Optimization of Selection for Nonoperative Management of Blunt Splenic Injury: Comparison of MDCT Grading Systems

1421.fmMarmery et al. MDCT Grading of Splenic Injury
A b d o m i n a l I m ag i n g • O r i g i n a l R e s e a rc h
Optimization of Selection for Nonoperative Management of Blunt Splenic Injury: Comparison of MDCT Grading Systems
Helen Marmery1,2
Kathirkamanthan Shanmuganathan1
Keywords: CT, grading system, splenic injury, trauma
DOI:10.2214/AJR.07.2152
Received February 28, 2007; accepted after revision June 24, 2007.
1Department of Diagnostic Radiology, University of Maryland School of Medicine, 22 S Greene St., Baltimore, MD 21201. Address correspondence to K. Shanmuganathan ([email protected]).
2Present address: Department of Radiology, Nuffield Orthopaedic Hospital, Oxford, UK.
3National Study Center for Trauma and Emergency Medical Systems, Baltimore, MD.
OBJECTIVE. The purpose of this study was to compare the usefulness of two CT grading systems of blunt splenic trauma in predicting which patients need surgery or angioembolization.
MATERIALS AND METHODS. Four hundred patients in hemodynamically stable condition admitted with blunt splenic injury were included in the study. All patients underwent contrast-enhanced MDCT. Grade of splenic injury was prospectively assigned according to the American Association for the Surgery of Trauma (AAST) splenic injury scale. Patients were treated with surgical intervention, splenic arteriography with or without embolization, or ob- servation alone. All MDCT images were retrospectively reviewed and regraded according to a novel grading system that specifically incorporates the findings of active bleeding or splenic vascular injury, including pseudoaneurysm and arteriovenous fistula. Receiver operating char- acteristics curves were generated with both grading systems for all splenic interventions, and statistical analyses were performed.
RESULTS. The area under the ROC curves for the new splenic grading system for splenic arteriography, surgery, and both interventions exceeded 80%. The area under the curve for the new splenic grading system was greater than that for the AAST injury scale for all interven- tions. Differences were found to be statistically significant for splenic arteriography (p = 0.0036) and the combination of arteriography and surgery (p = 0.0006).
CONCLUSION. The proposed CT grading system is better than the AAST system for predicting which patients with blunt splenic trauma need arteriography or splenic intervention.
onoperative management of blunt splenic injury is now commonly practiced [1–8]. The decision to at- tempt nonoperative management is
largely determined by the splenic CT injury grade among other clinical factors, including patient age, presence of concurrent injuries, and the ability to perform reliable serial clini- cal assessments. The most widely used grading system for blunt splenic injury in trauma cen- ters across the United States is the American Association for the Surgery of Trauma (AAST) splenic injury scale [1, 2]. This organ injury scale is based on the appearance of the spleen at surgery (Table 1). Similar CT-based grading systems, derived from the AAST scale, are based on the extent of anatomic dis- ruption of the spleen. Previous studies [3–5] have shown that the traditional AAST injury grade and the CT-based injury grading system derived from it are poor predictors of which pa- tients can best be treated with observation and which need angiographic or surgical interven- tion. The use of nonoperative management
with splenic arteriography and embolization has substantial support [6–8]. Aggressive management of active splenic bleeding and vascular injuries, including pseudoaneurysm and arteriovenous fistula, with splenic artery embolization has helped to prevent failure of nonoperative management [6–9].
We have had extensive experience in the use of CT combined with arteriographic find- ings to identify patients most likely to need intervention for splenic injury as opposed to observation alone. We conducted a retrospec- tive review of our experience with 400 pa- tients to describe and compare the efficacy of two CT grading systems to optimize selection of patients for nonoperative management of blunt splenic injury to achieve a high salvage rate with minimal complications.
Materials and Methods This study was compliant with the requirements
of the HIPAA and was approved by our institutional review board. Written informed consent was ob- tained from 76 patients. The institutional review
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board waived informed consent from 324 patients because this study was solely observational and in- cluded no additional interventions and because ob- taining consent in these emergency and sometimes disoriented patients would have precluded the timely performance of imaging studies.
Between October 2002 and May 2005, a total of 496 patients 18 years or older were admitted to our in- stitution with blunt splenic trauma. Patients who un- derwent angiography (n = 5), laparotomy (n = 8), or splenectomy (n = 32) before MDCT were excluded from the study. An additional 51 patients were ex- cluded because of death without splenic angiography or surgery within 24 hours as a result of multiple in- juries (n = 10), inadequate follow-up (n = 17), pre- sentation from an outside hospital (n = 4), delayed performance of CT (n = 2), iatrogenic splenic injury (n = 1), unavailable images (n = 7), technically inad- equate CT scans (n = 9), and inadequate clinical in- formation (n = 1). A total of 400 patients (261 men, 139 women; mean age, 38.5 years; range, 18–86 years) in hemodynamically stable condition with blunt splenic injury formed the study group. All pa- tients underwent either 4- or 16-MDCT.
