Blunt renal trauma: is the AAST grading scale still a good predictor of therapeutic management and clinical outcomes? Added value of CT findings.

Department of Translational Research and New Technologies

Residency P

Chairman

Blunt renal trauma: is the AAST

therapeutic management and cl

Supervisor

Prof. Davide Caramella, MD

University of Pisa

Department of Translational Research and New Technologies

in Medicine and Surgery

Residency Program in Diagnostic Radiology

(2012-2017)

Chairman: Prof. Davide Caramella

enal trauma: is the AAST grading scale still a good predictor of

management and clinical outcomes? Added value of

Dr.

Academic Year 2015-2016

Department of Translational Research and New Technologies

ology

grading scale still a good predictor of

inical outcomes? Added value of CT findings.

Candidate

Abstract

Objectives.

The purpose of our study is to assess the role of multidetector computed tomography (MDCT) in predicting therapeutic management and clinical outcomes of patients with renal trauma in terms of statistical significance. Furthermore, the work aims to analyze the current effectiveness of the American Association for the Surgery of Trauma (AAST) injury scale as a severity grading system and indicator for operative/non-operative approach.

Materials and methods.

The study includes sixty-one polytraumatized patients admitted to the Emergency Department of Pisa from January 2013 to March 2017 that underwent a MDCT examination with diagnosis of renal trauma. CT features were retrospectively evaluated and ranked according to the revised AAST injury scale, with a final grade assignment to each renal trauma; findings like vascular contrast extravasation (active hemorrhage) and contained vascular injuries (pseudoaneurysm) were also recorded. The chi-squared test was used to determine the statistical correlation between AAST renal injury grade and the need for operative (surgical/endovascular) management, CT findings of active hemorrhage/pseudoaneurysm and the need for operative (surgical/endovascular) management, AAST renal injury grade and CT findings of active hemorrhage/pseudoaneurysm.

Results.

Renal trauma injuries were classified as low-grade and high-grade as follows: 39 (64%) AAST I-III and 22 (36%) AAST IV-V. The presence of active hemorrhage and/or pseudoaneurysm was found in 28/61 (45%) patients, of which 21 (75%) required surgical/endovascular intervention. Twenty-one out of 22 (96%) of renal injuries handled operatively showed active bleeding at CT examination (n = 12 low-grade; n = 9 high-grade). Statistical analysis demonstrated significant correlation (p value < 0,0001) between the presence of active hemorrhage/pseudoaneurysm and the need for operative management. On the contrary, no statistically significant association was found between the AAST grade and the need for operative management (p value = 0,251), and

between the AAST grade and the presence of active hemorrhage/pseudoaneurysm (p value = 0,958).

Conclusion.

Vascular CT findings, not mentioned in the AAST injury scale, represent an important added value in establishing the severity grade of traumatic renal injuries and the best approach to decide the appropriate therapeutic options. In contradistinction to the AAST grade, active vascular contrast extravasation and/or contained vascular injuries are significant predictor of the need for operative management.

Introduction

Renal trauma occurs in 8-10% of all trauma cases and about the 90% of renal injuries result from a blunt mechanism including motor vehicle collision, falls from height, pedestrian accidents or direct blow to the flank during sports activities [1, 2]. Polytraumatized patients have always represented a big diagnostic challenge for clinicians, surgeons and radiologists in the emergency setting. The advent of multidetector computed tomography (MDCT) has led to an increase in the non-invasive diagnosis of traumatic injuries, given its ability to detect a wide spectrum of lesions ranging from subtle vascular injury to shattered organs, and to a significant decrease of the previously used, more invasive, diagnostic approaches such as laparotomy. Furthermore, as a result of advances in imaging and treatment strategies, the need for surgical intervention has diminished in favour of a greater percentage of kidney preservation, as most renal injuries can be managed conservatively [3]. Thus, MDCT plays a major role in investigation of renal trauma and is currently the imaging modality of choice [4].

