1. Radiological imaging of mesenteric ischemia.
Dr/ ABD ALLAH NAZEER. MD.

2. Introduction:
Mesenteric ischemia is a rare disease associated with a high
mortality rate, especially in the acute setting. This disease is
responsible for fewer than one in 1,000 hospital admissions, but its
mortality rate ranges between 30%-90% . It is more prevalent in the
elderly population, with comorbidities largely influencing the
mortality rate.
Another factor associated with the high mortality rate is the clinical
presentation with nonspecific symptoms and relatively benign
physical examination, which leads to a low index of suspicion and
therefore delays in the diagnosis. Most of the data in the incidence
of this disease is based on autopsy studies. Most cases of mesenteric
ischemia are due to an acute event leading to decreased blood
supply to the splanchnic vasculature. Chronic mesenteric ischemia is
uncommon, accounting for <5% of cases of mesenteric ischemia, and
is almost always associated with diffuse atherosclerotic disease.

3. Pathophysiology
Acute mesenteric ischemia is most commonly secondary to acute
embolism to the superior mesenteric artery (SMA), which accounts
for approximately 40%-50% of all episodes. Acute mesenteric artery
thrombosis is the second most common cause of acute mesenteric
ischemia (20%-30%) followed by nonocclusive mesenteric ischemia
(25%) and less commonly mesenteric and portal venous thrombosis
(5%-15%). In the chronic setting, mesenteric ischemia is almost
always caused by severe atherosclerotic disease, with rare causes
including fibromuscular dysplasia, median arcuate ligament
syndrome, and vasculitis Chronic mesenteric ischemia occurs due to
occlusive or stenotic atherosclerotic disease and most commonly
involves at least two or three main vessels. It is more prevalent in
the elderly population and in patients with major risk factors for
atherosclerosis such as hypertension, hyperlipidemia, and smoking
history.

4. Clinical Presentation
Patients with acute mesenteric ischemia present with abdominal
pain out of proportion to the physical examination. A high index of
suspicion is necessary to achieve early diagnosis. The main challenge
is to differentiate acute mesenteric ischemia from other more
common causes of acute abdominal pain such as appendicitis,
diverticulitis, peptic ulcer disease, acute pancreatitis,
gastroenterocolitis, nephrolithiasis, cholelithiasis, and cholecystitis.
Early in the course of disease, laboratory findings are of little value
in differentiating among these causes, with the results usually
demonstrating leukocytosis, hemoconcentration, elevated amylase
levels, abnormal liver enzymes, and/or metabolic acidosis.
In the setting of chronic mesenteric ischemia, patients classically
present with the clinical triad of postprandial abdominal pain,
weight loss, and food avoidance. Nausea and vomiting, postprandial
diarrhea, and signs of malabsorption may also be present.

5. Imaging of Mesenteric Ischemia.

7. Acute Mesenteric Ischemia
Radiographs
Radiography is usually the first imaging modality ordered for patients with
acute abdominal pain but has a limited role in demonstrating primary and
secondary signs of acute mesenteric ischemia. A normal radiograph does not
exclude the diagnosis of acute mesenteric ischemia. Radiography findings in
patients with acute mesenteric ischemia are usually nonspecific, late, and
associated with a high mortality rate, as they often first appear when bowel
infarction has already occurred. A radiograph typically shows bowel dilatation
in the elderly patients and a gasless abdomen in younger patients with acute
mesenteric ischemia . Hepatic portal venous gas is a rare but important
radiographic finding associated with several pathological processes, including
bowel necrosis secondary to acute mesenteric ischemia. Hepatic portal venous
gas can occur alone or in association with pneumatosis intestinalis. When
associated with pneumatosis intestinalis, it usually indicates the presence of
advanced mesenteric ischemia. Abdominal CT appears to be superior to
radiographs for detecting pneumatosis intestinalis and hepatic portal venous
gas, and their underlying cause. Therefore, CT should be used as the primary
diagnostic tool rather than radiography.

