mdctof blunt renal trauma: imaging findings and ... · withother visceral injuries, with the...

PICTORIAL REVIEW

MDCTof blunt renal trauma: imaging findingsand therapeutic implications

M. Bonatti & F. Lombardo & N. Vezzali & G. Zamboni &F. Ferro & P. Pernter & A. Pycha & G. Bonatti

Received: 23 December 2014 /Revised: 13 January 2015 /Accepted: 20 January 2015 /Published online: 14 February 2015# The Author(s) 2015. This article is published with open access at Springerlink.com

AbstractObjectives To show the wide spectrum of computed tomog-raphy (CT) findings in blunt renal trauma and to correlatethem with consequent therapeutic implications.Methods This article is the result of a literature review and ourpersonal experience in a level II trauma centre. Here we de-scribe, discuss and illustrate the possible CT findings in bluntrenal trauma, and we correlate them with the American Asso-ciation for the Surgery of Trauma (AAST) classification andtheir therapeutic implications.Results CT findings following blunt renal trauma can begrouped into 15 main categories, 12 of them directly correlat-ed with the AAST classification and 3 of them not mentionedin it. Non-operative management, which includes the “watch-ful waiting” approach, endourological treatments andendovascular treatments, is nowadays widely adopted in bluntrenal trauma, and surgery is limited to haemodynamically un-stable patients and a minority of haemodynamically stablepatients.Conclusions The interpretation of CT findings in blunt renaltraumamay be improved andmade faster by the knowledge oftheir therapeutic consequences.

Teaching Points• The majority of blunt renal injuries do not require surgicaltreatment.

• CT findings in blunt renal injury must be evaluated consid-ering their therapeutic consequences.

• Some CT findings in blunt renal trauma are not included inthe AAST classification.

Keywords Acute renal injury . Blunt injury . Computedtomography . Kidney . Trauma

AbbreviationsAAST American Association for the Surgery of TraumaNOM Non-operative managementCT Computed tomographyMDCT Multidetector computed tomographyCEUS Contrast-enhanced ultrasoundMPR Multiplanar reconstructionMIP Maximum intensity projectionVR Volume renderingHU Hounsfield units

Introduction

Renal injuries represent a relatively common event, involving8–10 % of the patients admitted to an emergency departmentbecause of abdominal trauma, and the incidence is increasingparallel to the increase in motor-vehicle accidents [1–4]. In80–95% of the cases renal injuries occur in the setting of blunttrauma, as a result of a direct trauma to the back, flank, lowerthorax or upper abdomen or of a rapid deceleration, whereaspenetrating traumas are responsible for the remaining 5–20 %[3, 5–7]. Renal traumamay occur in isolation or in association

M. Bonatti (*) :N. Vezzali : F. Ferro : P. Pernter :G. BonattiDepartment of Radiology, Bolzano Central Hospital, 5 Boehler St.,39100 Bolzano, Italye-mail: [email protected]

F. Lombardo :G. ZamboniDepartment of Radiology, University of Verona, Piazzale L.A. Scuro10, 37134 Verona, Italy

A. PychaDepartment of Urology, Bolzano Central Hospital, 5 Boehler St.,39100 Bolzano, Italy

Insights Imaging (2015) 6:261–272DOI 10.1007/s13244-015-0385-1

with other visceral injuries, with the majority of isolated renalinjuries represented by low-grade lesions [8–10].

Although gross haematuria is the typical presenting symp-tom of renal injury, it may be absent in about 5 % of renalinjuries, and its presence is not directly correlated with injuryseverity: for example, haematuria is typically absent in vascu-lar pedicle injuries and ureteral-pelvic injuries [11, 12].

According to the American Association for the Surgery ofTrauma (AAST), on the basis of surgical findings renal inju-ries can be subdivided into fivemain categories (Table 1), witha progressively poorer prognosis [13]. The suggested treat-ment options, according to the AAST injury grade, in haemo-dynamically stable patients affected by renal injuries are re-ported in Table 2. In the past decades, the indications forsurgical treatment of renal trauma have progressively de-creased with a consequent drastic reduction in nephrectomyrates, and, nowadays, non-operative management (NOM),which includes the simple watchful waiting (Bwait-and-see^)strategy, endovascular treatments and endourological treat-ments, can be considered the most appropriate first line ap-proach for about 90–95 % of renal injuries [14–20]. On theother hand, renal exploration remains mandatory in every caseof haemodynamic instability following renal trauma and if apulsatile or expanding retroperitoneal haematoma is identifiedduring exploratory laparotomy performed for other abdominalinjuries.