Nowadays, Advanced Trauma Life Support (ATLS) is the common language of trauma care, defining two phases in the initial management of patients with multiple injuries: a primary survey, which aims to identify and treat injuries that endanger the patient's life; and a secondary survey, which attempts to detect all the injuries and initiate definitive treatment [5]. Life-threatening conditions are rapidly identified and life-saving treatment is expeditiously initiated; hemodynamically unstable patients, with no or transient response to resuscitation, must be taken directly to surgery. Chest and pelvis radiographs and a Focused Assessment with Sonography in Trauma (FAST) are part of the primary evaluation of the patient in the shock room; the FAST examination is finalized to exclude hemoperitoneum, hemothorax or hemopericardium as causes of hemodynamic instability, but it is limited in characterizing abdominal viscera: indeed, although a positive FAST is a strong predictor of injury, a negative FAST does not rule out significant injury or bleeding. Specifically, in regard to renal parenchyma, sonography can detect renal lacerations but can not definitely assess their depth and extent and does not help in differentiating extravasated blood from an urinoma. Several studies have reported the sensitivity of ultrasound for the detection of renal lesions to be as low as 22% [6]. Thus a MDCT examination, which is recognized as the gold standard imaging technique in polytrauma, may be necessary to better delineate abdominal blunt injuries in hemodynamically stable patients, defined as those who do not have vital signs consistent with shock and show stable serial hematocrit values over time [7, 8].

In particular, there is general agreement in the literature that intravenous contrast enhanced MDCT should be undertaken in stable blunt trauma if there is macroscopic hematuria, or microscopic hematuria and hypotension (systolic blood pressure < 90 mmHg). Anyway, there is a false-negative rate ranging from 5 to 20%, and the degree of hematuria does not correlate with the degree of injury. The kidney is especially vulnerable to rapid deceleration event because it is fixed in space only by the renal pelvis and the vascular pedicle. That is the reason why the patient’s history and the details about the mechanism of blunt trauma, combined to the presence of flank ecchymosis and fracture of the lower ribs or thoracolumbar spine may be signs suggestive

of renal injury, and accepted indications for renal imaging regardless of presence or absence of hematuria [2, 7-9].

CT images characterize with high sensitivity and specificity rate the various features of renal trauma and allow for detection of both renal vascular and parenchymal injuries, as well as collecting system injury. Several types of classification for renal trauma based on pathogenesis, morphologic features, and clinical parameters have been proposed in the literature. Over the last few decades, the most commonly used and widely accepted has been the American Association for the Surgery of Trauma (AAST) grading system. The AAST renal injury scale grades renal trauma on a scale of I to V, according to the severity of injury. It was developed in 1989, based on the gross appearance of organs seen in surgery, and created to provide physicians with a standardized lexicon of organ injury as well as a classification system for clinical and scientific research purposes [3, 10, 11]. The AAST grading system has been validated as the most important prognostic indicator and tool in predicting the need for intervention and the clinical outcomes in patients with both blunt and penetrating renal trauma [12]. Even though this classification is based on surgical evidences, it has a strong correspondence with CT findings allowing to correlate them with consequent therapeutic implications [13].

Most renal traumatic lesions are represented by minor injuries (75-98%), ranked as AAST I-III, that will heal spontaneously just following the simple “wait and see” management and usually without requiring follow-up imaging [14].

Contusions appear as ill-defined, irregularly shaped areas of decreased and delayed contrast enhancement within the renal parenchyma. Lacerations can be either superficial, involving the cortex, or deep extending into the medulla and are visualized as irregular or linear low attenuation areas best depicted during the nephrographic phase and typically associated witha small amount of perirenal blood; in presence of a parenchymal laceration, delayed CT acquisitions should be performed in order to rule out urine extravasation consistent with a collecting system traumatic involvement. A subcapsular hematoma is a well-delimited, non-enhancing fluid collection located between the renal cortex and the renal capsule, that may assume a crescent or biconvex shape depending on its size, with indented aspect of the adjacent parenchyma. Sometimes the capsule tears resulting in a perirenal hematoma, that

appears as a poorly delimited, non-enhancing fluid collection located in the fatty area between the renal capsule and Gerota’s fascia; its attenuation, as well as subcapsular hematoma, varies according to the age resulting hyperdense in the acute/subacute stage [6, 15-18].

More significant renal trauma, classified as AAST IV-V, are represented by severe injuries likely requiring major surgical intervention. Anyway this kind of therapeutic approach has been increasingly debated in the last two decades: a greater propensity is developing towards an attendence strategy and towards the choice of mini-invasive operative management like endovascular and endourological procedures, with the final aim to spare the kidney whenever possible [19-21]. A careful and closer clinical/laboratoristic monitoring is needed, in order to evaluate case by case the necessity of follow-up imaging.