8. Ultrasound
The efficacy of US in diagnosing acute mesenteric ischemia has
been evaluated in many studies. US can demonstrate proximal
mesenteric vessel thrombosis via Doppler mode. It was shown
that US is highly specific for identifying vascular occlusions (92%-
100%) but has a lower sensitivity (70%-89%). Unfortunately, the
presence of extensive gas within the loops of bowel limits the
accuracy of this imaging modality. Moreover, duplex US has a
limited role in detecting distal arterial emboli or in diagnosing
nonocclusive mesenteric ischemia.
US might be helpful in excluding other causes of acute abdominal
pain such as cholelithiasis, cholecystitis, nephrolithiasis, acute
pancreatitis, or even appendicitis, but it is not recommended for
initial evaluation of patients with suspected acute mesenteric
ischemia because timing of the diagnosis is very critical.

9. Computed Tomography Angiography
CTA is a fast and noninvasive diagnostic tool for evaluating
bowel and assessing intestinal vasculature. Recently the
application of CTA as the ideal first-step imaging approach in
patients with acute bowel ischemia has been advocated. CTA can
also be helpful in stratifying patients to identify those who would
benefit from angiography as opposed to the ones who should
undergo emergent surgery. Vascular CT findings include arterial
stenosis, embolism, thrombosis, arterial dissection, and
mesenteric vein thrombosis; nonvascular CT findings include
bowel wall thickening, hypoperfusion and hypoattenuation,
bowel dilatation, bowel wall hemorrhage, mesenteric fat
stranding, pneumatosis intestinalis, and portal venous gas.
Overall, combining vascular findings with the appearance of the
bowel wall resulted in a specificity of 94% with a sensitivity of
96%.

10. Magnetic Resonance Angiography.
MRA has high sensitivity and specificity for
diagnosing severe stenosis or occlusion at the
origins of the celiac axis and SMA. However, it has
a limited role in diagnosing distal stenosis as well
as nonocclusive mesenteric ischemia, and its use
may delay therapeutic options in acute settings
because it is a long examination that is not
readily available in most practices. MR without
contrast has lower sensitivity and specificity but
may be used in cases where both iodinated and
gadolinium contrast are contra-indicated.

11. Angiography.
Angiography has been the gold standard to aid in diagnosis and
preoperative planning in acute mesenteric ischemia, with
sensitivity in the range of 74%-100% and specificity of 100%.
Early angiography has shown to be associated with increased
survival in patients with mesenteric ischemia and allows for
initiation of therapeutic maneuvers. Whether angiography
should precede surgical intervention in the presence of
peritoneal signs is controversial. Some would favor immediate
surgery in this setting, as signs of peritonitis usually indicate
infarcted bowel. However, others advocate early angiography
because of the importance of determining the etiology of bowel
ischemia and providing a “roadmap” for revascularization
procedures. Nonetheless, angiography should not be considered
in patients with significant hypovolemia or hypotension.

12. Chronic Mesenteric Ischemia
Radiographs
Radiography has little to no role in the diagnosis of chronic mesenteric
ischemia since these patients have not yet developed bowel necrosis, and
therefore the radiograph will likely be normal or demonstrate nonspecific
findings. A negative radiograph also does not exclude the diagnosis of
chronic mesenteric ischemia.
Ultrasound
US with B-mode and Doppler waveform analysis is a useful initial
screening tool for chronic mesenteric ischemia. Visualizing the mesenteric
vessels with duplex US can be technically challenging. The SMA and celiac
arteries are visualized in approximately >90% and 80%, respectively. On
the other hand, the inferior mesenteric artery can hardly be visualized on
transabdominal US studies due to its anatomical location and course.
Peak systolic velocity has been widely used for diagnosing stenosis, with
a cutoff value of 275 cm/s for the SMA and 200 cm/s for the celiac artery.
US can also help in excluding other causes of chronic abdominal pain such
as cholelithiasis, nephrolithiasis, and chronic pancreatitis.