Indications for renal imaging and imaging modalities

In case of blunt thoraco-abdominal trauma, a clear distinctionmust be made between haemodynamically unstable and hae-modynamically stable or stabilised patients; indeed, the

former must immediately undergo surgical exploration in or-der to try to improve their outcome, whereas the latter shouldundergo imaging studies in order to better assess the presenceof visceral injuries and guide treatment. Although some con-troversies still exist, in haemodynamically stable (orstabilised) patients who have suffered blunt thoracic and/orabdominal trauma, absolute indications for imaging in thesuspicion of renal injuries are gross haematuria, microscopichaematuria associated with hypotension, suspicion of majorinjuries to other viscera and trauma dynamics strongly associ-ated with renal injury (i.e., rapid deceleration, fall from greatheight and direct contusion to the flank) [3, 5].

Several different imaging techniques have been consideredas the initial imaging tool in the suspicion of renal injury inhaemodynamically stable patients; nowadays, however,thanks to its wide availability, reproducibility, scan speedand high spatial resolution, contrast-enhanced multidetectorcomputed tomography (MDCT) is considered the gold stan-dard imaging modality in case of suspicion of renal injury andhas completely replaced intravenous urography for this pur-pose [3, 5, 21–24]. The great advantage of MDCT is its abilityto assess, in an extremely rapid scanning time, the presence oflesions of the parenchyma, vessels and collecting system andof injuries to other abdominal organs.

MDCTof renal trauma: technique and protocols

Multidetector CT systems are nowadays ubiquitously avail-able in trauma centres and represent the minimum requirementfor emergency renal imaging. The availability of modern scan-ners with a high number of detector rows (16 or more) enablesshortening acquisition times, therefore reducing the possibilityof motion artefacts and increasing image quality.

A correct positioning of the patient on the CT table repre-sents a fundamental prerequisite for performing high-qualityMDCT studies. Whenever possible, the patient should laysupine on the table, with the arms bent over the head in order

Table 1 American Association for the Surgery of Trauma (AAST)classification of renal trauma

Grade Type Description

I ParenchymaHaematoma

Microscopic or gross haematuria withnormal urologic studies (contusion)

Non-expanding subcapsular haematoma

II ParenchymaHaematoma

Laceration <1 cm in depth, withoutcollecting system rupture

Non-expanding perirenal haematomaconfined to retroperitoneum

III Parenchyma Laceration >1 cm in depth withoutcollecting system rupture

IV ParenchymaVascular

Laceration with collecting system ruptureMain renal artery/vein injury withcontained haemorrhage

V ParenchymaVascular

Shattered kidneyAvulsion of renal hilum thatdevascularises kidney

Table 2 Treatment options in haemodynamically stable patientsaffected by renal injury (according to the AAST classification)

Grade Type Treatment

I-III Every NOM wait and see

IV ParenchymaVascular

NOM endourologicalDebated, surgical vs. NOM interventionalradiological

V ParenchymaVascular

Debated, NOM is increasingly adoptedSurgical. NOM endourological in case ofpartial pielo-uretheral lacerations

??? Vascular NOM interventional radiological

NOM non-operative management, ??? = lesions not included in theAAST classification

262 Insights Imaging (2015) 6:261–272

to prevent beam-hardening artefacts; if that position cannot beobtained, the patient’s arms should be placed flexed on a largepillow ventrally to the patient’s chest [25]. Moreover, all themedical devices that are not strictly necessary should be re-moved from the scan area.

