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EDUCATION EXHIBIT 557

Imaging of RenalTrauma: A Comprehen-sive Review1

LEARNINGOBJECTIVESFOR TEST 1After reading thisarticle and takingthe test, the reader

will be able to:

� Describe the spec-trum of posttrau-matic renal injuries.

� Identify the keyimaging features oftrauma-related renalinjury.

� Correlate the clini-cal and imaging find-ings in renal trauma.

Akira Kawashima, MD ● Carl M. Sandler, MD ● Frank M. Corl, MSO. Clark West, MD ● Eric P. Tamm, MD ● Elliot K. Fishman, MDStanford M. Goldman, MD

Computed tomography (CT) is the modality of choice in the evalua-tion of blunt renal injury. Intravenous urography is used primarily forgross assessment of renal function in hemodynamically unstable pa-tients. Selective renal arteriography or venography can provide detailedinformation regarding vascular injury. Retrograde pyelography is valu-able in assessing ureteral and renal pelvic integrity in suspected ure-teropelvic junction injury. Ultrasonography is useful in detecting he-moperitoneum in patients with suspected intraperitoneal injury but haslimited value in evaluating those with suspected extraperitoneal injury.Occasionally, radionuclide renal scintigraphy or magnetic resonanceimaging may prove helpful. Renal injuries can be classified into fourlarge categories based on imaging findings. Category I renal injuriesinclude minor cortical contusion, subcapsular hematoma, minor lac-eration with limited perinephric hematoma, and small cortical infarct.Category II lesions include major renal lacerations extending to themedulla with or without involvement of the collecting system and seg-mental renal infarct. Category III lesions are catastrophic renal injuriesand include multiple renal lacerations and vascular injury involving therenal pedicle. Category IV injuries are ureteropelvic junction injuries.CT is particularly useful in evaluating traumatic injuries to kidneyswith preexisting abnormalities and can help assess the extent of pen-etrating injuries in selected patients with limited posterior stab wounds.Integration of the imaging findings in renal injury with clinical informa-tion is critical in developing a treatment plan.

Index terms: Kidney, CT, 81.1211 ● Kidney, infarction, 81.77 ● Kidney, injuries, 81.41, 81.77 ● Renal angiography, 81.124 ● Renal arteries, injuries,961.41 ● Trauma, 81.40

RadioGraphics 2001; 21:557–574

1From the Departments of Radiology (A.K., C.M.S., O.C.W., E.P.T., S.M.G.) and Urology (C.M.S., S.M.G.), University of Texas-Houston MedicalSchool, Houston, Tex; the Department of Radiology, Memorial Hermann Hospital, Houston, Tex (A.K., C.M.S., O.C.W., E.P.T., S.M.G.); the Depart-ment of Radiology, Lyndon B. Johnson General Hospital, Houston, Tex (A.K., C.M.S., E.P.T.); and the Russell H. Morgan Department of Radiology andRadiological Science, Johns Hopkins Medical Institutions, Baltimore, Md (F.M.C., E.K.F.). Recipient of a Certificate of Merit award for a scientific exhibitat the 1999 RSNA scientific assembly. Received June 20, 2000; revision requested July 13 and received August 21; accepted August 22. Address corre-spondence to A.K., Department of Radiology, Mayo Clinic, 200 First St SW, Rochester, MN 55905 (e-mail: [email protected]).

©RSNA, 2001

CME FEATURESee accompanying

test at http://www.rsna.org

/education/rg_cme.html

IntroductionInjury to the kidney is seen in approximately 8%–10% of patients with blunt or penetrating ab-dominal injuries (1). The vast majority (80%–90%) of cases involve blunt rather than penetrat-ing injury (1). Serious renal injuries are frequentlyassociated with injuries to other organs; multior-gan involvement occurs in 80% of patients withpenetrating trauma and in 75% of those withblunt trauma (2,3). The vast majority (98%) ofisolated renal injuries are classified as minor inju-ries (4).

In this article, we describe the indications forradiologic assessment of renal injury and the rolethat various imaging modalities (computed to-mography [CT], intravenous urography, angiog-raphy, retrograde pyelography, ultrasonography[US], radionuclide renal scintigraphy, magneticresonance [MR] imaging) play in patient treat-ment. In addition, we describe a radiologic classi-fication system for renal injuries following blunttrauma with an emphasis on CT findings. Wealso discuss and illustrate penetrating renal injury,traumatic injuries to kidneys with preexisting ab-normalities, and urologic complications in renalinjury.

