Diagnostic ultrasound ( PDFDrive )

658 PART II Abdominal and Pelvic Sonography
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B
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FIG. 18.41 Renal Artery Stenosis: Donor Portion. (A) Color Doppler ultrasound of donor renal artery anastomosis shows focal area of aliasing
(arrow). (B) Power Doppler shows area of narrowing in this region (arrow). (C) Spectral Doppler shows elevated angle-corrected velocities at the
site of the arrow, greater than 400 cm/sec.
Intraparenchymal arterial stenosis may be observed in
chronic rejection as a result of scarring in the tissues surrounding
the involved vessels. On spectral Doppler ultrasound, a prolonged
AT may be observed in the segmental and interlobar arteries,
with a normal main renal artery waveform. 45
Treatment options for renal artery stenosis include percutaneous
transluminal angioplasty, endovascular stent placement, and
surgery. Surgical management of these transplants involves
resection and revision of the stenosis with insertion of a patch
grat at the stenotic segment. 46
A false-positive Doppler diagnosis of renal artery stenosis
can occur if there is an abrupt turn in the main renal artery, if
the artery is severely tortuous, or if there are errors in Doppler
technique (Fig. 18.44). Inadvertent compression of the main
renal artery by the sonographer while performing spectral interrogation
may also produce transient narrowing of the artery and
elevated PSV readings. Turning the patient in a decubitus position
such that the anterior abdominal or pelvic wall tissues are displaced
from lying over the transplant can reduce external pressure
on the allograt during scanning.
Venous Thrombosis
Occlusive renal vein thrombosis is slightly more common than
arterial thrombosis, occurring in up to 4% of transplants, and
is associated with acute pain, swelling of the allograt, and an
abrupt cessation of renal function between the third and eighth
postoperative day. Risk factors include technical diiculties at
surgery, hypovolemia, propagation of femoral or iliac thrombosis,
and compression by luid collections. 58,64
On gray-scale ultrasound, the allograt may appear
enlarged, and in rare cases intraluminal thrombus may be
detected in a dilated main renal vein or within the intraparenchymal
venous system. Spectral and color Doppler ultrasound
will show a lack of venous low in the renal parenchyma,
absence of low in the main renal vein, and reversal of diastolic
low in the main renal artery, as well as sometimes in
the intraparenchymal arteries 65,66 (Fig. 18.45). he sonographer
should be aware that reversal of low in diastole in the
main renal artery or the intraparenchymal arterial branches
is highly suggestive of renal vein thrombosis only in the
absence of venous low in the renal parenchyma and main
renal vein.
Reversed diastolic arterial low, with preservation of
venous low, is a nonspeciic inding indicating extremely high
vascular resistance in the small intrarenal vessels or main hilar
vessels. he outcome for these patients is generally poor, with
allograt loss rates of 33% to 55%. Potential causes of reversed
diastolic low include acute rejection, ATN, peritransplant
hematomas (compressing renal grat or hilar vessels), and
glomerulosclerosis. 67
Renal Vein Stenosis
Renal vein stenosis most oten occurs from perivascular ibrosis
or external compression by adjacent luid collections. he renal
cortex appears either normal or hypoechoic, and on color Doppler,
aliasing is identiied at the stenotic region because of focal,
high-velocity turbulent low. On spectral Doppler sonography,
a threefold to fourfold increase in velocity across the region of