The MDCT scanning protocol in the setting of suspectedrenal trauma should always be always tailored according tothe clinical conditions of the patient. Most authors sustain thata non-enhanced acquisition should always be performed inorder to detect intraparenchymal, subcapsular or perinephrichaematomas, which will appear as slightly hyperattenuatingareas or collections during this phase, whereas they might bebarely recognisable on post-contrast images [26–28]. Accord-ing to our experience, however, the performance of nativescans is not necessary in the setting of renal trauma for tworeasons: first, the large majority of the above-mentioned le-sions are clearly recognisable also on post-contrast images;second, those lesions that might eventually be missed (i.e.,small intraparenchymal or subcapsular haematomas) do nothave any therapeutic consequences. In any case, when acquir-ing post-contrast images using a dual-energy technique, virtu-al non-enhanced images may be retrospectively generatedfrom post-contrast ones by means of commercially availablesoftware and show similar accuracy to true non-contrast onesfor the detection of haematomas [29].

On the other hand, post-contrast acquisitions must alwaysbe performed in case of suspicion of renal injuries. About 1.7–1.5 ml/kg of 350–370 mgI/ml iodinated contrast material mustbe administered using a flow rate of at least 3.5 ml/s, followedby a 50-ml saline flush. Contrast-enhanced scans should beacquired cranio-caudally, with thin collimation (0.625 mm).Multi-planar reformats (MPR), maximum intensity projection(MIP) and volume-rendering (VR) reconstructions representextremely useful tools for imaging interpretation. Accordingto the wide variability of circulatory conditions in trauma pa-tients, post-contrast scans should be always performed using abolus-tracking technique. A late arterial/corticomedullaryphase acquisition should be acquired with a 15-s delay froma 100-HU peak aortic enhancement when using a bolus-tracking technique or with a 30-s fixed delay after injectionif bolus-tracking is not available; this phase is mandatory forrecognising arterial vascular lesions (i.e., renal artery avulsionor thrombosis, pseudoaneurysms and artero-venous fistulae)and for detecting active arterial contrast material extravasa-tion; moreover, it enables to accurately depict the arterial vas-cular anatomy and eventual variants. The portal-venous ornephrographic phase, acquired 70-80 s after the start of con-trast material injection, represents the best phase for detectingparenchymal lesions (i.e., lacerations and segmental infarc-tions), venous vascular lesions (i.e., avulsion or thrombosisof the renal vein) and haematomas and should be always per-formed in case of suspicion of renal injury; moreover, it rep-resents a useful aid for assessing the relevance of an active

arterial contrast material extravasation and enables accuratelyruling out injuries to other parenchymatous abdominal organs.The decision to acquire a delayed excretory scan is strictlydependent on the patient’s clinical conditions and the findingsin the previous phases. The timing of the delayed acquisitiondepends on renal function and may vary from 5 to 15 or moreminutes; 8 min may represent a good compromise in the ma-jority of the cases. Delayed acquisitions are fundamental forthe detection of collecting system injuries, by showinghyperdense urine extravasation, and may also help in the dif-ferential diagnosis between renal contusion and infarction [3].

MDCT findings and therapeutic consequences

MDCT can generate a wide spectrum of findings in renaltrauma and the majority of these can be easily categorised intothe above-mentioned five AAST grades; moreover, MDCTmay also show some findings that are not mentioned in theAAST classification, the latter being based on the kidney ap-pearance at surgery. The AAST classification must be kept inmind when reporting renal injuries, particularly because of itsprognostic implications; in any case, subtle differences inAAST grade do often not have practical consequences forpatient management. In the following paragraphs we will de-scribe the possible MDCT findings in renal trauma groupedby their therapeutical management and not simply by theAAST grading scale.

Non-operative management: Bwait-and-see^

& Parenchymal contusion (AAST grade I). Parenchymalcontusions (Fig. 1a–b) appear as ill-defined, irregularlyshaped areas of decreased and delayed contrast enhance-ment within the renal parenchyma. On non-enhanced im-ages their density varies according to the time elapsedfrom the traumatic event, the patient’s haematocrit andthe coagulation status: typically they appear isoattenuatingto the adjacent cortex, but hyperattenuation may also beobserved if blood clots are present. The corticomedullaryphase is not useful for identifying renal contusions be-cause of the physiological heterogeneity of parenchymalenhancement. On the other hand, in the majority of thecases renal contusions are clearly recognisable during thenephrographic phase in which they usually appear slightlyhypodense in comparison to the adjacent parenchyma;however, a substantial isodensity might be found if bloodclots are present. On delayed acquisitions, contusionsshow persistent contrast retention, and this characteristicmay be helpful for differentiating them from renal infarc-tions (Fig. 1c–d) that remain hypodense. A simple Bwait-and-see^ management is indicated in case of renal

Insights Imaging (2015) 6:261–272 263

contusions, and no follow-up imaging studies are requiredif the clinical and laboratory data remain stable [30–32].