Indications for Imaging EvaluationIn general, hematuria (�5 red blood cells perhigh-power field) is present in over 95% of pa-tients who sustain renal trauma (1). However, theabsence of hematuria does not preclude signifi-cant renal injury; its absence has been reported inup to 24% of patients with thrombosis of the re-nal artery (5) and in one-third of cases of uretero-pelvic junction injury (6). In a study conducted torefine the indications for radiologic assessment,Nicolaisen et al (7) found major renal injuries atintravenous urography in 23 of 85 consecutivepatients with hematuria and shock; there were nomajor renal injuries in 221 consecutive patientswith microscopic hematuria and no shock. Simi-lar results have been reported at other institutions(4,8,9). At our institutions, radiographic evalua-tion of the urinary tract is performed in patientswith penetrating injury and hematuria, blunttrauma if associated with gross hematuria, micro-scopic hematuria and hypotension (blood pres-sure �90 mm Hg at any time during the evalua-tion), or microscopic hematuria and significantassociated injuries (9,10). Radiologic investiga-tion of the kidney is also warranted after blunttrauma in patients with other injuries known to be

associated with renal injury (eg, direct contusionor hematoma of flank soft tissues; fractures of thelower ribs, transverse processes, or thoracolumbarspine) (9). Children with blunt trauma and hema-turia should undergo renal imaging regardless ofblood pressure or degree of hematuria (1,11).

Imaging Modalities

Computed TomographyCT has replaced intravenous urography as theprimary modality for the assessment of suspectedrenal injuries. CT is more sensitive and specificthan urography in the detection and characteriza-tion of suspected renal injury (8,12–14) and hasbecome the imaging method of choice for the as-sessment of blunt abdominal injuries in majortrauma centers in the Unites States (10). CT canprovide precise delineation of a renal laceration,help determine the presence and location of a re-nal hematoma with or without active arterial ex-travasation, and indicate the presence of urinaryextravasation or of devascularized segments ofrenal parenchyma. Most important, CT can helpdifferentiate trivial injuries from those requiringintervention.

Early and delayed CT scans through the kid-neys are necessary. The preferred technique con-sists of helical CT performed from the dome ofthe diaphragm 70 seconds after the initiation ofintravenous administration of 150 mL of 60%nonionic iodinated contrast material with a me-chanical power injector at an injection rate of2.0–2.5 mL/sec. Scanning parameters include acollimation of 7 mm, a pitch of 1.3, and imagereconstruction intervals of 7 mm. This scan delayallows optimal vascular enhancement, whichhelps identify severe injuries to the liver andspleen such as active bleeding (15–17). This pro-tocol typically results in the kidneys beingscanned approximately 80 seconds after the ini-tiation of contrast material injection, during thelate cortical or early homogeneous nephrographicphase. Optimal contrast material enhancementcan also be achieved with use of an optional soft-ware upgrade (SmartPrep; GE Medical Systems,Milwaukee, Wis), which allows visual monitoringof the time–contrast material enhancement track-ing curve by means of a series of low-milliamper-age scans and region-of-interest attenuation mea-surements (18). Excretory-phase contrast mate-rial–enhanced CT through the kidneys performed3 or more minutes after initiation of contrast ma-terial administration is necessary for completeassessment of a suspected renal injury so that acollecting system injury will not be overlooked(Fig 1) (19).

558 May-June 2001 RG f Volume 21 ● Number 3

Helical CT continues to evolve with the intro-duction of the new-generation scanners. With thedevelopment of a subsecond scanner and themore recent production of the multidetector arrayscanner, a larger area can be covered with similarcollimation. Motion artifacts can be minimizedwith the shorter acquisition time. When multide-tector array techniques are used, collimation canbe retrospectively changed. Faster scanning tech-niques can optimize the timing of renal imagingduring a given phase of contrast material excre-tion. We used a multidetector helical scanner(QX/i LightSpeed, GE Medical Systems) with thefollowing parameters: 4 � 5.0-mm detector con-figurations, 3.0 pitch, 15.0-cm/sec table speed,and 7.5-mm section thickness. Image reconstruc-tion at 5-mm intervals can be performed retro-spectively when vascular injury is suspected. Mul-tiplanar reformatted and three-dimensional im-ages generated from axial source images canprovide a great deal of additional information.

Intravenous UrographyAlthough urography is no longer the primary mo-dality for the assessment of suspected renal inju-ries, in situations in which there would be a sig-nificant delay in obtaining high-quality CT scans,high-dose intravenous urography with nephroto-mography can be performed for renal assessment(7,11). When urographic findings are abnormal,however, CT is necessary to help determine thenature and extent of a parenchymal injury.

