Sonography of TIPS
(Transjugular Intrahepatic Portosystemic Shunts)
Author:
Sharlene A. Teefey, M.D.
Objectives: Upon the completion of this CME article, the reader will be able to:
1.
Discuss the types of patients in which a TIPS stent might be placed, the benefits and
contraindications, and the reasons behind why the stent might malfunction.
2.
Describe the sonographic techniques that can be used to best visualize the vessels
involved in hepatic flow.
3.
Discuss the various sonographic parameters, such as stent velocity, main portal vein
velocity, hepatic artery velocity and flow direction, that can be utilized when
scanning a patient for the possibility of TIPS stent stenosis
Background:
In patient populations with cirrhosis, the prevalence of esophageal varices ranges
from 25% to 70% depending on the number of patients with end stage liver disease. Up to
33% of patients with documented varices will experience an episode of hemorrhage, usually
within the first two years of the diagnosis. The risk for re-bleeding approaches 70%.
Despite aggressive medical management, the mortality rate from variceal hemorrhage is
approximately 30 to 40%.
Currently, endoscopic sclerotherapy or variceal band ligation are the accepted
therapeutic interventions for acute variceal hemorrhage. Vasoactive drugs such as
vasopressin or octreotide may be used concomitantly. These drugs decrease splanchnic
arterial blood flow, which in turn decreases portal venous blood flow and pressure. Up to
90% of variceal bleeding episodes can be controlled with endoscopic and or pharmacologic
therapy. For the 10% of patients who fail medical therapy, either an operation (surgical
shunt or liver transplantation) or transjugular intrahepatic portosystemic shunt (TIPS) is
recommended.
Acute or recurrent variceal hemorrhage is the most common indication for TIPS
placement. TIPS is the procedure of choice in most patients with cirrhosis in whom the
mortality rate from a shunt operation is unacceptably high. Other indications include
refractory ascites or hydrothorax related to liver disease and Budd-Chiari Syndrome.
Improved control of ascites has been reported in 75% to 90% of patients. One recent study
showed that the combination of a low bilirubin and creatinine was strongly associated with
resolution of ascites, whereas patients with advanced liver failure and renal failure did not
benefit from TIPS placement.
There are several contraindications to TIPS placement. Patients with severe hepatic
encephalopathy and liver failure are at high risk for a worsening of their encephalopathy and
liver function post TIPS and probably should not be stented. Likewise, patients with
chronic portal vein thrombosis, in particular, those with narrowed sclerosed veins or
cavernous transformation are not candidates for TIPS placement. Nevertheless, some
experienced centers have been successful in re-canalizing the portal vein in patients with a
subacute or acute thrombus prior to the creation of a shunt. Severe right heart failure with
an elevated central venous pressure is also a contraindication to TIPS placement. Relative
contraindications include polycystic liver disease, systemic or hepatic infection, and
hypervascular liver neoplasms.
TIPS is successful in controlling variceal bleeding in approximately 90% of patients.
In those patients in whom a TIPS has been created but who still experience recurrent
variceal bleeding, most have evidence of stent malfunction (thrombosis, stent retraction into
the hepatic parenchyma, or stenosis). Early TIPS occlusion (within the first two to three
weeks) usually results from thrombosis. After a few weeks, pseudointimal hyperplasia is the
cause of stent stenosis or obstruction. Bile extravasation has been implicated in the
formation of pseudointimal hyperplasia.
The frequency of TIPS stenosis and occlusion is fairly high (figure 1). Past studies
have shown a primary patency rate (time to first intervention) at one year ranging from only
23% to 66% (meaning that 34% to 77% occlude in less than a year). A more important
timeframe is the one-year primary assisted patency rate of approximately 85% (or time to
occlusion regardless of the number of interventions to maintain patency), which emphasizes
the need for close surveillance of the shunt to detect stenoses prior to recurrence of
symptoms. Although venography is the gold standard for detecting stent malfunction, it is
invasive and not an ideal screening test in the asymptomatic patient. Thus, several centers
have turned to duplex and color Doppler sonography as a means to evaluate and follow
patients with TIPS.
