DSA Of Gastric ischemia

                 Gastric ischemia in a neonate is usually a complication of acute anoxia or shock. Intestinal ischemia in children is often superimposed on underlying congenital vascular or metabolic abnormalities. Thus vascular thromboemboli are a known complication in a setting of homocystinuria, a rare inborn error of amino acid metabolism manifesting as a multisystemic disease associated with mental retardation and vascular disease, consisting of premature arteriosclerosis and thrombosis.
                 Does the use of umbilical artery catheters in newborns impair mesenteric blood flow? Doppler US performed before and after removal of umbilical artery catheters found that after catheter removal mean peak celiac artery systolic blood flow velocity increased from 50cm/sec to 62 cm/sec and superior mesenteric artery flow from 52 cm/sec to 72 cm/sec; end diastolic blood flow velocity and vessel diameters did not change significantly.
                  Umbilical arteriovenous fistulas are uncommon. They can be either congenital or acquired. Even in a neonate an arteriovenous fistula between the umbilical artery and umbilical vein can result in bowel ischemia. Bowel perfusion improves in some after umbilical vein ligation.
Imaging
Angiography is the historic gold standard in suspected acute mesenteric ischemia. It is more time-consuming and often less available than CT, which is the current examination of choice in many centers. Mesenteric CTA detects superior mesenteric artery embolism or thrombosis and superior mesenteric vein thrombosis with a sensitivity approaching that of angiography. In addition to acute ischemia, CT also evaluates other causes of an acute abdomen.
                    Conventional radiography findings in patients with intestinal ischemia reflect the underlying spectrum of pathologic changes. They are normal initially or reveal variable degrees of gaseous bowel distention and fluid levels. Dynamic CT findings range from  ischemic ileus, bowel wall edema, and hematoma manifesting as bowel wall thickening, major vessel stenosis, or occlusion (either arterial or venous) to eventual bowel wall necrosis identified as intramural gas and lack of bowel wall contrast enhancement. In patients requiring surgery for acute mesenteric ischemia, detection of at least one of these CT findings achieves a specificity of over 90% but a considerably lower sensitivity. At times a contrast-enhanced CT target sign is evident during the arterial phase, especially if ischemia is due primarily to venous obstruction. Gas–fluid levels and dilated bowel loops, both nonspecific signs of acute mesenteric ischemia, are seen equally well with conventional radiography and CT. Major ischemia leads to gas within the bowel wall (pneumatosis intestinalis) and mesenteric and portal vein gas. With few exceptions, in adults detection of mesenteric and portal venous gas implies mesenteric infarction. Such gas occasionally migrates to the internal spinal venous plexus, presumably from the pelvic veins.  Pneumoperitoneum and even pneumoretroperitoneum are uncommon manifestations of bowel ischemia  resumably reflect a perforation. Some authors preach the superiority of CT in detecting portal venous gas and probably rightly so, although a formal comparison with conventional radiography is lacking. Nevertheless,
quite often conventional radiographs suffice to suggest the diagnosis. Computed tomography in patients with acute superior mesenteric artery occlusion identifies intravascular blood clots as high-density regions on precontrast images and as filling defects after contrast enhancement. A sometimes useful finding in acute superior mesenteric artery occlusion is a CT ratio of the external diameter of the superior mesenteric vein divided by the external diameter of the superior mesenteric artery; this ratio becomes <1 in patients with acute occlusion.
               Sonographic findings range from normal to nonspecific distended loops of bowel. Doppler US is useful for detecting high-grade celiac artery and superior mesenteric artery stenoses and occlusion.When successful in evaluating mesenteric vessel patency, however, Doppler US findings need to be placed in a proper clinical perspective because not all stenoses are symptomatic.
               Celiac artery narrowing is found in some patients if the study is performed at expiration (median arcuate ligament syndrome), a finding minimized at inspiration. These patients have chronic abdominal pain, at times mimicking gastric outlet obstruction. Doppler US measurement of mesenteric vascular flow is difficult in a setting of suspected acute ischemia, being successful only in a minority of patients. Various MR techniques such as MRA, cine phase contrast MRA, and flow-independent T2- weighted imaging not only identify anatomic stenoses but also provide physiologic data about blood flow. Currently the use of MRI in bowel ischemia is still in its infancy.
             Vessel obstruction is best identified with MRI on early contrast-enhanced images. Thus major arterial or venous thrombosis is seen on postcontrast images as a signal void, often surrounded by increased enhancement in a thickened vessel wall. A similar wall thickening is found with bowel wall edema, such as in hypoproteinemia, but no increased postcontrast wall enhancement is evident. Systolic gating is helpful when using a 3D phase contrast MRA technique to evaluate celiac and superior mesenteric artery stenoses. Gadoliniumenhanced 3D spoiled gradient-refocused acquisition in the steady state (GRASS) MRA identifies any stenosis in celiac and superior mesenteric arteries.
               Deoxyhemoglobin in blood cells is paramagnetic, but oxyhemoglobin is not. This difference can be used to measure superior mesenteric vein blood oxygen saturation in hemoglobin, obtained using flow-independent MR T2 data; it appears useful in confirming suspected chronic mesenteric ischemia. In patients without ischemia, superior mesenteric vein blood oxygen saturation increases after a meal, but in symptomatic patients with chronic mesenteric ischemia blood saturation tends to decrease. In spite of research on this topic for over a decade, the clinical relevance of such measurements is yet to be established. In an occasional patient positive uptake of Tc-99m–HMPAO–labeled leukocytes appears to reflect underlying chronic ischemia rather than primary inflammation.
Therapy
Acute Ischemia

                  Different therapy is employed for acute and chronic ischemia. Without therapy, acute nonocclusive ischemia often progresses to infarction. The treatment of choice in some patients with nonocclusive ischemia is papaverine infusion via a vascular catheter. Resection and anticoagulation are therapies for infarcted bowel. Recurrent bowel ischemia is a complication
of surgical bypass grafting for acute ischemia. Fibrinolytic therapy using urokinase, rather than surgical embolectomy, appears effective in a majority of patients with a mesenteric embolus and without evidence of intestinal infarction; others require laparotomy. The best sign of successful therapy is pain abatement; persistent pain suggested intestinal infarction. Rather than surgical embolectomy, in selected individuals mechanical thrombolysis of mesenteric and portal vein thrombosis, using a jugular vein approach, is an alternate approach.
Chronic Ischemia                 Either percutaneous transluminal angioplasty or a surgical bypass graft is employed in a setting of chronic mesenteric ischemia. At times transaortic endarterectomy is performed. All of these techniques have their associated complications. The published success rates of percutaneous transluminal angioplasty are difficult to put in perspective because different criteria are used and are operator dependent.
           Similar to surgical mesenteric vascular graft placement,  percutaneous transluminal angioplasty has a technical procedure success rate of about 90% and short term clinical success of about 80%. Procedure related mortality and the major complication rate appear similar for operative bypass grafting and percutaneous transluminal angioplasty; long term pain relief is similar or better with grafting.
image
This is radiology images of the Celiac trunk compression by median arcuate ligament. Inspiration (A) and expiration (B) lateral digital subtraction angiography (DSA) views show a transient compression (arrow).


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