enhanced scans to determine the need for delayed scanning while the patient remains on the CT table. In an era of increasing study volume coupled with the need to interpret scans in a timely manner, it is often difficult for a radiologist to be present at every initial CT to make such a determination.
At our institution, a level 1 trauma center, radiologists routinely acquire 5-minute delayed CT scans of the abdomen and pelvis by using a reduced radiation dose in patients suspected of having abdominal injury due to blunt trauma. The purpose of the study, therefore, was to retrospectively evaluate the utility of 5-minute delayed CT of the abdomen and pelvis by using a reduced radiation dose in patients with blunt abdominal trauma.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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During the study period, 717 patients were evaluated with multi–detector row CT for the indication of blunt abdominal trauma. Fifty-five (9%) patients were subsequently excluded because delayed CT was not performed (n = 41) or because delayed CT was performed by using a standard radiation dose and distention of the urinary bladder with contrast material by means of an indwelling Foley catheter as part of CT cystography (n = 14). Thus, our study included 662 patients (497 men, 165 women) with a mean age of 40.5 years (men, 39.9 years; women, 43.5 years) and a range of 18–94 years (men, 18–90 years; women, 18–94 years). By using the Student t test, there was a significant difference in age between men and women (P < .05). Mechanisms of injury included motor vehicle collision (n = 385), fall from a height (n = 101), pedestrian struck by motor vehicle (n = 65), assault (n = 70), and others (n = 41).
CT Technique
All CT scans were acquired by using a four–detector row scanner (MX8000; Philips Medical Systems, Andover, Mass). CT parameters were as follows: 120–140 kVp; 200–250 mAs; pitch, 1.5; field of view, 240–350 mm; collimation, 2.5 mm (3.2 mm effective); and reconstruction interval, 3 mm. All patients received 100 mL of contrast material containing 320 milligrams of iodine per milliliter (iohexol, Optiray; Mallinckrodt Imaging, Hazelwood, Mo) intravenously with a power injector at a rate of 2–3 mL/sec. No oral contrast material was administered.
CT of the abdomen and pelvis was performed from the superior surface of the diaphragm through the lesser trochanters 60 seconds after the beginning of intravenous contrast material injection. CT of the chest, abdomen, and pelvis was performed from the thoracic inlet to the lesser trochanters 30 seconds after the beginning of intravenous contrast material injection. Delayed CT was performed through the abdomen and pelvis 5 minutes following the administration of intravenous contrast material. We used a reduced radiation dose technique when acquiring delayed CT scans by decreasing the tube current to 100 mAs for all patients. This choice of radiation dose has been shown to be adequate for imaging of the abdomen and pelvis in the setting of nephrolithiasis (15) and acute appendicitis (16). The parameters used for the 5-minute CT were as follows: 120–140 kVp; 100 mAs; pitch, 1.5; field of view, 240–350 mm; collimation, 2.5 mm (3.2 mm effective); and reconstruction interval, 3 mm.
For comparison, since the tube current of the 5-minute CT was reduced from 200–250 to 100 mAs, the radiation dose was reduced by 50%–60% (assuming kilovolt peak is the same), as if CT was performed with the same technique as that used during the initial 60-second acquisition. By decreasing the tube current to 100 mAs during the 5-minute CT, the patient receives only an additional 40%–50% radiation dose, as opposed to a double radiation dose.
Data Acquisition
All CT scans were initially interpreted by an attending radiologist in the emergency radiology department at our institution. During the study period, reports were generated by nine radiologists with a wide range of experience (2–20 years) in the interpretation of trauma CT scans. Each report was reviewed by one of three investigators (J.W.S., J.A.S., B.C.L.) with various experience (3–15 years) in interpretation of trauma CT scans. On the basis of CT findings recorded in the initial report, we divided the population into two groups: group 1, patients with no evidence of injury to the abdomen or pelvis, and group 2, patients with or suspected of having traumatic injury to the abdomen and pelvis. Criteria for inclusion in group 2 included the presence of (a) solid organ injury; (b) bowel or mesenteric injury; (c) free fluid only; (d) active contrast material extravasation only; or (e) pelvic fracture without solid organ, bowel, or mesenteric injury.
CT scans for each patient in group 2 were reviewed independently by two radiologists (J.W.S., J.A.S.) who were blinded to the initial CT results. The reviewers were asked to record the quality of the delayed CT scan as being either diagnostic or nondiagnostic on the basis of the adequacy of image quality. CT scans were considered nondiagnostic if artifact or image noise prohibited appropriate evaluation of the organ or area of interest in each patient. Each reviewer was also asked to record findings after review of the initial CT scan obtained 60 seconds after contrast material administration, findings based on a subsequent review of delayed scans, and whether or not delayed CT was useful in the overall study interpretation. Delayed CT scans were considered useful when they (a) helped to better characterize findings on the initial CT scan, (b) demonstrated findings not detected on the initial CT scan, (c) increased reader confidence of the initial CT result, or (d) helped exclude findings suggested on the initial CT scan. There were no disagreements between the reviewers about the image quality; disagreements between reviewers regarding the utility of delayed CT were settled by consensus review in one case.