Sonographic Technique
Because most TIPS are placed deep within the liver, usually between the right or
middle hepatic vein and the right portal vein, a low frequency transducer is required for
optimal penetration. Given the high velocity flow through the shunt, artifact due to aliasing
can also be minimized or eliminated using a lower frequency transducer. At our institution,
we use a transducer with a center frequency of 2.5 MHz. While scanning the stent, the
Doppler scale should be adjusted to reflect the very high velocities within it. The scale
should be increased until homogeneous color opacification is demonstrated. This will allow
the detection of focal areas of color aliasing suggestive of a stenosis.
When determining peak systolic velocity, it is important to obtain an angle corrected
waveform at 60° or less. Several approaches can be used. The distal (portal venous) portion
of the stent is usually best imaged from a high anterolateral intercostal or subcostal
subxyphoid approach. It is important when obtaining a waveform to place the cursor
beyond the right portal vein and within the intraparenchymal portion of the stent so as not
to obtain an artifactually low peak systolic velocity that reflects portal vein velocity rather
than true stent velocity. The proximal (hepatic vein) portion of the stent and hepatic vein
are often best seen from a low intercostal or subcostal subxyphoid approach.
When evaluating the intrahepatic portions of the right and left portal vein branches,
the main portal vein, and the peripheral portion of the draining hepatic vein, the Doppler
scale should be decreased. The right portal vein and main portal vein are best imaged
through an intercostal approach. The left portal vein can be imaged sagittally in the
subxyphoid region.
The abdomen and pelvis should also be scanned to determine if there has been an
increase or decrease in ascites, particularly in those patients in whom the stent was placed for
control of ascites refractory to conventional therapy. It is also important to search for
collaterals, which would further suggest shunt malfunction.
Sonographic Parameters for the Detection of Stent Stenosis
A large number of studies have been published which have suggested various
Doppler parameters that can be used to diagnose shunt malfunction. These include peak
systolic velocity within the stent, the difference between the maximum and minimum
velocity in the stent, temporal change in the stent velocity, velocity in the main portal vein,
flow direction in the right and left portal vein branches, peak systolic velocity in the hepatic
artery, and flow direction in the draining hepatic vein. Although most studies suggest that
Doppler sonography is accurate in identifying shunt malfunction, many of the parameters
used to differentiate a patent from a stenotic shunt are not uniformly agreed upon.
Furthermore, the angiographic criteria used to diagnose stent stenosis vary from institution
to institution, as well.
Stent Velocity
Stent stenoses can be diffuse (with narrowing throughout the stent) or be focal.
Focal stenoses are much more common. While several studies have found that most focal
stenoses occur in the hepatic vein at the entry site of the stent, at our institution, we found a
nearly equal distribution of stenoses between those in the shunt and those in the hepatic
vein. Interestingly, Saxon et al recently reported that patients with shunt stenoses were
much more likely to experience recurrent variceal bleeding than those with hepatic vein
stenoses.
Stent velocity is the most common parameter that has been used to diagnose a
stenosis. Several centers have reported that 50 to 60 cm/sec is the lower limit of normal for
stent velocity. Values below this level would reflect the expected decrease in velocity
proximal or distal to a stenosis. However, these studies are limited by the small number of
stent stenoses reported in the studies (in part because many of the sonograms were obtained
in the immediate post procedure period); by the lack of a uniform angiographic definition of
stent stenosis; and by the use of different site(s) of velocity measurement.
Dodd et al failed to detect a stenosis in 14 out of 15 cases when applying the stent
threshold of 50 to 60 cm/sec. On the other hand, Feldstein et al reported a specificity of
99% and a sensitivity of 78% using 50 cm/sec as the lower limit of normal in 32 stenotic
shunts. Using this same value, we reported a similarly high specificity of 88% but a
sensitivity of only 32% in 34 stenotic shunts. Likewise, when Haskal et al and Murphy et al
applied the value of < 60 cm/sec to their patient populations, their specificities for
indicating shunt malfunction were 89% and 93% but their sensitivities were only 57% and
25%, respectively. While it appears that this threshold value is very specific for stent stenosis
(meaning that the Doppler study correctly identified that there was no stenosis), it is at the
expense of missing many less severe stenoses.
