ACUTE ARTERIAL EMBOLIA
In the most frequent cause of mesenteric ischemia (40% -50%) where the plunger lodges in the SMA.
The proximal branches of the SMA (jejunum and middle colic arteries) are generally conserved,
because generally the embolus lodges 3 to 10 cm distally at the origin of the SMA,
where the artery narrows,
just after the first main branch of the SMA (the middle colic artery).
As a result,
the proximal small and large intestines are usually saved.
Due to poor collateral circulation,
the onset of symptoms in emboli is usually severe and dramatic.
When the intestine becomes ischemic,
it has a tendency to empty itself,
which leads to vomiting or diarrhea,
the so-called intestinal emptying.
This is one of the reasons why mesenteric ischemia is often misdiagnosed as gastroenteritis.
Common predisposing factors include atrial fibrillation,
cardiomyopathy,
recent angiography,
and valvular disorders,
such as rheumatic valve disease.
ACUTE ARTERIAL THROMBOSIS
Patients with long-term atherosclerosis may experience plaque development at the origin of SMA,
a site of turbulent blood flow.
This posterior stenosis can cause long-lasting postprandial pain ("intestinal angina") and "fear of food" with consequent weight loss.
These symptoms of chronic mesenteric ischemia can be seen in up to 80% of patients who develop arterial thrombosis.
If the plaque breaks acutely or the stenosis reaches a critical level,
patients may present with acute pain,
similar to those with arterial emboli.
VENOUS THROMBOSIS MESENTERIC
It represents 10% to 15% of the total cases.
This form of mesenteric ischemia is usually found in patients with a state of underlying hypercoagulability.
Patients usually present pain less severe and more insidious than those with arterial occlusion.
Patients can demonstrate weight loss,
depending on the duration of the symptoms.
Most patients present after more than 24 hours of symptoms.
Predisposing risk factors include malignancy,
sepsis,
liver disease or portal hypertension,
sickle cell disease,
and pancreatitis.
Many patients have inherited hematologic disorders that include protein C and S deficiency,
antithrombin III deficiency,
and factor V Leiden mutation.
Half of patients with mesenteric venous thrombosis have a personal or family history of venous thromboembolism.
NOT OCLUSIVE
It occurs in 20% of patients due to lack of self-regulation in low-flow states such as hypovolaemia,
use of vasopressors,
heart failure or sepsis.
The underlying ischemia of splanchnic vasoconstriction can cause hypotension from endogenous substances,
perpetuating a vicious circle.
This explains the extremely high mortality rate,
generally due to poor health of the affected population with multiple comorbidities,
combined with difficulty in treating the primary cause of decreased intestinal blood flow.
FINDINGS:
Angiography has historically been the reference standard for the diagnosis of AMI,
making the diagnosis as the possibility of carrying out therapeutic procedures simultaneously.
We could see the filling defect of the affected vessel,
although it is not present in all centers and is an invasive test.
In the X-ray,
intestinal obstruction,
edema of the intestinal wall,
intraperitoneal free gas,
portal gas and pneumatosis intestinalis can be identified; however,
these findings are usually identified late,
often when intestinal ischemia / infarction has already developed.
The abdominal X-ray will be normal in 25% of the cases.
Fig.
1
In ultrasound in the early phase of arterial occlusive AMI,
ultrasonography may show occlusion of SMA and intestinal spasm.
Later,
there are fluid-filled handles,
diminished or absent peristalsis,
thinning of the intestinal wall or peritoneum-free fluid.
In the venous occlusive AMI,
portal thrombus can be seen,
decreased peristalsis,
increased intraluminal secretions and segmental mural thickening.
In advanced cases,
intramural gas and portal venous gas may be evident.
On CT The findings in the image are grouped into: 1) Findings that occur in the intestine and the mesentery: mural thickening of the intestine and edema or focal thickening of the submucosa,
dilation of intestinal loops,
mucosal hemorrhage,
alteration in the uptake of contrast of the intestinal wall due to perfusion problems (enhancement or a decrease in uptake),
mesenteric edema and pneumatosis.
2) Vascular findings: arterial occlusion,
mesenteric or portal venous thrombosis,
mesenteric vein engorgement and portal gas.
3) Findings in other organs (kidneys,
spleen or liver) by vascular hypoafflux and ascites.
Fig.
2,
Fig.
3,
Fig.
4 and Fig.
5
The thickening of the intestinal wall is the most frequently observed finding in the IMA,
in fact it has a high sensitivity but is not very specific.
The intra-luminal defects or occlusions of the mesenteric vessels are not very sensitive but highly specific.
The combination of abnormalities of the intestinal wall (thickening / lack of wall enhancement) with intestinal pneumatosis increases the specificity between 97 and 100%.
Paradoxically,
hyperrealce of the intestinal wall can also be an indicator of acute ischemia.
This may be secondary to hyperemia (due to mesenteric venous occlusion or reperfusion injury).
Pneumatosis intestinalis refers to the gas inside the bowel wall,
and a good rule of thumb is to look for intramural gas in the colon-dependent.
Fig.
6,
Fig.
7 and Fig.
8
The importance of isolated intestinal pneumatosis is controversial,
in fact in patients with cancer there may be benign pneumatosis (which does not require intervention and that resolves in later images) more frequent in the colon.
There is a benign variant of intestinal pneumatosis called cystoid pneumatosis that occurs with the formation of submucosal / suberose cyst that can lead to pneumoperitoneum.
It has a more benign clinical course and is associated with connective tissue disorders,
chronic obstructive airway disease and use of steroids.
The study technique of CT: Water is administered as an oral contrast (the patient's clinical conditions do not allow oral intake in most cases).
Abdominal-pelvic CT without and with IV contrast (arterial and portal phases) is performed by angio-CT protocol with SmartPrev optimization technique in the abdominal aorta.
For contrast-enhanced CT,
100-120 ml of iodinated contrast is administered at a rate of 2-4 ml / sec.
The CT images are obtained with multidetector TC scanners that use a collimation of 0.5 to 2.5 mm and a pitch of 1.0-2.0.
Images with a thin cut thickness (1-2 mm) are acquired,
which will be very useful to perform reconstructions in the work station (post-processing) allowing to obtain multiplanar and volumetric images in 3D.
Sagittal images are useful to evaluate the origin of the mesenteric arteries and their variations.
Magnetic resonance angiography (MRA) at 1.5 T has a high sensitivity and specificity for the evaluation of occlusions or high-grade stenosis of the proximal celiac trunk or AMS.
It has a limited value in the evaluation of distal mesenteric occlusions.
MRA is slow and is not as available as CT,
which limits its usefulness in the acute context.
The differential diagnosis includes small bowel obstruction,
Crohn's disease,
mesenteric arteritis,
omental infarction,
hemorrhage or submucosal hematoma,
radiation enteritis,
typhlitis,
neoplasia,
ulcerative colitis,
infectious colitis (pseudomembranous,
amebiasis,
schistosomiasis),
diverticulitis,
lymphoma or carcinoma.
Fig.
9