Endovascular Treatment of Popliteal Artery Aneurysms



Endovascular Treatment of Popliteal Artery Aneurysms



Ignace F. Tielliu and Eric L. Verhoeven


Popliteal artery aneurysms (PAAs) are rare, occurring usually in men older than 60 years. The incidence is significantly higher in patients with an abdominal aortic aneurysm (AAA), where up to 30% may be affected. These aneurysms have a tendency to occur bilaterally. PAAs exhibit symptoms in up to 70% of the cases within 5 years. Symptomatic PAAs can manifest with progressive intermittent claudication as a result of chronic peripheral embolization. In some cases this follows thrombosis of the PAA. Other cases manifest with severe ischemia of the limb as a consequence of acute thrombosis or embolization. In these patients, limb loss can follow if treatment is not immediately instituted. Both chronic and acute embolization make treatment tedious as the outflow vessels become less suitable for a bypass or interposition graft reconstruction. Elective treatment before symptoms occur is therefore indicated.


PAA growth rate per year is approximately 10% of its maximal diameter. The best timing for treatment of asymptomatic PAA with regard to the diameter is still the subject of continued debate. A PAA larger than 3 cm, especially with mural thrombus, is a clear indication for treatment. For a PAA between 2 and 3 cm in diameter there is no consensus.


Some advocate using a combination of aneurysm size and distortion of the popliteal artery as a guideline to treat asymptomatic PAAs. The highest predictive value for symptomatology is a diameter of at least 3 cm and a distortion of more than 45 degrees measured as the angle of the most proximal curve in the popliteal artery. It is unclear what the impact of thrombus is in the wall of the aneurysm on the occurrence of symptoms, although it is reasonable to recognize that thrombus can dislodge and cause peripheral embolization.


Indications for treatment and technical options have evolved across history. In the 18th and 19th centuries, indication was often rupture or symptomatic swelling of the limb. Compression or ligation was the only means to treat a symptomatic PAAs in those times. The 20th century was dominated by open arterial reconstructions with an interposition or bypass graft.


In 1994, the first report of endovascular repair of a PAA marked the beginning of a new era. Endovascular repair of a PAA involves introducing a covered stent at the level of the aneurysm, with landing zones both proximal and distal to the PAA in a healthy part of the popliteal or superficial femoral artery (SFA).



Preoperative Evaluation


Duplex ultrasound examination is the preferred method to confirm the clinical diagnosis of a PAA. When the diameter has met the criteria for treatment, additional imaging modalities are available to assess suitability for endovascular repair, including conventional angiography, computed tomography (CT) angiography, and magnetic resonance (MR) angiography.


Duplex examination should be repeated to confirm patency of the PAA before any invasive treatment. In addition, the diameters of the proximal and distal landing zones are measured from intima to intima to aid in deciding on the diameter of the stent graft to be used. Marks should be drawn on the patient’s leg to delineate proximal and distal borders of the PAA. Mural thrombus in the aneurysm sac can hide transition zone between healthy vessel and aneurysm wall during the procedure.


In theory it is possible to do the endovascular repair based solely on the information of the duplex examination, but additional angiography is generally performed. This defines iliofemoral inflow and crural outflow vessel patency. In addition, angiography is better suited to adequately measure the length of the aneurysm and its landing zones. Conventional angiography has been replaced by CT angiography for this specific purpose in our practice. It is less invasive, and mural thrombus, calcifications, and vessel angulations are imaged in a better way. Central lumen line multiplanar reconstructions can easily be created on a workstation to accurately assess vessel diameters and lengths.



