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== Pathophysiology ==
== Pathophysiology ==
==Overview==
==Overview==
*Intestinal muscosa has a high metabolic rate and accordingly a high blood flow requirement. The majority of blood supply of the intestine comes from the superior mesenteric artery, with a collateral blood supply from superior and inferior pancreaticoduodenal arteries(branches of the celiac artery) as well as the inferior mesenteric artery. The splanchnic circulation(arteries supplying the viscera) receives 15-25% of the cardiac output, making it sensitive to the effects of decreased perfusion, The blood supply must be reduced by 50% of the original blood flow for the mesenteric ischemia to occur. Ischemia disrupts the mucosal barrier, allowing the release of toxins, bacteria and vasoactive mediators before the complete necrosis(which takes around 6 hours after the onset of ischemia). This further leads to myocaridal depression, sepsis, multiorgan failure and without prompt intervention, death.<ref name="pmid9146713">{{cite journal| author=Rosenblum JD, Boyle CM, Schwartz LB| title=The mesenteric circulation. Anatomy and physiology. | journal=Surg Clin North Am | year= 1997 | volume= 77 | issue= 2 | pages= 289-306 | pmid=9146713 | doi= | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=9146713  }} </ref>
*The anatomy and physiology of the small intestine plays a vital role in the develpoment of mesenteric ischemia. Intestinal muscosa has a high metabolic rate and accordingly a high blood flow requirement. The majority of blood supply of the intestine comes from the superior mesenteric artery, with a collateral blood supply from superior and inferior pancreaticoduodenal arteries(branches of the celiac artery) as well as the inferior mesenteric artery. The splanchnic circulation(arteries supplying the viscera) receives 15-25% of the cardiac output, making it sensitive to the effects of decreased perfusion, The blood supply must be reduced by 50% of the original blood flow for the mesenteric ischemia to occur. Ischemia disrupts the mucosal barrier, allowing the release of toxins, bacteria and vasoactive mediators before the complete necrosis(which takes around 6 hours after the onset of ischemia). This further leads to myocaridal depression, sepsis, multiorgan failure and without prompt intervention, death.<ref name="pmid9146713">{{cite journal| author=Rosenblum JD, Boyle CM, Schwartz LB| title=The mesenteric circulation. Anatomy and physiology. | journal=Surg Clin North Am | year= 1997 | volume= 77 | issue= 2 | pages= 289-306 | pmid=9146713 | doi= | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=9146713  }} </ref>
It is thought that [disease name] is the result of / is mediated by / is produced by / is caused by either [hypothesis 1], [hypothesis 2], or [hypothesis 3].
It is thought that [disease name] is the result of / is mediated by / is produced by / is caused by either [hypothesis 1], [hypothesis 2], or [hypothesis 3].



Revision as of 16:12, 21 November 2017


Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Feham Tariq, MD [2]


Overview

Mesenteric ischemia is a type of intestinal ischemia primarily affecting the small intestine. It is one of the life-threatening gastrointestinal vascular emergencies which requires prompt surgical/medical intervention depending upon the underlying cause.

It can be divided into occlusive/non-occlusive, arterial or venous, localized/generalized and superficial or transmural.[1]

Pathophysiology

Overview

  • The anatomy and physiology of the small intestine plays a vital role in the develpoment of mesenteric ischemia. Intestinal muscosa has a high metabolic rate and accordingly a high blood flow requirement. The majority of blood supply of the intestine comes from the superior mesenteric artery, with a collateral blood supply from superior and inferior pancreaticoduodenal arteries(branches of the celiac artery) as well as the inferior mesenteric artery. The splanchnic circulation(arteries supplying the viscera) receives 15-25% of the cardiac output, making it sensitive to the effects of decreased perfusion, The blood supply must be reduced by 50% of the original blood flow for the mesenteric ischemia to occur. Ischemia disrupts the mucosal barrier, allowing the release of toxins, bacteria and vasoactive mediators before the complete necrosis(which takes around 6 hours after the onset of ischemia). This further leads to myocaridal depression, sepsis, multiorgan failure and without prompt intervention, death.[2]

It is thought that [disease name] is the result of / is mediated by / is produced by / is caused by either [hypothesis 1], [hypothesis 2], or [hypothesis 3].

