Acute thrombosis of the superior mesenteric artery (SMA) and/or its branches is a catastrophic event that can lead to ischemia and death of most of the small intestine and the right colon if not recognized and surgically treated. The inner lining of the small bowel (the mucosa) is affected first; it is the most metabolically active layer of the intestine. Ischemia of the mucosa results in the production of lactic acid. In turn, this causes visceral pain–the pain is severe, but not well-localized. A patient may complain of severe pain in the epigastrium or other areas of the abdomen. At this point, the physical examination of the abdomen is totally benign because there is no localized tenderness or guarding as the outer layer of the bowel (the serosa), which lies against the wall of the abdomen, is not yet ischemic. The classic description of these patients with the sudden onset of acute arterial mesenteric thrombosis is pain out of proportion to the physical findings; the patient is found to be writhing in pain on the stretcher but have minimal findings on abdominal examination.
As the mucous becomes more ischemic, it breaks down. Enzymes, cytokines, and bacteria found in the gut now enter the blood stream. The lactic acid produced by the ischemic bowel also enters the circulation. As the bowel becomes more ischemic, the lactic acid levels in the blood rise. Associated with the breakdown of the mucosa is a rise in the WBC count. The patient may become nauseated and experience vomiting and diarrhea. The leads to dehydration. The release of cytokines and bacteria into the circulation leads to sepsis.
Acute thrombosis of the superior mesenteric artery medical expert witness specialties include vascular surgery, general surgery, gastroenterology, pathology, radiology, and critical care medicine.