Management of Visceral Aneurysms



Management of Visceral Aneurysms


James E. Jackson


False aneurysms (pseudoaneurysms) of the visceral arteries represent an area of contained hemorrhage and are relatively uncommon but at high risk of rupture, with subsequent acute gastrointestinal or retroperitoneal hemorrhage. They always require treatment regardless of their size. Many are related to acute or chronic pancreatitis but may also occur after surgery or without an obvious cause. There should be a high index of suspicion for the presence of a pseudoaneurysm in a patient with a history of pancreatitis in whom upper gastrointestinal bleeding subsequently develops, although other causes (e.g., segmental portal venous hypertension secondary to splenic venous occlusion or unrelated peptic ulceration) are still more likely. However, if the episodes of hemorrhage in such patients are related to severe epigastric pain radiating to the back, a pseudoaneurysm communicating with the pancreatic duct and causing hemosuccus pancreaticus is likely.1


True aneurysms of the visceral arteries are rare. The splenic artery is the vessel most commonly involved, and the majority of aneurysms are an incidental finding on cross-sectional imaging. Their risk of rupture is not clear, but if less than 2 cm in diameter, they are unlikely to cause problems, except perhaps during pregnancy. A combination of atheromatous disease and aneurysm formation may be seen in association with enlargement of the pancreaticoduodenal arcade vessels as a result of either atheromatous stenosis of the celiac axis or, more commonly, compression of the celiac axis origin by the median arcuate ligament of the hemidiaphragm. These aneurysms may rarely rupture into the retroperitoneum.



Indications


All visceral artery pseudoaneurysms require treatment, and the vast majority can be managed successfully by embolization, which should be the procedure of first choice.2-4 Surgery should be reserved for patients in whom complex anatomy precludes an endovascular approach.


Indications for treatment of true visceral artery aneurysms are less clear-cut because prospective data on the risk of rupture are lacking. The splenic artery is the vessel most frequently involved, and aneurysms, when present, are commonly related to branch origins. Those less than 2 cm in size can probably be ignored. The American College of Cardiology and American Heart Association guidelines for management of patients with peripheral arterial disease5 conclude that:



Although few would disagree with the first of these guidelines, the wording of the second is less helpful. There are undoubtedly patients in whom an asymptomatic visceral artery aneurysm measuring up to 2.5 cm in size is found on imaging performed for other reasons and can be managed conservatively. Indeed, some authors suggest that 2.5 cm rather than 2 cm should be the size above which therapy is required.6 There is no doubt, however, that symptomatic aneurysms or those that show a gradual increase in size on follow-up will require treatment. An additional indication for treatment of renal artery aneurysms is renovascular hypertension.


The decision whether to proceed with open surgical or endovascular repair of a true visceral artery aneurysm depends on a number of factors, including the size and site of the aneurysmal disease. In the context of acute rupture, the patient may stabilize after the initial hemorrhage because of tamponade of the ruptured aneurysm by surrounding hematoma, especially when the hemorrhage occurs into the retroperitoneum, and such individuals may be treated by embolization. Patients who are hemodynamically compromised are more likely to need to proceed straight to open surgery.




Technique


Anatomy and Approach


Thorough knowledge of conventional and variant visceral arterial anatomy is essential, as is recognition of the many collateral pathways that can develop via normal anastomoses in response to visceral artery occlusive or stenotic disease.7 This rich collateral supply to most of the abdominal viscera means that embolization of major visceral vessels can often be performed without causing organ infarction. Lack of appreciation of the extent of this collateral network can, however, result in failure of endovascular therapy. For example, a pseudoaneurysm involving a right hepatic artery branch should be definitively treated by placing embolization coils on either side of the arterial defect to exclude it completely from the circulation. An angiographer who fails to recognize that intrahepatic arterial branches will receive a collateral supply from several possible sources (e.g., other hepatic, internal mammary, and inferior phrenic arteries) immediately after proximal hepatic artery occlusion is more likely to perform an inadequate embolization by placing coils only proximal to the pseudoaneurysm neck.