Although the mortality rate from recurrent variceal hemorrhage in patients with
TIPS is probably lower than in patients without TIPS, if ultrasound is to be used as a
screening test, ideally it should have a high sensitivity for the detection of shunt malfunction.
It should be emphasized that in many cases, as sensitivity increases, specificity decreases.
Therefore, increasing sensitivity must be balanced against the resultant lowered specificity,
which would lead to an increased risk and cost of performing unnecessary angiographic
studies. Our data suggest that 90 cm/sec is a more appropriate lower limit of normal.
When Feldstein et al used this value as a lower limit of normal, their sensitivity increased to
93% and their specificity decreased to 55% for detecting stent stenoses. While this value
allows us to detect less severe stenoses earlier than might otherwise be detected by using a
lower threshold (and also theoretically decreases the incidence of variceal re-bleeding due to
stent malfunction), it also results in an increased number of sonographic follow-up studies
and or venograms, which our center currently chooses to accept.
Several centers have also determined the upper limit of normal for stent velocity.
Values above this level would reflect the expected increase in velocity that can also be seen
at the site of a stenosis. The reported upper limit of normal ranged from 185 to 220 cm/sec.
We reported a similar value of 190 cm/sec. When we combined the upper and lower limits
of normal to produce a velocity range of 90 to 190 cm/sec, we achieved a sensitivity of 82%
and specificity of 72% for detecting shunt malfunction.
Because the velocity proximal to a stenosis decreases, whereas it increases through a
stenosis (figure 2), the difference between the two (velocity gradient) should increase in the
presence of a stenosis. Our data from the 25 most recent cases in which we correlated
velocity gradient with the absence or presence of a stenosis showed that a gradient of > 100
cm/sec has a positive predictive value of 82% for a stenosis. However, our sensitivity was
only 56% indicating that many patients with stenoses do not have abnormal velocity
gradients. Although uncommon, a diffuse stenosis may account for some of the cases.
Temporal differences in peak stent velocity have also been evaluated in an attempt to
diagnose stent stenoses. If the portion of the stent proximal to the stenosis were evaluated,
a temporal decrease in velocity would be expected, whereas if the stenotic segment itself
were evaluated, the velocity would increase over time. Dodd et al reported that an increase
or decrease of > 50 cm/sec from the post-TIPS baseline sonogram resulted in a sensitivity
of 93% and specificity of 77% for the detection of stent stenoses. Our results were
somewhat similar to Dodds; a decrease of 40 cm/sec or an increase of 60 cm/sec had a
sensitivity of 75% and specificity of 84%.
Main Portal Vein Velocity
Main portal vein velocity increases after placement of a TIPS because the stent
serves as a low resistance conduit and bypasses the high resistance hepatic circulation. The
reported average for the main portal vein velocity in patients with patent shunts ranged from
37 to 47 cm/sec. Our reported value of 43 cm/sec falls within this range. A decrease in
main portal vein velocity suggests a stent stenosis or occlusion. The reported average for the
main portal vein velocity in patients with compromised shunts ranged from 31 to 33 cm/sec.
In fact, in the study by Murphy et al, the best predictor for determining shunt stenosis was
the main portal vein velocity. Our data showed a similar value of 30 cm/sec as the lower
limit of normal for main portal vein velocity with a sensitivity of 82% and specificity of 77%.
Portal Vein Branch Flow Direction
After placement of a TIPS, flow direction in the right and left portal vein branches
reverses from hepatopetal to hepatofugal (i.e. towards the shunt) in most patients because of
the decreased resistance to flow provided by the shunt. However, if the shunt becomes
occluded or stenosed, it can no longer serve as a low resistance conduit and flow direction in
the portal vein branches may again change from hepatofugal to hepatopetal (figure 3). This
finding was reported in a limited number of patients and was indicative of stent stenosis or
occlusion. In our study, change in portal vein branch flow direction (from hepatopetal to
hepatofugal) had a specificity of 83% and positive predictive value of 86%, but a sensitivity
of only 15% to 31%. Based on our most recent experience, it appears that change in portal
vein branch flow direction is a late sign of stent malfunction.