OR

[Pathogen name] is usually transmitted via the [transmission route] route to the human host.

OR

Following transmission/ingestion, the [pathogen] uses the [entry site] to invade the [cell name] cell.

OR


[Disease or malignancy name] arises from [cell name]s, which are [cell type] cells that are normally involved in [function of cells].

OR

The progression to [disease name] usually involves the [molecular pathway].

OR

The pathophysiology of [disease/malignancy] depends on the histological subtype.

Pathophysiology

Pathogenesis

The pathophysiology of mesenteric ischemia can be explained on the basis of etiology:[3][4]

  • Acute mesenteric arterial embolism: Attributes to 50% cases of mesenteric ischemia.
  • Mesenteric embolus can oringinate from the left atrium, associated with cardiac arrythmias such as atrial fibrillation.
  • Recent myocardial infarction resulting in segmental wall motion abnormality leading to poor ejaction fraction and embolus formation.
  • Infective endocarditis: vegetations on the cardiac valves resulting in turbulence in blood flow predisposing to formation of emboli into the blood stream.
  • Embolus can typically lodge into points of normal anatomic narrowing, making superior mesenteric artery the most vulnerable because of its relatively large diameter and low take off angle from the aorta.
  • The majority of emboli lodge 3-10cm distal to the origin of superior mesenteric artery, classically sparing the proximal jejunum and colon.
  • Acute mesenteric arterial thrombosis:
  • 25% cases of mesenteric ischemia result from mesenteric arterial thrombosis.
  • Most likely due to underlying atherosclerosis leading to stenosis.
  • An underlying plaque in the superior mesenteric artery leads to critical stenosis over the years forming collaterals.OR
  • It is thought that [disease name] is the result of / is mediated by / is produced by / is caused by either [hypothesis 1], [hypothesis 2], or [hypothesis 3].
  • [Pathogen name] is usually transmitted via the [transmission route] route to the human host.
  • Following transmission/ingestion, the [pathogen] uses the [entry site] to invade the [cell name] cell.
  • [Disease or malignancy name] arises from [cell name]s, which are [cell type] cells that are normally involved in [function of cells].
  • The progression to [disease name] usually involves the [molecular pathway].
  • The pathophysiology of [disease/malignancy] depends on the histological subtype.

Genetics

  • [Disease name] is transmitted in [mode of genetic transmission] pattern.
  • Genes involved in the pathogenesis of [disease name] include [gene1], [gene2], and [gene3].
  • The development of [disease name] is the result of multiple genetic mutations.

Associated Conditions

Gross Pathology

  • On gross pathology, [feature1], [feature2], and [feature3] are characteristic findings of [disease name].

Microscopic Pathology

  • On microscopic histopathological analysis, [feature1], [feature2], and [feature3] are characteristic findings of [disease name].

References

  1. Corcos O, Nuzzo A (2013). "Gastro-intestinal vascular emergencies". Best Pract Res Clin Gastroenterol. 27 (5): 709–25. doi:10.1016/j.bpg.2013.08.006. PMID 24160929.
  2. Rosenblum JD, Boyle CM, Schwartz LB (1997). "The mesenteric circulation. Anatomy and physiology". Surg Clin North Am. 77 (2): 289–306. PMID 9146713.
  3. Acosta S (2015). "Mesenteric ischemia". Curr Opin Crit Care. 21 (2): 171–8. doi:10.1097/MCC.0000000000000189. PMID 25689121.
  4. Acosta S, Ogren M, Sternby NH, Bergqvist D, Björck M (2005). "Clinical implications for the management of acute thromboembolic occlusion of the superior mesenteric artery: autopsy findings in 213 patients". Ann Surg. 241 (3): 516–22. PMC 1356992. PMID 15729076.

