Popliteal artery aneurysms per se are not very common, but popliteal artery pseudoaneurysms are quite a common sequel to penetrating or blunt trauma, iatrogenic surgeries and procedures [rarely acupuncture] and adjacent bone tumors. Constant and repeated vascular wall trauma triggers the formation of the pseudoaneurysm. These vascular masses may present with pain and with palpable masses around the knee and may be pulsatile. If younger patients without a known history of trauma are diagnosed with popliteal artery aneurysms, underlying bone pathologies need to be ruled out as asymptomatic bone tumors may repeatedly irritate the popliteal artrey and present as popliteal artery aneurysms.
Many patients with true aneurysms are asymptomatic and these may be detected incidentally, owing to their accessibility to palpation. Atherosclerosis likely plays some role in pathogenesis. Usually a popliteal artery is considered aneurysmal when the diameter is 1.2 cm or larger, a definitive aneurysm when it is 2 cm or greater or if it is more than 1.5 times the caliber of the proximal popliteal artery. Thrombosed aneurysms when symptomatic are usually found to be larger [3 cm or more]. Complications of these aneurysms include rupture, thromboemboli, and flexion deformities of the leg. Once thrombosis sets in, which is the most common complication, morbidity increases considerably.
Lowell, et al in their study predicted aneurysm size greater than 2 cm, presence of thrombus and poor distal run-off as poor prognostic factors. The presence of these risk factors makes the patient an ideal candidate for an elective surgical treatment and prevents inadvertent amputations. Recent studies by Galland, et al have suggested 3 cm as the cut-off for the size of the aneurysm, after which intervention is needed.
Real time ultrasound and color Doppler imaging are the initial non-invasive diagnostic modalities used to evaluate popliteal artery aneurysms. A dilated artery or a vascular mass arising from the artery is identified. Pseudoaneurysms can be seen connected to the main popliteal vessel via a neck or tract, the demonstration of which is pathognomonic for a pseudo aneurysm. If an aneurysm contains thrombus, echogenic material is seen within, which may partially or completely occlude the cavity. The hemo-dynamics can be studied by color Doppler, which may demonstrate swirling flow within the aneurysm or no color flow if it is completely occluded. The neck of the pseudoaneurysm may show a to- and –fro movement. Very importantly, the presence of thrombosis, distal run-off and collaterals can be assessed, which have prognostic value for the effectiveness and outcome of surgery.
CT angiography, MR angiography and conventional angiography can all provide additional important preoperative information.