**2. Anatomy of the visceral arteries**

The celiac artery arises from the abdominal aorta just caudal to the diaphragm at the level of L1 and is bordered by the median arcuate ligament at the aortic hiatus superiorly and the superior border of the pancreas inferiorly.Traditionally, the three branches from this common trunk include the left gastric, splenic, and common hepatic arteries. However, multiple variations of the true "trifurcation" can exist. Most frequently, the common hepatic artery and its branches arise from the SMA or directly from the abdominal aorta (1).

The SMA arises a few centimeters caudal to the celiac trunk, and its origin is crossed by the neck of the pancreas and the splenic vein.

The IMA is usually located 3 to 4 cm cephalic to the aortic bifurcation, just to the left of midline, and usually arises at the level of the third lumbar vertebra.

#### **2.1 Acute mesenteric ischemia**

#### **2.1.1 Embolism**

The most common cause of AMI is embolization to the SMA. Arterial emboli are responsible for 40% to 50% of cases of AMI (2, 3, 4).The proximal source of the embolus is frequently intracardiac mural thrombus. Mural thrombus in proximal aneurysms in the thoracic or proximal abdominal aorta can also serve as embolic sources. Because the SMA arises at a less acute angle from the abdominal aorta compared with the other mesenteric vessels, it appears to be the most common final destination for mesenteric emboli. Additionally, such emboli tend to lodge several centimeters from the vessel's origin, usually distal to the middle colic artery.

#### **2.1.2 Arterial thrombosis**

Arterial thrombosis constitutes the next most common cause of AMI and occurs in 20% to 35% of cases (4, 5). Preexisting atherosclerotic plaque affecting all visceral vessels is the

Mesenteric Vascular Disease 237

MVT constitutes 5% to 15% of all cases of mesenteric ischemia (10). Involvement is usually limited to the superior mesenteric vein but can also involve the inferior mesenteric vein and portal vein. The extent of bowel ischemia depends largely on the degree of venous involvement. Inherited or acquired hypercoagulable diseases, including protein-C and -S deficiency, polycythemia vera, antithrombin III deficiency, antiphospholipid antibody

The most common symptom of AMI associated with arterial thromboembolic disease is the sudden onset of abdominal pain. Lack of collateral flow to the visceral organs leads to a more dramatic presentation in AMI, with severe, rapid clinical deterioration. Nausea, vomiting, diarrhea, emptying symptoms, and abdominal distention can also occur. Patients with NOMI or MVT typically present with a slower clinical course. Frequently, patients with NOMI are critically ill, hospitalized, intubated patients who experience a sudden

Postprandial abdominal pain and progressive weight loss are the most common symptoms in patients with CMI. Pain is often described as dull and crampy and located in the midepigastric region. The course of symptoms can be equated with intestinal claudication. Lack of energy leads to failure of the intestinal smooth muscle to relax, which intensifies the cramping pain. Pain often occurs 15 to 45 minutes after a meal, and the severity varies according to the size and type of meal. Patients typically develop "food fear" and decrease their oral intake in anticipation of severe pain after meals. Changes in bowel habits, nausea,

**2.1.4 Mesenteric venous thrombosis** 

**3. Clinical presentation** 

**3.1 Acute mesenteric ischemia** 

deterioration in their clinical condition.

**3.2 Chronic mesenteric ischemia** 

syndrome, and factor V Leiden mutation, are frequent causes.

Fig. 2. Acute Mesenteric Ischemia (intraoperative photograph)

Fig. 1. Anatomy of the visceral arteries

most common finding. The affected segment of artery is usually its origin at the level of the aorta. Patients with acute arterial thrombosis frequently have preexisting symptoms of CMI. Acute extension of an aortic dissection can also serve as a mechanism for abrupt mesenteric vessel occlusion and thrombosis. The degree of intestinal infarction was significantly greater in patients with SMA thrombosis compared with embolus.

#### **2.1.3 Nonocclusive mesenteric ischemia**

Impaired intestinal perfusion in the absence of thromboembolic occlusion is termed nonocclusive mesenteric ischemia (NOMI). Symptomatic patients are frequently found to have extensive atherosclerosis, with involvement of all three visceral arteries. However, NOMI can also occur in patients without mesenteric arterial occlusive disease (6, 7, 8). Visceral ischemia can occur due to low-flow states, especially in conjunction with intestinal atherosclerotic disease. NOMI most commonly occurs secondary to cardiac disease, particularly severe congestive heart failure (9).

most common finding. The affected segment of artery is usually its origin at the level of the aorta. Patients with acute arterial thrombosis frequently have preexisting symptoms of CMI. Acute extension of an aortic dissection can also serve as a mechanism for abrupt mesenteric vessel occlusion and thrombosis. The degree of intestinal infarction was significantly greater

Impaired intestinal perfusion in the absence of thromboembolic occlusion is termed nonocclusive mesenteric ischemia (NOMI). Symptomatic patients are frequently found to have extensive atherosclerosis, with involvement of all three visceral arteries. However, NOMI can also occur in patients without mesenteric arterial occlusive disease (6, 7, 8). Visceral ischemia can occur due to low-flow states, especially in conjunction with intestinal atherosclerotic disease. NOMI most commonly occurs secondary to cardiac disease,

Fig. 1. Anatomy of the visceral arteries

**2.1.3 Nonocclusive mesenteric ischemia** 

particularly severe congestive heart failure (9).

in patients with SMA thrombosis compared with embolus.

## **2.1.4 Mesenteric venous thrombosis**

MVT constitutes 5% to 15% of all cases of mesenteric ischemia (10). Involvement is usually limited to the superior mesenteric vein but can also involve the inferior mesenteric vein and portal vein. The extent of bowel ischemia depends largely on the degree of venous involvement. Inherited or acquired hypercoagulable diseases, including protein-C and -S deficiency, polycythemia vera, antithrombin III deficiency, antiphospholipid antibody syndrome, and factor V Leiden mutation, are frequent causes.