Segmental infarctions appear as sharply demarcated, wedge-shaped areas of absent contrast enhancement, consequence of dissection and/or thrombosis of segmental vessels; sharp margins and lack of enhancement during the delayed phase are the characteristics that must be identified to perform a differential diagnosis with renal contusions. A simple “wait-and-see” management is indicated in the majority of cases; some authors support that surgical debridement should be taken into consideration only in case of infarctions involving more than 50 % of the renal parenchyma, to avoid the risk of abscess formation. “Shattered kidney” is a term used to describe a kidney ruptured in multiple fragments by severe and deep lacerations; renal fragments are usually subdivided by a fluid collection that occupies the entire renal loggia and may sometimes appear devitalized because of traumatic occlusion of their arterial supply. Surgical exploration and nephrectomy is often required because of severe hemodynamic instability, even though an increasingly number of patients are managed conservatively or at least by means of endovascular treatment. Thrombosis of the main renal artery appears as an endovascular filling defect, hyperdense on nonenhanced images and hypodense in post-contrast scans; it is usually secondary to traumatic dissection of the main renal artery with resulting complete or partial occlusion and consequent completely devascularised or hypovascularised kidney. Main renal vein thrombosis is rare and causes delayed enhancement of the kidney in comparison with contralateral, renal enlargement and parenchymal oedema. Management of these injuries is extremely controversial; both surgical and endovascular revascularization have shown good results, anyway in case of complete arterial occlusion the 2-h time limit for revascularization must be considered [22]. Avulsion of the main renal artery or vein represents a life-threatening emergency that, in the majority of cases, preclude the patient to undergo CT because of hemodynamic instability. Renal artery avulsion in the majority of the cases results in a completely or at least largely devascularized kidney, whereas in case of renal vein avulsion renal enhancement is usually delayed and reduced, but uniformly present. In case of vascular pedicle avulsion no delayed CT scans must be performed and immediate surgical exploration is mandatory. Collecting system injuries occur in case of parenchymal laceration extending deeply into the medulla and can be highlighted during the CT delayed phase as markedly hyperdense material within the perirenal hematoma, consistent with urinary contrast extravasation. Ureteral stenting is the treatment of choice, as well as for ureteropelvic junction laceration characterized by normal contrast material excretion and intact calyceal system, with hyperdense urine extravasation detected in the delayed phase at the renal hilum. On the contrary, avulsion of the ureteropelvic junction requires surgical repair; CT features are the same of ureteropelvic junction laceration, except for a complete absence of opacified urine in the downstream ureter [1, 9, 23, 24].

Furthermore, CT shows nearly 100% sensitivity and specificity rate in detecting important findings like vascular contrast extravasation and contained vascular injuries. Active bleeding from renal arterial branches appears as poorly delimited contrast material extravasation, sometimes flame-shaped, usually located in the setting of a perirenal hematoma, hyperdense in the arterial phase

and progressively increasing in quantity in the following post contrastographic acquisitions. Contained vascular injuries include arterial pseudoaneurysm (PSA) and artero-venous fistula (AVF): the former is a well-delimited ovoid lesion located within the renal parenchyma, enhancing as much as the adjacent arteries during the arterial phase and maintaining the same density of the surrounding vessels during the subsequent scans, without increasing in size; the latter usually have the same CT appearance of arterial pseudoaneurysm, except for the identification of a dilated renal vein that enhances early during the arterial phase of the study. In hemodynamically stable patients, conventional angiography with endovascular selective arterial embolization represents nowadays the treatment of choice in these cases [1, 9,15, 24].

These vascular CT findings are not mentioned in the AAST grading system, even though they seriously influence the therapeutic approach both because often occur in low-grade injuries (AAST I-III) and because require operative management [25-27]. As a consequence of this, it has been hypothesized that the AAST grading system is inadequate as a severity injury scale and limited in its ability to provide clinicians with an evidence-based approach in making management decisions [3]. Several authors, like Bonatti et al, have underlined its limitations and proposed for changes to the classification. Dugi et al, subsequently supported by Chiron et al, suggested a substratification of the intermediate grade injury into grade 4a (low-risk cases likely to be managed non-operatively) and grade 4b (high risk-cases likely to benefit from angiographic embolization, repair or nephrectomy), based on the presence of radiographic risk factors including perirenal hematoma, vascular contrast extravasation and laceration complexity [28, 29]. In 2011, Buckley and McAninch created a revision to the AAST renal grading system, expanding grade IV injuries to include all collecting system injuries, pelvis injuries and segmental vascular injuries, and limiting grade V to severe hilar pedicle injuries including thrombotic events (Table 1) [30]. Nevertheless, also this most recent revision lacks the fundamental CT features of vascular injuries encountered in solid organ trauma and mentioned above.

