ECR 2018 / C-2016
Certificate of Merit
Renal Trauma: Tips for successful imaging and diagnosis
Congress: ECR 2018
Poster No.: C-2016
Type: Educational Exhibit
Keywords: Imaging sequences, Diagnostic procedure, CT, Abdomen, Trauma, Kidney, Acute
Authors: M. L. Bambrick, R. M. Heaney, C. Ní Leidhin, D. Mulholland, P. Beddy; Dublin/IE
DOI:10.1594/ecr2018/C-2016

Findings and procedure details

Indications for Imaging

 

Both the European Association of Urology [6] and the American Urologic Association [7] have published guidelines outlining the indications for CT in renal trauma. Both guidelines broadly agree and can be summarised as follows:

 

1)    Haemodynamically unstable patients should be brought directly to  

       theatre for exploratory laparotomy.

2)    Stable patients who have undergone blunt abdominal trauma and either

       a.     have gross haematuria

               OR

       b.     have microscopic haematuria AND evidence of shock i.e. SBP <  

               90mmHg

       should undergo contrast enhanced CT.

 

3)    Stable patients who have undergone blunt abdominal trauma and have  

       microscopic haematuria only with nothing else to suggest renal injury do

       not require imaging.

4)    Patients who have undergone trauma where the mechanism of injury

       raises a suspicion of renal injury (e.g. rapid deceleration, significant blow

       to flank, penetrating trauma, extensive bruising over flank or rib

       fracture) should undergo contrast enhanced CT.

 

It should be noted that if the mechanism of injury or clinical picture indicates significant injury, the absence of haematuria should not act as a barrier to imaging as haematuria is only present in a minority of renal trauma and does not correlate with severity of the injury [2].

 

Table 1: Indications for imaging in renal trauma
References: Radiology Department, St James's Hospital - Dublin/IE

 

 

CT Imaging Protocol

 

In the setting of renal trauma the imaging protocol used should adequately assess three key components of the kidney: the parenchyma, vasculature and collecting system. Imaging usually occurs in the setting of general abdominal trauma for which a trauma protocol is employed to assess for a wide range of injuries. A trauma protocol for the abdomen involves portal venous phase imaging which corresponds with the corticomedullary phase thus enabling assessment of renal parenchyma. There is also increasing tendency to include an arterial phase in the trauma protocol to assess for arterial injury [8]. In cases of penetrating trauma preliminary non-contrast images may be of benefit in identifying and distinguishing extravasation from foreign bodies.

 

If there is suspicion of an injury to the collecting system based on the initial scan, a delayed or excretory phase should be performed at 10-20 minutes. Collecting system injury may be indicated on the initial scan by evidence of a laceration which appears to extend to the collecting system or by the presence of perinephric free fluid. Delayed phase images are also useful in evaluating vascular injuries such as active bleeding and pseudoaneurysm.

 

 

Grading System of Renal Injury

 

The American Association for the Surgery of Trauma (AAST) have developed a scale (Grade I-V) for classifying renal injury in the setting of trauma [9]. This scale is widely used to grade the severity of renal injury and is helpful in planning patient management.

 

 

Grade of Injury

       Nature of injury

I

·      Contusions

·      Subcapsular haematomas

II

·      Lacerations <1cm of the renal cortex but not  

       involving the collecting system

·      Perinephric haematomas

III

·      Lacerations >1cm of the renal cortex but not

       involving the collecting system

IV

·      Lacerations extending to involve the cortex, medulla

       and collecting system

·      Vascular injuries involving main renal artery/vein

       with contained haemorrhage

V

·      Vascular injuries involving the main renal artery or

       vein with complete devascularisation of the kidney

·      Shattered kidney

*Move up one grade for bilateral injuries grade I-III

 

 

CT Appearances of Renal Injuries & Management

 

A.    Grade I Injuries

 

Contusions

 

 

CT Findings

·      Poorly defined areas of low attenuation relative to

       surrounding parenchyma, often subtle.