13. Computed Tomography Angiography.
CTA with 3D volume reformatting has sensitivity and specificity of
96% and 94%, respectively, for detecting chronic mesenteric
ischemia. Therefore, it should be considered as a first-line
alternative to angiography for diagnostic purposes . Moreover, CTA
is an accurate diagnosing tool for detecting SMA syndrome. CT can
also accurately exclude other causes of chronic abdominal pain.
Magnetic Resonance Angiography.
MRA is a noninvasive test that has become increasingly accurate in
recent years for diagnosing chronic mesenteric ischemia, with
sensitivity and specificity of 100% and 95%, respectively.
Nonetheless, obtaining high-resolution angiograms is still limited
to the inferior mesenteric arteries, where it depicts only 25% of this
vessel due to its anatomical course. MR without contrast has lower
sensitivity and specificity but may be used in cases where both
iodinated and gadolinium contrast are contraindicated.

14. Conventional angiography.
of the mesenteric arteries remains the gold
standard for diagnosing chronic bowel ischemia,
with its therapeutic role allowing physicians
performing endovascular procedures at time
of diagnosis.
The success rate of angiography is reported to be
as high as 88%-100%, with initial relief of
symptoms in 82%-100% of cases. Nevertheless,
traditional angiography is an invasive test that
exposes patients to radiation and is associated
with complications related to the procedure itself.

15. Anatomy of the mesenteric vessels.

16. Anatomy of the mesenteric vessels.

17. Drawing shows the main
collateral vessels in occlusion of
the CA or SMA. The
pancreaticoduodenal arteries
(arrow) connect the CA and the
proximal SMA. The marginal
artery of Drummond and the
paracolic arcade (arrowhead)
run between the SMA and IMA.
When the IMA is also occluded,
the systemic vessels (mainly the
internal iliac artery) can feed the
IMA (reverse flow) and the other
vessels via previously described
anastomosis (*).

18. Mesenteric ischemia. Plain abdominal radiograph in a 49-year-old woman with
acute bloody bowel movements shows thumbprinting of the transverse colon.

19. Mesenteric ischemia. Plain abdominal radiograph in a 17-year-old male patient
with encephalitis reveals pneumatosis of the colon dissecting the bowel wall.

21. Thumbprinting in
a patient with
ischemic colitis.

23. Mesenteric ischemia. Ultrasonographic evaluation in an 83-year-old woman with abdominal
pain reveals multiple echogenic foci within the liver, which are suggestive of portal venous air

24. Mesenteric ischemia. Ultrasonographic evaluation
with spectral analysis and color Doppler imaging.

25. Duplex US findings in isolated stenosis of
the CA. (a) Lateral US image obtained in color
mode shows color aliasing. (b) Lateral US
image obtained in Doppler mode shows signs
of moderate stenosis with increases in systolic
and diastolic velocities, as well as
mild turbulence. (c) Lateral US image obtained
in Doppler mode shows major poststenotic
turbulence and Doppler aliasing, which
indicate a stenosis of greater than 75%.

26. Median arcuate ligament syndrome. (a) Lateral US image obtained with energy and
pulsed mode imaging during inspiration shows that the CA and SMA course downward.
The velocities in the CA are slightly increased. (b) Lateral US image obtained with
energy and pulsed mode imaging during expiration shows that the proximal part of the
CA is lowered and impinged on by the median arcuate ligament (arrow). The velocities
are markedly increased, and aliasing associated with turbulence is seen.

27. Duplex ultrasound of the superior mesenteric artery demonstrates a peak systolic
velocity (PSV) >275 cm/second correlating with a stenosis of at least 70%.

28. Superior mesenteric artery stenosis Maximum peak systolic velocity of
304 cm/s and spectral broadening in the proximal SMA. This velocity
exceeds the accepted PSV of 275 cm/s for the grading of a >70% stenosis.

29. Mesenteric ischemia. CT scan shows thickening
of the transverse colon suggest a distribution
in the superior mesenteric artery territory.
Mesenteric ischemia. CT scan
shows wall thickening of the
ascending colon. This finding also
can be seen with infectious colitis.

