Development of Renal Scars on CT After Abdominal Trauma: Does Grade of Injury Matter?

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1 Genitourinary Imaging Original Research Dunfee et al. Renal Scars on CT fter bdominal Trauma Genitourinary Imaging Original Research rian L. Dunfee 1,2 rian C. Lucey 3 Jorge. Soto 4 Dunfee L, Lucey C, Soto J Keywords: ST scale, emergency radiology, renal function, renal injuries, renal scarring, trauma DOI: /JR Received pril 29, 2007; accepted after revision November, Department of Radiology, Division of ody Imaging, oston University Medical Center, oston, M. 2 Present address: Department of Radiology, Section of Interventional Radiology, Northwestern Memorial Hospital, 251 E Huron St., Feinberg 4-710Y, Chicago, IL 011. ddress correspondence to. L. Dunfee (brianldunfee@yahoo.com). 3 Chief Radiology Service, oston V Healthcare System, oston University School of Medicine, oston, M. 4 Department of Radiology, Division of ody Imaging, oston University Medical Center, oston, M. JR 200; 190: X/0/ merican Roentgen Ray Society Development of Renal Scars on CT fter bdominal Trauma: Does Grade of Injury Matter? OJECTIVE. The objective of our study was to determine whether there is an association between the grade of a traumatic renal and the subsequent development of renal parenchymal scars on CT. MTERILS ND METHODS. We performed a retrospective study encompassing all acute trauma patients admitted to our institution over a 42-month period found to have renal parenchyma injuries on initial MDCT and also to have undergone a follow-up CT performed at least 1 month after trauma. We identified 54 patients who sustained blunt (n = 44) or penetrating (n = 10) abdominal trauma. The renal injuries were graded by two radiologists according to the Organ Injury Scaling Committee of the merican ssociation for the Surgery of Trauma (ST), grades I through V. Follow-up CT was reviewed for the presence of parenchymal distortion, scarring, or perfusion defects. RESULTS. Of the 54 patients, 12 had grade I, eight had grade II, 22 had grade III, 10 had grade IV, and two had grade V. Grades I and II traumatic renal injuries were undetectable on follow-up CT. Grade III injuries resulted in the development of renal scars in 14 of 22 (4%) patients. Scarring resulted in all patients with grades IV and V injuries. CONCLUSION. Grades I and II renal injuries heal completely, whereas higher grades of renal trauma result in permanent parenchymal scarring. Hence, incidentally discovered renal scars in patients with a history of minor renal trauma should be attributed tentatively to other causes that may or may not require additional investigation. R enal parenchymal scars are often identified on abdominal CT scans obtained for a variety of indications. The scars are often generically attributed to prior infection, trauma, or infarction. lthough correlation with history or imaging may assist in narrowing the differential diagnosis, this may not be possible for all patients. Studies have shown a direct relationship between severe pyelonephritis and long-term renal parenchymal scarring [1 3]. If the appropriate history is given, prior trauma, regardless of its severity, is often assumed to be the cause of incidentally found renal parenchymal scars. The relationship between severe renal trauma and scarring has also been previous described in children [4, 5]. However, no study to date has shown an unequivocal relationship between the grade of renal injuries and the development of scars in adults. We decided to evaluate the incidence of renal scarring after all grades of renal in patients who had undergone both diagnostic CT and follow-up imaging. y defining an association between grade of and the subsequent development of scars, one may be able to predict whether a parenchymal abnormality identified on CT is possibly due to a prior traumatic or to other, nontraumatic causes such as a prior infection or infarction. The purpose of this study was to determine whether there is an association between the grade of a traumatic renal and the subsequent development of renal parenchymal scars on CT. Materials and Methods Patient Population We performed a retrospective analysis of a 42-month period (January 2002 June 2005) of all adult patients (age, 1 years) who were evaluated on MDCT at our institution, a level 1 trauma center, after sustaining abdominal trauma. total of 1,473 patients underwent CT for blunt (n = 91) 1174 JR:190, May 200