·      May have striated appearance due to differential

       blood flow through the region and on delayed phase  

       images may demonstrate a persistent  

       nephrogram.

·      Can be distinguished from segmental infarctions

       which are well defined, wedge shaped areas of low

       attenuation which do not demonstrate post

       contrast enhancement.

Management

·      Conservative management.

·      No follow up imaging required.

 

 

Fig. 2: (a) Illustration of renal contusion. (b) 43 year old male post assault. CT shows an ill-defined area of low attenuation in the left kidney consistent with a renal contusion (Grade I injury).
References: Radiology Department, St James's Hospital - Dublin/IE

 

 

Subcapsular Haematoma

 

Subcapsular haematomas are well encapsulated haematomas that develop between the renal parenchyma and the capsule.

 

 

CT Findings

·      Typically convex in shape, appearing as an area of

       low attenuation relative to the kidney on

       corticomedullary phase imaging. 

·      As they enlarge they can become biconvex. 

·      Can cause indentation of the kidney contour.

·      On non-contrast studies, the haematoma appears

       hyperattenuating relative to unenhanced renal

       parenchyma in the acute phase, and hypodense

       when chronic. 

Management

·      No intervention required, they will resolve

       spontaneously. 

·      No follow up imaging required.

·      In rare cases the haematoma can enlarge to the

       extent that it compresses the underlying kidney and

       restricts blood flow. This in turn activates the RAAS

       system with the patient developing secondary

       hypertension. This condition is known as a Page

       Kidney. Initial conservative management is

       recommended with surgical intervention being second

       line [10]. 

 

 

Fig. 3: (a) Illustration of a subcapsular haematoma. (b) & (c) In this 37 year old woman post blunt trauma, a subcapsular haematoma is seen as a well encapsulated area of low attenuation along the lateral border of the left kidney.
References: Radiology Department, St James's Hospital - Dublin/IE

 

 

A.    Grade II/III Injuries

 

Lacerations (not involving collecting system)

 

CT Findings

·      Linear or jagged hypodensity extending into

       otherwise normal renal parenchyma from the

       periphery of the kidney.

·      No extension into the collecting system.

·      Grade II if < 1cm in length and Grade III if > 1cm.

·      Can mimic segmental infarction.

Management

·      No intervention required. 

·      No follow up imaging required.

 

 

Fig. 4: Illustrations depicting (a) grade II and (b) grade III lacerations.
References: Radiology Department, St James's Hospital - Dublin/IE

 

Fig. 5: A 21 year old male post stab wound to the left flank. A grade III laceration to the left kidney is visible as an area of low attenuation extending from the periphery of the kidney (a) & (b).
References: Radiology Department, St James's Hospital - Dublin/IE

 

 

Fig. 6: 46 year old man post blunt trauma following assault. A linear focus of low attenuation is visible in the lower pole of the left kidney representing a grade III laceration.
References: Radiology Department, St James's Hospital - Dublin/IE

 

 

Perinephric Haematoma

 

CT Findings

·      Irregular and poorly defined hyperdense fluid. 

·      Contained within the retroperitoneum by Gerota’s

       fascia

·      May extend laterally causing thickening of the lateral

       conal fascia

·      Unlike subcapsular haematomas, do not cause

       indentation of underlying kidney.

Management

·      No intervention required. 

·      No follow up imaging.

  

 

Fig. 7: This 52 year old male involved in an RTA has a right perinephric haematoma. The irregular area of free fluid is hyperattenuating on the non-contrast study (a) indicating it is an acute haematoma.
References: Radiology Department, St James's Hospital - Dublin/IE

 

 

A.    Grade IV Injuries

 

            Lacerations involving the collecting system

 

CT Findings

·      Suspicion of a collecting system injury should be

       raised if free fluid is seen around the kidney on the

       initial scan.

·      On delayed images contrast-opacified urine is seen

       leaking from the collecting system into the

       perinephric space.

Management

·      The majority of collecting system injuries resolve

       spontaneously and do not require intervention.

·      Persistent leaks may require insertion of

       nephrostomies or JJ ureteric stents to allow healing

       of the urothelium.