30. Mesenteric ischemia. CT scan shows thickening
of the ascending colon and hepatic flexure.
The differential diagnoses included conditions
with an infectious etiology versus ischemia.
Mesenteric ischemia. CT scan shows
inflammatory changes and thickening of
the hepatic flexure. Colonoscopy with
biopsy showed focal mucosal necrosis with
ulceration consistent with ischemic colitis

31. Mesenteric ischemia. CT scan obtained by using lung window parameters in
a 17-year-old male patient with encephalitis reveals free retroperitoneal air.

32. Old man with mesenteric infarction. Contrast-enhanced CT images of upper
(A), mid (B), and lower (C) abdomen show gas in portal venous branches (A),
gas in mesenteric veins (circle, B), and gas in bowel wall (arrowheads, C).

34. Mesenteric ischemia. CT scan in a 76-year-old woman with a 4-day history of
abdominal pain and leukocytosis shows congested, edematous, central small
bowel loops. Thrombosis was found in the superior mesenteric vein.

35. Contrast-enhanced CT image in patient
with embolism of superior mesenteric
artery shows defect (arrowhead) in
superior mesenteric artery.
Contrast-enhanced CT image with superior
mesenteric vein thrombosis shows defect
in superior mesenteric vein (arrowhead).
Distal branches of vein are engorged.

36. Contrast-enhanced CT image of abdomen in
with superior mesenteric vein and portal vein
thrombosis. Wall thickening of ascending and
transverse colon (arrowheads) is shown.
Engorgement of mesenteric veins is also visible.
Contrast-enhanced CT image of abdomen
with embolism of superior mesenteric artery.
Bowel loops are distended with air and their
wall is “paper-thin.”

37. Superior mesenteric artery embolism. Contrast-enhanced CT image
shows that mural enhancement is absent at most intestinal loops.

38. Superior mesenteric artery embolism
after reperfusion. Mural thickening
of intestine (circle) is visible, showing
target appearance.
Superior mesenteric artery embolism shows
defect (arrowhead) in superior mesenteric
artery. In addition, contrast enhancement of
right kidney (arrow) is absent, which
indicates embolism of right renal artery.

39. Superior mesenteric vein thrombosis. Contrast-enhanced CT image obtained cephalad
to B shows thrombi in superior mesenteric vein (arrowhead) and splenic vein (arrow).
engorgement of mesenteric veins (arrowhead) and mural thickening of intestine.

41. Mesenteric ischemia. CT scan in a 59-year-old man with pancreatic adenocarcinoma
shows a large mass encasing the superior mesenteric artery. The patient did not have
abdominal symptoms of ischemia because the superior mesenteric artery remained
patent. Tumor encasement is a rare cause of mesenteric ischemia.

43. Bowel infarct due to mesenteric arterial occlusion of the ileocolic branch.

45. Shock bowel after cesarean section with diffuse bowel wall thickening in the
ileum(arrows) with large intra-peritoneal fluid collection due to hemoperitoneum.

46. Venous mesenteric ischemia

52. Aneurysmal dissection of the CA in a 59-year-old patient who had severe epigastric
pain for several years. (a) Color Doppler US image shows an aneurysm of the celiac trunk
(arrow). (b) Contrast-enhanced CT scan also shows the aneurysm (arrow). The very thin
aspect of the splenic artery and the hypoattenuating crescent anterior to the splenic
artery (arrowhead) are suggestive of an associated splenic artery dissection.

53. Contrast-enhanced CT image shows closed-loop obstruction at right lower abdomen.
Distended loops are seen filled with fluid and mesentery is converging toward site of
obstruction (circle). Bowel wall is slightly thickened and density of mesentery is increased.

54. Contrast-enhanced coronal CT image shows closed-loop obstruction at lower
abdomen. Distended loops are seen around their mesentery. Contrast
enhancement is absent at bowel loops on right-hand side (arrowheads) and
attached mesentery shows increased density, which indicates mesenteric ischemia.

