Genitourinary Tract Trauma

Imaging Technique for Renal Injury

In many instances, high-impact trauma is imaged with whole-body CT, which will include the kidneys, ureters and bladder as part of the examination. In our institution, a whole-body protocol using 128-slice MDCT includes an unenhanced data set followed by arterial phase imaging from the lower cervical region to the proximal femurs immediately after an intravenous bolus of 100 mL of iodinated contrast agent (350 mg/mL) given at 4 mL/s by power injector. CT data acquisition is triggered to begin when a threshold density of 100 HU is reached in the ascending aorta. A portal venous phase data set of the abdomen and pelvis to the proximal femurs at 70 seconds is then obtained. Axial images at 5 mm are provided for immediate review at the time of data acquisition. If there is any suggestion of renal injury on these initial images or a strong clinical suspicion, delayed imaging at 5 and/or 10 minutes is performed. This enables assessment of the opacified collecting system for extravasation of contrast material. Reduced radiation dose is adequate for additional delayed images, as these images are used primarily for detection of high-density contrast material rather than parenchymal injury. Images are then reconstructed in 5 mm, 2 mm and 0.75 mm axial slices and 3 mm coronal slices and provided for review on a PACS (Picture and Archiving System) workstation.

The arterial phase images are most useful in demonstrating the presence and symmetry of enhancement in the kidneys and potential active bleeding or traumatic pseudoaneurysm, while the portal venous images provide more information about the extent of parenchymal damage and help differentiate active bleeding from traumatic pseudoaneurysm.

Grading of Renal Injury and Implications for Management

Management of renal trauma depends to a large degree on the extent of the injury and clinical status of the patient. In 1989, the American Association for the Surgery of Trauma (AAST) created a renal injury grading system, which was based on surgical observations. This grading system was found to be valid in that increasing renal injury grade was directly correlated with the increasing need for intervention.

In 2011, a review of 3580 renal injuries by Buckley and McAninch led to the revision of the original AAST renal grading system ( Table 36.2 ). The 2011 revision is not solely based on surgical findings but takes into account certain radiological findings. The revised grading system includes renal injuries not described in the original grading scale (segmental vascular injuries and ureteral pelvic injuries) and reclassifies grade IV and grade V injuries. In the revised grading system, grades I to III remain the same as the original 1989 renal injury staging. Surgical literature was inconsistent in the definition of a grade IV or grade V injury, and no clear management and outcome data could be obtained for these severe injuries. Grade IV and grade V injuries were thus reclassified in the revised system with more precise language to optimise management, standardise clinical research and improve outcomes.

Generally, most renal injuries (75% to 98%) are grades I to III and require no intervention. With the gradual shift in trauma care to a more conservative approach, most revised AAST grade IV injuries will likely be managed with interventional angiography and active surveillance, while grade V injuries have the highest incidence of exploration and lowest renal salvage rate. If surgical exploration of a renal injury is performed, there is a 64% chance of nephrectomy, regardless of operative intent. Surgery is currently required in less than 10% of blunt renal injuries, and its use will likely continue to decrease. A higher proportion of penetrating renal injuries requires operative intervention.

Computed Tomography Findings of Grade I Renal Injury

A grade I renal injury is a contusion or a non-enlarging subcapsular haematoma. Contusions are visualised as ill-defined, low-attenuation areas with irregular margins within the renal parenchyma ( Fig. 36.3 ). They may appear as regions with a striated nephrogram pattern owing to differential blood flow through the contused parenchyma. A subcapsular haematoma appears as a typically convex fluid collection indenting the underlying parenchyma ( Fig. 36.4 ). On an unenhanced CT, an acute haematoma appears hyperdense in comparison to the adjacent renal parenchyma and becomes hypodense as it ages. On contrast-enhanced CT, contained haematomas display similar attenuation patterns to the aorta, with enhancement during arterial phase imaging and ‘wash out’ on delayed imaging. The haematoma remains similar in size and appearance on these delayed images. Large subcapsular haematomas may have a biconvex appearance. Some delay in renal perfusion may be seen with these injuries, secondary to increased resistance to arterial perfusion. Acute or delayed onset of hypertension can develop from renal parenchymal compression resulting in activation of the renin–angiotensin–aldosterone system, the so-called ‘Page kidney’. Large subcapsular haematomas could theoretically compress the kidney to near systolic level pressures, preventing perfusion.

Management: Contusions and small subcapsular haematomas are managed conservatively and do not require routine follow-up. The presence of a large subcapsular haematoma resulting in renal compression or tamponade can initially be managed expectantly; however, occasionally, surgical evacuation is required.