MDCT Technique Contrast-enhanced MDCT was performed with a
4-MDCT scanner (MX 8000, Philips Medical Sys- tems) before April 2003 and one of two 16-MDCT scanners (Brilliance 16 Power and Brilliance Big Bore, Philips Medical Systems) after April 2003, ac- cording to the techniques described in Table 2. IV and oral contrast media were administered. A bi- phasic IV injection of contrast material (iohexol, Omnipaque 300, GE Healthcare) was administered routinely with a power injector and a 16- to 20-gauge IV cannula. Unenhanced CT images were not ob- tained through the abdomen or pelvis. A 2% solution of 600 mL of meglumine diatrizoate (2% Hypaque, GE Healthcare) in water was administered orally or through a nasogastric tube if the patient was unable to drink; 300 mL was given 30 minutes before scan- ning and 300 mL in the scanning suite. Images of the abdomen and pelvis were acquired as part of the scan from the thoracic inlet to the symphysis pubis on the 4-MDCT scanner and as part of the whole-body scan from the circle of Willis to the symphysis pubis with the arms extended superiorly and placed next to the neck on the 16-MDCT scanner. Images of the
TABLE 1: American Association for the Surgery of Trauma Splenic Injury Scale (1994 Revision)
Gradea Type Description of Injury
1 Hematoma Subcapsular, < 10% surface area
Laceration Capsular tear, < 1 cm parenchymal depth
2 Hematoma Subcapsular, 10–50% surface area
Intraparenchymal, < 5 cm in diameter
Laceration 1–3 cm parenchymal depth; does not involve a trabecular vessel
3 Hematoma Subcapsular, > 50% surface area or expanding; ruptured subcapsular or parenchymal hematoma
Laceration > 3 cm parenchymal depth or involved trabecular vessels
4 Laceration Laceration involving segmental or hilar vessels and producing major devascularization (> 25% of spleen)
5 Laceration Completely shattered spleen
Vascular Hilar vascular injury that devascularizes spleen
Note—Adapted with permission from [2]. aAdvance one grade for multiple injuries up to grade 3. The American Association for the Surgery of Trauma uses roman numerals.
TABLE 2: MDCT Injection Technique
Imaging Type
6 4
Ascending aorta
6 4
Ascending aorta
Note—Automatic triggering threshold, 90 H.
abdomen and pelvis were acquired during the portal venous phase of contrast enhancement, and delayed images were acquired from the diaphragm to the il- iac crest during the excretion phase, approximately 2–3 minutes after injection. Evaluating the spleen during these two phases was helpful in more accu- rately visualizing splenic vascular injuries and the renal collecting system.
Modified Grading System The new grading system (Table 3) was based on
experience from multiple trauma centers, including ours, indicating that CT evidence of active splenic hemorrhage and vascular injuries is predictive of the need for splenic arteriography and transcatheter embolization or splenic surgery [6–10]. Because of the risk of failure of nonoperative management [7–9], it is important to identify patients with these CT findings even when AAST classifications of in- juries are low-grade. In the new system, such pre- viously low-grade splenic injuries are upgraded to grade 4a or 4b. In the new system, patients with grade 4 injuries are candidates for splenic arteriog- raphy or splenic surgery. The quantity of blood in the peritoneal cavity was not taken into consider- ation in assigning grades with this modified system.
Definitions and Image Analysis Initial reconstructed axial MDCT images (3- or
5-mm slice thickness) in each case were prospec- tively and independently reviewed by a fifth- or sixth-year resident with 1–2 years of experience or
TABLE 3: Proposed New Grading System Incorporating Splenic Vascular Injury
Grade Criteria
Laceration < 1 cm parenchymal depth
Parenchymal hematoma < 1 cm diameter
2 Subcapsular hematoma 1- to 3-cm thick
Laceration 1–3 cm in parenchymal depth
Parenchymal hematoma 1–3 cm in diameter
3 Splenic capsular disruption
Laceration > 3 cm in parenchymal depth
Parenchymal hematoma > 3 cm in diameter
4a Active intraparenchymal and subcapsular splenic bleeding
Splenic vascular injury (pseudoaneurysm or arteriovenous fistula)
Shattered spleen
AJR:189, December 2007 1423
A B
Fig. 1—36-year-old man with active splenic bleeding who was admitted after motor vehicle collision. A and B, Portal venous phase (A) and renal excretory phase (B) axial maximum-intensity-projection MDCT images show active bleeding (arrowheads) into peritoneum from splenic injury. Active bleeding was increased on delayed image.
