Small bowel ischemia & infarction – causes, symptoms, diagnosis, treatment, pathology

Small bowel refers to the small intestine
and infarction is when ischemia, which is an inadequate blood supply, causes necrosis,
or tissue death. So, a small bowel infarction happens when
there’s a reduced blood supply to the small intestine causing parts of the intestinal
wall to necrose or die which can be life threatening. Now, the small intestine is made of several
layers. The innermost layer is the mucosal layer and
it’s composed of a few of its own layers. The first layer is the epithelial lining and
it faces the lumen; next is the lamina propria, which is rich with blood and lymph vessels;
and finally the muscularis mucosae, which has smooth muscle. Deep to this mucosal layer is the submucosal
layer, which has connective tissue with proteins like collagen and elastin, as well as glands,
and additional blood vessels. The submucosal layer also contains the Meissner
plexus which is a part of the enteric nervous system. Below the submucosal layer is the muscularis
propria which is basically two layers of smooth muscle with the myenteric plexus, another
part of the enteric nervous system, sandwiched between them. These muscles are particularly important in
helping to move food through the bowel. Finally, there’s the serosal layer which
is the outermost layer of the small intestines that faces the abdominal cavity. The superior mesenteric artery is the main
supplier of blood to the small intestine. Branches of the artery spread through the
mesentery – called mesenteric arteries – and penetrate the serosa layer and travel to the
submucosa where they branch further into arterioles. Because the small intestine has a high demand
for oxygen and nutrients to sustain digestion, it is highly susceptible to tissue injury
from ischemia. To reduce the risk of that happening, the
mesenteric arteries branch and reconnect at points forming collateral circulation. That’s protective because if blood flow
is reduced in one pathway, then the tissue can still receive blood through another pathway. Once the small intestines have gotten oxygenated
blood, that blood leaves through the superior mesenteric vein. Small bowel infarction happens when there’s
a significant decrease in blood flow to the small intestine. This reduction in blood flow decreases blood
pressure, and can cause an insufficient blood flow throughout the collateral circulation
which initiates ischemic injury in a wide region of tissue. At the cellular level, ischemic injury can
lead to the production of reactive oxygen species which can damage DNA, RNA, and proteins
in the cell, leading to cell death. If blood flow returns to the ischemic tissue,
it’s called reperfusion. Unfortunately, though, that process can cause
further injury – called reperfusion injury. In reperfusion injury, the influx of oxygen
into an already damaged cell can be overwhelming and can cause even more oxidative stress,
which worsens the cell damage. As damaged cells release reactive oxygen species,
it triggers an inflammatory response which attracts immune cells, like neutrophils. The immune cells remove dead and damaged cells
and release of cytokines, like Tumor necrosis factor-alpha. The cytokines cause blood vessels to become
more permeable to fluid and more immune cells – resulting in bowel edema or swelling of
the small intestinal wall. Small bowel ischemia and infarction becomes
more severe as the damage extends from just the mucosal layer, called a mucosal infarct,
to all layers, known as a transmural infarction. Early on bowel ischemia can make the bowels
simply not work – resulting in an ileus – where food lingers and doesn’t get pushed along. Severe damage to the small intestines can
also cause a break in the epithelial lining of the small intestines, allowing bacteria
in the lumen to get into the blood vessels in the wall. Alternatively, bacteria can completely cross
the small intestinal wall and get into the peritoneal space, and from there get into
lymphatics or blood vessels. Ultimately, if bacteria get into the bloodstream
then it can lead to a massive inflammatory response called sepsis. In sepsis, blood vessels throughout the body
can get leaky, and if enough fluid moves from the blood vessels into the interstitial space,
it can lead to septic shock, which is where organs throughout the body get insufficient
blood. And this can lead to organ failure and death. Small bowel ischemia and infarction, can happen
due to occlusive and nonocclusive causes. Occlusive causes are physical blockages that
prevent blood flow through the vasculature, and they usually cause transmural infarcts. This can happen when a thrombus, a blood clot,
forms in the superior mesenteric artery or vein and causes thrombosis or occlusion of
the vasculature; it can also happen when a thromboembolism, which is a piece of a blood
clot that has broken off, travels through the blood and becomes lodged in the superior
mesenteric artery. Another type of occlusive cause is when something
like a tumor, hernias, volvulus–or a twisting of the bowel–or intussusception– which is
telescoping of the bowel, physically compresses the vasculature and occludes blood flow. Nonocclusive causes of small bowel ischemia
and infarction are related to systemic decreases in blood flow, and they usually cause mucosal
infarcts. This can happen in the setting of hypovolemia
due to severe hemorrhage or dehydration, or low cardiac output conditions like after a
myocardial infarction. A classic symptom of small bowel ischemia
is severe abdominal pain, even though the abdomen itself may be soft and easy to press
into. Small bowel infarction usually occurs about
twelve hours later and commonly causes vomiting, and sometimes even bloody diarrhea. Over time, the abdomen can get distended and
bowel sounds can go away as the bowels stop moving. In severe cases, when there’s sepsis, a
person can develop a fever, low blood pressure, and a fast heart rate and breathing rate to
help compensate. If fluid accumulates in the abdomen, it can
cause signs of peritoneal inflammation like rebound tenderness and guarding. Early diagnosis of small bowel ischemia and
infarction is crucial. An abdominal CT can show bowel dilation, and
bowel wall thickening from edema and inflammation, as well as intestinal pneumatosis which refers
to air in the bowel wall. CT angiography can help visualize blood flow
through the small intestines. Typically, lab studies are done and these
show a high white blood cell count and metabolic acidosis. Treatment of small bowel ischemia and infarction
is generally aimed at giving enough fluids, managing pain, and giving antibiotics if needed. Definitive treatment, though, requires reestablishing
blood flow through surgery or by using a thrombolytic enzyme if a clot is suspected. Sometimes, surgical resection of infarcted
tissue might be needed as well. Alright, as a quick recap … Small bowel
ischemia and infarction can happen when blood vessels are occluded from something like a
blood clot or a nearby tumor, a hernia, a volvulus, or intussusception. It can also occur due to a nonocclusive event
like low blood pressure throughout the body. In either situation, the wall of the small
intestines can be severely damaged and inflamed. The result can be anything from an ileus to
bacterial peritonitis. Rapid diagnosis by CT scan, and treatment
to reestablish blood flow, are essential to survival.


  1. Are there diseases that can lead to these issues? For example, can Celiac disease lead to these issues, especially if it is undiagnosed?

  2. Thank you so much for your videos! I am currently a nursing student and your videos are so helpful and easy to understand.

  3. A good video overall (a great visualization and description of pathogenesis for pathology lessons), but the given info is still NOT enough for clinical practise. Please, take this into consideration.

  4. My younger brother experienced digestive issues for 19 months, including severe diarrhea which resulted in a loss of over 15% of his body weight. A weeks stay in a Pittsburgh (UPMC) hospital provided no diagnosis. A return trip to the ER was unproductive. My brother had bypasses and/or stents placed in both femoral arteries, several years ago. The arteries had been 90% blocked. I had CABGX5 in my 40s. Atherosclerosis and infarction is common in our family tree. Brother finally went to another ER in the UPMC network, in severe distress. Sepsis was observed, emergency surgery took place, his large intestine was removed due to necrosis, and he is undergoing vascular surgery, to alleviate the blockage in his stomach aorta. Do you think this was a difficult diagnosis to make?

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