55. Nonocclusive mesenteric ischemia. Contrast enhancement is prominently diminished or
absent at distal ileal loops (arrowheads). Bowel wall thickening is not present. After
reperfusion, bowel loops show prominent wall thickening with appearance of target sign (B).

56. Top CT image shows gas in
portal venous system (blue
circle); center image
shows absence of contrast
in superior mesenteric
artery due to thrombosis
of this vessel (blue arrow)
[The patient also has a
markedly dilated common
duct, not related to
mesenteric ischemia];
lower image shows
extensive pneumatosis
intestinalis (red arrows).

57. Coronal venous-phase maximum intensity projection (MIP) image from contrast-enhanced CT
shows that the caliber of the superior mesenteric vein is diminutive (large white arrows) relative
to that of the inferior mesenteric vein (black arrowheads) and that there is a further size
discrepancy to the superior mesenteric vein (SMV) at the junction (large black arrows) of the
splenic vein (small white arrow) with the portal vein (small black arrow), representing partial
SMV thrombosis. Note the resulting engorgement of the venous arcades (white arrowheads).

58. Noncontrast computed tomography (CT) image shows characteristic abnormalities that may be
present in the later stages of acute mesenteric ischemia: pneumatosis intestinalis (small white arrows),
intravascular air within the main portal vein (large white arrow) as well as within intrahepatic
branches and small foci of free air (small black arrows) representing Pneumoperitoneum.

60. Closed-loop obstruction. Axial MR image in 52-year-old woman shows site of obstruction
(arrowhead), closed loop (C), proximal loop (P), and distal loop (D) with bowel loop ischemia.

61. Acute mesenteric ischemia in a 43-year-old man
with acute abdominal pain but no peritoneal
signs. (a, b) CT scans obtained in the emergency
department. (a) CT scan shows a thrombus in
the SMA (arrow) and nonspecific jejunal wall
thickening (arrowhead), which produces the
target sign. (b) CT scan obtained 2 cm lower
shows enhancement of the distal SMA (arrow),
which is fed by collateral vessels, and thinning
of the mesenteric wall of a jejunal loop
(arrowhead), which is a more specific sign of
acute ischemia. (c) Image from selective
angiography of the SMA shows a thrombus in
the trunk of the artery (arrow). (d) Image from
selective angiography of the IMA
shows that the distal SMA (arrow) is fed by a
prominent marginal artery of Drummond
(arrowhead). Acute thrombosis complicating
preexistent distal stenosis of the SMA was
suspected, and urokinase was given as an
intraarterial injection of 600,000 U in 6 hours.
(e) Control angiogram shows an irregular
persistent stenotic lesion (arrow). (f) Angiogram
shows a balloon-expandable stent, which was
placed to prevent reocclusion and distal
migration. Surface irregularities (arrowheads)
are visible proximal and distal to the stent and
may represent sites of restenosis. The patient
returned home on day 5 and was asymptomatic
8 months later.

62. Acute SMA Thrombosis.

63. Acute SMV Thrombosis.

64. Collateral vessels in a 79-year-old patient with thrombosis of the two main visceral arteries
but no abdominal symptoms. (a) Global lateral angiogram shows thrombosis of the SMA
(arrowhead) and CA (arrow). (b) Image from selective angiography of the IMA shows a
prominent marginal artery of Drummond connected to the paracolic arcade. (c) Angiogram
shows that the paracolic arcade is connected to the SMA (arrowhead) downstream from
the occlusion and feeds the jejunal arteries (). Note that the paracolic arcade is located low
in the abdomen due to ptosis of the transverse colon, which is common in elderly patients.

65. Collateral vessels in a 66-year-old patient with abdominal angina. (a) Lateral
angiogram shows thrombosis of the SMA (arrowhead) and severe stenosis of the
CA (arrow). (b) Angiogram obtained with selective injection of contrast material
into the IMA shows unusual serpentine collateral vessels emerging from the
marginal artery of Drummond, which is not connected to the paracolic arcade. (c)
Late-phase angiogram shows the SMA (arrow) and CA (arrowhead).