Follow-up
Follow-up of patients for whom delayed scans were considered useful was performed by one of the authors (J.W.S.) through review of patient electronic medical records and results of follow-up radiologic examinations.
Data Analysis
The number of examinations in which delayed scans were considered useful was calculated among the various criteria for inclusion in group 2: solid organ injury; bowel or mesenteric injury; pelvic fracture without solid organ, bowel, or mesenteric injury; active contrast material extravasation only; or free fluid only. Overall utility of delayed CT scans was calculated for the study population and for group 2 patients with positive CT findings. Delayed CT scans of patients in group 1 were considered to be of no utility because no injury was present on the initial CT scan.
Statistical Analysis
Ninety-five percent confidence intervals were calculated for the overall utility of delayed scans in the study population and for patients in group 2 with positive CT findings by using the R statistical package, version 2.0.1 (2005). We used the standard Wald test for confidence intervals around an estimated binomial proportion.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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Solid Organ Injury
Among 44 patients with a diagnosis of solid organ injury, delayed CT was considered useful in 12 (27%) patients. Delayed CT further aided in characterizing findings at initial CT (n = 7), identifying findings not present at initial CT (n = 2), and excluding injury suggested at initial CT (n = 3). In the group of patients for whom delayed CT further aided in characterizing the findings that were present at initial CT, six patients had findings consistent with splenic injury and focal contrast material collections that could not be definitively characterized as either active contrast material extravasation or splenic pseudoaneurysm formation. In three patients, delayed CT was useful because it depicted an increased amount of extravasated contrast material and a change in the location of the contrast material over a 5-minute period, which is consistent with active contrast material extravasation (Fig 1). All three patients were subsequently taken to the operating room for splenectomy.
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Injury to the ureter and bladder was identified in two patients for whom the initial CT scan was inconclusive. In one patient, the initial CT scan demonstrated a normal enhancing right kidney with perinephric fluid, hematoma, or both. The delayed CT scan depicted laceration of the proximal right ureter, with extravasated contrast material observed in the perinephric space along the inferior pole of the right kidney (Fig 3). The patient required cystoscopy and stent placement for the treatment of injury. In the second patient, the initial CT scan demonstrated liver laceration with intraperitoneal blood, multiple pelvic fractures, and fluid-attenuating material adjacent to the bladder. The delayed CT scan demonstrated perforation of the bladder with extravasation of contrast material into both the intra- and extraperitoneal spaces, which required primary surgical repair. In both cases, neither reviewer identified injury to the urinary system at review of the initial CT scan; instead, the diagnosis was suggested only after the delayed CT scan was viewed.
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Bowel or Mesenteric Injury
Of 17 patients suspected of having bowel injury on the initial CT scan, delayed CT was useful in one (5.9%) patient by increasing reader confidence of the initial CT findings. At review of the first set of scans, both reviewers suggested the possibility of small-bowel perforation due to the presence of focal bowel-wall thickening and free fluid. The initial scan also suggested the presence of a small bubble of free air, although this finding was believed to be equivocal because of the immediate contiguity of the bubble with the adjacent small bowel. The bubble was confirmed to be extraluminal on the basis of findings on the delayed CT scan because a plane of tissue was present between the bubble and the adjacent small bowel. After viewing the delayed CT scan, both reviewers concluded that there was definite evidence of proximal small-bowel perforation, which was confirmed at the time of surgery.
Pelvic Fracture
In 22 patients with pelvic fracture only, delayed CT was considered useful in one (4.5%) patient. In this case, delayed CT depicted extraperitoneal bladder injury, which was not seen at initial CT because of a lack of adequate opacification of the bladder with contrast material. In this patient, initial CT demonstrated fractures involving the bilateral pubic rami, sacrum, and both iliac wings. There was fluid anterior to a collapsed bladder, which contained a Foley catheter. Delayed CT demonstrated extravasation of contrast material into the extraperitoneal fluid collection, confirming bladder rupture (Fig 4 ). The patient was treated conservatively without primary repair of the bladder injury.
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Utility of CT
On the basis of the aforementioned findings, routine acquisition of delayed CT scans with a reduced radiation dose was considered useful in 14 (13.2%) of 106 patients (95% confidence interval: 6.8, 19.7) with positive initial CT scans and in 14 (2.1%) of 662 patients (95% confidence interval: 1.0, 3.2) referred for abdominopelvic CT in the setting of blunt abdominal trauma.
