The kidney is injured in up to 5% to 10% of all severe trauma cases. At most urban trauma centers, approximately 80% to 90% of kidney injuries are blunt, while the remainder are penetrating. Children are more likely to sustain blunt renal injuries because of the relative large size of their kidneys, scant perirenal fat, and incomplete rib ossiﬁcation. Blunt renal injuries are often minor and heal spontaneously, whereas penetrating renal injuries are typically signiﬁcant and often require intervention.
PRESENTATION AND DIAGNOSIS
Patients should be suspected of having renal injury if there is trauma to the ﬂank, abdomen, or lower chest; ﬂank ecchymosis or tenderness; low posterior rib fractures; or lumbar transverse process fractures. Although hematuria is the major symptom and is seen in the vast majority of cases, it may be absent in injuries to the renal pedicle or ureteropelvic junction. In addition, the degree of hematuria often does not correspond to the severity of the renal injury.
A detailed history must be obtained regarding the circumstances of the trauma. Falls or high-speed motor vehicle accidents, for example, may cause deceleration injuries to the renal pedicle. In the setting of gunshot wounds, it is important to determine if the injury is due to a high or low velocity missile because high velocity missiles often cause more extensive kidney injury and delayed necrosis.
The location of any abdominal penetration must also be carefully documented. For example, stab wound entrance sites posterior to the anterior axillary line and below the nipple line are unlikely to have associated intraperitoneal organ injury or to warrant abdominal exploration. The entrance and exit wound sites of a gunshot should be marked with radiopaque markers so that the missile path can be inferred on imaging.
In unstable patients who require immediate abdominal exploration, urologists often advocate for a one-shot intravenous pyelogram. Intravenous contrast is administered at 2 cc/kg of body weight, followed by a single abdominal radiograph 10 minutes later. The primary aim of this study is to determine the function of the contralateral kidney to avoid removing a solitary kidney. In many cases, however, it can produce ambiguous results that are difﬁcult to interpret. Therefore, many trauma surgeons instead simply palpate the contralateral side to assess for the presence of a second kidney. Another option is to infuse intravenous methylene blue and temporarily occlude the ureter ipsilateral to the injured kidney. Blue urine in the Foley bag indicates a functional contralateral kidney.
In stable patients, in ications for imaging a suspected kidney injury include:
1. Blunt trauma and gross hematuria
2. Blunt trauma, microscopic hematuria (5 RBC/ hpf), and shock
3. Major acceleration-deceleration injury
4. Penetrating ﬂank, back, or abdominal trauma associated with gross or microscopic hematuria, or with a missile path that is in line with the kidney
6. Associated injuries/physical signs suggestive of underlying renal injury
In stable patients, computed tomography (CT) with intravenous contrast is the imaging study of choice for demonstrating renal parenchymal injury, perirenal/retroperitoneal hematomas, urine extravasation, injuries to the renal hilum, and associated intraabdominal organ injuries. It is essential to obtain both an arteriographic phase to assess for major vessel injury and a delayed pyelographic phase to assess for contrast extravasation.
Parenchymal contusions are noted as areas of reduced enhancement, whereas lacerations appear as linear, blood-containing areas that interrupt the parenchyma. Hematomas are visible as hyperattenuating collections that, if large and conﬁned to the subcapsular space, can compress the adjacent renal parenchyma.
Ultrasonography is sometimes used as an initial screen but offers limited value. For example, although ultra-sound can demonstrate perirenal ﬂuid collections, it cannot distinguish fresh blood from extravasated urine.
Arteriography and superselective embolization have important roles in the evaluation and treatment of post-traumatic delayed renal bleeding or pseudoaneurysms. In select cases, arteriography and endoluminal stent placement have also been successfully used to manage renal artery intimal tears and thrombosis from blunt trauma.
Based on the ﬁndings from imaging studies, injuries can be graded according to criteria set by the American Association for the Surgery of Trauma. The odds of intervention and nephrectomy rise with each increase in grade.
Blunt renal injuries are often low-grade and can thus receive conservative management. Even if there is urine extravasation, spontaneous resolution is likely unless there is complete disruption of the UPJ (grade 5). Conservative management includes strict bed rest until hematuria resolves, frequent assessments of hematocrit, and reimaging after 3 to 5 days if there is urine extravasation. Persistent bleeding demands repeat imaging, arteriography, or surgical exploration. Worsening or symptomatic urine leaks often require ureteral stenting. Penetrating renal injuries generally require exploration because they are often high grade and associated with other major organ damage. Roughly three fourths of renal gunshot wounds and half of renal stab wounds demand exploration.
The absolute indication for surgical exploration of any renal injury is persistent and potentially life-threatening bleeding. Such bleeding will occur if there is avulsion of the main renal artery or vein, or if there is “shattering” of the kidney by multiple deep lacerations. A pulsatile, expanding or unconﬁned retroperitoneal hematoma suggests ongoing bleeding that requires intervention.
Relative indications for surgical exploration include:
· UPJ avulsion
· High-grade penetrating renal injuries
· High-grade blunt renal injuries where abdominal exploration is performed for other intraabdominal injuries
· Devitalized renal parenchyma exceeds 50% of total
· Persistent urinary leakage with failed endoscopic management
· Persistent vascular injury with failed angiographic management
· Bilateral renal artery thrombosis (or thrombosis in a solitary kidney)
· Incomplete staging that demands either further imaging or renal exploration
The injured kidney is best exposed through a midline transperitoneal incision. Proximal vascular control must be established before entering the renal fascia. If it is not, there is a high risk of releasing a tamponade and causing a massive bleed that necessitates a nephrectomy. When consistent proximal vascular control of the renal pedicle is performed, however, the nephrectomy rate for renal trauma is low.
Repair of the damaged kidney requires broad exposure of the injured area, sharp excision of all nonviable parenchyma, meticulous hemostasis, water-tight closure of the collecting system, and parenchymal defect closure over a bolster.
The most common complications after renal trauma include prolonged urinary extravasation, delayed bleeding, arterial pseudoaneurysm, abscess, urinary ﬁstula, and hydronephrosis. Renovascular hypertension may occur after renal trauma but is almost always transient. A rare, sustained hypertension is usually seen with sub-capsular hematomas that exert signiﬁcant parenchymal compression, causing decreased renal perfusion and subsequent re ease of renin (a phenomenon known as Page kidney).