A B
Fig. 2—76-year-old woman with splenic vascular injury who was admitted after motor vehicle collision. A and B, Portal venous phase (A) and renal excretory phase (B) axial MDCT images show vascular injury (arrowhead, A). Vascular injury loses density from washout of contrast material and becomes isodense with adjacent splenic parenchyma.
by four board-certified emergency radiologists with 3–20 years of experience. Splenic injury was graded according to the CT injury grade modeled on the AAST splenic injury scale (Table 1) [2]. Admission MDCT images in all cases were then reviewed by two radiologists who did not have ac- cess to the original interpretations or outcomes. These radiologists regraded injuries according to the modified injury grading system that specifically incorporates the findings of active bleeding or vas- cular lesions (Table 3).
Active bleeding (Fig. 1) was defined as a linear or irregular area of contrast enhancement with an attenuation value similar to or greater than that of the aorta or an adjacent major artery [11]. On CT, the area of active bleeding identified during the por- tal venous phase may appear to expand on delayed imaging during the renal excretory phase because of continuing bleeding. For this study, vascular in- juries (Fig. 2) included both splenic pseudoaneu- rysm and arteriovenous fistula. Pseudoaneurysm and arteriovenous fistula were defined as well-cir-
cumscribed areas of contrast enhancement with an attenuation value similar to that of an adjacent con- trast-enhanced artery. These vascular injuries may be surrounded by low-attenuation parenchyma or hematoma. On delayed imaging during the excre- tory phase, vascular injuries typically lose density from washout of IV contrast material, and the atten- uation becomes similar to or slightly higher than that of adjacent organ parenchyma.
Splenic Intervention Splenic intervention was defined as splenic arte-
riography or surgery performed as a result of the CT- diagnosed splenic injury. Splenic arteriography was performed on all patients in hemodynamically stable condition with high-grade splenic injury (AAST grades 3–5) and on patients with low-grade splenic injury (grades 1 and 2) who had active bleeding or a vascular injury on MDCT. Splenic arteriography was performed on 164 patients. A total of 130 splenic ar- tery embolizations were performed. Embolization was performed on 71 patients with active bleeding or vascular injury. Splenic artery embolization was per- formed on 59 other patients because of abrupt trun- cation of a splenic artery branch on arteriography or if, at the discretion of the interventional radiologist and attending trauma surgeon, the patient’s clinical condition warranted a more aggressive interven- tional approach. For example, main splenic artery embolization was performed to control blood pres- sure in some patients with major head injuries in or- der to prevent delayed hemorrhage from a high- grade splenic injury.
At our institution, hemodynamic instability is defined with the following criteria: systolic blood pressure less than 100 mm Hg, heart rate greater than 120 beats per minute, and lack of response to a fluid challenge of 2 L of a crystalloid solution. Splenectomy was performed on 45 patients after MDCT, usually because of hemodynamic instabil- ity after CT (n = 35). Other reasons (n = 10) in- cluded injuries to adjacent organs, need for antico- agulation, high-grade splenic injury in a pregnant patient, and initiation of splenic hemorrhage when the spleen was mobilized at laparotomy.
Clinical Review and Statistical Analysis Medical records were reviewed to determine out-
come of management of splenic injuries. Statistical analysis was performed with JMP statistical soft- ware, versions 5.1 and 6.0 (SAS Institute) and SAS, version 9.1 (SAS Institute). The Stuart-Maxwell and the McNemar tests of homogeneity were used to compute statistics for assessment of the association between the old and new grading systems. To discern whether the new splenic grading system was better than the AAST injury scale in identifying patients needing splenic arteriography or surgery, receiver
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operating characteristic (ROC) curves were gener- ated for both grading systems for all splenic inter- ventions. These curves were generated for splenic arteriography and surgery separately and for all splenic interventions combined.
Nonparametric approaches were selected because they provided the foundation on which the ROC curves were based. The nonparametric method of DeLong et al. [12] was used to compare the area un- der the correlated AAST grade curve with that of the new-grade ROC curve from the same subjects on the basis of concepts proposed by Hanley and McNeil [13, 14]. Hanley and McNeil used Kendall’s tau rank-order correlation to calculate the critical statis- tics for comparing the areas under two correlated ROC curves. DeLong et al. used generalized U sta- tistics to calculate the areas under the ROC curves and to test for differences between areas under cor- related ROC curves. The approach of DeLong et al. was selected because the computations yielded more precise estimates of the variance–covariance matri- ces and CIs of the ROC curve areas than did Hanley and McNeil’s approximated estimates.