·      Occasionally surgical repair may be needed. 

·      Urinomas can develop and may require drainage if

       they fail to resolve or become infected.

 

 

Fig. 8: Illustration of Grade IV laceration involving the collecting system.
References: Radiology Department, St James's Hospital - Dublin/IE

 

 

Fig. 9: This case of a 39 year old female involved in a RTA demonstrates the importance of delayed phase imaging in evaluating the collecting system. On the initial non-contrast (a) and corticomedullary phase images (b) free fluid is seen around the left kidney raising the suspicion for a collecting system injury. Delayed (excretory) phase images (c) & (d) show leakage of contrast opacified urine into the perinephric space of the left kidney confirming the injury.
References: Radiology Department, St James's Hospital - Dublin/IE

 

 

A.    Grade V

 

            Shattered Kidney

 

CT Findings

·      Extensive lacerations involving both renal

       parenchyma and the collecting system such that the

       kidney is separated into fragments.

·      Often devascularised fragments of kidney which are

       non-enhancing.

Management

·      Usually requires surgical intervention and often

       necessitates nephrectomy.

 

 

Fig. 10: Illustration of shattered kidney.
References: Radiology Department, St James's Hospital - Dublin/IE

 

 

Fig. 11: Shattered kidney in 16 year old male following blunt trauma in a sports match. The left kidney is divided in two (a) & (b). Extensive areas of non-attenuating parenchyma are visible in the upper pole (c) in keeping with devitalised fragments. On delayed phase imaging (d) & (e), extravasation of contrast material from the collecting system of the lower pole can be seen. This patient subsequently underwent left nephrectomy.
References: Radiology Department, St James's Hospital - Dublin/IE

 

 

Injuries at the renal pedicle

 

Rapid deceleration injuries such as those sustained in RTAs or following a fall from a height can cause injury at the renal pedicle. These can involve either the vascular structures, the pelvicoureteric junction (PUJ) or both. 

 

 

PUJ Injury

 

In cases of rapid deceleration the ureter can be stretched and damaged at its proximal fixation point - the PUJ. This injury can involve either a partial tear or complete avulsion. Delayed phase imaging is crucial to evaluate these injuries.

 

CT Findings

·      Extravasation of contrast into the perinephric space

       medially on delayed phase images. 

·      Examining the distal ureter will help distinguish between

       a partial tear and complete avulsion:

        o     Partial Tear: contrast will be seen to opacify the

                                  ureters distally

        o     Avulsion:      No contrast seen in ureters distally

·      There may be associated hydronephrosis in the affected

       kidney.

Management

·      Distinction between partial tear and avulsion important in

       determining management strategy:

        o   Partial Tear: can be managed conservatively with

                                stenting or urinary diversion with

                                nephrostomy to allow healing of the

                                urothelium.

        o   Avulsion:      requires surgical repair.

 

Fig. 12: Illustration showing PUJ avulsion
References: Radiology Department, St James's Hospital - Dublin/IE

 

 

Fig. 13: A 24 year old man following a fall from a height. (a) There is extravasation of opacified urine around the medial portion of the left kidney suggesting damage to the PUJ. (b) There is no contrast within the distal left ureter (dashed circle) unlike the right which is opacified (solid circle), confirming a complete avulsion at the left PUJ.
References: Radiology Department, St James's Hospital - Dublin/IE

 

 

Vascular Injuries at the renal pedicle

 

            Renal Artery Injury

 

Shearing forces cause stretching of the renal artery at the pedicle which can result in an intimal tear or dissection. This in turn promotes thrombosis at the site which can cause occlusion of the vessel.

 

CT Findings

·      Unenhanced kidney

·      Site of occlusion may be visible on maximum intensity

       projections.

·      Large perinephric haemorrhage with evidence of active      

       extravasation in cases of laceration or avulsion.

·      Retrograde filling of ipsilateral renal vein from the

       IVC is suggestive of renal artery injury [10,11].

