Endovascular Treatment of Peripheral Aneurysms



Endovascular Treatment of Peripheral Aneurysms


Kenneth R. Thomson, Stuart M. Lyon, Mark F. Given and James P. Burnes


Peripheral aneurysms are classified as true or false depending on the composition of the aneurysm wall. The type of treatment depends on the shape (saccular or fusiform), location, and cause.


Vascular surgery has been the preferred method of treatment, especially if the aneurysm is superficial,1 but more recently, computed tomography (CT) has shown that endoleaks occur in peripheral aneurysms post surgery, just as they do after aortic endovascular repair.2 Recent advances in endovascular methods of treatment and development of new endovascular tools for peripheral aneurysms have made this method a reasonable alternative to conventional surgery.


False aneurysms are most common after trauma (including angiographic access). The cause of an aneurysm may be obvious (trauma or iatrogenic) or more obscure (due to atheromatous change, increased flow, or infection), and it may be impossible to determine which type of aneurysm is present based on angiography alone. Multidetector-row CT and Doppler ultrasonography have increased detection of asymptomatic peripheral aneurysms. Aneurysms related to thoracic outlet compression are commonly symptomatic owing to peripheral embolization.3


Permanent occlusion of an aneurysm requires more than just proximal occlusion of the supplying artery. If arterial occlusion is performed, the vessel should be occluded both proximal and distal to the site of the aneurysm to prevent retrograde filling of it via collateral vessels. In the case of an abdominal pseudoaneurysm (e.g., splenic artery pseudoaneurysm) in an unstable patient, proximal arterial occlusion may provide equivalent results to the more conventional segmental occlusion.4



Indications


Aneurysms will eventually enlarge and rupture once the tension on the wall is greater than the intrinsic wall strength. Tension on the wall is a function of the pressure multiplied by the radius divided by the wall thickness (Laplace law).


Rupture is more common in false aneurysms, probably related to wall thickness. In the absence of trauma, peripheral aneurysms are less prone to spontaneous rupture than intracranial aneurysms. Larger aneurysms are believed to be at greater risk of rupture than smaller ones, and this is particularly so in the case of splenic aneurysms, whether they are true or false.


In addition, aneurysms may extrinsically compress surrounding structures like nerves or arteries and lead to symptoms.


In general, false aneurysms, particularly those caused by an arterial puncture, are more likely to be associated with pain than true aneurysms. Early treatment of false aneurysms is important to reduce the risk of rupture. Factors that influence rupture of cerebral aneurysms are disturbed flow patterns, small impingement regions, and narrow jets.5 The same factors probably apply in peripheral aneurysms.



Contraindications


Major contraindications to endovascular treatment of peripheral aneurysms are active/uncontrolled infection or arteritis, and an aneurysm that is unlikely to enlarge further or rupture (e.g., circumferentially calcified aneurysms). If an aneurysm is to be left untreated, careful follow-up is mandatory.


In the case of infection, aggressive treatment with high doses of intravenous antibiotics is required if endovascular treatment is contemplated. Most vascular surgeons prefer to perform an extra-anatomic bypass for infected aneurysms. However, if the risk of surgery and rupture is unacceptable, infected aneurysms can be treated by endovascular methods.


Patients with aneurysms related to arteritis should ideally be treated until the erythrocyte sedimentation rate and other inflammatory markers are within normal range and the etiologic disease is under control, if this is possible. However, aneurysms related to Behçet disease are more likely to arise suddenly and are prone to early rupture.6


Patients who know they have an aneurysm are usually very anxious about it and will request treatment, even when the aneurysm is small and asymptomatic.



Equipment




• Micropuncture access kit (Cook Inc., Bloomington, Ind.; AngioDynamics Inc., Queensbury, N.Y.)


• 0.035-inch guidewire (1.5-mm J or Terumo guidewire [Cook Inc.; Terumo Corp., Somerset, N.J.])


• 5F access sheath (Cook Inc.)


• 4F or 5F diagnostic catheter (Cobra 2) (Cook Inc., AngioDynamics Inc., Terumo Corp.)


• Guide catheters (Cordis Corp., Hialeah, Fla.; Abbott Vascular, Santa Clara, Calif.)


• Microcatheter (Terumo Progreat or equivalent)


• Ultravist 370 or equivalent nonionic contrast media


• Arterial stent (balloon-expandable or self-expanding), provided the interstices of the stent allow passage of a catheter


• Peripheral endograft (Symbiot [Boston Scientific, Natick, Mass.], Atrium [Atrium Medical, Hudson, N.H.], Jo-Graft [Abbott Vascular, Abbott Park, Ill.])


• Balloon angioplasty catheter for use with vinyl alcohol copolymer (Onyx [ev3/Covidien, Irvine, Calif.])


• Occlusion coils (fiber coils are preferred in 0.018- or 0.035-inch wire diameters [Cook Inc., Boston Scientific])


• Detachable coils (Micro Therapeutics Inc. [Irvine, Calif.], Cook Inc., Boston Scientific)


• Vinyl alcohol copolymer (Onyx)


• N-butyl cyanoacrylate (NBCA) adhesive and iodized oil (Cordis Corp.)


• Thrombin (USP), 1000 IU/mL or 5000 IU/5 mL (Thrombin-JMI [GenTrac Inc., Middleton, Wis.])



Technique


Anatomy and Approaches


Approach to the aneurysm will be determined by its site. If the aneurysm cannot be accessed angiographically, it may be possible to directly puncture it using a 22-gauge needle. Of the visceral aneurysms, splenic artery aneurysms are the most common.7


Because of the short gastric supply to the spleen, it is usually possible to occlude the main splenic artery without causing splenic infarction. However, preservation of pancreatic blood supply is critical to avoid pancreatitis. If possible, distal splenic artery embolization should be avoided to reduce the risk of splenic infarction. Provided it will adequately treat the aneurysm, proximal splenic artery embolization is preferred.


In the limbs, it is essential to maintain blood supply to the distal limb and avoid embolization of the distal vessels.



Technical Aspects


There are several methods of treating peripheral aneurysms.



Thrombin Injection Into a False Aneurysm


The concept of this procedure is that introducing a small amount of thrombin into the aneurysmal sac will induce a rapid and localized coagulation cascade that will be confined to the aneurysm and not lead to any thrombosis or distal embolization within the native vessel (Fig. 41-1).


image
FIGURE 41-1 A–C, Thrombin injection into false aneurysm (see text for description).

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Dec 23, 2015 | Posted by in INTERVENTIONAL RADIOLOGY | Comments Off on Endovascular Treatment of Peripheral Aneurysms

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