Diagnostic ultrasound ( PDFDrive )

1802 PART V Pediatric Sonography
A
B
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D
FIG. 52.41 Renal Laceration and Perirenal Hematoma. (A) Longitudinal gray-scale image shows swelling, contour irregularity, and loss of
corticomedullary differentiation in the midportion of the left kidney (arrows). (B) and (C) Longitudinal intravenous (IV) contrast-enhanced ultrasound
images readily depict the parenchymal defect (arrow) and adjacent hematoma (*). (D) Longitudinal reformatted IV contrast-enhanced computed
tomography image demonstrates the midrenal laceration and surrounding hematoma. See also Video 52.6.
of the pyramids. At the outer edge of the pyramids, the interlobar
arteries give rise to the arcuate arteries, which follow the outer
contour of the pyramids. Cortical arteries arise from the arcuate
arteries and radiate into the cortex, following a direction similar
to that of the interlobar vessels. he venous circulation follows
that of the arteries, and simultaneous adjacent signals are oten
depicted with both color Doppler sonography and on spectral
analysis (Fig. 52.42).
he renal arterial bed normally has low resistance, and there
is a constant low of blood into the kidney throughout the cardiac
cycle. he normal adult renal arterial RI is estimated at 0.58 ±
0.05. Renal RI is age dependent, with children having higher RI
values and a trend toward decreasing values with increasing age.
his age dependency of the renal RI and, therefore of renal
vascular resistance, has been postulated to be dependent on serum
levels of active renin, because the maturational proile of the
renal RI more closely parallels that of active renin than of other
renal functional parameters. 106 Because there is a range of normal
RI values in children, and the renal RI is highest in the irst 3
months of life, 106 the diagnosis of abnormal intrarenal resistance
is much more reliably made in children by comparing waveforms
from the pathologic kidney with those of the normal kidney, or
tracings of the pathologic kidney obtained from one day to the
next.
Pulsed Doppler ultrasound tracings from the normal intrarenal
and main renal veins are somewhat variable: in some children
the pulsations from right atrial systole and diastole are clearly
visible, whereas in others the low is steadier. To-and-fro venous
low throughout the cardiac cycle may be seen in right-sided
heart failure or in the absence of arterial perfusion, as in the
setting of end-stage renal disease.
Causes of Increased Resistance to
Intrarenal Arterial Flow
Any increase in intrarenal arterial pressure results in decreased
low. Diastolic low occurs at the lowest pressure during the
cardiac cycle, so it will decrease or disappear before systolic
Doppler low curves are appreciably afected. he causes of
increased intrarenal resistance to low can be classiied as