In regard to high AAST grade injuries, the raised diagnostic capabilities of MDCT and improved management of hemodynamically unstable patients have progressively led to a shift from nephrectomy towards conservative strategy and/or mini-invasive treatment, the latter considered the most appropriate first line approach for about 90–95 % of renal trauma especially in case of vascular injuries [3, 9, 31]. As significant vascular injuries may also occur in low AAST grade trauma, the purpose of our study is to assess the utility of MDCT in predicting therapeutic management and clinical outcomes of patients with renal injuries, in comparison with the AAST grading system.

Revised AAST renal injury grading system

Grade Injury location Definition

I Parenchyma Subcapsular hematoma and /or contusion

Collecting system No injury

II Parenchyma Laceration < 1 cm in depth and into cortex, small hematoma contained within Gerota’s fascia

Collecting system No injury

III Parenchyma Laceration > 1 cm in depth and into medulla, hematoma contained within Gerota’s fascia

Collecting system No injury

IV Parenchyma Laceration through the parenchyma into the urinary collecting system Segmental infarctions

Vascular Renal segmental artery or vein injury, or vessel thrombosis

Collecting system Laceration, one or more into the collecting system with urinary extravasation Renal pelvis laceration and/or complete ureteral pelvic disruption

V Parenchyma Shattered kidney

Vascular Main renal artery or vein laceration, avulsion or thrombosis

Table 1. Revised AAST renal injury scale created by Buckley and McAninch essentially concerns grade IV and V: collecting system injuries and segmental vascular injuries are included in grade IV, limiting grade V to severe main renal vessel injuries.

Materials and methods

This retrospective study includes 61 hemodynamically stable polytraumatized patients suffering from blunt abdominal trauma that were admitted to the Emergency Department of Pisa from January 2013 to March 2017 and were studied by MDCT with diagnosis of traumatic renal injuries. The study group consists of adult population aged 20-85 years old (mean age: 44 years old) and composed by 50 males and 11 females. Patients’data were extracted from the Emergency Department polytrauma registry and reviewed in our radiologic imaging archiving system (PACS: Picture Archiving and Communication System) by two investigators: an experienced emergency radiologist and a five-year trained radiology resident.

The MDCT examinations were performed with a 64 slices scanner (Lightspeed VCT;GE Healthcare, Milwaukee, USA) before and after intravenous administration of contrast material and saline solution (mechanical power injector: Medrad, Pittsburgh, USA). Acquisition parameters, radiation dose criteria and volume of contrast medium were established depending on the patient’s age and physical body characteristics, likewise the flow rate injection was chosen on the basis of the type of venous access. CT scans were overall performed with selection of 100-120 kV and mA automatic modulation (range between 100-650 mA), giving 100-120 mL of intravenous contrast medium with a iodine concentration of 320-400 mg/mL at a flow rate of 3.5-4 mL/sec and subsequent 30-40 mL of saline. Our standard polytrauma protocol consisted of a nonenhanced CT scan and a contrast

enhanced CT scan with a dual-phase acquisitionin the arterial and venous phase, obtained from the thoracic inlet to the symphysis pubis. The timing for the acquisition of the arterial phase was determined with bolus tracking. Whenever permitted by clinical conditions, delayed images (5-8 minutes post-injection of contrast) were also acquired through the abdomen and pelvis in order to assess for potential collecting system injuries. Images were archived in the PACS with slice thickness and interval reconstruction of 2.5 mm, with thinner slices of 1.25 mm when needed; multiplanar and 3D volume rendering reformations were also reviewed as additional post-processing options.

MDCT findings following blunt renal trauma detected in the retrospective CT images evaluation consist of subcapsular/perirenal hematoma, parenchymal lesions (contusion, superficial/deep laceration and infarction), vascular lesions (dissection, thrombotic occlusion, vessel narrowing, artero-venous fistula, pseudoaneurysm and active bleeding) and collecting system/renal pelvis lesions (urinary leakage). Renal injuries were classified basing on the revised AAST injury scale, which includes five grades of increasing severity. For statistical reasons AAST grades I-III, usually treated conservatively, and AAST grades IV-V, most likely managed operatively, were considered as low-grade and high-grade injuries respectively. The presence of vascular contrast extravasation and/or contained vascular injury, not mentioned in the AAST grading scale, was also recorded. In some patients, a subsequent CT examination was performed to exclude a hidden collecting system lesion with urinoma formation or an infected hematoma, needing ureteral stent or percutaneous drainage placement. Information about management outcomes like successful conservative approach, the requirement for surgical intervention, for conventional angiography and endovascular therapy, or for endourological treatment with respective procedural results were also archived.