66. CMI in a 75-year-old woman with arterial dysplasia of the renal and mesenteric
arteries. (a) Global angiogram. (b) Angiogram obtained with selective catheterization
of the SMA by using a 5-F sidewinder catheter shows an ostial stenosis (arrow). (c)
Post-angioplasty completion arteriograms obtained by using a long and armed 6-F
sheath, which is pushed to the level of the mesenteric ostium (arrow).

67. CMI in a 45-year-old man with occlusion of both the CA and the SMA. (a) Lateral angiogram
clearly shows a notch at the SMA (arrow). (b) Angiogram shows the occlusion being crossed
by using a hydrophilic wire (arrow). (c) Control angiogram obtained after angioplasty
shows good circulation in the SMA (arrowhead), but persistent recoil necessitated use of a
stent (arrow). (d) Final angiogram shows a good result after stent placement.

68. Superior mesenteric artery arteriogram shows a large embolus that appears as a central filling
defect (large black arrow) and has occluded the distal portion of the arterial trunk (small black
arrow). A very small portion of the jejunum remains perfused (small white arrow). Note the
abnormally dilated bowel loops (large white arrows) in this patient with acute mesenteric ischemia.

69. Digital subtraction angiography (DSA) image shows thrombosis (small black arrows)
of the superior mesenteric artery that occurred distal to a high-grade stenosis (large
white arrow). There is very little perfusion distal to the thrombosis. Note the
previously placed stent in the celiac trunk (large black arrow), which is also occluded.

70. A small embolus (white arrow) has lodged distally in the superior mesenteric artery and this
location allows for continued perfusion of most of the bowel in this arterial territory. This contrasts
with the severe bowel ischemia that occurs with proximal embolic or thrombotic occlusion.

71. An acute embolus within the superior mesenteric artery appears as a filling defect (large black
arrow) partially obstructing the artery. Smaller filling defects distally (small black arrows) represent
fragmentation of the embolus. Note the so-called tram-track appearance in which the filling
defects are partially outlined by contrast that courses between the emboli and the arterial wall.

72. Three-dimensional computed tomography angiography shows an extremely severe
superior mesenteric artery stenosis (small white arrow), an occluded celiac trunk (large
white arrow), and an enlarged and patent inferior mesenteric artery (black arrow) in a
patient with symptoms of intestinal angina. The initial imaging evaluation of suspected
chronic mesenteric ischemia should involve a noninvasive modality such as this.

74. Summary
Literature supports conventional angiography as the gold standard test for patients
with acute and chronic mesenteric ischemia except for hemodynamically unstable
patients with acute mesenteric ischemia.
CTA is an emerging diagnostic test with high sensitivity and specificity in the setting
of both acute and chronic mesenteric ischemia and should be considered the first-line
imaging test. CT can also accurately assess for other causes of acute and chronic
abdominal pain, and it provides excellent anatomic mapping of the mesenteric
vasculature, which is essential in the preoperative planning.
MRA is an evolving technique with high sensitivity and specificity for severe stenosis
or occlusions at the origin of the celiac axis and SMA, but it has a limited role in the
in the evaluation of distal embolism and nonocclusive mesenteric ischemia and is
only able to depict 25% of the inferior mesenteric artery. This is also a long test that
is not readily available in most centers, making its use even more limited in the acute
setting.
US of the abdomen with Doppler waveform analysis can depict proximal mesenteric
thrombosis and secondary signs of bowel compromise, but it is limited in the diagnosis
of distal occlusions/stenosis and nonocclusive mesenteric ischemia and therefore is not
recommended as the initial examination in evaluating patients with suspected acute
mesenteric ischemia.
Radiographs remain of limited value, being able to diagnosis only late stages of acute
mesenteric ischemia when bowel necrosis is already present.

75. Thank You.