Hepatic Artery Velocity
Following TIPS placement, there is a compensatory increase in hepatic artery flow
because of the diversion of portal vein blood flow into the newly created low resistance
conduit, which bypasses the liver. Foshager et al have shown an increase in hepatic artery
peak systolic velocity from 79 cm/sec prior to TIPS placement to 131 cm/sec one day after
TIPS placement. Although we found no statistically significant difference in hepatic artery
velocity or resistive index in patients with patent and stenotic stents, Haskal et al reported a
significant decline in hepatic artery velocity from 135 cm/sec to 108 cm/sec in patients with
shunt compromise.
Hepatic Vein Flow Direction
When a stenosis develops in the stent proximal to where it exits the hepatic vein or
in the hepatic vein itself (between the shunt and inferior vena cava) (figure 4), flow in the
hepatic vein distal to the shunt may be reversed (figure 5), that is, hepatopetal. This finding
has been reported, but its sensitivity is unknown.
Combining Parameters
Although some centers have reported that combining velocity parameters did not
improve their accuracy in predicting shunt stenosis, when we included in our analysis the
overall impression of the radiologist performing the sonographic examination, which was
based on multiple parameters as outlined in the Table, our sensitivity was 92% and
specificity 72%. Additional parameters not listed in the Table (such as reversal of flow in the
right and left portal vein branches and draining hepatic vein) were also used in formulating
an overall impression.
Table: Mallinckrodt Data – Suggested Doppler Criteria for TIPS Malfunction
Doppler Parameter
Vel. (cm/sec)
Sensitivity
Specificity PPV NPV
Peak Shunt Velocity
< 90 or > 190
84%
70%
82%
72%
Change in Peak Shunt
Decrease > 40 or
71%
88%
89%
67%
Velocity
Increase > 60
Main Portal Vein Velocity
< 30
82%
77%
86%
71%
Overall Impression
Not Applicable
92%
72%
84%
86%
Conclusions
From the above discussion, it is evident that many different parameters have been
studied in an attempt to determine which are the most accurate for detecting stent
malfunction. However, direct comparison of these parameters is difficult because the
ultrasound protocols varied from institution to institution, velocity measurements were
obtained from one or more different sites in the stent, and different sonographic parameters
were analyzed (peak systolic stent velocity versus temporal change in stent velocity). There
has also been little mention of intra or inter observer variability in obtaining these
measurements. But more importantly, the angiographic definition of a hemodynamically
significant shunt stenosis differed between centers. In addition, other factors such as the
patient’s clinical status must be taken into account when deciding when it is appropriate to
intervene and revise a stenosed shunt.
Until it is better understood which angiographic definition and value of shunt
malfunction (elevated portosystemic gradient versus percent anatomic stenosis) most
accurately reflects the redevelopment of portal hypertension (and subsequent increased risk
for a re-bleed) in the post TIPS patient, it will be difficult to determine which sonographic
parameters are most accurate in predicting a hemodynamically significant shunt stenosis. We
are currently analyzing both the sonographic and angiographic parameters in our
symptomatic and asymptomatic post TIPS patients in an effort to begin to answer this
question.
Figures:
1
Occluded TIPS
2
Mid stent stenosis with increased velocity through the stenosis
3
Stent stenosis with flow reversal in the RPV
4
Hepatic vein stenosis using color Doppler
5
Distal stent stenosis with flow reversal in the draining hepatic vein
References or Suggested Reading:
1.
Roberts LR, Kamath PS. Pathophysiology and treatment of variceal hemorrhage.
Mayo Clin Proc 1996; 71:973-983.
2.
Grace ND. Diagnosis and treatment of gastrointestinal bleeding secondary to portal
hypertension. Am J Gastroenterol 1997; 92:1081-1091.
3.
Sanyal AJ, Freedman AM, Luketic VA, Purdum PP, Shiffman ML, Tisnado J, Cole
PE. Transjugular intrahepatic portosystemic shunts for patients with active variceal
hemorrhage unresponsive to sclerotherapy. Gastroenterology 1996; 111:138-146.
4.
Brown RS, Jr., Lake JR. Transjugular intrahepatic portosystemic shunt as a form of
treatment for portal hypertension: indications and contraindications. Advances in
Internal Medicine. St. Louis: Mosby, 1997; 42:485-504.
5.
