A 67-year-old man presents to the clinic complaining of progressive pain and swelling behind his right knee that started one month ago. The pain caused him to quit his weekly golf lessons. This morning he felt his foot was "cooler than usual" and the pain was severe enough to force him to visit the clinic. The patient has a history of hypertension, diabetes mellitus and he is also a heavy smoker. He has been a former construction worker for 45 years and retired 2 years ago. Although his vitals are normal, physical examination reveals a palpable mass in the right popliteal fossa. His right lower limb is also cold with diminished distal pulses. The rest of the physical examination is unrevealing. The patient remains in the hospital for further evaluation.
The correct answer is: C. Localized dilation and thrombosis of a regional artery, leading to limb ischemia
The patient's symptoms of a cooler lower limb and sudden onset of severe leg pain with diminished distal pulses, in addition to the physical examination findings of a pulsatile mass, make the diagnosis of acute limb ischemia due to a popliteal artery aneurysm the most likely choice (Answer C).
Popliteal artery aneurysms (PAAs) represent the second most common type of peripheral arterial aneurysm following those located in the aortoiliac segment. The prevalence of PAA increases with age and peaks in the sixth or seventh decade of life. PAAs are typically caused by atherosclerosis but they have also been attributed to trauma, congenital defects, infection, inflammatory arteritis, or popliteal entrapment.1
The natural history of PAAs is variable. Approximately 60% of PAAs are symptomatic, causing lower extremity ischemia due to thrombosis with/without distal embolization in up to 85% of the symptomatic cases. In addition to acute limb ischemia (ALI), patients commonly present with claudication, rest pain, ulceration, or "blue toe" syndrome. Patients with ALI present with abrupt onset of foot coolness, leg pain, and/or numbness, while physical exam reveals a cold limb with diminished or absent distal pulses.2
Duplex ultrasonography (DUS) is the ideal screening and diagnostic imaging modality to detect a PAA and estimate its diameter. Computed tomography and magnetic resonance angiography are other alternatives that can accurately measure the true lumen dimensions and help with planning an aneurysm repair. All symptomatic popliteal artery aneurysms should be repaired due to their high risk for thrombosis and limb loss, whereas asymptomatic aneurysms with maximal diameter less than 2 cm can be safely managed via duplex surveillance.
Segmental thrombosing vasculitis of veins and nerves refers to the pathophysiologic mechanism behind Buerger's disease. Although this patient has a heavy smoking history, which is the major risk factor for the disease, the presence of a palpable pulsatile mass behind the knee cannot be explained by this diagnosis (Answer A).
Popliteal fluid collection in the gastrocnemius bursais is the pathogenic mechanism of Baker's cyst formation. Although this condition presents with swelling and a palpable mass behind the knee, the pulsatile feature of this patient's mass and the absence of distal pulses cannot be attributed to that condition (Answer B).
The patient's heavy smoking history and swelling behind the knee raise suspension of deep venous thrombosis (DVT). However, the presence of a pulsatile mass, the coolness of the limb (as opposed to warmth and erythema in DVT) and the absence of distal pulses are better explained by Answer C than DVT (Answer D).
The choice "tortuosity of popliteal fossa blood vessels" possibly describes a varicose vein behind the knee. Although a varicose vein could result in pain and swelling behind the knee, it would not be presented neither as a pulsatile mass nor as diminished distal pulses (Answer E).
Educational Objective:
Up to 50% of all popliteal artery aneurysms (PAA) present with acute limb ischemia (ALI). ALI due to PAA is a difficult surgical problem, with a 20% to 60% incidence of limb loss. Patients with ALI present with abrupt onset of foot coolness, foot or leg pain, and/or numbness, while physical exam reveals a cold limb with diminished or absent distal pulses.2 All symptomatic PAAs should be repaired due to the increased risk of limb loss.
References
- Verikokos C, Karaolanis G, Doulaptsis M, et al. Giant popliteal artery aneurysm: case report and review of the literature. Case Rep Vasc Med 2014;2014:780561.
- Varga ZA, Locke-Edmunds JC, Baird RN. A multicenter study of popliteal aneurysms. Joint Vascular Research Group. J Vasc Surg 1994;20:171-77.
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