Some popliteal aneurysms are congenital.

Although the majority of popliteal aneurysms are of atherosclerotic origin and are discovered in patients aged more than 50, the aetiology of a small minority may be attributed to arterial trauma, septic disruption, Behcet's disease, a medial fibromuscular dysplasia, or popliteal entrapment. The aim of this study was to propose a possible congenital origin for popliteal aneurysms without evidence of any other aetiology. A retrospective review of five younger patients (aged 20-45 years) with seven non-atherosclerotic popliteal aneurysms was performed. In patient nos 1 and 2, histological examination showed that the arterial wall had been replaced by an abundant collagenic tissue. After replacement by a saphenous bypass graft, these patients did well with a follow-up ranging from 1 to 15 years. Patient no. 3 was not operated on because of a symptomless occlusion of the tibial and peroneal arteries, and remains well 10 years later. Patients nos 4 and 5 were treated with a saphenous bypass graft. The last patient also had associated bilateral congenital anomalies of the division of the popliteal arteries. In the absence of any evidence of any classical aetiology, particularly fibromuscular dysplasia and popliteal entrapment, a congenital aetiology is proposed in aneurysms diagnosed in younger patients. The complex composition of the popliteal artery, being composed by an association of three original segments, may induce a fragility of the arterial wall that may be responsible for aneurysmal deterioration as well as abnormal branching or popliteal artery entrapment. These aneurysms are associated with the same risk of thrombosis as atherosclerotic aneurysms and therefore, they should be subjected to the same therapeutic considerations.