Choice of Radiographic Study for Evaluation and Staging of Renal System Injury

The following should be considered when ordering studies in the trauma patient: (1) intravenous contrast agents can cause false-positive scan results for blood; (2) the total quantity of contrast required may limit the number of contrast studies, especially with shock; (3) hypotensive patients are at risk for developing contrast-induced acute renal failure; (4) abdominal CT reveals more information but requires a hemodynamically stable condition; and (5) an intraoperative IVP during an emergency laparotomy is needed to determine the status of the contralateral kidney.

A guideline for the selection of diagnostic imaging modalities is shown in Iable..254.-4.

PLAIN FILM Plain films are helpful in determining likelihood of renal trauma when abnormalities such as lower rib fractures, lower thoracic and upper lumbar spinal fractures, and pelvic fractures are seen. Loss of the psoas shadow or scoliosis may suggest injury. However, plain films are inappropriate for evaluating the renal tract.

COMPUTED TOMOGRAPHY Indications for imaging the kidneys following blunt trauma include gross hematuria, hematuria with multiple injuries or hemodynamic instability, and mechanisms that include rapid deceleration. When renal injury is suspected, CT is considered superior to other imaging modalities, including sonography, angiography, or IVP. CT is most likely to allow appropriate staging of renal injury ( Table^M—) and has several advantages. CT is a noninvasive modality with superior imaging detail that allows detection of even minor injuries and minimal extravasation, estimation of extent of hematoma, and simultaneous evaluation of other organs. The major disadvantage is that it can be performed only in a stable patient. Other disadvantages are cost and the difficulty in detecting vascular, particularly venous, injury. In children with hematuria, CT is the radiographic study of choice in evaluating renal injuries because a significant nonrenal intraabdominal injury is more likely than a renal injury.

Certain considerations should be kept in mind. Routine abdominal CT evaluation often stops at the iliac crests. In situations where renal system trauma is under consideration, the examination should be extended to the pelvis. Also, contrast enhancement is usually indicated for appropriate evaluation. Both oral and intravenous contrast material is often given when other intraabdominal trauma is under consideration. However, if enhanced CT is required to image the kidneys and collecting system appropriately, gastrointestinal contrast studies may need to be delayed to allow accurate interpretation.

MAGNETIC RESONANCE IMAGING Magnetic resonance imaging (MRI) is generally not a first-line imaging modality. However, its accuracy appears to be similar to that of CT. It may prove useful in stable patients who have dye allergy.

ANGIOGRAPHY Angiography has largely been replaced by CT. It still has a role when vascular injury is suspected and remains the gold standard for detecting renal venous injury. Arteriography may be indicated in selected patients when no renal function is evident on IVP or CT. Other indications include penetrating trauma where vascular injury is high, and when embolization is considered for persistent or delayed hemorrhage. It should be kept in mind that the kidney can tolerate only 4 to 6 h of warm ischemia. Arteriographic confirmation may cause an undue delay.

ULTRASOUND Ultrasound examination of the right upper quadrant (Morrison pouch) and the left upper quadrant (splenorenal recess) is part of the Focused Assessment for the Sonographic Examination of the Trauma Patient (FAST) examination (see Chap...243 and Chap,.295) but has little accepted role to date in the initial detection (or exclusion) of significant renal injury in the United States. Certain conditions, such as patient position and fractured ribs, make such examinations difficult to perform. Furthermore, sonography reveals nothing about renal function. In Europe, however, ultrasound is used as a technique of choice for the initial imaging modality in some centers.10

RADIONUCLIDE IMAGING Radionuclide imaging has a very limited role now, given the superiority of CT. It may still be useful in patients with iodinated dye allergy in whom technetium-99m glucoheptonate can be safely used.

INTRAVENOUS PYELOGRAM Formal IVP with or without tomograms can be used in stable patients if CT is unavailable. However, it is not the ideal study in the trauma setting, given the need for quality imaging. If used, the dose of contrast material needs to be greater than the standard 1 mL/kg to account for hemodilution for intravenous fluid administration and possible impaired renal perfusion. The recommendation is 2 mL/kg up to 150 mL of 60% iodinated contrast. In patients with a history of allergy, a nonionic agent, such as iohexol, can be used. Alternatively, noncontrast CT, radionuclide imaging, or MRI may offer satisfactory results.

