Matthew J. Kruse and Bruce L. Gewertz

Introduction

Unimpeded access to the aorta and its visceral branches is essential to successful surgical treatment of mesenteric ischemia. This chapter briefly addresses clinical presentations of acute and chronic mesenteric ischemia that most often require surgery and considers the various options to achieve optimal exposure.

Clinical Presentation

Approximately half of the cases of acute mesenteric ischemia are caused by embolization of thrombus from cardiac pathology or arrhythmia. Patients present with the sudden, acute onset of epigastric pain not associated with rebound tenderness. The diagnosis is made by clinical correlation (e.g., history of cardiac arrhythmias) and angiographic findings of a focal arterial filling defect consistent with embolus. Radiographic findings of bowel ischemia (e.g., wall thickening, mesenteric edema) or bowel infarction (e.g., pneumatosis, portal venous gas) may be present.

The other primary cause of acute mesenteric ischemia is sudden thrombosis of one or more dominant mesenteric blood vessels. Although these patients frequently have symptoms similar to those with embolic events, prodromal symptoms such as postprandial abdominal pain (“intestinal angina”) and a history of atherosclerotic complications (peripheral vascular disease, myocardial infarction) are often elicited.

Chronic mesenteric ischemia is almost always caused by atherosclerosis of the mesenteric vessels; the classic symptoms are postprandial abdominal pain, weight loss, and food avoidance (“food fear”). The syndrome disproportionately affects women and heavy tobacco users. In most cases, two of the three major visceral vessels (celiac axis, superior and inferior mesenteric arteries) must be significantly narrowed or occluded for symptoms to occur. Arteriographic findings of multiple arterial plaques at the vessel origins confirm the diagnosis. Less common, nonatherosclerotic causes of chronic mesenteric ischemia include fibromuscular dysplasia, median arcuate ligament syndrome, and vasculitis.

The diagnosis of acute or chronic mesenteric ischemia requires both knowledge of the multiple clinical presentations and supporting findings from arterial imaging studies. Computed tomography angiography has an increasing role in diagnosis, with conventional angiography often reserved for potential therapeutic intervention such as fibrinolysis or angioplasty.

Surgical Anatomy

The celiac axis refers to a short arterial trunk originating from the anterior surface of the proximal abdominal aorta as it passes between the diaphragmatic crura at the level of the 12th thoracic vertebra (T12). The artery divides most often into three major branches within 2 cm of its origin: the common hepatic, splenic, and left gastric arteries (Fig. 34-1, A and B). These arterial branches and their tributaries provide the blood supply for the stomach, liver, spleen, portions of the pancreas, and proximal duodenum. The common hepatic artery gives rise to the superior pancreaticoduodenal arteries, cystic artery, and right gastric artery in addition to its left and right hepatic arteries. In approximately 18% of cases, the right hepatic artery is “replaced” and originates from the superior mesenteric artery. The splenic artery gives off the dorsal pancreatic artery, left gastroepiploic artery, and short gastric arteries before completing its tortuous course toward the spleen. The left gastric artery supplies the gastric cardia and fundus before anastomosing with the right gastric artery. A “replaced” left hepatic artery originates from the left gastric artery in approximately 12% of cases.

The next branch of the aorta, the superior mesenteric artery (SMA), provides the major arterial supply to the middle and distal small bowel as well as the ascending and transverse colon. The SMA is the major target artery for revascularization in patients with visceral ischemia caused by arterial insufficiency. The SMA typically arises about 1 cm distal to the celiac axis just inferior to the diaphragmatic hiatus at the level of the first lumbar vertebra (L1). It travels behind the neck of the pancreas, in front of the uncinate process and over the third portion of the duodenum. The SMA gives rise to the inferior pancreaticoduodenal artery, which anastomoses with the corresponding superior branch from the celiac circulation, and to the middle colic artery just before entering the base of mesentery of the small bowel.

Atherosclerotic pathology of the SMA most likely involves its origin, whereas emboli may lodge more distally in its course proximal or distal to the origin of the middle colic artery (Fig. 34-1, C and D).

Surgical Planning

The most common procedures for mesenteric ischemia are SMA embolectomy for acute embolic occlusion and antegrade and retrograde aorto-SMA bypass for atherosclerotic occlusive disease. When performing a surgical procedure for chronic mesenteric ischemia, it is generally wise to revascularize the celiac axis as well. The optimal procedure depends on the disease process, indication for operation, patient anatomy, comorbidities, and surgeon experience.

A technical goal common to all these procedures is accessing a portion of the SMA distal to the occlusion, to facilitate either the distal anastomosis of a bypass graft or the arteriotomy for introduction of balloon embolectomy catheters. Given anatomic constraints, the most accessible portions of the SMA are the origin of the vessel from the aorta and the more distal vessel within the mesentery at the inferior border of the pancreas.