2 Renal Scars on CT fter bdominal Trauma and penetrating (n = 512) injuries. The original reports of these CT examinations were reviewed, and a total of 10 patients (7%) were identified in whom a renal parenchymal was documented. Of these 10 patients, 54 (51%) had at least one follow-up CT scan obtained for a variety of indications no earlier than 1 month after. These patients constitute our study population. The remaining 52 patients (49%) had no follow-up CT performed later than 1 month after and were excluded. The mean time interval to the follow-up CT examination was 5 months (range, 1 15 months). No renal surgery was performed between initial and follow-up imaging on any of the patients included in the study population. Thirty-six (7%) of the 54 patients were male and 1 (33%) were female, with a mean age of 35 years (range, 1 1 years). Of the 54 patients, 44 patients (1%) sustained blunt injuries and 10 patients (19%) sustained penetrating flank injuries. The mechanisms of blunt injuries included motor vehicle collisions (n = 21), pedestrians struck by motor vehicle (n = 11), assaults (n = 9), and falls from a significant height (n = 3). The mechanisms of penetrating injuries comprised gunshot wounds (n = ) and stab wounds (n = 4). The study was approved by the investigational review board of our medical center and was conducted in a manner compliant with HIP. The review board waived the need for informed consent for all patients. CT Technique During the time period of the study, all trauma CT scans at our institution were obtained on either a 4-MDCT scanner (MX000, Philips Medical Systems) (January 2002 June 2005) (n = 37) or a 1-MDCT scanner (LightSpeed 4.X, GE Healthcare) (September 2004 pril 2005) (n = 17) within 1 hour of emergency department admission. The scanning parameters were as follows: kvp; ms; pitch, 1.5; field of view, mm; and slice thickness, 3.2 mm. ll patients received 100 ml of IV contrast material containing 320 mg I/mL (iohexol [Optiray, Mallinckrodt Imaging]) administered through an indwelling IV cannula, preferably located in an antecubital vein, at a rate of 3 ml/s using a power injector. Oral contrast material was not administered to any of the patients who suffered blunt trauma, in keeping with our departmental imaging protocol for that patient population. In addition to 100 ml of IV contrast material, patients with penetrating abdominal injuries were also given 900 ml of oral and 500 ml of rectal contrast material (2.2% barium sulfate suspension [Medescan arium Sulfate, Lafayette Pharmaceuticals]) for a more sensitive evaluation of bowel TLE 1: Classification of Renal Injuries ccording to the Organ Injury Scaling Committee of the merican ssociation for the Surgery of Trauma (ST) ST Grade I II III IV V []. Images of the abdomen and pelvis were acquired from the superior surface of the diaphragm through the ischial tuberosities in the portal venous phase after a 0-second delay from the beginning of IV contrast injection. ccording to our departmental protocol, the presence of a renal pedicle, perinephric stranding, or abnormal fluid collections within the retroperitoneum warranted a dedicated evaluation of the collecting system. s of November 2003, imaging through the abdomen and pelvis after a 5-minute delay was standard in all trauma patients who were found to have definite or possible intraabdominal injuries on the initial scan [7]. Imaging parameters were identical to those used 12 Grade I renal Healed Description of Injury Renal contusion or nonexpanding subcapsular hematoma without a parenchyma laceration Nonexpanding perirenal hematoma or a renal cortex laceration (< 1 cm) without urinary extravasation Renal cortex laceration (> 1 cm) and no urinary extravasation Renal cortical laceration extending into the collecting system, a segmental renal artery or vein, or main renal artery or vein with a contained hematoma Shattered kidney, avulsion of the renal pedicle, or thrombosis of the main renal artery 54 Single-detector CT or 4-MDCT follow-up imaging Grade II renal Healed Fig. 1 Diagram shows study population. Healed for the initial scan except the ms, which was reduced to 100 ms to decrease radiation exposure to the patient. These delayed scans were acquired in 1 (30%) of the 54 patients who are the focus of this study. Data nalysis ll images were analyzed using a PCS with digital workstations. Two radiologists, both fellowship-trained in abdominal imaging and who had 7 and 13 years experience interpreting abdom inal trauma CT scans, retrospectively reviewed the initial CT images. Renal injuries were graded by consensus according to the Organ Injury Scaling Committee of the merican ssociation for the 1,473 Imaged trauma patients 10 Renal injuries 22 Grade III renal 1 1,37 No renal injuries 52 No follow-up imaging available 10 Grade IV renal Grade V renal 2 2 JR:190, May