IVP remains the mainstay of diagnosing ureteral injuries, although it is not infallable. 11 Extravasation of die is the classic finding, although on occasion there is absence or delay of contrast in the distal collecting system. However, many are now using spiral CT to diagnose ureteral injuries, since it offers the advantage of viewing the entire retroperitoneal space and has the ability to detect urinomas.

A "one-shot" IVP can be obtained in unstable patients in the emergency department or operating room. This technique entails injecting 2 mL/kg intravenous contrast material about 5 min before the film is taken. However, if the patient's blood pressure is 70 mmHg or less, the kidneys may not concentrate the contrast material and are more susceptible to injury by it.

CYSTOGRAPHY For suspected bladder injuries, plain-film cystogram is classically used. About 300 to 500 mL (5 mL/kg in children) of contrast media is instilled retrograde into the bladder under gravity from 2 ft (60 cm) above the patient. At a height of 2 ft, the intravesical pressure generated approximates the physiologic voiding pressure. Unless adequate bladder pressure is generated, the cystogram may be falsely negative. Ideally, the procedure is performed under fluoroscopy to avoid filling the peritoneal cavity with contrast material in the event of a tear. A film of the distended bladder is taken, and a postdrainage view is obtained to note any extravasation not evident on the initial film. Some authorities suggest that the bladder be "washed out" with saline solution prior to obtaining the post-"wash-out" view.

Allowing intravenous contrast material to flow into the bladder following intravenous injection is not considered an appropriate technique, 12 although some continue to advocate clamping a urinary catheter to allow antegrade filling of the bladder. 13 A CT cystogram may be preferred in a patient who requires intravenous contrast-enhanced CT imaging for other indications.14 However, contrast material must still be injected retrograde.15 Postvoiding scans are generally not required, since CT allows full imaging of the retrovesicular space.

A prospective investigation studying indications for cystography in blunt trauma with hematuria or pelvic fracture concluded that it was appropriate and cost effective to restrict this procedure to patients with gross hematuria only.16 The authors contend that patients with pelvic fracture and microscopic hematuria do not routinely require cystography.

Urethral injuries are also investigated by retrograde cystography. An unlubricated urinary catheter is placed about 2 to 3 cm into the navicular fossa of the distal urethra, and the balloon is inflated with 1 to 3 mL water. Approximately 20 to 30 mL of contrast material is injected. An oblique view is obtained. The entire length of the urethra is seen on the plain film when the x-ray is taken as the last 10 mL of the contrast solution is injected. Occasionally, a patient may be transferred from another facility with an indwelling urethral catheter in place. A retrograde urethrogram can still be performed without removing the catheter, by injecting contrast solution into the urethra through a small feeding tube placed adjacent to the urethral catheter.

Urethral injuries should not be investigated in cases of pelvic trauma until it is certain that pelvic angiography or embolization is not required. Also, if the prostate gland was grossly displaced on rectal examination, the urethra is transected, and a retrograde study is not needed, at least not during the initial evaluation.

CONTRAST STUDIES When both upper and lower tract injuries are suspected, imaging needs to be approached with particular attention to order. While the most serious potential injury should guide the order of obtaining images, oral contrast material should generally not be given before an IVP or cystogram because gastrointestinal contrast may obscure important findings. Patients with potential bladder injuries may require a retrograde urethrogram to evaluate possible urethral disruption first. If injury is noted, cystography can be accomplished by suprapubic puncture.

IMAGING CONSIDERATIONS FOR OTHER CONDITIONS A perinephric hematoma may initially be difficult to distinguish from a urinoma. A delayed CT image may demonstrate contrast, indicating a urinoma. Patients with such perinephric collections can be followed with ultrasound studies. A nuclear 99mTc renal scan can also detect a persistent urine leak.

Significant adrenal injuries are relatively rare. Adrenal hematomas may be found in up to 3 percent of patients with blunt abdominal trauma. They are usually associated with other significant thoracic and abdominal injuries. Adrenal hematomas can be followed by CT or sonography and usually resolve over a few months. Long-term sequelae are unlikely.

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