Introduction
Chronic mesenteric ischemia develops due to insufficient blood flow within the splanchnic vasculature, most typically in the presence of a gradually occlusive disease state like atherosclerosis. An estimated one-fifth of the elderly population lives with some degree of significant stenosis within their mesenteric vasculature, but they often remain asymptomatic due to sufficient collateralization. However, when the blood supply fails to meet the demand, symptoms referred to as “splanchnic syndrome” develop, highlighted by postprandial pain, which in turn leads to food fear and weight loss.
Once diagnosed, lifestyle modifications are recommended, though a majority of patients ultimately require invasive treatment via percutaneous endovascular revascularization or open surgical revascularization. Before corrective surgical treatment, pain can be temporized with interventions such as celiac plexus and epidural blocks. For nonsurgical candidates, the placement of a spinal cord stimulator (SCS) can be considered.
Etiology and Pathogenesis
A majority of cases of chronic mesenteric ischemia are due to atherosclerotic narrowing, although rare causes include median arcuate ligament syndrome, fibromuscular dysplasia, aortic or mesenteric dissection, vasculitis (polyarteritis nodosum, Takayasu’s disease), and retroperitoneal fibrosis.
The three major vessels that supply the abdomen are the celiac trunk (esophagus, stomach, proximal duodenum, liver, gallbladder, pancreas, and spleen), superior mesenteric artery (distal duodenum, jejunum, ileum, and colon to the splenic flexure), and the inferior mesenteric artery (descending colon, sigmoid colon, and rectum). Approximately 18% of the elderly (>65) are thought to have significant stenosis in one of their splanchnic vessels without any known prior symptoms, and only 1.3% are thought to have two or more significantly stenotic vessels. Despite this, many patients remain asymptomatic in the setting of sufficient perfusion supplied by collateral vessels. One area at high risk is the splenic flexure, as it is a vulnerable area between territories of SMA (Superior Mesenteric Artery) and IMA (Inferior Mesenteric Artery) vasculature distribution. The majority of cases of mesenteric ischemia involve narrowing of the origins of the celiac or SMA, although the single-vessel disease was found to occur much more commonly in the celiac artery than SMA (81% vs. 19%, respectively).
Clinical Features
As previously mentioned, a vast majority of patients who have atherosclerotic mesenteric vasculature are asymptomatic due to the extensive splanchnic collaterals. Most patients who are symptomatic are over age 60 and are three times more likely to be female. An estimated 60% of patients have a smoking history and 50% have been shown to have known vascular disease.
The result of poor perfusion to the gut causes symptoms referred to as splanchnic syndrome: postprandial pain (i.e., intestinal angina), food fear, weight loss, and 50% of patients have an epigastric bruit. The pain after eating is typically described as colicky, dull, and crampy. This pain often occurs within the first hour and subsides over the following 2 h, although this time may be longer in meals with high-fat content. It is typically localized in the epigastrium with occasional radiation to the back. The pain is thought to occur secondary to arterial steal. Blood is diverted from the intestinal to the gastric circulation and this develops when food is in the stomach, thus explaining its temporal nature. Patients with a constellation of symptoms including weight loss, postprandial pain, adapted eating patterns, and diarrhea were 60% likely to have chronic mesenteric ischemia, whereas they were only 13% likely if none of these symptoms were present. A third of patients have been shown to have symptoms that were less typical such as nausea, vomiting, early satiety, and lower gastrointestinal tract (GI) bleeding (secondary to foregut ischemia due to celiac artery insufficiency). If a thrombus forms, symptoms can progress and cause what is known as acute on chronic mesenteric ischemia, in which morbidity and mortality are much higher.
Diagnosis
Diagnosis of chronic mesenteric ischemia is initially clinical, requiring symptoms of splanchnic syndrome, diarrhea/malabsorption, or vomiting. Initial diagnosis can be difficult, as many of the symptoms overlap with other etiologies, such as malignancy. An inability to pinpoint an alternate etiology in those experiencing the aforementioned symptoms should highly increase suspicion for chronic mesenteric ischemia. Some studies have demonstrated that the time from symptoms to diagnosis is approximately 1.5 years on average. For an official diagnosis, one must have significant stenosis in two or more of the mesenteric vessels (>70% narrowing of the celiac artery, SMA or IMA). However, due to the vascular supplies’ vast collateral network, all but approximately 5% of patients were found to be asymptomatic even with complete occlusion of a single mesenteric artery.