All data were summerized by means of relative frequency and percentage measurements. The chi-squared test was used to study the association between the AAST renal injury grade and the need for operative (surgical/endovascular) management, between CT findings of active hemorrhage/pseudoaneurysm and the need for operative (surgical/endovascular) management, between the AAST renal injury grade and CT findings of active hemorrhage/pseudoaneurysm. A p value < 0.05 was considered statistically significant. All statistical, descriptive (including bar graphs) and inferential analysis were performed using the SPSS v.23 technology.

Results

AAST grade based on CT findings of 61 patients with blunt renal trauma resulted in: 14/61 (23%) grade I injuries, 12/61 grade II (20%) injuries, 13/61 (21%) grade III injuries, 17/61 (28%) grade IV injuries and 5/61 (8%) grade V injuries (Table 2). Partition in low-grade and high-grade lesions resulted in 39 (64%) AAST I-III and 22 (36%) AAST IV-V.

AAST renal injury scale Frequency (%) Grade I 14/61 (23%) Grade II 12/61 (20%) Grade III 13/61 (21%) Grade IV 17/61 (28%) Grade V 5/61 (8%)

Table 2. Frequency and percentage distribution of the five AAST injury grades among the study population. AAST I-III (64%) wereconsiderd to be low-grade injuries and AAST IV-V (36%) were considered to be high-grade injuries.

Of the 61 renal injuries 47 were found to have parenchymal involvement including contusions, lacerations less or greater than 1 cm, transected lacerations and shattered kidney; 7 were found to have segmental infarctions and 1 was found to have complete infarction. In 6 cases only minor perirenal hematoma was found, without detectable parenchymal lacerations.

CT demonstration of vascular injuries was made in 29/61 patients. One of them presented with

thrombotic occlusion of the main renal artery. The remaining 28 patients presented with vascular contrast extravasation and/or contained vascular injury: 21/28 active hemorrhage, 5/28 pseudoaneurysms and 2/28 concomitant active hemorrhage and pseudoaneurysm). Out of these 28 patients, 18 were graded as AAST I-III and 10 as AAST IV-V. The chi-squared test did not highlight a statistically significant correlation (p value = 0,958) between the AAST grade and the presence of active hemorrhage/pseudoaneurysm (Fig. 1). No cases of artero-venous fistula or vascular pedicle laceration were found.

Fig. 1 Vertical bar graph highlights no statistically significant correlation between the AAST grade and the presence of active hemorrhage/pseudoaneurysm.

Fig. 2 Vertical bar graph highlights no statistically significant association between the AAST grade and the need for operative (endovascular/surgical) management.

Concerning the 28/61 patients with diagnosis of active hemorrhage and/or pseudonaneurysm, 21/28 (75%) needed an operative management. In particular 3 nephrectomies and 18 conventional angiographies with subsequent angioembolization were required. A percutaneous hematoma drainage was positioned in one case. Of the above mentioned 21/28 renal injuries, 12 were AAST low-grade and 9 were AAST high-grade injuries. There was no statistically significant association (p value = 0,251) between the AAST grade and the need for operative (endovascular/surgical) management (Fig. 2). The remaining 7/28 (25%) patients were managed conservatively, even though a diagnostic conventional angiography was performed in 4 cases. Concerning the 33/61 renal injuries without CT findings of vascular contrast extravasation and/or contained vascular injuries, a conservative approach was overall chosen, except one case of main renal artery post-traumatic thrombosis in which a conventional angiography with endovascular stenting was performed (Table 3). Unlike the AAST injury scale, there was evidence of statistically significant correlation (p value < 0,0001) between the presence of active hemorrhage/pseudoaneurysm and the need for operative (endovascular/surgical) management (Fig. 3). All data and results obtained from the statistical analysis are shown in the contingency table (Table 4).

Cases of vascular contrast extravasation and/or contained vascular injuries 28/61

Low AAST grade I-III 18/28

High AAST grade IV-V 10/28

Presence of CT findings of vascular contrast extravasation and/or contained vascular injuries

Operative management 21/28 Low AAST grade I-III 12/21 High AAST grade IV-V 9/21 Non-operative management 7/28 Low AAST grade I-III 6/7

High AAST grade IV-V 1/7 Absence of CT findings of vascular contrast extravasation and/or contained vascular injuries

Operative management 1/33

Non-operative management 32/33

Table 3. CT findings of active renal hemorrhage and/or pseudoaneurysm per renal grade and management.

