Mesenteric ischemia refers to insufficient blood flow to the bowel and can be life-threatening if not treated emergently. Computed tomography angiography is the first-line imaging modality to diagnose mesenteric ischemia. CT findings can indicate the specific type of ischemia such as arterial embolism seen as filling defects in mesenteric arteries. Venous ischemia is suggested by bowel wall thickening and a target pattern on contrast-enhanced CT. Non-occlusive mesenteric ischemia shows small bowel wall thickening and hyperenhancement with colon sparing. Strangulation ischemia presents as closed loop obstruction on CT with decreased bowel wall enhancement.

1. Imaging in
mesenteric
ischemia

2. • refers to insufficient blood flow within the
mesenteric circulation to meet the
metabolic demands in the bowel. It is a
potentially catastrophic entity that may
require emergent intervention in the acute
setting

3. Mesenteric ischemia
Occlusive
Non -occlusive
Acute Chronic
Arterial Venous

4. Imaging modalities
• computed tomographic angiography (CTA) is the
first-line diagnostic modality for mesenteric
ischemia
• Once considered the gold standard for diagnosis of
mesenteric ischemia, catheter-based angiography
has been relegated to a second-line modality given
its invasive nature and lack of availability at some
centers
• Due to its longer image-acquisition times and
limited spatial resolution, magnetic resonance
angiography (MRA) is best suited for assessment
of chronic mesenteric ischemia

5. • MDCT has a high specificity and sensitivity and should be the first-line
imaging method in suspected AMI because of its high diagnostic accuracy
and ability to exclude other causes of acute abdominal pain .
• MDCT images should be obtained from the dome of the liver to the
level of the perineum to cover the entire course of the intestine. Sagittal
reconstructions are used to assess the origin of the mesenteric arteries
• triphasic CT involves the acquisition of scans in the pre-contrast,
arterial and venous phases.

6. • To evaluate intramural haemorrhage
• Identify intrinsically high attenuating material like calcified plaque,
intra luminal contents
• Pre-contrast comparison to assess the bowel wall enhancement
CT PROTOCOL –VALUE OF NON CONTRAST

7. • Very little evidence of use
• For bowel distension- main advantage
• The use of oral contrast is not recommended in patients with
AMI.The transit time for oral contrast through the bowel will
delay definitive treatment in AMI and the associated vomiting
and adynamic ileus limit the useful passage of oral contrast
material
Oral contrast ?

8. • Bowel wall thickness
• Bowel dilatation
• Bowel wall attenuation
Imaging in acute bowel Ischemia
Bowel wall signs Extra bowel wall signs
• Fat stranding and ascites
• Pneumatosis and
portomesenteric gas
• Vessels
• Emboli involving other visceral
organs
• Pneumoperitoneum

9. • Normal bowel wall thickness ranges from
3 to 5 mm
• Non specific finding but is the most
common CT finding in acute bowel
ischemia.
• In AMI, the bowel wall may be thickened
or thinned, depending on the etiological
mechanism.
• In cases of bowel ischaemia caused by
occlusions of mesenteric veins, bowel wall
thickening is more pronounced than in cases
caused exclusively by occlusions of mesenteric
arteries
Bowel wall thickness

10. Bowel dilatation
• Luminal dilatation and air-fluid levels are quite
common
• Bowel dilatation may result from interruption of
intestinal peristalsis as a reflex to ischemic injury or
from irreversible and transmural ischemic damage
to the bowel wall

11. • An ischaemic bowel segment may manifest with a hypo-attenuating or spontaneous
hyper attenuating bowel wall.
• A high-attenuating bowel wall at non-enhanced CT indicates a hemorrhagic
infarction.
• A hyper-attenuating bowel wall at contrast-enhanced CT is a nonspecific finding
caused by congestion or reperfusion.
• Filling defects in the mesenteric arteries and veins are specific findings that indicate
emboli or thrombi in the vessels.They may have high attenuation in the vessels on
non-enhanced CT images.
• The absence of wall enhancement is a specific finding that indicates cessation of
arterial flow. If it persists, the bowel will infarct and perforate
Bowel wall attenuation