& Subcapsular haematoma (AAST grade I). Subcapsularhaematoma (Fig. 2a–b) appears as a well-delimited, non-enhancing fluid collection located between the renal

parenchyma and the renal capsule. Depending on its size,the collection may show a crescent or a biconvex shape; inthe latter case, a mass effect is usually exerted on theadjacent parenchyma, which may become flattened or in-dented. The attenuation of the collection varies according

Fig. 1 a–d Renal contusion(AAST grade I) (a and b) andrenal infarction (AAST grade IV)(c and d). Axial multiplanarreconstruction (MPR) images(1.5 mm thick a and b; 3 mmthick c and d) acquired during thenephrographic phase (a and c)and the 8-min delayed phase(b and d) of the study in twodifferent patients. Renalcontusion appears as an ill-defined, irregularly shaped area ofreduced contrast enhancementduring the nephrographic phase(a, arrowhead) and tends toisodensity in the delayed phase(b, arrowhead), whereassegmental infarction appears as awedge-shaped, sharply definedarea of reduced/absent contrastenhancement during thenephrographic phase (c, arrow)and shows marked hypodensityalso in the delayed phase (d,arrow)

Fig. 2 a–b Subcapsular haematoma (AAST grade I) (a) and perirenalhaematoma (AAST grade II) (b). The 3-mm-thick multiplanarreconstruction (MPR) coronal image (a) acquired during the delayedphase of the study shows a well-delimited hypodense biconvex-shapedcollection (star), located between the renal parenchyma and renal capsule,which determines the mild mass effect on the adjacent parenchyma(arrowheads), representing subcapsular haematoma. A similar finding

may also be observed in the 3-mm-thick multiplanar reconstruction(MPR) axial image (b) acquired during the nephrographic phase inanother patient in which, however, an irregularly delimitedinhomogenously hypodense collection, representing perirenalhaematoma (arrowheads), is appreciable between the renal parenchymaand the Gerota fascia. In both cases neither parenchymal lacerations noractive contrast material extravasations can be observed


to its age, and hyperdensity may be seen if blood clots arepresent. To be classified as a grade I lesion, a subcapsularhaematoma must not be associated with parenchymal lac-erations and no active contrast material extravasationshould be observed; indeed, subcapsular haematomas areoften associated with higher grade parenchymal lesions.Moreover, if a capsular lesion coexists, the haematomaoften extends to the perirenal space (Fig. 2b). A simpleBwait-and-see^ management is indicated in case of sub-capsular haematoma, and no follow-up imaging studiesare required if the clinical and laboratory data remain sta-ble [30–32].

& Perirenal haematoma (AAST grade II). Perirenalhaematoma (Fig. 2b) appears as a poorly delimited, non-enhancing fluid collection located in the fatty area be-tween the renal capsule and Gerota fascia. Its attenuationvaries according to the age, appearing inhomogenouslyhyperattenuating in the acute/subacute stage and becom-ing progressively iso- or hypoattenuating in the chronicstage. Perirenal haematoma usually does not cause a masseffect on the adjacent renal parenchyma, but largehaematomas may displace the kidney and nearby boweland may also cross the midline, ventrally to the aorta andinferior vena cava, invading the contralateral perirenalspace. An extension to the pelvis may also be observedin large perirenal haematomas. Although perirenalhaematomas may represent isolated lesions, in most casesthey are associated with parenchymal lacerations and thepresence of opacified urine extravasation must be accu-rately ruled out by means of delayed scans. Moreover,particular attention must be paid to collections locatedmedially to the renal hilum: in these cases, the presenceof vascular pedicle and uretero-pelvic junction lesionsmust be ruled out accurately. The tiny perinephric strandsthat may be observed in patients with impaired renal func-tion should not be misdiagnosed as perirenal haematomas:indeed, these strands are homogeneously hypodense, bi-lateral and surround the entire kidneys. In case of isolatedperirenal haematomas, a simple Bwait-and-see^ manage-ment is indicated and no follow-up imaging studies arerequired if the clinical and laboratory data remain stable[30–32].

