Diagnostic ultrasound ( PDFDrive )

CHAPTER 18 Organ Transplantation 653
A
B
FIG. 18.34 Acute Tubular Necrosis. (A) Sagittal and (B) transverse sonograms show increased cortical thickness and echogenicity as well
as loss of the normal corticomedullary differentiation.
rises to the nondependent portion of the lumen, whereas milk
of calcium does not (Fig. 18.39).
A
B
C
D
FIG. 18.35 Intrarenal Spectral Waveforms in Four Patients. (A)
Normal waveform shows resistive index (RI) of 0.70. (B) RI in a gray
zone (0.85). (C) RI elevated (1.0) with no low in diastole. (D) Elevated
RI (>1.0) with reversal of low in diastole. This is seen with severely
increased vascular resistance in the kidney from rejection or renal vein
thrombosis.
Gas can be observed within the collecting system in emphysematous
pyelonephritis, appearing as a bright echogenic focus
with distal dirty shadowing. Milk of calcium cysts can produce
dirty shadowing, mimicking an intrarenal abscess. Scanning the
patient in a decubitus position allows for diferentiation; gas
Prerenal Vascular Complications
Arterial Thrombosis
Renal artery thrombosis occurs in less than 1% of transplants,
usually within the irst month of surgery, and is oten initially
asymptomatic. he most common cause is hyperacute or acute
rejection, which results in occlusion of the intraparenchymal
arterioles with retrograde main renal artery thrombosis. Other
predisposing factors include a young pediatric donor kidney,
atherosclerotic emboli, acquired renal artery stenosis, hypotension,
vascular kinking, cyclosporine, hypercoagulable states, intraoperative
vascular trauma, and poor intimal anastomosis. 58
Global infarction of the allograt occurs when there is
occlusive thrombosis of the main renal artery, with no perfusion
to the renal parenchyma. On gray-scale ultrasound, the kidney
may appear difusely hypoechoic and enlarged. On color and
spectral Doppler ultrasound, complete absence of arterial and
venous low distal to the occlusion, within both the hilar and
the intraparenchymal vessels, is observed. Although surgical
thrombectomy with arterial repair is oten attempted, nephrectomy
is frequently indicated in these patients. 46
Segmental infarction of the allograt may occur in transplants
with a single main renal artery with thrombosis of a major arterial
branch (Fig. 18.40), in transplants with multiple renal arteries
where a single artery is thrombosed, and in patients with systemic
vasculitis. On gray-scale sonography, a segmental infarct may
appear as a poorly deined hypoechoic region, a hypoechoic
mass, or a hypoechoic mass with a well-deined echogenic wall.