The primary role for intravenous urography isthe assessment of gross function and the evalua-tion of the uninjured kidney in hemodynamicallyunstable patients (7). Limited intravenous urog-raphy (“one-shot intravenous pyelography”) canbe performed in patients who are brought to atrauma room in the emergency department andmay be too unstable to undergo CT and in thosewho are already in the operating room. This pro-cedure frequently consists of more than just oneexposure and should include a scout radiographas well as additional images obtained immediatelyafter intravenous administration of iodinated con-trast material and again 5–10 minutes later.

AngiographyThe use of arteriography in the assessment of re-nal injuries has diminished because most vascularinjuries can be assessed with CT. However, selec-tive renal arteriography can provide more detailedinformation regarding the exact anatomic area ofvascular injury than is possible with CT. Arteriog-raphy with transcatheter embolization may beused for nonsurgical therapy in hemodynamicallystable patients with renal injuries associated withongoing hemorrhage and for the evaluation ofsuspected vascular complications of injury (eg,arteriovenous fistula, pseudoaneurysm).

Venography may be performed to assess sus-pected injuries to the renal veins or inferior venacava.

Figure 1. Urine extravasation from the collecting system in a 9-year-old boy who had sustained blunt abdominaltrauma. (a) Contrast-enhanced generalized-nephrographic-phase helical CT scan reveals what appears to be only alarge perinephric hematoma (H) secondary to a distinct renal laceration (not shown). Because this is an early-phaseimage, there is no contrast material in the collecting system. The descending colon (C) is displaced anteriorly by thehematoma. Note the thickening of the renal (arrow) and lateroconal (arrowhead) fascia. (b) Excretory-phase CTscan demonstrates extensive extravasation of contrast-enhanced urine admixed with the hematoma, a finding thatdemonstrates that the laceration has disrupted the integrity of the collecting system.

RG f Volume 21 ● Number 3 Kawashima et al 559

Retrograde PyelographyRetrograde pyelography is valuable in the assess-ment of ureteral and renal pelvic integrity whenureteropelvic junction injury is suspected. How-ever, it is not helpful in evaluating renal parenchy-mal injuries.

UltrasonographyUS is well accepted as a method for detecting he-moperitoneum in patients with suspected intra-peritoneal injuries following blunt trauma but islimited compared with CT in the evaluation ofthe renal parenchyma. In one recent study com-paring US with CT in this setting, several renalinjuries were missed at trauma US (20).

Radionuclide Renal ScintigraphyOccasionally, radionuclide renal scintigraphy maybe helpful in documenting the presence of a func-tioning kidney in patients with a contraindicationfor iodinated contrast material or in following uprepair of renovascular trauma (21). Renal scintig-raphy can be performed with technetium (Tc)–99m glucoheptonate, Tc-99m mercaptoacetyl-triglycine, or Tc-99m diethylenetriamine penta-acetic acid (22–24).

MR ImagingMR imaging may be used to assess suspected re-nal injury when there is a contraindication foriodinated contrast material or when CT is notavailable (25). Like contrast-enhanced CT, MRimaging with use of intravenous gadolinium-based contrast material has proved helpful in theassessment of urinary extravasation (26).

Radiologic Classifi-cation of Renal Injuries

Renal injuries can be classified into four large cat-egories as shown in the Table.

Category IMinor injuries include renal contusions, subcap-sular hematomas, minor lacerations with limitedperinephric hematoma without extension to thecollecting system or medulla, and small corticalinfarcts. Category I renal injuries constitute 75%–85% of all renal injuries in most series and aregenerally managed conservatively (3,27).

Radiologic Classification of Renal Injuries

Category Description

I Minor injury (renal contusion, intrarenal and sub-capsular hematoma, minor laceration with limitedperinephric hematoma without extension to thecollecting system or medulla, small subsegmentalcortical infarct)

II Major injury (major renal laceration through the cor-tex extending to the medulla or collecting systemwith or without urine extravasation, segmentalrenal infarct)

III Catastrophic injury (multiple renal lacerations, vas-cular injury involving the renal pedicle)

IV Ureteropelvic junction injury (avulsion [completetranssection], laceration [incomplete tear])

Source.—Reference 27.

Figure 2. Drawing illustrates a focalintrarenal hematoma.

Figure 3. Renal contusion (category I) in a 46-year-old man who had sustained blunt abdominal trauma.Contrast-enhanced nephrographic-phase helical CTscan demonstrates a focal area of decreased contrastenhancement in the interpolar region of the left kidney(arrowhead).