Nazarian GK, Bjarnason H, Dietz CA, Jr., Bernadas CA, Foshager MC, Ferral H,
Hunter DW. Refractory ascites: midterm results of treatment with a transjugular
intrahepatic portosystemic shunt. Radiology 1997; 205:173-180.
6.
Kerlan RK, Jr., LaBerge JM, Gordon RL, Ring EJ. Transjugular intrahepatic
portosystemic shunts: current status. AJR 1995; 164:1059-1066.
7.
Sanyal AJ, Freedman AM, Luketic VA, Purdum PP, III, Shiffman ML, DeMeo J,
Cole PE, Tisnado J. The natural history of portal hypertension after transjugular
intrahepatic portosystemic shunts. Gastroenterology 1997; 112:889-898.
8.
Ducoin H, El-Khoury J, Rousseau H, Barange K, Peron J-M, Pierragi M-T, Rumeau
J-L, Pascal J-P, Vinel J-P, Joffre F. Histopathologic analysis of transjugular
intrahepatic portosystemic shunts. Hepatology 1997; 25:1064-1069.
9.
Sterling KM, Darcy MD. Stenosis of transjugular intrahepatic portosystemic shunts:
presentation and management. AJR 1997; 168:239-244.
10.
Saxon RR, Ross PL, Mendel-Hartvig J, Barton RE, Benner K, Flora K, Petersen BD,
Lakin PC, Keller FS. Transjugular intrahepatic portosystemic shunt patency and the
importance of stenosis location in the development of recurrent symptoms. Radiology
1998; 207:683-693.
11.
Haskal ZJ, Pentecost MJ, Soulen MC, Shlansky-Goldberg RD, Baum RA, Cope C.
Transjugular intrahepatic portosystemic shunt stenosis and revision: early and
midterm results. AJR 1994; 163:439-444.
12.
Rössle M, Haag K, Ochs A, Sellinger M, Nöldge G, Perarnau J-M, Berger E, Blum
U, Gabelman A, Hauenstein K, Langer M, Gerok W. The transjugular intrahepatic
portosystemic stent-shunt procedure for variceal bleeding. N Engl J Med 1994;
330:165-171.
13.
Kanterman RY, Darcy MD, Middleton WD, Sterling KM, Teefey SA, Pilgram TK.
Doppler sonography findings associated with transjugular intrahepatic portosystemic
shunt malfunction. AJR 1997; 168:467-472.
14.
Chong WK, Malisch TA, Mazer MJ, Lind CD, Worrell JA, Richards WO.
Transjugular intrahepatic portosystemic shunt: US assessment with maximum flow
velocity. Radiology 1993; 189:789-793.
15.
Foshager MC, Ferral H, Nazarian GK, Castaneda-Zúniga WR, Letourneau JG.
Duplex sonography after transjugular intrahepatic portosystemic shunts (TIPS):
normal hemodynamic findings and efficacy in predicting shunt patency and stenosis.
AJR 1995; 165:1-7.
16.
Feldstein VA, Patel MD, LaBerge JM. Transjugular intrahepatic portosystemic
shunts: accuracy of Doppler US in determination of patency and detection of
stenoses. Radiology 1996; 201:141-147.
17.
Dodd GD, III, Zajko AB, Orons PD, Martin MS, Eichner LS, Santaguida LA.
Detection of transjugular intrahepatic portosystemic shunt dysfunction: value of
duplex Doppler sonography. AJR 1995; 164:1119-1124.
18.
Haskal ZJ, Carroll JW, Jacobs JE, Arger PH, Yin D, Coleman BG, Langer JE,
Rowling SE, Nisenbaum HL. Sonography of transjugular intrahepatic portosystemic
shunts: detection of elevated portosystemic gradients and loss of shunt function.
JVIR 1997; 8:549-556.
19.
Murphy TP, Beecham RP, Kim HM, Webb MS, Scola F. Long-term follow-up after
TIPS: use of Doppler velocity criteria for detecting elevation of the portosystemic
gradient. JVIR 1998; 9:275-281.
20.
Surratt RS, Middleton WD, Darcy MD, Melson GL, Brink JA. Morphologic and
hemodynamic findings at sonography before and after creation of a transjugular
intrahepatic portosystemic shunt. AJR 1993; 160:627-630.
