Popliteal Artery Aneurysm
What is a popliteal artery aneurysm?
Popliteal artery aneurysm refers to an abnormal dilatation of the artery behind the knee. Although uncommon in the general population they are the second most common peripheral arterial aneurysm and are often associated with aneurysms elsewhere in the body including aortic and femoral artery aneurysms. The majority of popliteal artery aneurysms occur in men over the age of 60 and cause symptoms in two thirds of patients leading to the initial diagnosis.
What causes popliteal artery aneurysms?
The majority of popliteal artery aneurysms develop secondary to atherosclerosis but may also occur as a result of trauma, infection or mechanical causes, such as popliteal entrapment syndrome.
Why are popliteal artery aneurysms important?
The most common complication of popliteal artery aneurysms is clot formation (thrombosis) causing limb ischaemia (See table 1). This may present as an emergency, threatening the viability of the leg due to sudden occlusion of the popliteal artery necessitating emergency treatment to prevent amputation. Alternatively, a more insidious presentation may occur with development of claudication (pain in the affected leg upon walking) that slowly progresses to severe limb ischaemia with leg pain at rest with or without skin ulceration. Large popliteal artery aneurysms may compress neighbouring structures behind the knee, including the popliteal vein, leading to leg swelling and skin discolouration. Very rarely the a politeal artery aneurysm may rupture threatening the patient’s life, as well as the leg, due to sudden blood loss.
How are popliteal artery aneurysms investigated?
If your surgeon suspects a popliteal artery aneurysm a number of imaging investigations will be organised aimed to assess a) the size and extent of the aneurysm, b) the patency of arteries above and below the popliteal artery, and c) the presence of a suitable vein to act as a bypass conduit should surgical repair be necessary. Information about the effect on neighbouring structures is also important for aneurysms producing compression related symptoms. Typically, a duplex Doppler ultrasound scan will be performed initially to confirm the diagnosis and assess. Occasionally a CT (see figure 1) or MRI scan is required to further assess the anatomy of the aneurysm particularly if a minimally invasive method of repair (endovascular) is being considered.
When does a popliteal artery aneurysm require treatment?
All patients with symptomatic aneurysms require intervention for the relief of symptoms and prevention of limb loss. Patients in whom a popliteal artery aneurysm has been identified coincidentally may still require intervention to prevent the aforementioned complications. In general, we advocate elective repair for all asymptomatic popliteal artery aneurysms measuring greater than 2cm in maximum diameter, particularly those which contain large volumes of thrombus (clot).
What are the treatments for popliteal artery aneurysms?
There are two main techniques for repairing popliteal artery aneurysms: open surgery and endovascular stenting. The most widely utilised technique is open surgery treatment which aims to exclude the aneurysm from the circulation by ligating (tying off) the artery above and below the aneurysm whilst re-routing the blood flow around the aneurysm with a bypass. This can be performed either from behind the knee (posterior approach) or from alongside the knee (medial approach). Alternatively, your surgeon may recommend endovascular repair (see figure 2) which involves placing a stent-graft through the popliteal artery aneurysm, excluding it from the circulation. Only certain shapes and sizes of popliteal artery aneurysms are suitable for endovascular repair and being a relatively new technique there is little data relating to the long-term durability. Your surgeon will discuss in length the merits of each technique based on your particular circumstances.
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Table 1: Presentation of popliteal artery aneurysm
Fig. 1 Bilateral Large PAAs
Fig. 2: (a) Pre-stent repair, (b) post-Stent Repair