3 Dunfee et al. Surgery of Trauma (ST), grades I through V (Table 1). The kidney (right, left, or both) and the type of with the highest grade were documented and targeted for follow-up analysis. Follow-up contrast-enhanced CT of the abdomen and pelvis for 54 patients (51%) of the 10 patients was performed on a 4-MDCT scanner (n = 39), a 1-MDCT scanner (n = 9), or a single-detector CT scanner (n = ) (PQ5000, Picker International) using scanning parameters similar to those used for the admission CT scan. Imaging was performed for various clinical indications relating to a previous trauma or for unrelated reasons. Delayed images were not acquired as part of these follow-up CT exami nations. The same radiologists evaluated both kidneys for the presence of parenchymal distortion (loss of corticomedullary differentiation), scarring (cortical thinning), or perfusion defects (decreased regional attenuation). When a renal scar was identified, the location correlated with the site of the initial for each case. The follow-up images were reviewed 1 month after the initial interpretation to eliminate any possibility of recall bias. In an attempt to quantify the potential effect of renal on renal function, blood pressures and serum creatinine levels were identified from the patients medical records at the time of the initial CT examination and at the time of follow-up imaging examination to assess for any change. ny other factor in the interim that may have influenced renal function, such as nephrotoxic medications or multiorgan failure, was not considered. Statistical nalysis The data obtained from both the initial and follow-up imaging examinations were integrated for statistical analysis. To assess for an association between incidence of scarring and the severity of, we used Fisher s exact test for 2 2 contingency tables. Results The renal injuries sustained by the 54 individuals who underwent follow-up imaging performed at least 1 month after were classified as follows: grade I (n = 12, 22%), grade II (n =, 15%), grade III (n = 22, 41%), grade IV (n = 10, 19%), and grade V (n = 2, 4%) (Fig. 1). Grade I renal injuries were present in 12 patients and comprised perinephric hematomas (n = 9) and small contusions (n = 3). The mechanism of was blunt trauma for all patients. Follow-up CT scans, obtained from 1 to 15 months after (mean, months), showed no parenchyma abnormalities and complete resolution of the initial findings (Table 2 and Fig. 2). Grade II injuries were identified in eight patients, and all were parenchymal lacerations that were less than 1 cm in depth (n = ). The mechanism of in all cases was secondary to blunt trauma. Follow-up CT scans were acquired weeks 7 months (mean, 3 months) after and showed no parenchyma abnormalities or residual hematomas (Table 2 and Fig. 3). Grade III injuries were present in 22 patients and included parenchymal lacerations extending more than 1 cm deep but without evidence of collecting system (n = 22). dditional findings in these patients included perinephric hematomas and contusions (n = 15) and additional lacerations extending less than 1 cm (n = ). The mechanism of trauma included both blunt (n = 1) and penetrating (n = ) injuries. On follow-up CT scans, renal scars were seen in 14 of the 22 (4%) patients who sustained grade III injuries. These follow-up CT scans were obtained 1 13 months after trauma (mean, 5 months). Scars were seen in eight of the 1 patients who sustained blunt injuries and in all six patients who sustained penetrating injuries. The scarring included regions of cortical retraction, irregularity, or decreased enhancement compared with the remaining renal parenchyma (Fig. 4). The location of each renal scar correlated with the site of on the initial CT scan. The remaining eight of 22 patients TLE 2: merican ssociation for the Surgery of Trauma (ST) Grades of Renal Injury over a 42-Month Period ST Grade No. (%) of Patients with Documented Renal Injury (n = 10) No. of Patients with Renal Injury and Follow-Up Imaging (n = 54) Mean Interval etween