·      There may be peripheral enhancement of the kidney, the

       ‘cortical rim sign’ due to collateral supply from capsular,

       peripelvic and periureteric branches. However, this is a

       late finding (>8 hours post injury) and may not be seen

       in the acute setting [10].

Management

·      Stenting may be performed in cases of arterial occlusion.

·      Surgical repair is often required

·      Partial/total nephrectomy may be necessary where there

       are devitalised fragments.

 

 

Fig. 14: Illustration of renal artery thrombosis with devascularisation of the kidney.
References: Radiology Department, St James's Hospital - Dublin/IE

 

 

            Renal vein Injury

 

Renal vein injury is uncommon and it rarely occurs in isolation but is usually associated with injury to either the artery or PUJ. 

 

CT Findings

·      In renal vein thrombosis the vein is enlarged. There can

       be associated nephromegaly, interstitial oedema and

       delayed excretion of contrast into the collecting system.

·      Lacerations of the renal vein are not reliably identified

       on CT but should be suspected where there is a large

       perinephric haematoma [10].

Management

·      In cases of isolated renal vein thrombus, a conservative  

       approach with anticoagulation is usually preferred.

·      Extravasation from a lacerated renal vein may

       tamponade and in such cases conservative management

       can be employed.

·      In cases of haemodynamic instability urgent surgical

       repair or nephrectomy may be required.

 

 

Injuries not covered by AAST grading:

 

The AAST grading system was developed based on appearances at surgery. While for the most part it can also be used to classify radiological findings, some CT findings are not specifically covered:

 

Active bleeding

 

CT Findings

·      Irregular linear or flame shaped areas of high attenuation

       within a larger area of free fluid.

·      On the delayed phase images the area of high attenuation

       will have increased in size indicating ongoing

       haemorrhage.

Management

·      Arterial embolisation can be used in cases of active

       arterial bleeding.

·      In cases of haemodynamic instability nephrectomy may

       be necessary.

 

Fig. 15: A small focus of high attenuation in a left perinephric haematoma (a) and (b) is seen to have increased in size on the delayed images (c) indicating active haemorrhage.
References: Radiology Department, St James's Hospital - Dublin/IE

 

 

Pseudoaneurysm

 

CT Findings

·     Rounded or oval area which follows the enhancement

      pattern of the aorta with high attenuation during the

      arterial phase and washout on delayed phase images.

Management

·     Arterial embolisation

 

 

Segmental Renal infarctions

 

 

CT Findings

·      Well defined, wedge shaped areas of low attenuation.

·      Base of the wedge at the periphery of the kidney

       with apex pointing towards the renal hilum.

·      No post contrast enhancement

·      Often involving the poles

Management

·      Most heal spontaneously and are managed

       conservatively

·      If they involve >50% of the renal parenchyma

       surgical debridement may be necessary to prevent

       abscess formation.

 

Fig. 16: Illustration of segmental infarct.
References: Radiology Department, St James's Hospital - Dublin/IE

 

Other abdominal injury

 

Renal trauma rarely occurs in isolation as, relative to other abdominal viscera, the kidneys are well protected. It is vital that the radiologist fully assess all injuries. 

 

The liver is commonly injured in cases of both blunt and penetrating trauma. 

Where the mechanism of action involves rapid deceleration, other relatively mobile structures such as the aorta can be injured. 

 

Fig. 17: 18 year old girl kicked by a horse in her right flank. In addition to the renal injury – shattered right kidney (a) a linear area of low attenuation is seen in the liver (b) & (c) consistent with a liver laceration.
References: Radiology Department, St James's Hospital - Dublin/IE

 

 

Role of Interventional Radiology

 

The role of radiology in renal trauma is not limited to diagnosis of injury. With the trend in management of renal trauma moving away from surgical exploration, minimally invasive techniques are proving more important. Interventional Radiology can be of benefit in:

  • Arterial embolisation for active bleeding or pseudoaneurysms.
  • Ureteric stenting or percutaneous nephrostomy to facilitate urothelial healing.
  • Drainage of infected urinomas.
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