21.
Longo JM, Bilbao JI, Rousseau HP, García-Villareal L, Vinel JP, Zozaya JM, Joffre
FG, Prieto J. Transjugular intrahepatic portosystemic shunt: evaluation with Doppler
sonography. Radiology 1993; 186:529-534.
22.
Feldstein VA, LaBerge JM. Hepatic vein flow reversal at duplex sonography: a sign
of transjugular intrahepatic portosystemic shunt dysfunction. AJR 1994; 162:839841.
About the Author:
Sharlene A. Teefey, M.D. is currently an Associate Professor of Radiology at the
Mallinckrodt Institute of Radiology at Washington University School of Medicine in St.
Louis Missouri. She is a member of numerous societies and organizations including the
American College of Radiology, the Society of Radiologists in Ultrasound, and the American
Institute of Ultrasound in Medicine.
She is a reviewer of manuscripts for Radiology, the American Journal of Roentgenology, and
Radiographics. She has more than 45 publications in peer review medical journals and has
been a speaker at numerous institutions and conferences across the country.
Examination:
1.
In patient populations with cirrhosis, the prevalence of esophageal varices ranges
from 25% to 70%. Up to ____ of patients with documented varices will experience
an episode of hemorrhage, usually within the first two years of the diagnosis.
A.
3%
B.
33%
C.
16%
D.
45%
E.
7%
2.
In patients with esophageal varices who bleed, most can be controlled with
endoscopic and or pharmacologic therapy. For the ______ of patients who fail
medical therapy, either an operation or TIPS is recommended.
A.
.01%
B
1%
C.
10%
D.
25%
E.
32%
3.
Which of the following reasons might a TIPS stent be placed?
A.
In patients with an acute or recurrent variceal hemorrhage.
B.
In most patients with cirrhosis in whom the mortality rate from a shunt
operation is unacceptably high.
C.
In patients with refractory ascites or hydrothorax related to liver disease and
Budd-Chiari Syndrome.
D.
A & B above.
E.
All of the above.
4.
There are several contraindications to TIPS placement, which include
A.
Patients with severe hepatic encephalopathy and liver failure because TIPS
might worsen their problems.
B.
Patients with chronic portal vein thrombosis, in particular, those with
narrowed sclerosed veins or cavernous transformation.
C.
Severe left heart failure with an elevated systemic arterial blood pressure.
D.
A & B above.
E.
B & C above.
5.
Relative contraindications to TIPS placement include
A.
polycystic liver disease
B.
systemic or hepatic infection
C.
hypervascular liver neoplasms
D.
all of the above
E.
Only A & B above
6.
In those patients in whom a TIPS has been created but who still experience recurrent
variceal bleeding, most have evidence of stent malfunction, which is due to
A.
thrombosis
B.
stent retraction into the hepatic parenchyma
C.
stenosis
D.
A & C above
E.
All of the above
7.
The frequency of TIPS stenosis and occlusion is fairly high. Regarding time to
occlusion, a more important timeframe is the one-year primary assisted patency rate,
which is approximately
A.
85%
B.
65%
C.
45%
D.
35%
E.
25%
8.
Most TIPS are placed deep within the liver, usually between the
A.
right or middle hepatic vein and the right portal vein
B.
right or middle hepatic vein and the left hepatic vein
C.
left hepatic vein and the right hepatic artery vein
D.
right or middle hepatic artery and the left portal vein
E.
left hepatic artery and the right or middle hepatic vein
9.
Which of the following statements is (are) true?
A.
When scanning a patient who has a TIPS, a high frequency transducer is
required for optimal penetration.
B.
Given the high velocity flow through the shunt, artifact due to aliasing can
also be minimized or eliminated using a lower frequency transducer.
C.
While scanning the stent, the Doppler scale should be adjusted to reflect the
very low velocities within it.
D.
The scale should be decreased until a non-homogeneous color opacification
is demonstrated.
E.
All of the above are true.
10.
When determining peak systolic velocity, it is important to obtain an angle corrected
waveform at
A.
60° or more.
B.
30° or less.
C.
60° or less.
D.
30° or more.
