This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Small Intestine - Mesenteric Ischemia, Subject name: Surgery
[{'content': 'Most common arterial involvement causing ischemia of intestine is: \nSelect and explain. \nA. Superior mesenteric artery thrombosis, B. Inferior mesenteric artery thrombosis, C. Hepatic artery thrombosis, D. Celiac artery thrombosis', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans: A (Superior mesenteric artery thrombosis) Ref: Schwartz Textbook of Surgery, 10th edition, pg: 860; Mastery of Vascular and Endovascular Surgery - Gerald B. Zelenock - 2006, pg: 294 and Essentials of General Surgery, Peter F. Lawrence, 2006, pg: 459Explanation:"The SMA is the most commonly involved vessel in acute mesenteric ischemiaRef: Mastery of Vascular and Endovascular Surgery"Embolization to the superior mesenteric artery accounts for approximately 50% of ail cases of acute mesenteric ischemia Ref: Essentials of General SurgerySuperior Mesenteric Artery EmbolusMost common cause of mesenteric ischemia (40 to 50% of cases).The prognosis is poor (70% mortality).Sudden embolus with no time for collaterals to form.Presents with abdominal pain out of proportion to examination findings.Risk Factors:o Arrhythmias (atrial fibrillation),o Post-myocardial infarction with mural thrombi,o Valvular heart disease.o Structural heart defects.Superior Mesenteric Artery ThrombosisAccounts for 25 to 30% of mesenteric ischemia cases.Has worst prognosis with a mortality of 90%.Occurs near the origin of the SMA.Causes enormous amount of bowel necrosis.Most patients have a history of chronic mesenteric ischemia with vague and insidious symptoms such as:o Weight loss.o Abdominal angina (abdominal pain after meals),o Diarrhea,o Fear of food.Risk Factors:o Systemic atherosclerosis,o Old age.Angiography is the gold standard for mesenteric ischemia allowing for diagnosis and therapy.', 'role': 'assistant'}]