Contraindications for Endovascular Repair


Lack of proximal and/or distal landing zones are usually considered a contraindication for endovascular repair. Adequate inflow and outflow vessels are also needed to attain a successful endovascular repair. Inflow vessels can be treated by angioplasty or conventional surgery to optimize their patency before endovascular repair. At least one good-quality outflow vessel in the lower leg is required. A marked discrepancy in the diameter of the proximal and distal landing zones is another contraindication for endovascular repair. A minor discrepancy in diameter can be managed by overlapping stent grafts of different diameter. When this discrepancy exceeds 3 mm in diameter, patients should not undergo endovascular repair (at least with a tubular stent graft). Finally, a marked stenosis at the edge of the aneurysm, as sometimes seen in larger PAAs crossing the hinge point of the popliteal artery, is a relative contraindication. Collapse of the stent graft with subsequent occlusion can occur in these cases.



Stent Grafts


Since the first report of popliteal stent grafting with a homemade device, several types of stent grafts have been used. In the literature, the most reported stent graft is the nitinol-expanded polytetrafluoroethylene (ePTFE) Hemobahn/Viabahn (W.L. Gore & Associates, Flagstaff, Arizona). They have an outer skeleton of nitinol and are available in lengths ranging from 5 to 25 cm and in diameters from 5 to 13 mm. Wallgrafts (Boston Scientific, Natick, MA) and Anaconda limbs (Vascutek, Renfrewshire, Scotland) have also been used in treating PAAs.


Ideally, a stent graft for the treatment of PAA should be flexible in order to cope with flexion–extension movements across the hinge points of the popliteal artery, and the skeleton should resist fracture. A tapered stent design has the advantage that addresses the physiological tapering of the popliteal artery.



Endovascular Procedure and Follow-Up


The procedure is performed with a small ipsilateral cut down in the groin to expose the common femoral artery or by a percutaneous route. Heparin is given intravenously (5000 IU), and a sheath is introduced in the superficial femoral artery. A straight-tip calibrated angiocatheter is advanced over a soft guidewire down to the level of the tibioperoneal trunk. The duplex-guided pencil marks on the patient’s leg are now replaced by radiopaque needles to mark the borders of the PAA, which is now visible under fluoroscopy.


The length of the aneurysm including the landing zones indicate the stent graft length needed. Recommended landing zone length is at least 2 cm. If the measured length to be stented exceeds the length of one stent graft, one or more additional stents will be needed. Overlap zone between stent grafts should be at least 3 cm to avoid a disconnection and type III endoleak. Smaller stent grafts should be deployed first, followed by wider ones, to ensure a fluent transition zone downstream. The most distal stent graft is deployed first in most cases. Introduction over a stiff guidewire (e.g., Amplatz Super Stiff, Boston Scientific, Galway, Ireland) is recommended, to ensure correct positioning and deployment. Balloon dilatation is usually recommended to achieve complete apposition of the stent graft to the landing zone wall. Completion angiogram is easily performed through the sheath to confirm exclusion of the aneurysm and unimpaired outflow.


Postoperative antiplatelet therapy protocol includes dual therapy for 1 year with aspirin 100 mg and clopidogrel 75 mg daily. The addition of clopidogrel has been shown to be a significant predictor of success of endovascular PAA repair in terms of patency of the stent graft. However, there are no data to indicate the optimal dosage or treatment duration of clopidogrel in this setting. After 1 year clopidogrel is discontinued, but lifelong aspirin is continued.


A radiograph of the knee is performed before discharge as a reference for the future detection of graft migration, disconnection, or stent fractures. Duplex ultrasound is particularly suited to detect both endoleaks and stenoses and to evaluate the diameter of the PAA. Our protocol includes follow-up at 6 weeks, 6 months, 1 year, and then yearly with physical examination, duplex ultrasound, ankle-to-brachial index, and knee radiographs with the knee extension (anteroposterior and lateral view) and with the knee in 90 degrees of flexion (lateral view only) (Figures 1 and 2).


image
FIGURE 1 Postoperative radiograph, anterior view with knee in extension, in a patient with aborted open repair, showing no particular angulation in the Viabahn graft.

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Aug 25, 2016 | Posted by in CARDIOLOGY | Comments Off on Endovascular Treatment of Popliteal Artery Aneurysms

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