The vast majority of minor injuries representsmall intrarenal hematomas (renal contusions),which may appear as ill-defined, round or ovoidhypoattenuating areas at CT (Figs 2, 3). Theymay also appear as focal areas of striation on de-layed nephrograms or persistent contrast materialstaining on nephrograms obtained after evengreater delay. A subcapsular hematoma appearsas a round or elliptic hyperattenuating fluid col-lection indenting or flattening the renal margin(Figs 4, 5). Occasionally, hematoma between the

renal capsule and the renorenal septum in theperirenal space can appear identical to a subcap-sular hematoma. High-attenuation fluid (40–70HU; mean, 51 HU) is most consistent with acuteclotted blood (15). Minor lacerations appear asdefects in the periphery of the renal parenchymawithout involvement of the collecting system(Figs 6, 7). A limited perinephric hematoma maybe present. Subsegmental infarcts are increasinglyrecognized at CT and appear as small, sharplydemarcated, wedge-shaped areas of decreased

Figure 4. Drawing illustrates a sub-capsular hematoma.

Figure 5. Subcapsular hematoma (category I) in a40-year-old man who had sustained blunt abdominaltrauma. Contrast-enhanced helical CT scan demon-strates a subcapsular fluid collection (straight whitearrows) flattening the posterolateral contour of the leftkidney. There is minimal cortical laceration (black ar-row). Note also the subcutaneous emphysema in theleft side of the back (curved arrow). A chest tube hadbeen inserted for a left pneumothorax (not shown).

Figure 6. Drawing illustrates a smallcortical laceration.

Figure 7. Simple renal laceration (category I) in a30-year-old woman who had sustained blunt abdomi-nal trauma. Contrast-enhanced multidetector helicalCT scan reveals a small, hypoattenuating lacerationcrossing the interpolar region of the left kidney (whitearrow) associated with a limited perinephric hema-toma. A hepatic laceration (black arrow) and hemo-peritoneum in the Morrison pouch (arrowheads) arealso seen.


contrast enhancement (Figs 8, 9), whereas renalcontusions are not as well defined or sharply de-marcated. Subsegmental infarcts are caused bystretching and thrombotic occlusion of an acces-sory renal artery, capsular artery, or intrarenalsubsegmental branch. Subsegmental infarctionresults in a renal scar.

“Renal pseudofracture” appears as sharp in-dentation of the renal contour near the renal hi-lum and is created on CT scans by sectioningthrough the hilar lip of the kidney (28). The char-

acteristic location of this “pseudofracture” andthe absence of perirenal fluid allow proper diag-nosis. “Pseudosubcapsular hematoma” appears asa region of decreased attenuation along the sur-face of the kidney caused by patient motion dur-ing data acquisition (28). The presence of similarfindings in the anterior abdominal wall, liver, andcontralateral kidney on the same image are cluesto the diagnosis. This artifact is also confirmedwhen the region of low attenuation is not presenton adjacent or repeat scans.

Category IILesions in category II comprise approximately10% of renal injuries (27) and include major lac-erations through the cortex extending to the me-

Figure 8. Drawings illustrate a seg-mental infarct.

Figure 9. Subsegmental renal infarction (category I)in a 47-year-old man who had sustained blunt abdomi-nal trauma. Contrast-enhanced CT scan demonstratesa sharply demarcated, wedge-shaped area of decreasedattenuation in the interpolar region of the right kidney(solid arrow). Note also the evidence of subtle hemor-rhage in the right renal hilum (open arrow).

Figure 10. Drawing illustrates a lac-eration that extends to the medulla butdoes not involve the collecting system.

Figure 11. Major renal laceration without involve-ment of the collecting system (category II) in a 32-year-old woman who had sustained blunt abdominal trau-ma. Contrast-enhanced helical CT scan reveals a lac-eration in the posterolateral aspect of the middle por-tion of the left kidney (arrows) associated with peri-nephric hematoma. No urine extravasation was seen onexcretory-phase scans (not shown).


dulla or collecting system with or without urinaryextravasation. Major lacerations of the renal pa-renchyma appear as deep clefts that fill with he-matoma with or without devascularized renal pa-renchyma and extend through the renal capsuleassociated with a perirenal hematoma (Figs 10,11). When the laceration extends into the renalcollecting system, extravasation of excreted con-trast material will be present on delayed views(Figs 12, 13). Urine leakage due to a deep renal

parenchymal laceration usually occurs into thelateral perinephric space.

Segmental infarcts appear as a sharply demar-cated, dorsal or ventral segmental region of de-creased enhancement of the parenchyma (Fig 14).

The management of category II lesions is vari-able. Affected patients are usually treated con-servatively but occasionally require surgical

Figure 12. Drawing illustrates a deepparenchymal laceration involving thecollecting system.