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Risk Factors

Common Risk Factors

The following conditions pose a signifiacnt risk towards the development of mesenteric ischemia either by interrupting the blood flow through the artery or vein supplying the small intestine (e.g.thromboemboli) or by reducing the blood supply (e.g. vasoconstriction). Also, there are certain life-style related risk factors which predominantly cause mesenteric ischemia in the older age group. [1][2][3]

Risk factors
Occlusive Embolic Atrial fibrillation
Cardiac arrhythmia
Valvular heart disease
Infective endocarditis
Recent myocardial infarction
Ventricular aneurysm
Aortic atherosclerosis
Thrombotic Advanced age
Low cardiac output states
Peripheral arterial disease
Traumatic injury
Inherited thrombophilia-
Acquired thrombophilia- malignancy, oral contraceptives intake.
Non-occlusive Heart failure
Aortic insufficiency
Septic shock
Vasoconstrictive drugs:
Cocaine abuse or ergot poisoning
Hemodialysis
Other causes Lifestyle related risk factors:
  • High cholesterol levels
  • History of smoking
  • Immobility
  • Recent surgery

Less common risk factors:

  • Fibromuscular dysplasia
  • Beta receptor blocking agents
  • Hepatitis
  • Common risk factors in the development of mesenteric ischemia include:
    • Occlusive causes
      • Embolic causes:[1]
      • Atrial fibrillation
      • Cardiac arrhythmias
      • Valvular heart diseases
      • Infective endocarditis
      • Recent myocardial infarction
      • Ventricular aneurysm
      • Aortic atherosclerosis
      • Aortic aneurysm
    • Thrombotic causes:[2]
      • Advanced age
      • Low cardiac output states
      • Traumatic injury
      • Peripheral artery disease
  • Non-occlusive causes:[3]

Less Common Risk Factors

  • Less common risk factors in the development of mesenteric ischemia include:
    • Fibromuscular dysplasia
    • Hepatitis
    • Beta recpetor blocking agents
    • Polyarteritis nodosa

Causes

Narrowing of the arteries that supply blood to the intestine causes mesenteric ischemia. The arteries that supply blood to the intestines run directly from the aorta. Mesenteric ischemia is often seen in people who have hardening of the arteries in other parts of the body (for example, those with coronary artery disease or peripheral vascular disease). The condition is more common in smokers and in patients with high blood pressure or blood cholesterol. Mesenteric ischemia may also be caused by an embolus that suddenly blocks one of the mesenteric arteries. The emboli usually come from the heart or aorta. These clots are more commonly seen in patients with arrhythmias, such as atrial fibrillation. They can be broadly classified into four categories:[4]

Classification based on etiology
Etiology Cause Incidence Examples
Occlusive causes Aterial embolism 50-70%
Arterial thrombosis 15-25%
Venous thrombosis 5%
  • Right-sided heart failure
  • Previous deep venous thrombosis (20-40% risk)
  • Primary clotting disorder
  • Pancreatitis
  • Polycythemia
  • Sickle cell anemia
  • Recent abdominal surgery or infection
Non-Occlusive causes Non-occlusive ischemia 20-30%
  • Low cardiac output states(most commom cause)
  • Hypovolemia
  • Vasoconstrictive drugs (Digoxin, alpha-adrernergic agonists)
  • Septic schock
  • Aortic insufficiency
  • Cocaine abuse or ergot poisoning

References

  1. 1.0 1.1 Fitzgerald T, Kim D, Karakozis S, Alam H, Provido H, Kirkpatrick J (2000). "Visceral ischemia after cardiopulmonary bypass". Am Surg. 66 (7): 623–6. PMID 10917470.
  2. 2.0 2.1 Martinelli I, Mannucci PM, De Stefano V, Taioli E, Rossi V, Crosti F; et al. (1998). "Different risks of thrombosis in four coagulation defects associated with inherited thrombophilia: a study of 150 families". Blood. 92 (7): 2353–8. PMID 9746774.
  3. 3.0 3.1 Acosta S, Ogren M, Sternby NH, Bergqvist D, Björck M (2006). "Fatal nonocclusive mesenteric ischaemia: population-based incidence and risk factors". J Intern Med. 259 (3): 305–13. doi:10.1111/j.1365-2796.2006.01613.x. PMID 16476108.
  4. Reinus JF, Brandt LJ, Boley SJ (1990). "Ischemic diseases of the bowel". Gastroenterol Clin North Am. 19 (2): 319–43. PMID 2194948.

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References