Initial and Follow-Up Imaging (mo) Mechanism of Injury a Trauma Trauma No. of Patients with Scarring Trauma I 45 (42) 12 (22) II 19 (1) (15) III 24 (23) 22 (41) 5 1 IV 15 (14) 10 (19) 4 4 V 3 (3) 2 (4) Note Incidence of scarring was 4% for grade III injuries (14/22), 100% for grade IV injuries (10/10), and 100% for grade V (2/2). a Data are number of patients. Trauma Fig year-old man with grade I right renal after motor vehicle accident., Small right subcapsular hematoma (arrow) is present without evidence of underlying cortical ; note contrast-mixing artifact is present within inferior vena cava., Follow-up image obtained 5 weeks after reveals only minimal regional perirenal fat stranding. 117 JR:190, May 200

4 Renal Scars on CT fter bdominal Trauma Fig year-old woman with grade II left renal after fall from second-story balcony., Small (< 1 cm) cortical laceration (arrow) is present with large perirenal hematoma., Follow-up CT image obtained weeks after reveals absence of parenchyma scarring with minimal surrounding perinephric stranding. (3%) who sustained grade III injuries had no evidence of developing scar (Table 2). The mechanism of for these eight patients was blunt trauma, with follow-up imaging performed from weeks to 7 months after (mean, 3 months). Grade IV injuries were observed in 10 patients. The injuries included segmental infarcts (n = 7) and collecting system injuries (n = 3). Small renal hematomas and contusions were also present in seven of the patients. The interval between initial imaging and follow-up imaging ranged from 1 to 9 months (mean, months). The mechanisms of included blunt (n = ) and penetrating (n = 4) causes. In all 10 patients (100%), the grade IV injuries resulted in the development of scars in the same region (Table 2). The scarring included regions of cortical retraction, irregularity, or decreased enhancement compared with the remaining renal parenchyma (Fig. 5). Grade V injuries were identified in two patients. oth patients had renal pedicle injuries with occlusion of the main renal artery due to severe blunt trauma. Initial CT scans showed complete lack of parenchymal enhancement Fig year-old man with grade III left renal after stab wound to left flank., Wide left renal laceration (arrow) is present with small surrounding hematoma., Twenty weeks after trauma, CT image reveals cortical thinning and retraction in region of previous laceration (arrow). and delayed collecting system opacification. Follow-up CT scans, obtained 4 and 9 months later, showed persistent lack of enhancement of the entire parenchyma with marked cortical and medullary atrophy (Table 2 and Fig. ). The Fisher s exact test showed a significant association between the severity of on the initial CT scan and subsequent development of renal scarring (p < ). Thus, the degree of renal scarring in each patient correlated with the degree of the initial. Mean blood pressures and serum creatinine levels were available for many of the patients Fig year-old man with grade IV left renal after being struck by car while walking., Wedge-shaped perfusion defect (arrow) is present in interpolar region of left kidney with surrounding hematoma., Follow-up CT image obtained 12 weeks after shows cortical thinning and retraction in same region (arrow). JR:190, May

5 Dunfee et al. Fig. 34-year-old woman with grade V left renal after rollover motor vehicle accident., Initial image reveals filling defect in left main renal artery (arrow) with complete absence of renal enhancement., Five weeks after, image shows significant atrophy of left kidney. at both the time of initial trauma and during follow-up imaging. significant change in mean blood pressure was defined as greater or less than 10% of the initial measurement. Of the grade I renal injuries, mean blood pressures and serum creatinine values were documented in seven of the 12 patients. There were no significant changes identified in documented blood pressure measurements. In addition, the creatinine values remained within normal limits (< 1.3 mg/dl) for all seven patients. Initial and follow-up mean blood pressures and serum creatinine levels were available for five of the eight grade II renal patients. The values remained within normal limits for both intervals without significant change. Of the grade III injuries, serial mean blood pressures and serum creatinine values were available for 1 of the 22 patients. The levels did not show a significant change throughout the