Figure 13. Major renal laceration involving the collecting system (category II) in an 8-year-old boy who had sus-tained blunt abdominal trauma. (a) Contrast-enhanced nephrographic-phase CT scan shows a large, distracted renalfracture through the interpolar portion of the right kidney. (b) Contrast-enhanced excretory-phase CT scan showsextravasation of contrast material from a laceration of the renal pelvis into the medial perinephric space. (c) DelayedCT scan shows extensive extravasation around the lower pole of the right kidney. Note the antegrade filling of theureter (white arrow). A small laceration is also seen in the lower pole (black arrow). (Fig 13 reprinted, with permis-sion, from reference 19.)

Figure 14. Segmental renal infarction (category II) ina 34-year-old man. Contrast-enhanced helical CT scandemonstrates a sharply demarcated area of decreasedcontrast enhancement in the posterior upper pole of theright kidney, a finding that is consistent with occlusionof the dorsal segmental branch of the renal artery. Notealso the splenic laceration with perisplenic hematoma (ar-rows). (Reprinted, with permission, from reference 29.)


exploration depending on hemodynamic statusand the evolution of the injury. For instance, apatient with an expanding perinephric hematomaand a decrease in hematocrit often requires inter-

vention. Most urinary extravasation resolvesspontaneously. However, a patient with impairedantegrade urine flow often requires surgical re-pair. Follow-up CT may be necessary to assessinterval change in the appearance of the injury.

Figure 15. Drawing illustrates mul-tiple renal lacerations.

Figure 16. Multiple renal lacerations (category III)in a 9-year-old boy who had sustained blunt abdominaltrauma and intraabdominal injury. Contrast-enhancednephrographic-phase helical CT scan shows severaldeep lacerations of the interpolar region of the rightkidney (straight arrows) associated with areas of activearterial extravasation (curved arrows). Note the ante-rior displacement of the duodenum (D), pancreas (P),and inferior vena cava (V). Hemoperitoneum (H) isseen in the Morrison pouch.

Figure 17. Shattered kidney (category III) in a 28-year-old man who had sustained blunt abdominal trauma.(a) Contrast-enhanced helical CT scan demonstrates a devitalized upper pole of the right kidney due to segmentalinfarction (R). Note the perinephric hyperattenuating blood clot (arrow). Note also the flattened inferior vena cava(V), a finding that indicates hypovolemic shock. (b) CT scan obtained caudad to a demonstrates a large parenchymallaceration extending horizontally across the middle to lower pole of the right kidney (R), which is displaced anteriorlyby a large, perinephric hematoma (H).


Category IIILesions in category III are catastrophic injuries;they account for approximately 5% of cases andgenerally require surgical exploration, often ne-phrectomy (14). Category III injuries includemultiple renal lacerations (Figs 15, 16) and vas-cular injuries involving the renal pedicle.

Multiple severe renal lacerations (“shatteredkidney”) are usually associated with one or moredevitalized fragments, severe compromise in theexcretion of contrast material, lacerations of therenal pelvis and collecting system, extensive hem-orrhage, and active arterial bleeding (Figs 15–17).A devitalized segment due to a major lacerationmay not be appreciated at CT if it is surroundedby a hematoma. Active arterial extravasation ap-pears as patchy areas of hyperattenuating contrastmaterial (85–370 HU; mean, 132 HU) within alower-attenuation hematoma that is best appreci-ated at dynamic contrast-enhanced CT (15). Thepresence of active arterial bleeding indicates a

category III renal injury (14). Intraarterial embo-lization may be used to salvage the kidney (Fig18).

The most significant vascular injury followingblunt trauma is thrombosis of the main renal ar-tery (29,30). Deceleration causes stretching andtearing of the intima, which is less elastic than themedia and adventitia (31). The resultant intimalflap initiates thrombosis, which quickly propa-gates distally (31). Global infarction is less com-mon than segmental or subsegmental infarctionin patients who sustain blunt trauma. Nonvisual-ization of the kidney is consistent with thrombosisof the main renal artery (Figs 19, 20) but can alsocharacterize other conditions including congenitalor surgical absence of the kidney, renal ectopia,renal vascular spasm due to severe contusion,avulsion of the renal pedicle, and high-grade uri-nary obstruction. Contrast-enhanced helical CT

Figure 18. Active arterial extravasation(category III). Selective angiogram of the rightmain renal artery obtained following explor-atory laparotomy demonstrates vascular ex-travasation from the upper pole of the rightkidney (arrow). Intraarterial embolization wassuccessfully performed to control bleeding.