Anterior Transperitoneal Exposure

Anterior transperitoneal exposure is a simple and serviceable approach to the visceral vessels and aorta, although it does not afford continuous exposure of the abdominal and distal thoracic aorta unless combined with a medial visceral rotation. An upper midline incision provides adequate exposure in most patients, whereas bilateral subcostal incisions may be advantageous in patients with previous midline incisions or large abdominal girth.

For antegrade bypass of the SMA, attention is first directed to exposing the supraceliac aorta. This portion of the aorta is often the last to be involved in patients with extensive atherosclerosis and is the preferred site of proximal anastomosis for a bypass graft. The esophagus and lesser curvature of the stomach are identified and retracted to the patient’s left after division of the gastrohepatic ligament. The triangular ligament of the left lobe of the liver is divided (Fig. 34-2, A), and the left lateral segment of the liver is gently retracted to the right.

Care is taken to avoid excessive force when using self-retaining retraction systems, to prevent damage to liver parenchyma as the left lobe is folded toward the right. The right crus of the diaphragm is divided by electrocautery and the underlying median arcuate ligament incised, often through dense lymphatic and neural tissue. The posterior peritoneum may then be incised and the supraceliac aorta visualized and evaluated for its suitability for proximal anastomosis. Dissection in an inferior direction will expose the origin of the celiac axis and its primary branches. If the pancreas can be anteriorly retracted, the celiac origin and a limited portion of the SMA origin can be accessed (Fig. 34-2, B). If bypass to the celiac axis is planned, adequate exposure will be available for graft anastomosis to either the common hepatic artery or the cut end of the main celiac trunk.

Most patients with atherosclerotic disease will require a bypass to a more distal portion of the SMA. Through the main peritoneal cavity, elevating and superiorly displacing the transverse colon allows palpation of its mesentery and identification of the middle colic artery and the SMA. The main vessel is exposed by incising the peritoneum directly above it at the root of the mesentery (Fig. 34-2, C). The vessel usually is easily identified, but care must be taken to avoid injury to parallel veins and often-sizable arterial branches. A retropancreatic tunnel is formed by blunt finger dissection to allow passage of a graft from the supraceliac aorta to the exposed portion of the SMA (Fig. 34-2, D).

The SMA may also be approached from a right lateral direction by mobilization of the 4th portion of the duodenum and incision of the ligament of Treitz. Alternatively, the SMA can be located in the lesser sac by incising the gastrocolic ligament, although the exposure is limited distally.

If a retrograde bypass is planned, the infrarenal aorta or left iliac arteries are exposed directly by either retracting the duodenum to the right and incising the retroperitoneum or medially reflecting the left colon. The vessel least involved with atherosclerosis is selected as the originating anastomotic site for a bypass graft, to be directed in a gradual curved path back to the SMA. Retrograde bypass is less favored because of extensive atherosclerotic involvement of the distal aortoiliac segment and potential kinking of grafts. Specific indications for retrograde bypass include a “hostile” upper abdomen or severe heart disease, which makes supraceliac aortic occlusion undesirable.

A most useful alternative to the transcrural approach to the SMA origin is medial visceral rotation. This approach is preferred for more extensive proximal revascularization, such as transaortic endarterectomy of the celiac artery, SMA, and renal vessels or repair of suprarenal aortic aneurysms. Incising the left lateral peritoneal reflection from the diaphragm to the pelvis allows mobilization of the descending colon (Fig. 34-3, A).

Next, the splenorenal and phrenocolic ligaments are carefully divided. With extension of the surgeon’s hand under the descending colon, stomach, pancreas, and spleen, the visceral bundle is rotated anteriorly and medially. The plane of the dissection can be anterior or posterior to the left kidney (Fig.34-3, B). The posterior approach provides continuous exposure of the visceral aorta as well as the proximal SMA and celiac axis (Fig. 34-3, C). As discussed next, rotating the patient to a lateral position with the right side down facilitates this exposure.

Retroperitoneal Exposure

Retroperitoneal exposure to the abdominal aorta and its visceral branches is the favored approach for many vascular surgeons. In addition to affording excellent and continuous aortic exposure, the retroperitoneal route is particularly useful in patients with an ostomy or prior abdominal surgery and dense intraperitoneal adhesions. Further, retroperitoneal approaches have been associated with overall decreased perioperative morbidity and fewer respiratory complications, more rapid return of bowel function, and shorter ICU and hospital stays.

The patient is positioned with the left side up, rotated about 60 degrees from the supine position. Care is taken to position the “break” of the operating room table equidistant between the rib cage and pelvis and properly pad both the torso and the left arm, which is secured on a special arm holder and positioned crossing the chest (Fig. 34-3, D). Depending on how high an exposure is needed, the left flank incision is made along the 9th, 10th, or 11th rib. The selected rib is carefully dissected free from the intercostal neurovascular bundle on its underside. The OR table is flexed upward in its midpoint, enlarging the musculoskeletal portal. The peritoneal envelop is identified laterally and posteriorly and the dissection carried out as previously described for transperitoneal medial visceral rotation.

In patients with suspected acute ischemia, the surgeon may need to enter the peritoneal cavity at the conclusion of the procedure to assess bowel viability.

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