& Parenchymal laceration not involving the collectingsystem (AAST grade II-III): Parenchymal lacerations(Fig. 3a–b) appear as irregular or linear clefts of absentcontrast enhancement, starting from the renal surface andextending deep into the renal parenchyma, and they arebest depicted during the nephrographic phase. Their atten-uation varies according to their age and the presence ofblood clots, and they are usually associated with perirenalhaematomas. If a parenchymal laceration is present, de-layed acquisitions should be performed in order to rule outurine extravasation (Fig. 3b). Moreover, it is extremely

important to exclude the presence of active contrast mate-rial extravasation. The AAST subdivides parenchymallacerations into grade II if they extend less than 1 cm indepth and grade III if they extend more than 1 cm; in anycase, there is no difference in the treatment of grade II andIII lesions, which must follow the simple Bwait-and-see^management. No follow-up imaging studies are requiredif the clinical and laboratory data remain stable [30–32].

& Segmental infarction (AAST grade IV). Segmental infarc-tions (Fig. 1c–d) appear as sharply demarcated,wedge-shaped areas of absent contrast enhancement,showing a subcapsular basis and apex directed to thehilum, and are the consequence of dissection and/orthrombosis of segmental vessels. Sharp margins andlack of enhancement during the delayed phase arethe characteristics that must be identified in orderto perform a differential diagnosis with renal contu-sions (Fig. 1a–b). The coexistence of multiple in-farctions is quite frequent. A simple Bwait-and-see^management is indicated in the majority of cases,whereas surgical debridement is indicated in caseof infarctions involving more than 50 % of the renalparenchyma. No follow-up imaging studies are re-quired if the clinical and laboratory data remain sta-ble [30–32], whereas a CT scan is mandatory in caseof pain development in order to exclude colliquationor abscess formation, findings that imply surgicalexploration.

& BShattered kidney^ (AAST grade V). The term Bshatteredkidney^ is used to describe a kidney ruptured in mul-tiple fragments by severe and deep lacerations(Fig. 4a–b). Renal fragments are usually surroundedand subdivided by a fluid collection that occupies theentire renal loggia; some parenchymal fragments mayappear devitalised or non-enhancing because of trau-matic occlusion of their arterial supply. Particular at-tention must be paid to excluding the presence ofactive contrast material extravasation and urine leak-age: indeed, if these are ruled out, an increasing num-ber of reports suggest that haemodynamically stablepatients can be safely treated conservatively bymeans of a simple Bwait-and-see^ treatment, whereassurgical exploration should be reserved for haemody-namically unstable patients and endovascular and/orendourological treatments for patients showing bloodand/or urine extravasation [16, 17, 20, 33–38]. Dueto the severity of the injury, follow-up CT studiesmight represent a reasonable option in these patients,also in case of clinical and laboratory stability, inparticular in order to detect vascular complicationsearly, such as pseudoaneurysms and artero-venousfistulae, which might have life-threatening effects inan acute setting.


Non-operative management: endourological treatment

& Parenchymal laceration involving the collecting system(AAST grade IV). Parenchymal lacerations involving thecollecting system (Fig. 5a–b) extend deep into the medullaand are univocally associated with perirenal fluid collec-tions secondary to blood and urine accumulation. Urineextravasation can be highlighted during the delayed phaseof the study as markedly hyperdense material within theperirenal haematoma (Fig. 5b). Ureteral stenting is thetreatment of choice in collecting system injuries and atleast one follow-up CT examination is indicated in orderto assess the evolution of the urinoma and to detect

eventual complications early, such as superinfection; at-tention must be paid to the proximal extremity of the JJcatheter, which should be located within the uppercalyceal group in order to maximise its effectiveness inurine drainage.