Figure 19. Drawings illustrate throm-bosis of the main renal artery.


typically reveals an abrupt termination of therenal artery just beyond its origin and global renalinfarction with or without the cortical rim sign(Fig 21) (32). The cortical rim sign usually ap-pears several days after the initial injury (33) buthas been reported to occur as early as 8 hours af-terward (34). The absence of a perinephric hema-toma is characteristic of a renal arterial occlusion,although a hematoma may be present around theproximal renal artery. In most cases, catheter an-giography is not needed to confirm the CT diag-nosis of renal artery thrombosis. A review of theliterature showed that only five (14%) of 35 pa-tients with unilateral posttraumatic occlusion ofthe renal artery who underwent revascularizationhad return of normal renal function; in all fivepatients, the duration of the ischemia was lessthan 12 hours (35). Nevertheless, revasculariza-tion may be attempted in patients with only onekidney or with bilateral renal arterial thrombosis(30,35).

Avulsion of the renal artery is a rare but life-threatening injury caused by tearing of the tunicamuscularis and adventitia. CT reveals global in-

Figure 20. Traumatic occlusion of the main renal ar-tery (category III) in a 17-year-old boy who had sus-tained blunt abdominal trauma. (a) Intravenous uro-gram demonstrates poor visualization of the left kidney.(b) CT scan obtained without additional contrast mate-rial following urography demonstrates rim enhancementof the outer cortex of the left kidney (arrows). (c) Digi-tal subtraction aortogram demonstrates the characteris-tic tapered occlusion of the proximal left main renal ar-tery (arrow).

Figure 21. Traumatic occlusion of the main renalartery (category III) in a 38-year-old man who had sus-tained blunt abdominal trauma. Contrast-enhancedhelical CT scan demonstrates a diminished rightnephrogram. The proximal right renal artery (straightarrow) is enhanced; however, the distal main renal ar-tery is not visualized. Note also the hepatic laceration(curved arrow) and hemoperitoneum in the Morrisonpouch (H).


farction of the kidney associated with extensivemedial perirenal hematoma (28). Active arterialbleeding may also be seen.

Thrombosis or laceration of the renal vein isanother rare form of renal pedicle injury (14,28,36). Venography may be performed when inju-ries to the renal vein and inferior vena cava

are suspected because CT may not reliably detectvenous laceration (Fig 22) (1). Immediate surgi-cal repair of venous injuries may be required tocontrol bleeding. Isolated renal vein thrombosis israre (36). Contrast-enhanced CT reveals an in-traluminal thrombus in the distended renal veinand renal changes secondary to acute venous hy-pertension including nephromegaly, a diminishednephrogram, delayed nephrographic progression,and decreased excretion of contrast material intothe collecting system (36).

Category IVUreteropelvic junction injuries are a rare conse-quence of blunt trauma and are caused by suddendeceleration, which creates tension on the renalpedicle (37). The diagnosis may be delayed be-cause hematuria is absent in one-third of patients(6). Intravenous urography and CT typically re-veal excellent excretion of contrast material withan intact intrarenal collecting system but withmedial perinephric urinary extravasation (19,38).A circumferential (circumrenal) urinoma may beseen around the affected kidney, but typicallythere is no perinephric hematoma. Ureteropelvicjunction injuries are classified into two groups:avulsion (complete transection) (Figs 23, 24)

Figure 22. Laceration of the renal vein (category III) in an 18-year-old woman who had sustained blunt abdominaltrauma. (a) Contrast-enhanced helical CT scan demonstrates minimal perinephric hematoma without parenchymallaceration (arrows). (b) CT scan obtained 3 days later shows an interval increase in the amount of perinephric hema-toma (H), resulting in deformation of the contour of the right kidney and a heterogeneously diminished nephrogram.The origin of the bleeding was not identified at CT. Laceration of the renal vein was found at surgery.

Figure 23. Drawing illustrates com-plete transection of the ureter.


and laceration (incomplete tear) (Fig 25). Thepresence of contrast material in the ureter distalto the ureteropelvic junction helps differentiatelaceration from avulsion. However, when neitherCT nor intravenous urography unequivocallydemonstrates ipsilateral ureteral filling, retrogradepyelography should be performed. Ureteropelvicjunction avulsion is usually treated with surgicalrepair, whereas laceration may be treated conser-vatively or with stent placement.

Pyelosinus contrast material extravasation fol-lowing blunt trauma has rarely been reported andcan be differentiated from ureteropelvic junctioninjury at excretory urography (39). It typicallyresolves quickly, unlike extravasation caused bymore significant renal injuries. Patients with post-

traumatic pyelosinus contrast material extravasa-tion do not require urologic intervention.