The JMP nominal logistic platform was used to generate logistic regression (logit) models for the old and new grading systems, compute the areas under the ROC curves, and produce the plots shown in Figures 3–5. The JMP logit model was reproduced with the SAS LOGISTIC procedure. The SAS %ROC macro was used to compute the 95% CIs for areas under the ROC curves and to test for significance of differences between the ar- eas under the correlated ROC curves of the old and new grading systems.
Results The numbers of patients with each splenic
injury grade for both the AAST injury scale and the new splenic grading system are shown in Table 4. In the new system, splenic injuries in 54 patients were upgraded to grade 4a or 4b. Thirty-four of these patients would have undergone splenic arteriography according to our institutional policy of performing routine arteriography on all patients with AAST grade 3–5 injuries. However, the low-grade injuries of 20 patients according to the AAST scale were upgraded to grade 4a or 4b in the new system. Sixteen of the 20 patients needed splenic artery embolization, and two needed splenectomy. In seven cases, injuries were downgraded with the new system. In these cases, no change in management would have resulted from the new classification. No pa- tients in our study group had a devascularized spleen on MDCT.
Nonoperative management was attempted in the cases of 89% (355/400) of the patients
with blunt splenic injury. Within this group, 341 (96%) of the patients were successfully treated without splenic surgery. The overall splenic salvage rate for blunt splenic injury was 85% (341/400). For high-grade injuries (grades 3–5), the success rate of nonoperative management was 95% (136/143), with an overall splenic salvage rate of 76%.
The areas under the ROC curves for the new splenic grading system for splenic arteriogra- phy, surgery, and both interventions exceeded 80%. This result means that the logistic model for the new splenic grading system had a greater than 80% chance of correctly differen- tiating patients needing splenic arteriography or surgery from patients who could be treated successfully with conservative management.
All areas under the ROC curves for the new splenic grading system were larger than those for the AAST injury scale (Figs. 3–5). Statis- tically significant differences were found be- tween the new splenic grading system and the AAST injury scale for splenic arteriography (p = 0.0036) and for both interventions com- bined (p = 0.0006), according to the DeLong test results.
The larger area under the ROC curve for the new grading system suggests that use of this system provides better discriminating ability when screening patients for arteriogra- phy or surgery than does the AAST injury scale. In addition, the diagnostic accuracy of the new grading system was as effective as the AAST injury scale in screening patients for surgery (p = 0.3694).
Discussion The purpose of a grading system is to stan-
dardize reporting, plan appropriate manage- ment, and enable comparisons between insti- tutions and studies. The AAST Organ Injury Scaling Committee was formally organized in 1987 to devise injury severity scores that could facilitate clinical investigation and out- comes research [1]. The organ injury scale is a classification scheme based on the anatomic disruption caused by injury to an individual organ. The complexity of the injury increases with the grade. The primary purpose of this injury scale is to compare outcomes of equiv- alent injuries managed with different proto- cols [1]. The organ injury scale for the spleen was revised in 1994 [2], in part as a result of the more widespread use of CT in the setting of blunt abdominal trauma and as a result of increased understanding of the relatively be- nign course of certain low-grade injuries. However, active bleeding and vascular inju-
ries were not incorporated in the revised sys- tem of assigning splenic injury grades.
Although MDCT is accurate in depicting splenic injury, it has been reported [3–5] that grade of injury alone is a poor predictor of the success of nonoperative management. Treat- ment of patients with low-grade injuries on the AAST injury scale may fail with observa- tion alone when vascular lesions are present and not managed appropriately. Several pre- vious studies [6–9] have shown that the pres- ence of splenic vascular injuries, including active bleeding, pseudoaneurysm, and arteri- ovenous fistula, is a predictor of failure of nonoperative management. Identification on MDCT and appropriate management of these injuries are therefore critical in achieving a high rate of success of nonoperative manage- ment. Therefore, injury grade based on the AAST injury scale cannot be used as the sole criterion for guiding management.
Unlike the AAST injury scale, the new CT- based grading system we propose incorpo- rates MDCT findings of vascular lesions and active bleeding in assigning the splenic injury grade. In this grading scheme, all patients with active bleeding or vascular injury are considered to have grade 4 injury. Patients with…