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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Patients for whom delayed CT had the most utility were those with solid organ injury evident at initial CT, especially when the injury involved the spleen. Of the 12 patients for whom delayed scans were considered useful, seven patients had splenic injuries that were better characterized on delayed CT scans. Delayed CT appeared to have the greatest effect when the initial CT scan showed foci of high attenuation in the splenic parenchyma; these foci were suggestive of either active contrast material extravasation or pseudoaneurysm. Delayed CT was useful in distinguishing these two entities, which is helpful to the trauma surgeon when deciding which subgroup of patients may require surgery or endovascular intervention to stabilize the injuries.
The other subgroup of patients for whom delayed CT improved diagnostic capability were those with injuries to the kidneys and urinary system. Delayed CT depicted two bladder perforations and one ureter injury and helped exclude urinoma in three patients in this group. The diagnosis of bladder, ureteropelvic junction, and ureteric injury is important, because many injuries require subsequent surgical repair. Indeed, one of the two patients with bladder injury required surgical intervention to repair an intraperitoneal bladder rupture that was identified at delayed CT.
One interesting topic that is raised because of the results from this group of patients concerns the use of routine delayed CT versus CT cystography. As previously mentioned, a number of patients in our study with pelvic fractures were excluded because they underwent CT cystography immediately following the initial CT instead of the reduced dose delayed CT included in our standard trauma protocol. If bladder injury is detected on delayed scans, does that exclude the need for CT cystography? This seems unlikely, because without adequate bladder distention one might not detect subtle intraperitoneal injury, which is generally considered an indication for primary bladder repair. Thus, if a pelvic fracture is observed at radiography or initial CT, should CT cystography be performed routinely regardless of clinical signs and symptoms or is delayed CT without the addition of additional contrast material appropriate? This is a topic needing further investigation, in our opinion.
Finally, in our continuing efforts to decrease the radiation dose to each patient, the results of our study suggest that the acquisition of reduced dose delayed CT scans in the setting of blunt abdominal trauma can be adequately performed without the risk of obtaining nondiagnostic scans. Since delayed CT is used primarily for detection or characterization of contrast material, the decreased radiation dose is not likely to affect our ability to diagnose such injuries. One wonders whether a reduced dose technique might not also be optimal for other delayed sets of images, such as CT cystograms, where subtle contrast material abnormalities may not be important. Given our experience, it is unlikely that a reduced dose technique would have any effect on our ability to identify extravasation of contrast material outside of the bladder.
Limitations of this study include its retrospective nature and lack of comparison between routine and selective imaging protocols for the acquisition of delayed scans. In addition, we did not review scans obtained in patients with negative initial CT scans, so it is possible that we have underestimated the utility of delayed CT scans in the setting of blunt abdominal trauma. For example, it is likely that delayed CT was useful in some cases for characterizing incidental findings such as focal liver lesions or anatomic anomalies of the genitourinary system. Finally, the two authors who reviewed the CT scans also were involved in the initial interpretation of all trauma CT scans and in the search of CT reports. Thus, it is possible that recall bias may have affected the study results as to the utility of delayed CT.
While the results of our study suggest that routine acquisition of delayed scans is not necessary, it remains to be determined whether a trauma protocol requiring selective acquisition of delayed scans can be implemented under the current conditions experienced by most radiologists in practice. It may well be that a protocol requiring routine acquisition of delayed scans is the only method for ensuring that important findings will not be missed. If this is the case, then we can safely decrease the radiation dose for delayed scans.
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FOOTNOTES |
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Author contributions: Guarantor of integrity of entire study, J.W.S.; study concepts/study design or data acquisition or data analysis/interpretation, all authors; manuscript drafting or manuscript revision for important intellectual content, all authors; approval of final version of submitted manuscript, all authors; literature research, J.W.S.; clinical studies, B.C.L., J.A.S.; statistical analysis, J.W.S.; and manuscript editing, all authors
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References |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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This article has been cited by other articles:
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  P. Ramchandani and P. M. Buckler Imaging of Genitourinary Trauma Am. J. Roentgenol., June 1, 2009; 192(6): 1514 - 1523. [Abstract] [Full Text] [PDF]
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T. E. Drasin, S. W. Anderson, A. Asandra, J. T. Rhea, and J. A. Soto MDCT Evaluation of Blunt Abdominal Trauma: Clinical Significance of Free Intraperitoneal Fluid in Males with Absence of Identifiable Injury Am. J. Roentgenol., December 1, 2008; 191(6): 1821 - 1826. [Abstract] [Full Text] [PDF]
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B. L. Dunfee, B. C. Lucey, and J. A. Soto Development of Renal Scars on CT After Abdominal Trauma: Does Grade of Injury Matter? Am. J. Roentgenol., May 1, 2008; 190(5): 1174 - 1179. [Abstract] [Full Text] [PDF]
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