Multislice computed tomography (CT) performed during the arterial phase of contrast medium enhancement will usually provide exquisite images, in a variety of planes, of both true and false aneurysms, which can be of great help in documenting the anatomy and planning endovascular therapy (Fig. 73-1). Most visceral arterial aneurysmal disease that requires therapy will be approached via a common femoral artery puncture. Occasionally an axillary or brachial artery approach will provide a more favorable route, such as when the aneurysmal disease involves a superior mesenteric artery that has a very acute origin from the aorta, or when there is marked compression of the origin of the celiac axis by the median arcuate ligament of the hemidiaphragm.




Technical Aspects


Visceral Angiography


It is essential that high-quality diagnostic angiographic images be obtained to document completely the anatomy of the diseased segment of the vessel so that treatment is successful. Considerable experience is necessary to routinely acquire high-quality diagnostic images of the visceral arteries. Unfortunately, it is increasingly difficult to obtain sufficient experience, because the indications for visceral angiography have decreased substantially over the last decade as alternative noninvasive imaging studies and ready access to endoscopy have become available. It is not the purpose of this chapter to discuss the technique of diagnostic visceral angiography, but it is such an important part of the procedure that some of the most useful technical points will be mentioned briefly. Interested readers are referred to other texts for a more detailed description.8


One of the major problems with digital subtraction angiography, currently the method of image acquisition used almost exclusively for visceral angiography, is that of movement artifact; this is the most common cause of serious image degradation during abdominal imaging. There are two sources of movement during visceral angiography. The first, bowel peristalsis, can easily be abolished in the majority of patients by the administration of smooth muscle relaxants, but a common mistake, and one that is often the cause of poor-quality images, is to rely on a single dose of drug. For example, many radiologists will give 20 mg of hyoscine butylbromide (Buscopan) intravenously at the beginning of the procedure and rely on this dose to provide bowel paralysis for much of the study; this will very rarely suffice. A starting dose of 40 mg is recommended and should be increased by 20-mg increments when required. It is common to administer 100 mg during an arteriogram taking between 45 and 60 minutes to complete. Complete bowel paralysis may occasionally not be produced by hyoscine butylbromide alone, and the addition of glucagon in 1-mg aliquots may be necessary.


The second type of movement, which may be much more difficult to deal with, is that of respiration. Several techniques may be used to obtain diagnostic images. Very few individuals are able to hold their breath without any abdominal movement for more than about 15 seconds, and most will manage less than 10. This means that severe image degradation commonly occurs during the late arterial/early venous phase, which is often the most important part of the angiogram for determining the site of pathology in patients being investigated for gastrointestinal bleeding. Movement is likely to be even more pronounced if the patient is asked to take a deep breath and hold it during image acquisition. It is better to ask the patient to stop “at a comfortable position” in the middle of respiration and try to stop breathing at the same position for each run. A substantial improvement in abdominal stillness can also be achieved by simply pinching the nose (with a nose clip) during breath-holding. It is always worthwhile to practice these techniques with the patient before obtaining images.


In many individuals, considerable movement persists on early images, despite use of the aforementioned techniques, and it is rare, even with the fittest of patients (indeed, it is usually the younger, fitter patients who experience the most difficulty keeping still during breath-holding), to find an individual who is able to hold the abdomen completely still to allow good-quality venous images. The technique that is useful in practically all patients is that of acquisition of images during normal respiration. More than 90% of visceral arteriograms performed at this author’s institution include at least one run (and sometimes all) acquired during normal breathing. This underused technique often produces the best diagnostic images. It relies on regular breathing and the acquisition of several images before the injection of contrast medium, each of which may then be used as a mask for the subsequent angiographic images. When performed in this manner, a different mask will usually be available for each stage of the respiratory cycle, and perfectly subtracted images will be obtained throughout the run in the arterial, capillary, and venous phases. The best results are obtained if images are acquired at one frame per second, and two (and sometimes more) full respiratory cycles are imaged before contrast medium is injected.



Embolization


Although the endovascular techniques used to treat false and true visceral artery aneurysms are often similar, each will be discussed separately because there are some important differences.



False Aneurysms (Pseudoaneurysms)

The success of treatment depends on complete, persistent thrombosis of the pseudoaneurysm sac. There are several possible methods by which this may be achieved, each of which will be discussed.


Dec 23, 2015 | Posted by in INTERVENTIONAL RADIOLOGY | Comments Off on Management of Visceral Aneurysms
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