& Ureteropelvic junction laceration (AAST grade V).Ureteropelvic junction laceration (Fig. 6a–b) is usually aconsequence of fast deceleration traumas and is associatedwith a large perirenal fluid collection, mostly located me-dially to the renal hilum and often extending caudally overthe psoas. Renal contrast material excretion is normal andthe calyceal system is usually intact, while hyperdenseurine extravasation can be highlighted in the delayed

Fig. 4 a–b Shattered kidney (AAST grade V). The 3-mm-thickmultiplanar reconstruction (MPR) coronal image (a) acquired during thenephrographic phase of the study shows a large inhomogenouslyhypodense collection occupying the renal and perirenal spaces withmultiple vascularised kidney fragments within, representing a so-called

shattered kidney. On the 10-mm-thick para-coronal maximum intensityprojection (MIP) of the same series (b), the main branches of the rightrenal artery (arrowheads) can be accurately delimited and no activecontrast material extravasation can be observed

Fig. 3 a–b Parenchymal laceration not involving the collecting system(AAST grade II–III). On these 3-mm-thick multiplanar reconstruction(MPR) axial images acquired during the nephrographic (a) and 8-mindelayed phase (b) of the study in the same patient, a linear cleft ofabsent contrast enhancement (arrow) starting from the renal surface and

extending deep into the renal parenchyma is clearly appreciable,representing parenchymal laceration. On delayed image (b), no lack ofhyperdense urine can be seen, excluding collecting system rupture. Aperirenal haematoma (star) coexists posteriorly to the kidney


phase at the renal hilum. Ureteropelvic junction avulsion,which otherwise shows the same CT findings (Fig. 6c–d),can be excluded if hyperdense urine is seen in the down-stream ureter (Fig. 6b). Ureteral stenting is the treatment ofchoice for ureteropelvic junction laceration, and at leastone follow-up CT examination is indicated in order toassess urinoma evolution and detect any complicationsearly; attention must be paid to the proximal extremity

of the JJ catheter, which should be located within the up-per calyceal group.

Non-operative management: interventional radiology

& Active contrast material extravasation from branching re-nal arteries (not included in the AAST classification).

Fig. 5 a–b Parenchymal laceration involving the collecting system(AAST grade IV). On these 3-mm-thick multiplanar reconstruction(MPR) axial images acquired during the nephrographic (a) and 8-mindelayed phase (b) of the study in the same patient, multiple irregularclefts of absent contrast enhancement (arrows), starting from the renal

surface and extending deep into the renal parenchyma, are clearlyappreciable, representing parenchymal lacerations. On delayed image(b), hyperdense urine leakage (arrowhead) is recognisable as a sign ofcollecting system rupture

Fig. 6 a–d Laceration of theureteropelvic junction (a and b)and avulsion of the ureteropelvicjunction (c and d) (AAST grade Vboth). On the 3-mm-thickmultiplanar reconstruction (MPR)axial images acquired during thedelayed phase of the study in twodifferent patients (a and c) ahyperdense urine leakage can beobserved medially to the kidneyhilum (arrowheads), a findingsuspicious for a ureteropelvicjunction lesion. The volume-rendering technique (VRT)reconstructions of the same series(b and d) show that, in the firstcase (b), the downstream ureter isopacified by hyperdense urine,therefore excluding a completeureteropelvic disconnection,whereas in the second case (d), noopacified urine can be observed inthe downstream ureter, indicatingtherefore a complete ureteropelvicavulsion


Active contrast material extravasation from peripheral ar-terial branches (Fig. 7a–b) is not directly mentioned in theAAST classification of renal trauma. At CT, small arterialbleedings appear as poorly delimited contrast material ex-travasations, sometimes flame-shaped, usually located inthe setting of a perirenal haematoma, that appearhyperdense in the arterial phase and increase in quantityand density in the following phases. Active arterial con-trast material extravasation is often associated with high-grade parenchymal lesions, but occasionally it may alsooccur in low-grade ones. Non-operative management isindicated in haemodynamically stable patients if no otherlesions requiring surgery are detected at CT, and digitalsubtraction angiography with superselective arterial em-bolisation represents the treatment of choice [39, 40];angioembolisation might be avoided in patients with smallperirenal haematomas and minimal signs of active bleed-ing [41]. A CT follow-up should be considered afterangioembolisation in order to detect eventual complica-tions, such as pseudoaneurysms and large ischaemicevents.