12. Fat stranding and ascites
• nonspecific CT findings
• their presence depends heavily on the cause,
pathogenesis and se- verity of the ischemia as well as on
its location in the small or large bowel.
• In exclusively arterial occlusive mesenteric ischemia, the
presence of segmental mesenteric fat stranding and free
fluid interleaved between the mesenteric folds associated
with the poorly enhancing bowel is highly suggestive of
transmural infarction
• In venous outflow obstruction.The vascular engorgement
and edema of the bowel wall in turn lead to leakage of
extravascular fluid into the bowel wall and mesentery

13. Pneumatosis and
portomesenteric gas
• less common but more specific finding
• Pneumatosis may manifest with small isolated
gas bubbles in a circumferential distribution
within an ischemic bowel wall or as broad rims
of air dissecting the entire bowel wall into two
layers
• Portomesenteric venous gas may consist only
of some small gaseous inclusions within the
mesenteric veins or may extend into the
intrahepatic branches of the portal vein, where
it is typically found in the periphery of the liver

14. • can be used to evaluate for chronic
mesenteric ischemia, with peak systolic
velocities above 275 cm/s in the SMA and 200
cm/s in the CA correlating with 70% stenosis
in these vessels.
• However, the accuracy of US is heavily
operator dependent, and the presence of gas
within the bowel lumen or large patient size
can impede visualisation of the mesenteric
vessels and their distal course. For these
reasons, US is not routinely used to diagnose
AMI
DOPPLER USG

16. • Embolic arterial obstruction is the most common cause of AMI
• The classic triad –
• pain out of proportion to exam findings,
• bowel emptying (vomiting and diarrhoea),
• and a potential embolic source are inconsistent findings.
Acute mesenteric ischemia
(AMI)

17. EMBOLIC OCCLUSION
• most frequent cause
• caused by emboli of cardiac origin,
including atrial thrombi associated
with atrial fibrillation, mural thrombi
after myocardial infarction, and
emboli from aortic atheromatous
plaques.
• The SMA is the visceral arterial
branch that is most vulnerable to
embolism owing to its low branching
angle from the aorta.
THROMBOTIC OCCLUSION
• Most common in >70yrs
• The main risk factors for MAT are
atherosclerotic disease and dyslipidemia,
followed by hypertension, diabetes,
dehydration, antiphospholipid syndrome, and
oestrogen therapy
• MAT may also be associated with arterial
aneurysm and aortic or SMA dissection.
Arterial occlusion

18. • Emboli in the SMA at non-enhanced CT may have high attenuation or cause
filling defects near the orifice of the middle colic artery and in its distal
branches at contrast-enhanced CT ,which often enlarge the diameter of the
SMA.With the simultaneous reduction of the diameter of the SMV owing to the
diminished venous return,
• contrast enhancement of the bowel wall is absent or diminished because of the
decrease or cessation of the arterial supply The involved bowel wall seldom
thickens unless reperfusion occurs.As ischemic damage progresses, the bowel
loses muscular tone and starts to demonstrate paralytic ileus.
• When bowel ischemia advances to transmural infarction, the bowel wall
becomes thinner (paper-thin wall) and intramural gas and/or gas in the
mesenteric and/or portal veins is visualised. In addition, extrabowel gas can be
seen in cases with bowel perforation.
• In cases with reperfusion or rich collaterals, the involved bowel segments may
become thick and show a halo or target pattern on contrast-enhanced CT
images.
• In this situation, mesenteric strands may be observed.The presence of an
associated arterial embolism in other organs, such as the brain, spleen, kidneys,
and extremities, is supportive of an MAE diagnosis
Imaging findings

19. Irreversible bowel ischemia from an SMA embolism in
an 85-year-old woman

20. SMA embolism and arterial reperfusion in a 63-year-old
man who experienced severe abdominal pain while
undergoing treatment of atrial fibrillation

21. • On non-enhanced CT images, calcification
from atherosclerotic changes may be seen at
the origins of the SMA, celiac artery, and
inferior mesenteric artery.
• At these sites, stenosis or occlusion of the
lumen is observed at contrast-enhanced CT
and is well appreciated on sagittal images and
reformatted angiograms
Imaging findings