Penetrating InjuriesIn a study by Sagalowsky et al published in 1983(2), all 122 patients with renal injuries from ante-rior gunshot wounds had associated intraabdomi-nal injuries at surgery. Stab wounds less fre-quently have associated intraabdominal injury,with reported prevalence ranging from 30% to70% (2,40). In patients with a stab wound limitedto the flank and back, contrast-enhanced CT canbe used to assess the extent of injury and to po-tentially obviate surgical exploration (Fig 26)(41). CT is not usually performed in patients withan anterior stab wound because these patientsgenerally require exploratory laparotomy due tothe high prevalence of bowel injury associatedwith this form of trauma.

Figure 24. Avulsion of the ureteropelvic junction (category IV) in a 49-year-old man who had sustained blunt trau-ma. (a, b) Contrast-enhanced nephrographic-phase helical CT scans (a obtained at a higher level than b) throughthe lower pole of the right kidney demonstrate a perinephric fluid collection with no renal laceration. (c, d) Con-trast-enhanced excretory-phase CT scans (c obtained at a higher level than d) demonstrate medial contrast materialextravasation (arrow). No ureteral contrast material filling is noted. The patient underwent exploratory laparotomyfor a mesenteric laceration. A diagnosis of ureteropelvic junction avulsion was made, and primary surgical repair ofthe ureter was performed.


Figure 25. Ureteropelvic junction laceration with pre-existing obstruction (category IV) in a 27-year-old manwho had sustained blunt abdominal trauma. (a) Con-trast-enhanced excretory-phase CT scan demonstratesleft-sided pelviectasis and right-sided pelvocaliectasis. Alarge blood clot is present in the left renal pelvis. (b) AxialCT scan obtained inferior to the lower pole of the leftkidney shows contrast material extravasation at thepoint of laceration of the ureteropelvic junction (straightarrow). A periureteral urinoma is also present. The en-hanced ureter contains a filling defect (curved arrow),presumably secondary to a blood clot. (c) Intravenousurogram shows medial perinephric contrast materialextravasation on the left side with a normal-caliber ure-ter distally (arrows), findings that indicate that ureteralcontinuity has been maintained. Pelvocaliectasis is alsopresent, a finding that is consistent with bilateral ure-teropelvic junction obstruction. (Reprinted, with per-mission, from reference 19.)

Figure 26. Renal laceration in a 25-year-old man whohad sustained a stab wound to the right posterolateral as-pect of the abdomen. Contrast-enhanced nephrographic-phase helical CT scan reveals laceration of the anterolat-eral aspect of the right kidney (curved arrow) with a bloodclot in a right extrarenal pelvis (B). Note the small hepaticlaceration (straight black arrow) and minimal hemoperito-neum (H). The stab wound is seen in the abdominal wall(white arrow). An extrarenal pelvis is also present on theleft side.


Ureteral obstruction caused by intramural mis-siles or migrating retained missiles in shotgun,gunshot, or shrapnel wounds (“bullet colic,”“buckshot colic,” “birdshot calculus”) is an un-usual complication of penetrating injuries to theabdomen (42,43). Bullet colic involving bulletsand shrapnel fragments usually involves long la-tent periods after initial injury and often requiressurgery to remove the obstructing projectile (43).In contrast, buckshot colic from shotgun pelletsmanifests earlier and often resolves with sponta-neous passage of the pellets (43). Excretory urog-raphy and CT are useful for investigation (Fig27).

Traumatic Injuries to Kidneyswith Preexisting Abnormalities

A kidney with a preexisting abnormality is at in-creased risk for injury (23). An underlying renaldisorder may be first brought to medical attentionbecause the severity of the patient’s symptoms isdisproportionate to the degree of injury suffered.Trauma to an abnormal kidney occurs more fre-quently in children than in adults. Such injuriesinclude disruption of the renal pelvis or uretero-pelvic junction in patients with hydronephrosis oran extrarenal pelvis (Fig 25), intracystic hemor-rhage or rupture of a renal cyst with or withoutcommunication with the collecting system (Figs28, 29), rupture of a tumor, laceration of poorlyprotected ectopic or horseshoe kidneys (Fig 30),and laceration of fragile, infected kidneys. CTprovides more specific and clinically useful infor-mation than excretory urography in this context(44).

Figure 27. Renal injury in a 20-year-old man who hadsustained a gunshot wound. (a) Conventional radiographof the right upper quadrant of the abdomen shows mul-tiple pellets. (b) Unenhanced CT scan reveals a pellet inthe upper pole of the right kidney. Note the minimal peri-nephric hematoma (arrow). (c) On a contrast-enhancedexcretory-phase helical CT scan, the pellet is seen inproximity to the collecting system. Retained pellets maypotentially migrate into the collecting system and result inureteral obstruction (“buckshot colic”).