& Arterial pseudoaneurysm (not included in the AASTclassification). Arterial pseudoaneurysm (Fig. 8a–b) ap-pears as a well-delimited ovoid lesion located within therenal parenchyma, enhancing as much as the adjacent ar-teries during the arterial phase and not increasing in size ordensity during the subsequent phases in which, indeed, itbecomes isoattenuating to the blood pool; these character-istics enable a differential diagnosis with active contrastmaterial extravasation. Digital subtraction angiography(Fig. 8c) with superselective arterial embolisation repre-sents the treatment of choice in order to prevent delayedrupture; surgery may be limited to the few cases in which

haemostasis and arterial wall defect repair are required[42].

& Artero-venous fistula (not included in the AASTclassification). Artero-venous fistulae (Fig. 8d–e) usu-ally have the same CT appearance as arterialpseudoaneurysms. An important finding that enablesthe differential diagnosis between the two lesions is theidentification of a dilated renal vein that enhances earlyduring the arterial phase of the study; anyway, a true arte-rial phase should be acquired in order to appreciate thisfinding that might be obscured by the physiological ve-nous return during the corticomedullary phase. Digitalsubtraction angiography (Fig. 8f) with superselective arte-rial embolisation represents the treatment of choice in or-der to prevent delayed rupture and arterial hypertensiondevelopment.

Surgical management

& Avulsion of the main renal artery or vein (AAST grade V).Avulsions of the main renal artery or vein (Fig. 9a–b)represent extremely dangerous lesions that, in the majorityof cases, preclude the patient to undergo CT because ofhaemodynamic instability. Both lesions are associatedwith large perirenal haematomas, prevalently located me-dially to the renal hilum, with abundant contrast materialextravasation between the kidney and the aorta in the ar-terial and/or portal venous phase. Renal artery avulsion inthe majority of the cases results in a completely or at leastlargely devascularised kidney, whereas in case of renalvein avulsion renal enhancement is usually delayed andreduced, but uniformly present. Vascular pedicle avulsion

Fig. 7 a–b Active arterial contrast extravasation from a capsular artery(lesion not included in the AAST classification). On these 3-mm-thickmultiplanar reconstruction (MPR) axial images acquired during thearterial (a) and nephrographic (b) phases of the study in the samepatient, a large perirenal haematoma (star) determining a ventral

dislocation of the kidney is clearly recognisable. No parenchymallacerations can be observed, but an active contrast materialextravasation (arrow) is recognisable within the haematoma during thearterial phase, showing a mild increase in size during the nephrographicphase as a consequence of a capsular artery rupture


represents a life-threatening emergency: no delayed CTscans must be performed and immediate surgical explora-tion is mandatory.

& Avulsion of the ureteropelvic junction (AAST grade V). CTfindings in case of complete ureteropelvic junction tran-section (Fig. 6c–d) are the same as in case of ureteropelvic

Fig. 9 a–bMain renal vein laceration (AAST grade V). On these 3-mm-thick multiplanar reconstruction (MPR) axial images acquired during thearterial (a) and nephrographic (b) phases of the study in the same patient,a large perirenal-pararenal haematoma (star) is recognisable medially-

ventrally to the kidney. No active contrast material extravasation can beobserved during the arterial phase of the study, whereas a large contrastmaterial extravasation (arrow) appears ventrally to the renal vein in thesubsequent nephrographic phase, representing renal vein laceration

Fig. 8 a–f Arterial pseudoaneurysm and artero-venous fistula (lesionsnot included in the AAST classification). On the 3-mm-thickmultiplanar reconstruction (MPR) axial images acquired during thearterial (a and d) and nephrographic (b and e) phases of the study intwo different patients, a well-delimited oval lesion (arrowheads in thefirst patient and arrows in the second one) with a density that varies

parallel to the density of the arterial vessels is clearly recognisable.Digital subtraction angiography characterised these lesions as an arterialpseudoaneurysm in the first patient (c) and as an artero-venous fistula inthe second one (f) in which an early venous output (arrowheads) wasrecognisable


junction laceration, with the only important difference acomplete absence of opacified urine in the downstreamureter (Fig. 6d). Differently than in case of ureteropelvicjunction laceration, ureteropelvic junction avulsion re-quires surgical repair because endourological treatmentsare usually ineffective.

