Endovascular Treatment of Popliteal Aneurysm

Historical Background

Although open surgical treatment remains the gold standard for treatment of popliteal artery aneurysm, endovascular repair has become a viable alternative. In 1994 Marin and colleagues described the first endovascular approach to exclusion of a popliteal artery aneurysm, using an expanded polytetrafluoroethylene (ePTFE) graft supported by two Palmaz stents. Since that report, flexible, self-expanding endoprostheses, including the Wallgraft (Boston Scientific, Natick, Mass.) and the Viabahn endoprosthesis (W.L. Gore and Associates, Newark, Del.) have been introduced. These commercial devices have been adapted for endovascular popliteal aneurysm repair (EVPAR). To date, a multicenter, randomized trial of EVPAR has not been conducted, but multiple single-center series have documented acceptable primary and secondary patency rates in select patients with favorable anatomy.

Indications

The primary goals of repairing popliteal artery aneurysms are the prevention of thromboembolic complications and limb loss. Complication rates of 15% to 25% at 1 year and 60% to 75% at 5 years have been reported for untreated popliteal artery aneuryms. Thus in all ambulatory patients, elective repair of popliteal artery aneurysms greater than 2 cm in diameter, especially those with mural thrombus, should be undertaken to prevent embolization, thrombosis, and major amputation.

Selection of open surgical treatment or EVPAR requires an individualized assessment of the patient. Suitable operative candidates with adequate saphenous vein should be offered surgical repair of popliteal artery aneurysm. Patients with symptomatic compression of the adjacent tibial nerve or popliteal vein should also undergo open surgical repair with aneurysm decompression and aneurysmorrhaphy, maneuvers best accomplished via the posterior approach. Finally, when thromboembolic complications require immediate revascularization, open surgical reconstruction with on-table adjunctive endovascular therapy offers the most expedient and anatomically flexible approach. However, a number of factors favor the choice of EVPAR, including patients with inadequate saphenous vein conduit or those with critical limb ischemia in the contralateral extremity who will require a venous conduit for tibial bypass. Likewise, the diagnosis of concomittant aortoiliac and popliteal aneurysms poses a challenge for frail patients. In those recovering from aortoiliac reconstruction, EVPAR permits timely popliteal artery aneurysm exclusion with minimal periprocedural morbidity. Patients undergoing endovascular repair should be able to tolerate lifelong antiplatelet therapy and potentially oral anticoagulation as well.

Several anatomic factors influence whether is EVPAR can be safely performed, including the diameters and lengths of the landing zones, the presence of mismatch between proximal and distal diameters of the landing zones, arterial angulation, and arterial runoff. Most experience has centered on use of the Viabahn endoprosthesis, which is available in 5- to 13-mm diameters. With appropriate oversizing, landing zone diameters may range from 4 to 12 mm, with at least 2 cm of nonaneurysmal artery proximal and distal to the popliteal aneurysm to affect a seal. Intravascular ultrasound (IVUS) may be used to verify the quality of the proposed seal zone. Excessive arterial angulation, which may occur at the junction of healthy and aneurysmal arterial segments, may predispose endografts to strut fracture and thrombosis. Tapered Viabahn endoprostheses are not commercially available. Therefore “pleating” or infolding of telescoped endografts to accomodate diameter mismatch may occur if the discrepancy between proximal and distal diameters is substantial. Partial or complete coverage of a patent tibial artery orifice must be avoided, and single-vessel tibial runoff should be present.

Preoperative Preparation

• Preoperative imaging. Although ultrasonography provides a cost-effective means of screening for popliteal artery aneurysms, computed tomography (CT) angiography with three-dimensional reconstruction is the imaging modality of choice for preoperative assessment and endovascular repair planning. CT angiography delineates the arterial wall, defining the extent of the aneurysm, permitting measurement of potential landing zones, and providing simultaneous screening for aortoiliac, femoral, and contralateral popliteal artery aneurysms.

• Antiplatelet therapy. Clopidogrel therapy is initiated before or immediately after endovascular repair to limit the risk of endograft thrombosis.

• Patient consent. Patients should be counseled with regard to expected outcomes and that endograft use in EVPAR is not an FDA-approved indication for these devices.

Pitfalls and Danger Points

• Inadequate recognition of spatial constraints in selecting a suitable endograft

• Inaccurate intraprocedural identification of landing zones

• “Bowstringing” of the Viabahn delivery catheter

Endovascular Strategy