Diagnostic ultrasound ( PDFDrive )

1006 PART III Small Parts, Carotid Artery, and Peripheral Vessel Sonography
seen, particularly in the AVF. In severe cases of arterial steal,
surgical revision may be necessary.
FIG. 27.65 Graft Wall Irregularity and Degeneration From Repeated
Punctures. Note bright linear parallel walls posteriorly seen in polytetraluoroethylene
hemodialysis grafts. Stars (*) denote areas of degeneration.
See also Video 27.28.
vein. 152,153 he juxta-anastomotic stenosis will show visible
narrowing and a PSV ratio of greater than or equal to 3 : 1
(Fig. 27.66). A draining vein stenosis is deined by visible narrowing
and a PSV ratio of 2 : 1 identiied within the draining
vein 2 cm cranial to the anastomosis 141 (Fig. 27.67). Feeding
artery stenosis greater than 2 cm proximal to the anastomosis
is uncommon; these are characterized by a PSV ratio of 2 : 1
with visible narrowing. Poststenotic waveforms show delayed
systolic upstrokes that may suggest proximal arterial stenosis
and prompt further direct evaluation of the feeding artery
more cranially.
Graft. Grat abnormalities are similar to those described
earlier for AVF, with difering diagnostic thresholds and criteria.
Several studies have indicated that grats with decreased blood
low are at increased risk for thrombosis. 141,154,155 he four
sonographic criteria used to characterize grat stenosis are
(1) luminal narrowing on gray-scale imaging, (2) a highvelocity
jet on color Doppler, (3) a PSV ratio greater than 2 : 1
for the venous anastomosis or draining vein, and (4) a PSV
ratio greater than 3 : 1 for the arterial anastomosis. he most
common site of grat stenosis is the venous anastomosis.
Other, less frequently used sites are the draining vein, intragrat
region, arterial anastomosis, and central veins (Fig. 27.68,
Video 27.29).
Arterial Steal
Arterial steal is deined as low reversal in the native artery caudal
to the anastomosis and may be asymptomatic, or associated with
clinical indings such as hand pain and paresthesias that can worsen
during hemodialysis. 156 In severe cases, ischemia or tissue necrosis
of the ingers can occur. Sonographic evaluation may show reversal
of low in the distal artery, and rarely shows an arterial occlusion
(Fig. 27.69). Brief manual compression of the grat can demonstrate
a change in the reversed arterial low, producing an antegrade
high-resistance low pattern toward the hand. 157
It is important to note that asymptomatic low reversal in the
artery downstream from the arterial anastomosis is frequently
Arm and Leg Swelling With Arteriovenous Fistula
or Graft
When there is upper extremity swelling associated with an AVF
or grat, the ipsilateral axillary, subclavian vein, and IJV should
be included in the postoperative sonographic evaluation. Occasionally,
a DVT of the brachial, axillary, or subclavian vein is
the cause of arm swelling in a patient with an AVF or grat. If
an upper extremity DVT is not found, spectral Doppler imaging
of the IJV and subclavian vein may provide indirect evaluation
of the brachiocephalic veins.
As discussed earlier in this chapter, monophasic venous
waveforms of the subclavian vein and IJV suggest central venous
stenosis or occlusion (Fig. 27.70). he absence of phasicity in
the central veins is less speciic for central venous occlusion in
patients with a grat than in patients with an AVF because of
the larger blood low volume rate within grats. Findings suggestive
of central stenosis or occlusion are visible narrowing, focal
turbulence, focally elevated velocity, and collaterals. If a central
stenosis or occlusion is suspected, central vein assessment with
magnetic resonance imaging (MRI) or venography may be useful
because a central stenosis severe enough to cause arm swelling
may be present despite adequate or high AVF low.
Arteriovenous Fistula and Graft Occlusion
Access occlusion can be determined by physical examination.
However, in the case of signiicant arm swelling or an inexperienced
examiner, ultrasound evaluation may be useful. hrombosis
can be visualized within the vessel lumen on gray-scale
imaging (Fig. 27.71) and conirmed by lack of color or spectral
Doppler low within the afected portion of the AVF, grat,
or draining vein. Slow low may be identiied with power
Doppler when nonocclusive thrombus is present. Arterial inlow
will typically be high resistance low in the occluded AVF or
grat.
CONCLUSION
Ultrasound plays an important role in evaluating the peripheral
vasculature. Although peripheral artery ultrasound is commonly
considered for its uses in peripheral artery atherosclerotic disease,
the technique can be applied in numerous clinical scenarios. For
evaluation of stenosis in native or bypassed vessels, the concepts
are similar, although threshold values may difer. For evaluation
of aneurysm, pseudoaneurysm, or AVF, the examination can be
more localized in its scope to determine the size of the abnormality
by gray-scale and the use of Doppler to focus on the inlow and
outlow characteristics.
For the upper and lower extremity deep venous system,
ultrasound is the initial imaging modality of choice. In the
occasional case where sonographic indings are equivocal or
nondiagnostic, especially when there is concern for central
thrombosis, correlation with MRI, CT, or catheter venography
may be helpful. Ultrasound can provide an accurate,
rapid, portable, low-cost, noninvasive method for screening,