Debated management

& Thrombosis of the main renal artery or vein (AAST gradeIV). Arterial thrombosis is usually secondary to traumaticdissection of the main renal artery (Fig. 10a–c), and theresulting occlusion may be complete or partial; conse-quently, the kidneymay appear completely devascularisedor hypovascularised. The thrombus, when detectable, ap-pears as an endovascular filling defect, hyperdense onnon-enhanced images and hypodense in post-contrastscans. Main renal vein thrombosis is rare and causes de-layed enhancement of the kidney in comparison with con-tralateral renal enlargement and parenchymal oedema.Management of these injuries is extremely controversial:in particular, in case of renal artery dissection both surgicaland endovascular revascularisations (Fig. 10b–c) haveshown good results [43, 44] and the treatment optionshould be determined according to the centre’s experience.Anyway, in case of complete arterial occlusion the 2-htime limit for revascularisation must be considered: in-deed, after 2 h of complete renal ischaemia also a goodtechnical result will bring a poor functional outcome.Nephrectomy is always recommended if conservativetreatments fail [45].

& Injuries to the main renal artery or vein with a containedhaematoma or partial vessel laceration (AAST grade IV).This type of injury manifests with the presence of aperirenal haematoma associated with active arterial or ve-nous bleeding from hilar vessels (Fig. 11). Thehaematoma is usually located medially to the renal hilumand may extend caudally along the psoas; the kidney isoften displaced laterally. Both surgical and endovasculartreatments may be considered, also according to the

Fig. 10 a–c Main renal artery dissection/thrombosis. The 10-mm-thickmaximum intensity projection (MIP) axial image acquired during thearterial phase of the study (a) shows a hypovascularised right kidney asa consequence of renal artery dissection (arrow). The finding was

confirmed at subsequent digital subtraction angiography (b, arrow) inwhich a residual flow was appreciable downstream from the dissection;a stent was placed (c, arrowheads) with good flow recovery

Fig. 11 Main renal artery laceration (AAST grade IV). On this 3-mm-thick multiplanar reconstruction (MPR) axial image acquired during thearterial (a) phase of the study, a large contrast material extravasation canbe observed adjacent to the right renal artery (arrow) as a consequence ofrenal artery laceration; to notice, the markedly reduced diameter of theaorta (star) as a consequence of the haemodynamic shock status.Moreover, the right renal parenchyma shows a large well-definedhypodense area (arrowheads), representing renal infarction


centre’s experience, with the latter associated with lowernephrectomy rates [16].

Conclusions

In case of renal trauma, MDCT can generate a wide spectrumof findings that a radiologist must be able to recognise in orderto correctly direct traumamanagement and allow accurate riskstratification. Anyway, it is important to notice that, in theemergency setting, the differentiation between AAST grade1, 2 and 3 renal injuries does not result in a change in patientmanagement, the Bwait-and-see^ approach being the most in-dicated in all cases of haemodynamic stability. On the otherhand, AAST grade 4 and 5 lesions must be promptlyrecognised and communicated to the clinician because theywill shift the treatment to an endourological, endovascular orsurgical one; indeed, the simple Bwait-and-see^ managementmay be considered only in case of segmental infarctions in-volving less than 50 % of the renal parenchyma and ofshattered kidney without urine or active blood extravasation.Moreover, CT may highlight some peripheral vascular lesions(i.e., active bleedings, pseudoaneurysms and artero-venousfistulae) that are not directly mentioned in the AAST classifi-cation, but that must be accurately recognised because ofrequiring, in the majority of the cases, an endovascularinterventional approach.

Open Access This article is distributed under the terms of the CreativeCommons Attribution License which permits any use, distribution, andreproduction in any medium, provided the original author(s) and thesource are credited.

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