22. • SMA thrombosis in a 52-year-old man with chronic renal failure requiring
treatment with dialysis

23. • AMI resulting from MVT may occur in younger populations
compared with the age populations of other causes of AMI
Venous occlusion
may occur without an underlying disease (primary MVT),
but it more commonly develops owing to various underlying
diseases
. Use of oral contraceptives, pregnancy, and puerperium are risk
factors in young women

24. • Thrombi in the mesenteric and portal veins causing venous
obstruction
• Bowel wall thickening is often prominent
• The bowel wall typically shows a halo or target pattern of
enhancement and rarely hyper enhancement; however, bowel wall
enhancement is absent or diminished in cases with severe ischemia.
In cases with irreversible infarction, pneumatosis and/or
portomesenteric venous gas and extrabowel gas may also be seen.
CT findings

25. Portomesenteric venous thrombosis in a
51-year-old man.

26. Non-occlusive mesenteric ischemia (NOMI)
conditions such
as cardiogenic
or hemorrhagic
shock, sepsis, or
arrhythmia
divert blood
flow to critical
organs such as
the heart and
brain
reflex splanchnic
vasoconstriction
intestinal
hypo-perfusion
increased vascular
permeability, with
seepage of plasma
and red blood
cells into the
bowel wall and
mesentery

27. • Characteristic CT findings include small bowel mural thickening and hyper enhancement with
sparing of the colon, luminal dilatation, a flat inferior vena cava (IVC), and ascites, a
constellation of features known as “shock bowel”
• narrowing origins of multiple branches of the SMA;
• alternate dilatation and narrowing of the intestinal branches (the “string of sausages” sign);
• spasms of the mesenteric arcades; and
• impaired filling of intramural vessels. Similar findings may also be seen in the branches of the
celiac artery and inferior mesenteric artery and in the renal arteries.
• Ischemic bowel loops lack contrast enhancement at CT
CT findings

28. Non-occlusive mesenteric ischemia

29. NOMI with arterial reperfusion in a 90-year-old woman
with abdominal pain.

30. Contrast-enhanced CT image (A) of pelvis in 69-
year-old man with nonocclusive mesenteric
ischemia

31. • Strangulation is the term used
• Mostly in closed loop obstruction- “C”
OR “U” configuration
• Typically, strangulation in a closed-loop
bowel obstruction is caused initially by
impairment of venous outflow followed
by arterial ischemia be- cause the arterial
pressure is higher than the venous
pressure.
Obstruction

32. • radial distribution of bowel loops; the presence of two
closely apposed, collapsed loops
• beak or triangular loop signs, which refer to fusiform
tapering of fluid-filled bowel loops .
• decreased bowel wall enhancement,
• the small-bowel feces sign
• and increased bowel wall attenuation on unenhanced
images, likely secondary to intramural hemorrhage
Imaging findings

33. • vascular inflammation and necrosis.
• The most common of the vasculitides to affect the gastrointestinal tract is
polyarteritis nodosa, a medium-vessel vasculitis
• . Other common vasculitides to involve the small bowel include Henoch-
Schonlein purpura, systemic lupus erythematous (SLE), and Behcet’s disease
Vasculitis/vascular disorders

34. • nonspecific and include mural thickening, mucosal ulceration,
hemorrhage, and stricture formation
• . Relatively unique features include involvement of the duodenum or
concurrent involvement of both the jejunum and ileum or the small
bowel and colon.
Imaging findings

35. Polyarteritis nodosa produces inflammation that can result in segmental weakening
of the vessel wall with characteristic formation of multiple small aneurysms.The
mesenteric, renal, and hepatic vessels are most commonly affected
CT in a patient with polyarteritis nodosa

37. • Post prandial abdominal pain
• Weight loss
• Food avoidance
• Nausea ,vomiting ,diarrhoea
Chronic mesenteric ischemia

38. • Most commonly bowel appears normal
• Mesenteric vascular stenosis, SMA -most common to cause symptoms
• Collateral formation
Imaging findings