DOI:10.2214/AJR.05.0543
AJR 2006; 187:541-547
© American Roentgen Ray Society
MDCT Findings of Renal Trauma
Soo Jin Park1,
Jeong Kon Kim1,
Kyoung Won Kim1 and
Kyoung-Sik Cho1
1 All authors: Department of Radiology, Asan Medical Center, 388-1
Poongnap-dong, Songpa-gu, Seoul 138-736, South Korea.
Received March 28, 2005;
accepted after revision June 7, 2005.
Address correspondence to J. K. Kim
(rialto{at}amc.seoul.kr).
Abstract
OBJECTIVE. The purposes of this pictorial essay are to show MDCT
findings of renal trauma and describe the indications and protocol for
MDCT.
CONCLUSION. CT is indicated when patients have gross hematuria,
hypotension, lumbar spinal injury, and fractures of lower ribs or the
transverse process. The CT examination must be designed specifically for
urinary tract evaluation, and MDCT is especially useful for this purpose.
Injury to the kidney is graded I to V according to degree of laceration and
amount of hematoma.
Keywords: CT • kidney • MDCT • trauma • urinary tract
Introduction
The urinary tract is commonly involved in abdominal trauma, accounting for
8-10% of trauma-related injuries to abdominal organs
[1-3].
Current concepts of management of renal trauma tend to promote the use of less
invasive procedures and conservative management. In some cases of severe
injury, however, surgical intervention is mandatory
[1,
3-5].
It therefore is important to precisely determine whether to provide
conservative or surgical treatment.
Among the various imaging tools, CT is the technique of choice for
evaluating renal trauma
[2-4].
MDCT in particular can give accurate information about the status of the renal
parenchyma, blood vessels, and collecting system because this technique can
cover a target organ in a shorter time and with a thinner section slice than
conventional CT. In this pictorial essay, we show MDCT findings of renal
trauma and discuss the indications and protocol for MDCT.
Indications for CT
Gross hematuria is the most reliable indicator of serious urologic injury,
although the degree of hematuria does not correlate with the degree of renal
injury
[1-3].
CT is generally indicated when injured patients have gross hematuria,
hypotension (systolic blood pressure < 90 mm Hg), lumbar spinal injury, and
fractures of the lower ribs or a transverse process
[1-3].
Whenever urinary tract injury is clinically suggested, it is necessary to
perform CT designed specifically for urinary tract evaluation. In particular,
children with blunt trauma should undergo renal imaging regardless of the
presence of hypotension or the degree of hematuria
[2]. Patients need to be able
to tolerate immobilization for several minutes during the examination, and
therefore CT sometimes is unsuitable for patients in hemodynamically unstable
condition.
MDCT Protocol for Evaluation of the Urinary System
For appropriate evaluation of the urinary system, it is necessary to
evaluate all parts of the urinary tract, including the renal vasculature and
parenchyma. Our institution therefore routinely obtains vascular phase scans
and nephrographic excretory phase scans. A late excretory phase scan can be
added for patients with urinary tract obstruction. Three-dimensional
reconstruction can be performed to supplement the information obtained on
transverse CT images.
It is difficult to determine scanning parameters because MDCT detector
array systems vary. The general rule, however, is to specify slice thickness,
table speed, voltage, and current. Scan delay is important in urinary tract
imaging. For vascular phase scans, a scan delay of 25-40 seconds is
reasonable. However, because hemodynamic status varies greatly according to
patient factors, automatic bolus tracking is better than a fixed scan delay.
For evaluating the urinary tract, the scan delay can vary (180 minutes or
more) according to the degree of urinary obstruction.
Section thickness is another important parameter in CT acquisition. For
renal vascular imaging, most MDCT systems operate with a section thickness of
0.5-1.25 mm, which seems adequate for visualization of the status of the renal
vasculature because the diameter of the main renal artery is 4-6 mm and that
of the accessory arteries is usually 0.5-3 mm. An overlapped reconstruction
interval is recommended for CT angiography. For evaluation of the renal
parenchyma, a section thickness of 2.5-5 mm is sufficient. For visualization
of the status of the rest of the urinary tract, a section thickness of 1.5-3
mm seems appropriate.
Beam pitch of 1 or 1.5 seems suitable for MDCT, and voltage of 120-140 kV
is appropriate. Tube current should be carefully considered in young patients
to reduce radiation hazard. According to one guideline
[6], the weighted CT dose index
for the entire CT examination should be less than 35 mGy. To meet that
criterion, our institution uses 180-200 mA of current for each scan phase.
