RENAL TRAUMA

Renal trauma: classification, mechanism, grading
Classification
Two categories: blunt and penetrating. Proportion of all renal injuries which are blunt—Europe 97%, USA 90%, South Africa 25 - 85%. Proportion depends on whether urban or non-urban community.
This classification is useful because it predicts the likely need for surgical exploration to control bleeding. Experience from large series shows that 95% of blunt injuries can be managed conservatively, whereas 50% of stab injuries and 75% of gunshot wounds require exploration.

Blunt injures
- direct blow to the kidney
- rapid acceleration or rapid deceleration
- a combination of (1) and (2)

Rapid deceleration frequently causes renal pedicle injuries (renal artery and vein tears or thrombosis, PUJ disruption) because renal pedicle is the site of attachment of kidney to other fixed retroperitoneal structures.
Most common cause motor vehicle accidents (e.g. pedestrian hit by a car; direct blow combined with rapid acceleration and then deceleration). Seemingly trivial injuries (e.g. fall from a ladder), direct falls onto the flank, or sporting injuries can lead to significant renal injuries.

Penetrating injuries
Stab or gunshot injuries to the flank, lower chest, and anterior abdominal area may inflict renal damage. 50% of patients with penetrating trauma and haematuria have grade III, IV, or V renal injuries. Penetrating injuries anterior to the anterior axillary line are more likely to injure the renal vessels and renal pelvis, compared with injuries posterior to this line where less serious parenchymal injuries are more likely. Thus, renal injuries from stab wounds to the flank (i.e. posterior to anterior axillary line) can often be managed non-operatively.
Wound profile of a low-velocity gunshot wound is similar to that of a stab wound. High-velocity gunshot wounds (>350m/s) cause greater tissue damage due to stretching of surrounding tissues (temporary cavity).

Mechanism
The kidneys are retroperitoneal structures surrounded by peri-renal fat, the vertebral column and spinal muscles, the lower ribs, and abdominal contents. They are therefore relatively protected from injury and a considerable degree of force is usually required to injure them (only 1.5 - 3% of trauma patients have renal injuries). Associated injuries are therefore common (e.g. spleen, liver, mesentery of bowel). Renal injuries may not initially be obvious, hidden as they are by other structures. To confirm or exclude a renal injury, imaging studies are required. In children, there is proportionately less peri-renal fat to cushion the kidneys against injury, and thus renal injuries occur with lesser degrees of trauma.

Staging of the renal injury
Using CT, renal injuries can be staged according to the American Association for the Surgery of Trauma (AAST) Organ Injury Severity Scale. Higher injury severity scales are associated with poorer outcomes.
- Grade I Contusion (normal CT) or subcapsular haematoma with no parenchymal laceration
- Grade II <1cm deep parenchymal laceration of cortex, no extravasation of urine (i.e. collecting system intact)
- Grade III >1cm deep parenchymal laceration of cortex, no extravasation of urine (i.e. collecting system intact)
- Grade IV Parenchymal laceration involving cortex, medulla, and collecting system OR renal artery or renal vein injury with contained haemorrhage
- Grade V Completely shattered kidney OR avulsion of renal hilum