Computed Tomography Findings of Grade II Renal Injury

Grade II renal injuries represent either minor renal lacerations extending less than 1 cm into the renal parenchyma without involvement of the renal collecting system or perinephric haematomas. Lacerations appear as non-enhancing linear or jagged defects on a background of otherwise normally enhancing renal parenchyma ( Fig. 36.5 ). These are usually self-limiting injuries, typically accompanied by small amounts of perinephric haemorrhage. Perinephric haemorrhage will appear as a poorly marginated, hyperdense fluid confined by Gerota fascia ( Fig. 36.6 ). Thickening of the lateral conal fascia may also be seen. Even if the perinephric haematoma is large, it will usually not indent the renal contour compared with a subcapsular haematoma; however, it can displace the kidney anteriorly.

Management: Conservative management without need for routine follow-up imaging.

Computed Tomography Findings of Grade III Renal Injury

A grade III renal injury is a laceration extending greater than 1 cm into the renal parenchyma without extension into the collecting system ( Fig. 36.7 ). The non-enhancing lacerations involve varying amounts of cortex and medulla, and appearances become more complex with increasing size. Associated perirenal haematoma remains encapsulated by Gerota fascia and may displace the kidney. Delayed imaging is essential to ensure that there is no underlying collecting system injury.

Management: Conservative management without the need for routine follow-up imaging.

Computed Tomography Findings of Grade IV Renal Injury

Grade IV renal injuries include deep renal lacerations that extend into the renal collecting system with urinary extravasation, segmental or main renal artery or vein injury with contained haemorrhage, renal pelvis laceration and/or complete ureteral pelvic disruption.

Lacerations of the collecting system are identified on CT by extravasation of urine into the perirenal space ( Fig. 36.8 ). A collecting system injury can be missed if the CT images are obtained before IV contrast medium has reached the collecting system. Visualisation of any fluid around the kidney on the initial CT requires additional delayed CT imaging. Delayed images will show the accumulation of high-density, contrast-enhanced urine adjacent to the site of injury. If the injury is not diagnosed on CT, the development of sepsis, decreasing renal function or unexplained increasing serum creatinine and blood urea nitrogen (BUN) should raise concern for urine leak.

Complete ureteral pelvic disruption manifests as gross extravasation near the PUJ. Extravasation of contrast-enhanced urine into the right anterior pararenal space can mimic a duodenal rupture with leakage of oral contrast medium. Renal pelvic injury with visualisation of the distal ureter indicates only partial disruption. A dilated renal pelvis resulting from congenital or acquired urinary outflow obstruction is at increased risk for rupture from a traumatic impact ( Fig. 36.9 ).

Main renal artery injury following blunt trauma is rare, with an estimated incidence of only 0.05%. It is common for the non-perfused kidney to otherwise appear intact. Using CE-MDCT, the absence of perfusion is obvious from the lack of renal opacification, diminished kidney size and, occasionally, preserved peripheral enhancement (rim sign) from intact collateral flow. The precise site of occlusion can often be seen, especially using multiplanar reformatted (MPR) images ( Fig. 36.10 ).

Clinically, significant renal vein injury is also rare. It can produce extensive perinephric bleeding, but as the venous pressure is low, this is usually limited to the retroperitoneum. CT findings include an enlarged renal vein containing thrombus, increased renal size, a delayed and progressively dense nephrogram owing to high venous outflow resistance and delayed excretion of IV contrast medium into the collecting system.

Management: Urine leaks from collecting system injury spontaneously resolve in up to 87% of cases and can often be managed with observation alone. Resolution is particularly likely if there is unimpeded antegrade urine flow. Urinomas can become infected because of urine stasis or bacterial contamination from penetrating injury and are managed by image-guided percutaneous drainage. Persistent collecting system leaks may be treated with nephrostomy or a double-J ureteral catheter insertion ( Fig. 36.11 ). Surgical repair may be required if non-surgical interventions do not resolve the leak. This is more likely in cases where the urine leak communicates with a low-pressure space such as the pleural or peritoneal cavity. Partial UPJ disruption can be managed with transurethral double-J catheter stenting, whereas large or complete disruptions require operative repair.

Optimal management of main renal artery occlusion remains controversial. Treatment options include immediate nephrectomy, non-operative management or endovascular or surgical revascularisation. Currently, non-operative management is usually chosen. Surgical revascularisation results are dismal, with long-term preservation of renal function in less than 25%. There are only case reports of treatment of main renal artery occlusion with endovascular stent placement ( Fig. 36.12 ); however, long-term results appear mixed.

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.