Per guidelines set by the American College of Radiology, computed tomography angiography of the abdomen and pelvis with intravenous contrast is the initial imaging of choice ( Fig. 17.1 ). It has high sensitivity in identifying or excluding atherosclerotic disease in the mesenteric vessels and is also helpful in ruling out other intraabdominal pathologies as the cause of symptoms. Magnetic resonance angiography (MRA) with contrast-enhancement is an alternative noninvasive imaging option, as it has high sensitivity in detecting proximal stenotic region within the mesenteric vasculature, though this is unreliable at detecting more distal lesions. In patients who cannot tolerate contrast loads, noncontrast MR angiography has proven to be an accurate method for detecting stenosis in the celiac trunk and superior mesenteric artery. In the event that the noninvasive imaging techniques are deemed equivocal, the next step would be to perform arteriography with possible intervention when necessary.
In an outpatient setting, it is often reasonable to first perform a duplex ultrasound of the mesenteric vasculature as a screening tool. It has a high negative predictive value of 99% for high-grade stenosis, which helps justify the pursuit of alternative causes of abdominal pain in the setting of a negative study. It is important to note that although duplex ultrasound is sensitive in diagnosing stenosis, it cannot diagnose intestinal ischemia.
Functional studies are being investigated for their possible role in the diagnosis of chronic mesenteric ischemia. Such modalities as tonometry may be utilized to assess intraluminal pH of the intestines to identify tissue ischemia. Currently, there are additional functional studies being assessed for their clinical utility including visible light spectroscopy oximeters and MR venography to assess mucosal saturations and blood flow, respectively.
Physical Exam Findings
On physical examination, there are typically no specific findings. Pain may be present but is nonlocalized. When present, its onset often occurs within 30 min following a meal and worsens over the course of an hour, classically resolving within 1–3 h. Approximately 80% of patients exhibit some degree of weight loss, some of whom will be cachectic with signs of severe malnutrition. Additionally, patients may show evidence of diffuse atherosclerotic disease, including coronary artery disease and peripheral vascular disease. Upon auscultation, approximately 50% will be found to have an epigastric abdominal bruit.
Treatment
Pharmacologic
Antiplatelet agents are often used as secondary prevention in those with atherosclerotic disease. If there is evidence of acute thrombus formation, systemic anticoagulation is then indicated. Proton pump inhibitors have shown some value given evidence of decreased oxygen demand of the gastric mucosa. Antispasmodic agents (i.e., papaverine hydrochloride) and nitrates have been shown to be helpful in attenuating symptoms of intestinal angina.
Revascularization
Revascularization is typically only warranted if symptoms are present with evidence of severe stenosis of the splanchnic vessels. When the need for vascularization arises, the two options are open surgical reconstruction (aortomesenteric and celiac bypass grafting, endarterectomy, and mesenteric reimplantation) and percutaneous transluminal angioplasty (PTA). PTA is becoming the more favored option given improvements in the technique. However, open surgical techniques may be preferred in patient populations where intravenous contrast loads are contraindicated. Systematic reviews of both techniques have shown no significant difference in perioperative mortality and 3-year cumulative survival between the two groups.
Injection Therapy
For patients with chronic abdominal pain, interventional pain techniques have been demonstrated to be effective adjunctive treatments. Patients may gain temporary relief with procedures like epidural blocks, which in turn may suggest benefit from the placement of more permanent devices like intrathecal pumps for refractory patients. To date, studies assessing the effectiveness of visceral blockade has been highly variable and included a limited number of patients. In a retrospective study by Rizk et al., patients with chronic visceral abdominal pain were evaluated and treated with the differential thoracic epidural regional blockade, also known as differential neural blocks. Incremental doses of local anesthetic are infused through the epidural catheter with subsequent blockade of the nerve supply to visceral organs, such as the celiac, hypogastric and splanchnic nerves. In Rizk et al. study, 81 patients underwent differential thoracic epidural regional block. Among this group, 70.4% of the patients reported a successful block, described as >50% reduction in their visual analog scale pain score. The findings of this study also suggested that more intense initial pain scores led to a greater degree of pain alleviation from the block.
Intrathecal Drug Delivery Systems
Intrathecal drug delivery systems (IDDS) deliver medications directly into the intrathecal space through an indwelling catheter that is connected to a reservoir system implanted in a subcutaneous pocket typically in the abdomen ( Fig. 17.2 ). Currently, FDA approved medications for IDDS are morphine, baclofen, and ziconotide. Additive and off-label medications include fentanyl, bupivacaine, clonidine, and hydromorphone among others. Opioids are most commonly used, and often as monotherapy, with subsequent additional of agents often guided by the Polyanalgesic Consensus Conference recommendations. Before placement of IDDS, an epidural or intrathecal trial is performed to determine the potential benefit of treatment. Alternatively, a single shot spinal may also be done. The catheter tip is placed according to the corresponding dermatomal distribution of the patient’s pain.