Fig. 3 Vertical bar graph highlights statistically significant correlation between the presence of active hemorrhage/pseudoaneurysm and the need for operative (endovascular/surgical) management.

Active hemorrhage/pseudoaneurysm p-value Yes No Operative management Yes 21 1 <0,0001 No 7 32 AAST grade I-III IV-V Operative management Yes 12 10 0,251 No 27 12 AAST grade I-III IV-V 0,958 Active hemorrhage/pseudoaneurysm Yes 18 10 No 21 12

Table 4. Contingency table: statistical correlation between all the variables that are object of the study.

Among the 61 traumatic renal lesions were found 6 (10%) collecting system injuries, of which five detected on admission CT and one identified at one month follow-up CT: one case was managed with major surgical intervention, as part of the three nephrectomized patients; five cases were treated with ureteral stent placement. The one with delayed urinary leak detection and consequent urinoma formation also required the positioning of a percutaneous drainage.

In summary, the total amount of operatively managed renal injuries was 22/61 (36%): 3 (5%) nephrectomies and 19 (31%) endovascular procedures were performed, of which 18 (29%) angioembolizations and 1 (2%) revascularization with stenting (Table 5). Furthermore, our results highlight that the 96% of patients treated had CT evidence of vascular contrast extravasation and/or contained vascular injury, whereas active bleeding was not present in the 83% of patients managed conservatively (Fig. 4).

Type of management Frequency (%)

Operative management 22 (36%)

Nephrectomy 3 (5%)

Endovascular treatment 19(31%)

Angioembolization 18 (29%) Revascularization and stenting 1 (2%)

Non-operative management 39 (64%)

Table 5. Operative and non-operative management of all the 61 traumatic renal injuries: schematic overview.

Fig. 4 Stacked bar graph represents the association in percentage between patients managed operatively and respective CT findings of vascular contrast extravasation/contained vascular injury.

Discussion

Over the past few decades the tendency towards a conservative or expectant management of traumatic renal injuries has considerably increased. Thanks to the widespread and improvement of mini-invasive therapeutic techniques, like endovascular and endourological procedures, a consequent reduction in the rate of major interventions has been recorded, as well as in the number of surgical exploration, also considering the technological advancement of MDCT which is the gold standard imaging modality in stable polytraumatized patients [9, 19-21].

The AAST injury scale is worldwide validated to classify renal trauma, suggests treatment options and predicts prognosis. Despite both the EAU (European Association of Urology) and AUA (American Urological Association) guidelines on urotrauma refer to this grading system, authors recognize its limitations and highlight that several proposals for changes have been published without an available current formal revision. Moreover guidelines recommend the non-operative approach even in cases of hemodynamically stable high AAST grade injuries in order to allow for preservation of the kidney, although maintaining a careful clinical, laboratoristic and radiological follow-up[2, 3,7, 32]. Therefore, the value of the AAST injury scale as severity grading system and predictor of operative management results nowadays substantially diminished.

The purposes of our study were to evaluate the limits of the AAST classification in characterizing and grading the severity of renal trauma, and to demonstrate the role of MDCT in establishing the correct therapeutic decision and clinical outcomes of renal injured patients. In particular, this work points out the added value of vascular CT findings that are not mentioned in the AAST grading system, but are importantly associated with the need for operative management, regardless of the AAST severity grade.

According to our experience the detection of vascular contrast extravasation and/or contained vascular injury (active hemorrhage/pseudoaneurysm) is a statistically significant indicator for the urgency of endovascular/surgical treatment. Of the 61 traumatic renal injuries, only 36% (n = 22) was managed operatively and among these patients 96% (n = 21) were found to have active bleeding at MDCT. The total amount of major surgical interventions resulted in three nephrectomies (5%): in two cases patients were hemodynamically instable and unresponsive to resuscitation efforts after the CT examination; in the third case severe concomitant abdominal viscera lesions were found, which required operative repair and contextual removal of the injured kidney (Fig. 5).

Fig. 5 CT examination of a 65 year-old male, involved in a motor vehicle collision, showed a shattered right kidney, with a voluminous parenchymal hematoma extending in the perirenal and pararenal space. Several hyperdense foci of contrast extravasation were visualized in the arterial phase (arrows in a, b, c), progressively increasing in the venous phase (arrows in d, e, f) and consistent with multiple active hemorrhages. Renal trauma was classified as AAST V and the patient underwent urgent nephrectomy because of severe hemodynamic instability occurred soon after CT examination.