Blunt Trauma-Induced Renal Injury
Blunt trauma can be associated with various kinds of trauma, such as motor
vehicle accidents, falls, and blunt physical contact
[1]. The main mechanism of
blunt trauma is exertion of deceleration force on the renal parenchyma, major
renal vessels, and renal collecting system
[4]. Rapid deceleration thrusts
the kidney against the rib cage or vertebral column, resulting in contusion,
laceration, hemorrhage, and avulsion of the renal pedicle
[7].
Severity Grade and Corresponding CT Findings
Grade I
Grade I renal injuries, which account for approximately 80% of renal
injuries, are characterized by contusion and nonexpanding subcapsular hematoma
without parenchymal laceration
[1-3].
The CT findings of renal contusion include ill-defined and discrete areas of
low density and decreased enhancement. Subcapsular hematoma shows high-density
fluid collection between the renal capsule and renal parenchyma on unenhanced
scans and no contrast enhancement
[1,
3] (Figs.
1A,
1B, and
1C).
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Fig. 4B —6-year-old boy with grade IV injury to right kidney.
Thin-slab maximum-intensity-projection CT scan in oblique coronal plane
obtained at corticomedullary phase shows laceration throughout parenchyma
(arrow).
|
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Fig. 5 —8-year-old girl with segmental renal artery infarction in
left kidney. Contrast-enhanced CT scan in early excretory phase shows
well-circumscribed wedge-shaped nonenhancing areas (arrow).
|
|
Grade II
Grade II renal injuries are characterized by nonexpanding perinephric
hematoma confined to the retroperitoneum and by cortical laceration < 1 cm
deep without involvement of the collecting system
[1]. The CT finding of
perinephric hematoma is ill-defined, high-density fluid collection between the
renal parenchyma and Gerota's fascia
[1] (Figs.
2A and
2B). On CT scans renal
parenchyma laceration appears as irregular or linear parenchymal defects,
which may contain blood clots.
Grade III
Grade III renal injuries are characterized by nonexpanding perinephric
hematoma confined to the retroperitoneum and by laceration more than 1 cm
deep. In this grade of injury, the collecting system is preserved, and
laceration involves the renal cortex and medulla
[1] (Figs.
3A,
3B, and
3C).
Grade IV
Grade IV renal injuries are characterized by lacerations extending through
the renal collecting system and by damage of main renal vessels
[1] (Figs.
4A,
4B,
4C, and
4D). Segmental infarction can
be caused by thrombosis, dissection, or laceration of segmental renal arteries
[1]. CT findings of segmental
infarction include well-circumscribed linear or wedge-shaped, multifocal
nonenhancing areas in the renal parenchyma
[1-3]
(Fig. 5).
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Fig. 7B —37-year-old man with grade V injury to left kidney.
Contrast-enhanced CT scan at nephrographic phase shows hematoma
(arrows) around left renal artery and lack of enhancement of
kidney.
|
|
Grade V
Grade V renal injuries are characterized by shattering or devascularization
of the kidney [1,
3], by avulsion of the
ureteropelvic junction, and by complete thrombus or laceration of the main
renal vessels. "Shattered kidney" refers to gross disruption of
the renal parenchyma by multiple lacerations (Figs.
6A and
6B). The CT findings of
traumatic renal infarction caused by complete thrombus or laceration of the
main renal artery include lack of enhancement in the nephrographic phase on
the affected side (Figs. 7A
and 7B) and retrograde
opacification of the renal vein from the inferior vena cava
[3].
Iatrogenic Injury
The kidneys can be exposed to iatrogenic injuries such as intraabdominal
surgery, needle biopsy, percutaneous nephrostomy, and extracorporeal shock
wave lithotripsy. These iatrogenic injuries can result in renal hematoma,
laceration, pseudoaneurysm, and arteriovenous fistula (Figs.
8A and
8B).
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Fig. 9 —28-year-old man with infected hematoma after cortical
laceration. Contrast-enhanced CT scan at early excretory phase shows fluid
collection with wall enhancement (arrows) around right kidney.
|
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Complications After Renal Trauma
The complication rate for renal trauma ranges from 3% to 10%
[2]. Early complications
include urinoma, delayed bleeding, urinary fistula, abscess, and hypertension
[2,
8]. Urinoma is the most common
complication of renal trauma, and delayed bleeding usually occurs within 1-2
weeks after injury [2]. Urinary
fistula and abscess can be associated with an undrained fluid collection or a
large segment of devitalized renal parenchyma
(Fig. 9). Late complications
after renal trauma include hydronephrosis, arteriovenous fistula,
pyelonephritis, calculus formation, and delayed hypertension
[2].
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Abstract
Introduction
