In blunt abdominal trauma the kidney is the most frequently involved organ in childhood because of its relatively large size, and because it is more mobile, more exposed, and less protected by comparison.
Mainly, schoolchildren and especially boys are involved.

1. Depending on the degree of trauma, the loss of the whole organ or of parts of it is possible.
2. In up to 10 % of the cases a combined urological malformation or a Wilms' tumor may be observed.

The etiology depends on the age. Falls in toddlers, motor vehicle trauma and sports injuries in schoolchildren.

Mostly blunt traumas. There are different grades of renal injuries:
Grade I: Contusion and/or subcapsular non-expanding hematoma without parenchymal laceration;
Grade II: Laceration and/or hematoma (less than 1 centimeter parenchymal depth);
Grade III: Laceration (more than1 centimeter parenchymal depth);
G rade IV: Laceration trough cortex, medulla and collecting system;
Grad V: Shattered kidney, avulsion of the hilus, thrombosis of the renal artery, or rupture of a single kidney, or malformed kidney.

The biomechanics of the blunt abdominal trauma.

- Pain in the flank and abdomen.
- Possibly, abrasions at the site of the blow e.g. of the abdominal wall, pain on palpation, and peritonism as well.
- Visible and palpable flank mass in case of large perirenal hematoma and/or urinoma.
- Gross and microscopic hematuria which does not occur in every case; however, the risk of a major injury is increased in case of gross hematuria. In pre-existing pathology of the kidney, gross hematuria occurs more frequently.

Lower grades of renal injuries recover without surgery and without major sequels. In severe grades the development of pseudocysts, caliceal diverticula (for instance an upper calix syndrome), and renal hypertension are possible; the former if no drainage of urinoma, reconstruction of pelvis and/or resection of major destroyed parts of the renal parenchyma is performed.

The differential diagnosis mainly includes causes of:
1. Hematuria.
2. Acute abdominal emergencies.
3. Abdominal tumor in case of not observed accident, and in incidental injury a history of trauma may be absent or, in case of late sequels, not remembered as in a pseuodocyst.

Work-up examinations depend on the degree of abdominal trauma. In general, blood and urine analysis, Doppler ultrasound (Doppler to exclude a renal artery thrombosis) and IVU for the evaluation of the pelvis and ureter. In severe trauma, immediate CT with contrast instead of the former imaging examinations, which allows to discover combined intraabdominal injuries and to assess the grade and precise anatomy of the renal trauma.
In one quarter of the injuries of the spleen the ipsilateral kidney is involved, too. In case of trauma to the kidney, other urogenital injuries also have to be considered.

In grade I and II injuries, non-operative management, and in grade IV and V, surgery is indicated. In grade III, the appropriate treatment depends on the precise pattern of kidney injury and on other factors, e.g. polytrauma or pre-existing pathology of the involved kidney. In urinoma, at least antibiotics are indicated. Hospitalization in case of severe kidney injury or polytrauma, and longterm follow-ups in operated patients and in those with border-line non-operative treatment.

Favourable prognosis except for grade V trauma with imminent loss of kidney and hemorrhagic shock; a thrombosis of the renal artery, which is typical for children and which is due to an endothelial damage, mostly leads to a loss of the kidney, even after immediate intervention.