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Fig. 15.4.12. Low-velocity bullet injury to the right kidney with arterial extravasation of contrast seen during the pyelographic phase of the CT examination indicates the presence of a urine leak (Harris et al. 2001). However, injury to the renal collecting system maybe missed during routine spiral CT. In all cases of suspected renal trauma evaluated with spiral CT, repeat scans of the kidneys should be performed 10 - 15 min after contrast injection (Brown et al. 1998b; Savage et al. 2003) (Fig. 15.4.11).

Contrast-enhanced CT can diagnose arterial extravasation in clinically stable patients. The extravasation can be used to localize anatomic sites of hemorrhage and to guide angiographic or surgical intervention. Although there is no statistical correlation between the number of patients with arterial extravasation and the need for surgical exploration (Yao et al. 2002), this finding should be considered an important indicator that a patient may be about to pass from hemodynamic stability to decompensation (Fig. 15.4.12).

Magnetic Resonance Imaging

While MRI is not used in the vast majority of renal trauma patients, Leppaniemi et al. investigated the use of high-field strength MRI (1.0 T) in the evaluation of blunt renal trauma. Magnetic resonance imaging scans were accurate in finding perirenal hematomas, assessing the viability of renal fragments, and detecting preexisting renal abnormalities, but failed to visualize urinary extravasation on initial examination. The authors concluded that MRI could replace CT in patients with iodine allergy and could be used for initial staging if CT was not available (Leppaniemi et al. 1997). The use of intravenous gadolinium-based contrast material has proved helpful in the assessment of urinary extravasation (Marcos et al. 1998). In a recent study comparing CT and MRI findings, the latter clearly revealed renal fracture with a nonviable fragment and was able to detect focal renal laceration not detected on CT due to perirenal hematoma (Ku et al. 2001).

However, MRI is not the first choice in managing the patient with trauma, because it requires longer imaging time, increases the cost, and limits access to the patient in the magnet during the examination. Thus, MRI may be useful in renal trauma only if CT is not available, in patients with iodine allergy, or in the very few cases where the findings on CT are equivocal.

Angiography

Computed tomography has largely replaced the use of angiography for staging renal injuries, since angiography is less specific, more time-consuming, and more invasive. Angiography, however, is more specific for defining the exact location and degree of vascular injuries and maybe preferable when planning selective embolization for the management of persistent or delayed hemorrhage from branching renal vessels (Kawashima et al. 2001).

Angiography can define renal lacerations, extravasation, and pedicle injury. Additionally, it is the test of choice for evaluating renal venous injuries. The most common indication for arteriography is nonvisualiza-tion of a kidney on IVP after major blunt renal trauma when a CT is not available. Common causes for nonvi-sualization are total avulsion of the renal vessels (usually presents with life-threatening bleeding), renal artery thrombosis, or severe contusion causing major vascular spasm (Fig. 15.4.13) (Kawashima et al. 2001).

Angiography is also indicated in stable patients to assess pedicle injury, if the findings on CT are unclear, and for those who are candidates for radiological control of hemorrhage (Eastham and Bennett 1992), and in cases of persistent symptomatology as well as laborato-

Fig. 15.4.13. Active arterial extravasation from the upper pole of the right kidney (arrow)

ry findings (decreasing hematocrit levels) suggestive of vascular renal injury, including prolonged hematuria (Sofocleous et al. 2005). Although complications following interventional embolization are rare, non-target vessel embolization or injury, hemodynamic compromise during or immediately after the procedure, repeated extravasation from the embolized site, pseudo-aneurysm or arteriovenous fistula formation, and loss of renal function or parenchyma have been reported.

Radionuclide Scans

Radionuclide scans may be helpful to document renal blood flow in the trauma patient with severe allergy to iodinated contrast material, or in following up repair of renovascular trauma (Kawashima et al. 2001), but are not generally used or needed. Renal scintigraphy can be performed with technetium (Tc)-99m glucohepto-nate, Tc-99m mercaptoacetyltriglycine, or Tc-99m die-thylenetriamine pentaacetic acid.

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