Eighteen (29%) successful angioembolizations were performed to treat the remaining renal injuries with active hemorrhage and /or pseudoaneurysm, of which twelve were classified as low AAST grade (Fig. 6). Among these patients an attempt of conservative approach was decided in one case, graded as AAST II and charaterized by CT findings of superficial lacerations and subcapsular hematoma with evidence of punctiform bleeding visible only in the arterial phase and likely originating from a small capsular artery; considering the good clinical conditions, the normal hematocrit value and the isolated kidney involvement, bed rest and close hemodynamic monitoring were the treatment of choice. In a few days, the patient complained worsening of the flank pain with hemoglobin reduction and a CT scan was performed, showing increase in size of the subcapsular hematoma extended in the perirenal space with better evidence of the active bleeding. Angioembolization was required and a subsequent percutaneous drainage was also placed because of the creatinine value increment, probably due to the hematoma compressive effect on the renal parenchyma (Fig. 7).

Fig. 6 CT scan of a 35 year-old female, following a fall from height, showed right traumatic renal injuries graded as AAST III, characterized by several cortical contusions and a posterior mesorenal deep parenchymal laceration without collecting system involvement. A perirenal hematoma of moderate extent was associated with signs of vascular contrast extravasation in the arterial phase (arrow in a), increasing in size in the venous (arrow in b) and delayed phase (arrow in c), and consistent with active bleeding. Angioembolization was performed.

Fig. 7 CT images of a 58 year-old male admitted to the Emergency Department because of a direct blow to the flank during a conflict. a) Admission CT detected right renal superficial lacerations and a subcapsular hematoma with evidence of punctiform active bleeding visible only in the arterial phase and likely originating from a small capsular artery (arrow). Renal trauma was classified as grade II according to the AAST scale and a conservative approach was first chosen. b) Follow-up CT a few days after trauma showed increase in size of the subcapsular hematoma extended in the perirenal space, with still evident signs of active bleeding (arrow). c) Follow-up CT after endovascular treatment demonstrated an area of parenchymal infarction (arrow) due to successful angioembolization: no vascular contrast extravasation was found. d) and e) Follow-up CT after percutaneous drainage placement showed correct location of the catheter within the perirenal hematoma (empty arrow).

Seven patients found to have active bleeding were managed with a non-operative approach. In one case, an attendence strategy was first adopted because of severe intracranial injuries that made the patient get quickly worse and brought to death. In four cases, patients underwent conventional angiography with no evidence of detectable contrast extravasation at the moment of the examination, probably due to tamponade effect created by the enlarging hematoma with consequent self-limitingbleeding; no further invasive or mini-invasive procedures were performed (Fig. 8). In the remaining two cases, patients showed small hyperdense foci at enhanced CT referable to limited bleeding from a cortical/capsular arterial branch; considering good clinical conditions and hemodynamic stability, joined to the technical difficulty to selectively embolize such a peripheral vascular district without causing a large area of devascularized renal parenchyma, a “wait and see” strategy was attempted maintaining a close clinical and laboratoristic follow-up. In these six patients bed rest, support therapy and vital parameters monitoring allowed for a successful conservative approach. It is indeed supposed that the retroperitoneal location of the kidney represents an advantage pertaining to the non-operative management in case of vascular injuries: thanks to their protected site between rib cage, vertebral column and peritoneal viscera, great part of renal injuries occur in the peripheral cortex, the bleeding expands into the perirenal space and is contained by the Gerota’s fascia with possible tamponade effect and subsequent self-limiting hemorrhage; hematoma expansion into the pararenal space is a severe prognostic factor correlated to the need for operative management [33]. Anyway, each case of renal trauma should be singularly evaluated and the therapeutic decision derive from a rigorous consultation between the emergency clinician, surgeon, radiologist and interventional radiologist; beyond CT findings, constant vital parameters measurements and hemodynamic stability influence the patient management, as well as concurrent life-threatening abdominal organ lesions requesting major surgical intervention may impact on the surgeon approach towards the injured kidney.

Fig. 8 CT (a e b) and conventional angiography (c) of a 85 year-old male involved in a bike accident. Images evidenced a left renal trauma ranked as low AAST grade and characterized by a perirenal hematoma with contextual vascular contrast extravasation detected in the arterial phase (arrow in a) and increasingly in quantity in the venous phase (arrow in b), consistent with active hemorrhage. c) Conventional angiography was performed with no evidence of contrast extravasation at the moment of the examination, probably due to self-limiting bleeding; the patient was managed conservatively.