E.
90° or more.
11.
Which of the following statements is (are) true?
A.
B.
C.
D.
E.
When evaluating the intrahepatic portions of the right and left portal vein
branches, the main portal vein, and the peripheral portion of the draining
hepatic vein, the Doppler scale should be increased.
The abdomen and pelvis should also be scanned to determine if there has
been an increase or decrease in ascites, particularly in those patients in whom
the stent was placed for control of ascites refractory to conventional therapy.
When scanning patients who have a TIPS, it is not important to search for
collaterals, because they are unaffected by shunt function.
All of the above.
Only B & C above.
12.
Some of the various Doppler parameters that can be used to diagnose shunt
malfunction include
A.
peak systolic velocity within the stent
B.
the difference between the maximum and minimum velocity in the stent
C.
temporal change in the stent velocity
D.
velocity in the main portal vein
E.
all of the above.
13.
_____ is the most common parameter that has been used to diagnose a stenosis.
A.
Stent velocity
B.
Main portal vein velocity
C.
Portal vein branch flow direction
D.
Hepatic artery velocity
E.
Hepatic vein flow direction
14.
When evaluating a patient who has a TIPS utilizing “stent velocity”,
A.
only lower limits of normal have been suggested.
B.
only upper limits of normal have been suggested.
C.
both upper limits and lower limits of normal have been suggested.
D.
velocity differences should be used not upper and lower limits.
E.
none of the above.
15.
“Velocity gradient” is the difference in velocity flow between
A.
the velocity distal to a stenosis and the velocity proximal to a stenosis
B.
the velocity proximal to a stenosis and the velocity through a stenosis
C.
the velocity through the portal vein and the velocity through a stenosis
D.
the velocity proximal to a stenosis and the velocity through the portal vein
E.
the velocity through the portal vein and the velocity distal to a stenosis
16.
“Temporal differences” in peak stent velocity have also been evaluated in an attempt
to diagnose stent stenoses. Which of the following is (are) true?
A.
If the portion of the stent proximal to the stenosis were evaluated, a
temporal decrease in velocity would be expected.
B.
If the stenotic segment itself were evaluated, the velocity would increase over
time.
C.
If the portion of the stent distal to the stenosis were evaluated, no change in
velocity would be very indicative of a significant stenosis.
D.
E.
All of the above.
Only A & B above.
17.
Regarding “main portal vein velocity”, after placement of a TIPS that is functioning,
the velocity ____ because the stent serves as a low resistance conduit and bypasses
the high resistance hepatic circulation.
A.
increases
B.
decreases
C.
remains the same
D.
increases very briefly, then decreases the remainder of time.
E.
none of the above.
18.
Regarding “portal vein branch flow direction”, after placement of a TIPS,
A.
flow direction in the right and left portal vein branches reverses from
hepatopetal to hepatofugal in most patients.
B.
If the shunt becomes occluded or stenosed, it can no longer serve as a low
resistance conduit and flow direction in the portal vein branches may again
change from hepatofugal to hepatopetal.
C.
Based on the recent experience from the author’s institution, it appears that
change in portal vein branch flow direction is an early sign of stent
malfunction.
D.
A & B above.
E.
B & C above.
19.
Regarding “hepatic artery flow”, following TIPS placement, there is
A.
a compensatory decrease in hepatic artery flow because of the diversion of
portal vein blood flow into the newly created low resistance conduit.
B.
usually no change in hepatic artery flow because TIPS stents involve the
veins.
C.
a compensatory increase in hepatic artery flow because of the diversion of
portal vein blood flow into the newly created low resistance conduit.
D.
a compensatory increase in coronary vein flow because of the diversion of
portal vein blood flow into the newly created high resistance conduit.
E.
none of the above.
20.
Regarding “hepatic vein flow direction”, when a stenosis develops in the stent
proximal to where it exits the hepatic vein or in the hepatic vein itself (between the
shunt and inferior vena cava),
A.
flow in the hepatic vein distal to the shunt may be reversed, that is,
hepatopetal.
B.
flow within the stent is unaffected.
C.
flow in the hepatic artery proximal to the shunt may be reversed, that is,
hepatopetal.
D
all of the above.
E.
none of the above.