documented time period. oth initial and follow-up mean blood pressure and serum creatinine values were available for only four of the 10 patients with grade IV renal injuries. However, there was no significant change in the values identified. One of the two grade V renal patients had mean blood pressures and serum creatinine levels documented initially and during follow-up imaging. Neither value showed a significant change during the interval. Discussion Renal trauma comprises up to 24% of all solid organ injuries resulting from blunt abdominal trauma, third only to hepatic and splenic trauma []. injuries to the abdomen and flank also commonly affect the kidneys. Renal trauma may involve the cortex, medulla, collecting system, or vessels [9, 10]. grading system to classify the severity of was developed by the merican ssociation for the Surgery of Trauma (ST). The scores range from grade I through grade V, with increasing severity and complexity, and the grading system contains strict CT criteria based on imaging findings [11]. Grade I renal injuries include small parenchymal contusions and nonexpanding subcapsular hematomas. Grade I lesions constitute approximately 75 5% of all renal injuries in most studies [12 14], and management of these patients is typically conservative [15]. Grade II injuries encompass approximately 10% of renal injuries [13] and include nonexpanding perinephric hematomas and cortical lacerations extending less than 1 cm deep into cortex. cortical laceration appears as a small linear hypoattenuating lesion originating from the periphery of the kidney. These injuries are also managed conservatively. The collecting system is not involved in grade I or II injuries. Grade III injuries include lacerations extending more than 1 cm into the renal parenchyma without urinary extravasation. Once the laceration extends through the corticomedullary junction into the collecting system, the is categorized as grade IV. Delayed images in the excretory phase are required to ensure collecting system integrity [1]. Thrombosis of a segmental artery is also included in grade IV injuries, appearing as a well-defined, wedge-shaped area of decreased enhancement [17]. In addition, to the main renal artery or vein may be present in grade IV injuries without complete vascular occlusion. Overall, grade III and IV injuries comprise approximately 7% of renal injuries [14]. Management may be either conservative or surgical [15]. Grade V renal injuries include thrombosis or avulsion of the main renal vasculature or multiple deep lacerations, defining a shattered kidney. These injuries occur in less than 5% of renal trauma cases [13, 14]. Whereas thrombosis of the main renal artery appears as a nonenhancing kidney, renal vein is often more difficult to detect [1]. Venous outflow is indicated by an intraluminal filling defect, distended renal vein, diminished nephrogram, or delayed nephrographic progression. Decreased excretion of contrast material into the collecting system may also be seen with renal vein [19]. Most renal trauma patients are managed nonoperatively. lthough the need for subsequent CT scans is not routine and is determined by both the severity and clinical evolution of the patient, follow-up scans are commonly obtained for a variety of other reasons. This study defines the association that exists between renal severity, as assessed by the CT classification of the ST, and the potential for developing permanent renal findings on follow-up CT scans. ecause the study population is limited to those individuals with follow-up CT scans, there is a greater proportion of patients with high-grade renal injuries than has been reported in other abdominal trauma series [14]. lso, a more severe renal is more likely to be associated with injuries to other organs [, 20], and multiorgan trauma typically requires follow-up imaging due to increased morbidity, as compared with patients with isolated low-grade renal injuries who are typically discharged from the hospital without long-term sequelae. Our study shows that there is a significant association between renal severity and the development of parenchymal scars in those regions. Numerous studies have previously shown the pathologic healing course of traumatized animal kidneys [21, 22]. The injuries progress from hematomas or active extravasation to fibrosis and eventually to scar 117 JR:190, May 200