Figure 28. Renal cyst complicated by intracystic hemorrhage with communication with the col-lecting system in a 23-year-old man who had sustained blunt abdominal trauma. (a) Contrast-en-hanced nephrographic-phase helical CT scan shows a cyst with hyperattenuating fluid in the upperpole of the left kidney (solid arrow), findings that are consistent with intracystic hemorrhage. Notethe splenic laceration (open arrow) and perisplenic hematoma (H). (b) Contrast-enhanced excre-tory-phase CT scan demonstrates contrast material in the cyst (arrow).

Figure 29. Rupture of a renal cyst in a 71-year-old man who had sustained blunt abdominaltrauma. Contrast-enhanced helical CT scandemonstrates a cyst with a fluid-fluid level in themidpolar region of the left kidney (straight solidarrow) with a perinephric fluid collection (curvedarrow). Note the thickening of the renal fascia(open arrow).

Figure 30. Renal injury in a 33-year-old man with ahorseshoe kidney. Contrast-enhanced helical CT scandemonstrates a large renal laceration through the isth-mus of a horseshoe kidney associated with perinephrichematoma (H). L � left kidney, R � right kidney.(Courtesy of Stephen Karasick, MD, Department ofRadiology, Thomas Jefferson University Hospital,Philadelphia, Pa.)


Urologic Compli-cations in Renal Injury

Early complications occur within 4 weeks of in-jury and include urinary extravasation and uri-noma formation, delayed bleeding, infected uri-noma, perinephric abscess, sepsis, arteriovenousfistula, pseudoaneurysm (Fig 31), and hyperten-sion (1). Late complications include hydrone-phrosis, hypertension, calculus formation, andchronic pyelonephritis (1). In a study performedto define the outcome of major blunt renal inju-ries with nonsurgical versus surgical treatment,Husmann and Morris (45) found that delayedurologic complications occur more frequently inpatients with a devascularized fragment than inthose with vascularized fragments. Infected urino-mas and perinephric abscesses frequently occur inpatients with an unrepaired, devitalized renal seg-ment and concomitant injury to the pancreas orbowel (46).

Posttraumatic renovascular hypertension is anuncommon complication of renal injury whoseprecise prevalence is difficult to establish. Possiblemechanisms for the development of posttrau-matic hypertension include renal artery occlusion,renal artery stenosis with or without an intimalflap, renal artery compression, severe renal contu-sion, arteriovenous fistula or pseudoaneurysmformation, and a chronic contained subcapsularhematoma (47). In a study by Cass and Luxen-berg (48), hypertension occurred in only 10 (6%)of 170 reported cases of traumatic thrombosis ofsegmental renal arteries. The majority of patientswho develop hypertension following segmentalarterial thrombosis can be treated nonsurgicallyunless there is cardiovascular instability (49). Tenpatients with documented traumatic injuries to abranch renal artery were followed up for 1 to 5years; in two (20%) of these patients, hyperten-sion developed immediately after injury but re-solved spontaneously within 1 year (49). In a re-cent review of seven patients who suffered hyper-tension 2 weeks to 8 months following blunttrauma, selective angiograms showed occlusion ofthe main renal artery in two patients, significantstenosis from an intimal flap in one, severe renal

contusion in two, and segmental renal arterialbranch injuries in two (50). Arteriovenous fistulaand pseudoaneurysms as a result of deep renallaceration can also produce renin-mediated hy-pertension. A chronic contained subcapsular he-matoma (Fig 32) and perirenal scarring mayrarely create a compressive force on the deformedkidney, reducing flow to the kidney and inducingrenin-mediated hypertension (Page kidney).

Selective renal angiography and renin samplingmay be preferred for the evaluation of patientswith suspected renovascular hypertension, al-though dynamic contrast-enhanced CT with an-giographic techniques can reveal vascular lesions.Page kidney may appear as a subcapsular fluidcollection or perirenal soft-tissue thickening andas a delayed nephrographic progression in theaffected kidney compared with the contralateralkidney. Percutaneous drainage of a chronic sub-capsular hematoma may be performed.

Figure 31. Pseudoaneurysm in a patientwho had sustained a stab wound and had un-dergone exploratory laparotomy. Selectivearterial-phase right renal angiogram demon-strates a false aneurysm in the lower pole ofthe right kidney (straight arrow). Subsegmen-tal infarction is noted in the upper pole(curved arrow). Bleeding was controlled withintraarterial embolization. Surgical staplesfrom the laparotomy are seen at the midline.


ConclusionsCT plays a major role in assessing patients withrenal injuries. Understanding the radiologic clas-sification of traumatic renal injuries is helpful inpatient triage. The imaging findings in renal in-jury should be integrated with clinical informa-tion to assist in developing a treatment plan.

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