RENAL INJURY

NAVDEEP SINGH

RENAL INJURY• Renal injury is common, occurring in 8–10% of cases.• About 90% of renal injuries result from blunt force injury and 10% from penetrating trauma.• imaging depends on - haemodynamic status - haematuria - other injuries - USG is relatively insensitive for detection of renal lacerations and contusions, extravasation of blood or urine, collecting system disruption and parenchymal haematoma - A positive ultrasound was more likely with higher grades of renal injury, but a negative renal ultrasound had a very low negative predictive value

• The significance of haematuria as an indicator of significant renal injury has been the subject of debate

• As a rule, all patients with penetrating flank and back trauma should have a CT examination

Indication Imaging studyPenetrating flank and back trauma Chest, abdominal–pelvic CT with IV and oral

contrast mediumGross haematuria Abdominal–pelvic CT with oral and IV

contrast medium if haemodynamically stable or resuscitated

Haemodynamically unstable requiring emergency surgery

Intraoperative IVU when stabilized

Haemodynamically stable with microscopic haematuria, but no other indication for abdominal–pelvic CT

Observation until resolution of haematuria

Haemodynamically stable with microscopic haematuria, but other indications for abdominal–pelvic CT (+ abdominal examination, decreasing haematocrit, indeterminate result of peritoneal lavage or abdominal ultrasound, unreliable physical examination)

Abdominal–pelvic CT with oral and IV contrast medium

Haemodynamically stable with or without microscopic haematuria with evidence of major flank impact (e.g. lower posterior rib or lumbar transverse process fracture, major contusion of flank soft tissues)

Abdominal–pelvic CT with oral and IV contrast medium

AAST injury grade DescriptionI Renal contusion or subcapsular haematoma

with intact capsule

II Superficial cortical laceration that does not involve the deep renal medulla or collecting system or nonexpanding perinephric haematoma

III Deep laceration(s) with or without extravasation of urine

IV Lacerations extending into the collecting system with contained urine leak

V Shattered kidney, renal vascular pedicle injury, devascularized kidney

• CT of renal contrast medium extravasation. (A) Nonenhanced CT performed approximately 24 h after intravenous contrast-enhanced study for blunt trauma shows iodinated urine that has extravasated into the right renal parenchyma at several points, possibly through disruption of the collecting system tubules. (B) Coronal reformation shows several areas (arrows) of residual extravasated contrast-enhanced urine.

            

• CT of renal infarct. IV contrast-enhanced CT image reveals a sharply demarcated region of low density (no enhancement) in the upper pole of the right kidney, indicating segmental infarction after blunt trauma.

• Subcapsular renal haematoma. The haematoma compresses the right renal parenchyma leading to delay in renal perfusion and contrast excretion. The renal parenchyma otherwise appears intact.

Description or CT finding

ISuperficial laceration(s) involving cortex

Renal contusion(s)

<1 cm subcapsular haematoma

Perinephric haematoma not filling Gerota's space and no

Segmental renal infarction

II Deeper renal laceration extending to medulla, with intact collecting system

> 1 cm subcapsular haematoma with intact renal function

Perinephric haematoma limited to and not distending the perinephric space; no active bleeding

IIILaceration extending into collecting system with urine extravasation limited to retroperitoneum

Perinephric haematoma distending perinephric space or extending into pararenal spaces; no active bleeding

IVFragmentation (three or more segments) of the kidney (usually partially devitalized with large perinephric haematoma)Devascularization > 50% of parenchyma

Main renal pedicle injury

Active bleeding by CT

Extravasation of urine into peritoneal cavity or extensive extravasation

Subcapsular haematoma compromising renal perfusion

• Most renal injuries are minor (75–98%)[16], represented by CT grades I and II, and are successfully treated without intervention. Contusions are visualized as ill-defined low attenuation areas with irregular margins. They may appear as regions with a striated nephrogram pattern due to differential blood flow through the contused parenchyma.

• Segmental renal infarcts are relatively common in blunt renal trauma, and result from stretching and subsequent occlusion ofan accessory renal artery, extrarenal or intrarenal branches of the renal artery, or a capsular artery[18]. These infarcts appear as sharply demarcated, wedge-shaped areas of very low attenuation, typically involving the renal pole

• Post-traumatic urinoma. Injury to the collecting system with contrast collection (urine) accumulating in the urinoma posterior to the right kidney.

• Major renal injury. Posterior view of a volumetric 3D image shows a renal split with the lower pole significantly displaced caudally. Blood supply is maintained by an attenuated single vessel.

• CT of active renal haemorrhage. Multiple foci of active bleeding are seen in the centre of a large perinephric haematoma displacing the kidney markedly anteriorly, indicating a high-pressure bleeding source. There is haemorrhage in both the anterior and posterior pararenal spaces. The posterior portion of the kidney is lacerated.

• Subcapsular renal haematomas are rare, particularly in older adults, as the renal capsule is not easily separated from the cortex. In most cases the injury will resolve without specific treatment, although acute or delayed onset of hypertension from renal parenchymal compression (Page kidney) should be sought. Large subcapsular haematomas could theoretically compress the kidney to near systolic level pressures, preventing perfusion and requiring surgical release of renal tamponade.

• Renal lacerations can be either superficial, involving the cortex only, or deep, extending to the renal medulla. Usually lacerations are self-limited injuries, typically accompanied by small amounts of perinephric haemorrhage.

• In blunt trauma the kidneys are displaced outward toward the lateral aspect of the retroperitoneum. This motion stretches the intima beyond its elastic limit, leading to dissection. Later, clot begins to form on and around the disrupted intima, leading to partial or complete occlusion of the renal artery.

• The artery usually occludes between the proximal and middle third of the vessel

• Using contrast-enhanced spiral CT, the lack of perfusion is obvious from the lack of opacification, diminished size and (occasionally) peripheral enhancement (rim sign) from collateral vessels.

• Clinically significant renal vein disruption is less common than injury to the renal artery. It can produce extensive perinephric bleeding, but as the venous pressure is low this is usually limited in the retroperitoneum

• Injury to the renal pelvis is most likely to result from hyperextension with secondary overstretching of the pelvis. The injury manifests as gross contrast/urine extravasation near the pelviureteric junction.

• The injury can be missed on helical CT and can mimic a duodenal rupture.

• Severe fragmentation of the renal parenchyma usually requires surgical treatment and typically results in nephrectomy