6 Renal Scars on CT fter bdominal Trauma contraction by 2 months [22]. The degree of pathologic scar formation has been correlated with the severity of. These studies support our CT findings of healing and scar formation of the posttraumatic kidney. The results of our study can have significant clinical impact on patient management and follow-up examinations. For example, if trauma can be excluded as a cause of the renal scarring discovered on routine imaging, the findings may be the first clue to discovering an underlying abnormality. These abnormalities may be related to the cardiovascular system, such as a cardiac thrombus or hypercoagulable disorder. The early detection may initiate further workup and treatment before a more severe sequela of the disease results, such as mesenteric or cerebral infarction. In addition, we have unveiled several cases of chronic reflux nephropathy to clinicians before the patient s laboratory values changed. However, if the finding of a renal scar can be definitively associated with previous trauma, no additional workup is required. Some potential bias should be briefly discussed. The CT images were reviewed by consensus and consequently the interobserver agreement in classifying renal injuries and in recognizing renal scars could not be estimated. In addition, six of the 54 patients had follow-up CT performed on a single-detector scanner. Theoretically, this may have decreased the effectiveness of detecting renal scarring from the. In our investigation, grades I and II injuries almost invariably underwent complete resolution without any identifiable morphologic abnormality on subsequent CT scans obtained at least 1 month after the. Parenchymal scars developed in most patients with grade III injuries and in all patients with grades IV and V injuries. The scarring is indicated by irreversible parenchymal changes, such as cortical retraction and atrophy. lso, as we suspected, any to the kidney s main vascular flow resulted in permanent. Of note, all 10 patients (100%) with grades III or IV injuries in our study population who sustained penetrating trauma developed a scar, whereas the frequency of scars in blunt trauma patients with grade III injuries was 4% (14/22). These results might indicate that, even though CT may show similar findings, a greater degree of parenchymal damage is present with penetrating trauma than with blunt trauma, leading to a higher frequency of scarring. Of the 54 patients included in the study, 35 had both mean blood pressures and serum creatinine levels documented at the time of initial and follow-up imaging. Each grade of renal was represented in the 35 patients identified. The mean blood pressures did not significantly change for any of the documented patients and remained within 10% of the initial measurement. In addition, the serum creatinine values did not show a change of greater than 0.2 mg/dl and remained within normal limits for all patients. Despite these findings, however, blood pressure measurements and serum creatinine levels have been shown to not always correlate with renal function. Many factors affect the level of renal function after, and further investigation is necessary to increase the power of these findings. In conclusion, grades I and II renal injuries were undetectable on follow-up CT performed at least 1 month after trauma in our study population. The majority of grade III and all grades IV and V renal injuries resulted in permanent parenchyma scarring in the same locations. Therefore, incidentally detected regions of renal parenchyma scarring, perfusion defects, or both can only be attributed to previous trauma if the severity of was grade III or higher (p < ). More importantly, however, the detection of renal scars in patients who have not sustained significant renal must be tentatively attributed to other causes such as prior infection or infarction. This early detection and attention may prompt additional investigation and treatment before more severe sequelae of the disease results. References 1. Soulen MC, Fishman EK, Goldman SM. Sequelae of acute renal infections: CT evaluation. Radiology 199; 173: Tsugaya M, Hirao N, Sakagami H, Ohtaguro K, Washida H. Renal cortical scarring in acute pyelonephritis. r J Urol 1992; 9: Meyrier, Condamin MC, Fernet M, et al. Frequency of development of early cortical scarring in acute primary pyelonephritis. Kidney Int 199; 35: Yale-Loehr J, Kramer SS, Quinlan DM, La France ND, Mitchell SE, Gearhart JP. 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