Diagnostic ultrasound ( PDFDrive )

454 PART II Abdominal and Pelvic Sonography
technique for screening for these more distal stenoses or
occlusions.
he evaluation of the celiac artery starts at its origin and
proceeds to its bifurcation into the splenic and common hepatic
arteries. As with all duplex Doppler studies, the sample volume
is advanced slowly through the celiac artery with waveforms
viewed every 2 to 3 mm and any abnormal sites documented
with an image. A standard set of waveforms from the proximal,
middle, and distal celiac artery is also obtained.
In patients with very severe celiac stenosis or occlusion, the
celiac artery oten receives its blood supply from the SMA through
the pancreaticoduodenal arcade. he blood low in the gastroduodenal
artery reverses, carrying the blood from the arcade
back to the common hepatic artery. Blood low then arrives at
the liver through the proper hepatic artery. To arrive at the
spleen, blood low from the gastroduodenal artery lows retrograde
in the common hepatic artery to reach the splenic artery.
Assessment of blood low direction in the common hepatic artery
should be part of the sonographic examination of the celiac
artery to detect cases in which this collateral low is present (see
Fig. 12.23).
he evaluation of the SMA starts at the origin and is carried
distally with viewing of waveforms every 2 to 3 mm, documenting
waveforms in the proximal, middle, and distal artery. he
examination can be performed with or without breath holding.
However, without breath holding, motion of the sample volume
with respect to the celiac artery and SMA oten occurs. With
the patient breathing, the sonographer may believe a waveform
is being obtained from the SMA when in fact the celiac artery
is being sampled or vice versa. Care should be exercised when
not using breath holding to guarantee that the proper vessel is
being evaluated. he SMA exam is also challenging because of
the very sharp turn it makes proximally. he turn creates problems
with accurate angle correction, and great care with the Doppler
angle is important.
he IMA has only a short trunk before it branches into the
let colic, sigmoidal, and superior hemorrhoidal arteries. In many,
perhaps most, patients the IMA is readily found, being the only
anterior branch of the abdominal aorta below the level of the
renal arteries. Its identiication can be impeded by patient size
and bowel gas and by the fact that it not as large of an artery as
the celiac artery or SMA. he IMA requires Doppler interrogation
only for 2 to 3 cm.
Finally, special maneuvers must be used when celiac artery
stenosis caused by the median arcuate ligament is suspected.
he traditional test is to remeasure low velocity in the artery
when the patient takes a deep inspiration. We have found this
test to be inconsistent. Reexamination of the artery with the
patient standing may be superior in its ability to show normalization
of velocities in the celiac artery in the setting of compression
by the median arcuate ligament. 120 Our experience supports that
remeasurement with the patient standing is greatly superior
compared with deep inspiration at normalizing blood low in a
compressed celiac artery (Fig. 12.26).
Mesenteric Artery Duplex Interpretation. Probably the
most widely accepted duplex criteria state that PSVs greater than
275 cm/sec in the SMA and 200 cm/sec in the celiac artery are
indicative of stenosis of greater than 70% in these arteries. 121
hese criteria are the ones suggested in the ACR Appropriateness
Criteria. 109 A more recent article suggests higher cutofs of 295 cm/
sec in the SMA and 240 cm/sec in the celiac artery as being
indicative of greater than 50% stenosis. 122 Other investigators
have found diastolic velocities to be a more accurate indicator.
One group found an end diastolic velocity (EDV) greater than
45 cm/sec with a PSV greater than 300 cm/sec to be an accurate
indicator of SMA stenosis greater than 50%. 123 Another group
found EDV greater than 70 cm/sec to be highly accurate for
diagnosing SMA stenosis of more than 50%, with an EDV greater
than 100 cm/sec needed to diagnose celiac artery stenosis of
over 50%. 124
In our laboratory, we have found the criteria using systolic
velocities (but not diastolic) to be highly sensitive but to result
in a substantial number of false-positive studies. Because of the
high sensitivity, we are conident that for a high-quality examination
that does not show systolic velocities higher than those
stated above (200 cm/sec in the celiac artery; 275 cm/sec in the
SMA), the diagnosis of chronic mesenteric ischemia is excluded.
When velocities reach one of the thresholds given above, we
look for secondary features that support the diagnosis of signiicant
stenosis before we become conident that the stenosis
is real. hese secondary features include an increased diastolic
velocity and the presence of signiicant poststenotic turbulence
(Fig. 12.27). Color bruit is also supportive of severe stenosis. In
the absence of secondary indings, the radiologist must consider
the possibility of a false-positive result. In this setting, we have
a low threshold to recommend either CTA or MRA to assist in
the diagnosis (Fig. 12.28).
here have been no widely accepted duplex Doppler criteria
for what constitutes signiicant stenosis of the IMA. herefore
evaluation for severe stenosis must be based on qualitative more
than on quantitative data. High systolic velocity in the presence
of high diastolic velocity and poststenotic turbulence is indicative
of severe stenosis. A PSV greater than 200 cm/sec in the IMA
may be an accurate indicator of severe stenosis. 125 Stenosis of
the IMA may be an important contributor to the development
of mesenteric ischemia. We have seen and treated many patients
with mesenteric ischemia in whom a stenotic IMA was the sole
blood supply to the gut.
Treatment of chronic mesenteric ischemia can be surgical or
endoluminal. Rates of restenosis with endoluminal treatment
are high, and thus, posttreatment surveillance is important. As
with all arteries treated with stents, restenosis is usually caused
by intimal hyperplasia, which is common within bare-metal
stents but even more common at the end of the stent (Fig. 12.29).
here is suggestion that covered stents may have a lower restenosis
rate in the mesenteric arteries. 126
Posttreatment duplex surveillance is confounded by Doppler
velocities oten remaining high in stented SMAs. 127,128 Some
speculate that this velocity elevation may be caused by a change
in the elastic properties of the arterial wall induced by its
incorporation of the stent.
he goal of stenting oten is not to restore normal low, but
only to restore enough low to make the patient asymptomatic.
hose arteries treated with stenting oten supply collateral low