The only patient with no sign of active hemorrhage that required an operative management was found to have a complete renal parenchymal devascularization due to main renal artery post-traumatic thrombotic occlusion. Urgent endovascular procedure of revascularization with stent positioning was performed, with good clinical outcome and evidence of large parenchymal rescue at subsequent CT follow-up (Fig. 9).

Fig. 9 CT scan of a 20 year-old male admitted to the Emergency Department following a car accident. Axial (a) and coronal (b) arterial phase CT images detected massive right kidney infarction: the complete parenchymal devascularization was due to main renal artery post-traumatic thrombotic occlusion (arrow in a), well demonstrated also in the oblique MIP reconstruction (arrow in c). Renal trauma was ranked as AAST V and interventional procedure of revascularization and stenting was performed. d) Subsequent follow-up CT examination showed a correct placement of the stent (arrow) and an almost recovered renal parenchymal enhancement with a small persistent hypoperfused cortical area (empty arrow).

In regard to collecting system injuries, not focused in this study because already included in the AAST injury scale, 6 cases were detected: five treated with ureteral stent and one with nephrectomy. The only delayed diagnosis was made at one month CT follow-up in a patient complaining hematuria and sense of heaviness on the affected side, with evidence of urinary contrast extravasation within a perirenal urinoma; the injury was missed on admission CT scan, that showed a voluminous perirenal hematoma and no evidence of urinary leakage (Fig. 10). Indeed, some authors describe cases of missed collecting system injuries concomitant to the presence of extensive hematoma and propose the hypothesis that large perinephric clots may exercise a tamponade effect on the site of the defect preventing contrast leakage on the pyelographic CT acquisition [3]. Besides, this results in a greater probability of delayed complications such as urinoma formation and superimposed infections, demonstrating the importance of imaging follow-up in such a renal trauma.

Fig. 10 CT examination of a 61 year-old female pedestrian struck by a car highlighted a deep parenchymal laceration of the middle-inferior third of the left kidney, associated to a very large perirenal hematoma. A round lesion as hyperdense as adjacent arteries in the arterial phase (arrow in a) and not increasing in size in the venous phase (arrow in b) corresponding to a pseudoaneurysm was found, and was successfully treated with angioembolization. c) Oblique MIP reconstruction did not evidence contrast extravasation consistent with collecting system injury in the pyelographic phase. d) One month follow-up CT, delayed acquisition: abundant urinary leakage within a voluminous perirenal urinoma (empty arrow).

In summary our study revealed that, in contradistinction to the CT evidence of active hemorrhage/pseudoaneurysm, the AAST grade does not statistically correlate with the need for surgical/endovascular therapy in patients with renal trauma. Its role as classification system and prognostic index is limited from the fact that active bleeding/PSA, important predictors of operative management, are not mentioned in the AAST scale and furthermore may occur both in low and high grade renal injuries. Thus, the AAST grading system can not be considered anymore an efficient measure of severity and a significant predictor of required intervention. It would be much better describe and refer to CT findings to manage renal trauma, as Mirvis et al. suggest in the CT-based classification used at the Maryland shock trauma center in Baltimore, that is composed of 4 grades in order of increasing severity and includes both active hemorrhage and pseudoaneurysmin grade IV [1, 15]. The radiologist should be especially focused on vascular and

urinary contrast material extravasation: once these are excluded, hemodynamically stable patients even in presence of a “shattered kidney” can be safely treated conservatively adopting an attendance strategy [9, 34-36].

Limitations of our work are the retrospective nature, the modest sample size and the only enrollment of blunt renal injuries; our data and results are anyway in agreement with the literature, also with recently published studies like that of Baghdanian et al [3].

Conclusion

The considerable improvement in imaging techniques, optimization of methodologies, and understanding of the natural history of renal trauma have contributed to remarkably reduce the rate of surgical treatment, as most injuries in hemodynamically stable patients can be safely handled with a conservative or mini-invasive management. MDCT features of renal trauma, combined with clinical criteria, have a fundamental role in taking the correct decisions to rescue the injured kidney. In particular, our study demonstrates the added value of vascular CT findings like active hemorrhage and pseudoaneurysm, that on one side represent a statistically significant predictor for the potential necessity of endovascular/surgical intervention, on the other side highlight the reduced effectiveness of the current AAST injury scale as a severity grading system and as a predictor of therapeutic management and clinical outcomes.

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