A 55-year-old male presents to the emergency department with acute right lower limb pain that began 2 hours ago. The patient's history includes heavy smoking, dyslipidemia and stable angina that are well controlled with medical treatment. He also reports a femoral fracture 2 years ago that was treated surgically with no further complications. Physical examination reveals a cold and pale right foot. Examination of the left foot is normal. Right femoral pulses are absent, whereas right distal pulses are palpable, but more weakened compared to pulses of the left foot. Neurological examination reveals no sensory or motor deficits in the right lower limb. Ankle-brachial pressure index (ABI) on the right side is 0.65 and on the left is 1.15. The patient undergoes digital subtraction angiography (DSA) that reveals an abnormal continuation of the internal iliac artery with a partially thrombosed aneurysm at the buttock region, and hypoplastic right external iliac and deep femoral arteries. An endovascular repair with stent graft placement is performed for aneurysm exclusion and blood flow restoration.
The correct answer is: B. An embryologic anatomic variant
This patient presents to the emergency department with obvious clinical signs of lower limb ischemia. Furthermore, DSA reveals an unusual continuation of the internal iliac artery with an aneurysm formation at the buttock region, as well as hypoplastic external iliac and deep femoral arteries. These findings indicate the presence of a persistent sciatic artery aneurysm (PSA). The absence of femoral pulse with the presence of distal pulses (Cowie sign) is pathognomonic for the disease.1,2
PSA is an embryologic remnant of the internal iliac artery and is classified into two main types: (1) complete, in which the PSA is the main arterial blood supply of the lower limb and (2) incomplete, in which the lower extremity obtains blood flow predominantly from the femoropopliteal artery. The most commonly reported type is the complete, with an incidence up to 80% of the PSA cases.1,2
A common complication of PSA is the formation of an aneurysm due to external compression from the piriformis muscle and sacrospinous ligaments during hip flexion. Thromboembolic complications can lead to lower limb amputation in 8-10% of patients with PSA. Computed tomography angiography (CTA) is mainly used for diagnosis.2,3 PSA aneurysms can be managed endovascularly with coil assisted stenting or stent graft deployment and with surgery as well. Open repair has been associated with high risk for sciatic nerve damage.3
Heavy smoking (Answer A) is the strongest risk factor for Buerger's disease (i.e. thromboangiitis obliterans), a medium- and small-vessel vasculitis that usually affects male smokers younger than 50 years. Most commonly it presents with manifestations in two or more extremities. Raynaud's phenomenon, distal ischemic ulcers and/or toe gangrene are commonly observed in patients with Buerger's disease.
Vasculitis of large vessels (Answer C), that includes giant cell arteritis and Takayasu arteritis, occur mostly in adults older than 50 years and affects predominantly the aorta and its branches causing multiple segmental occlusions at the affected vessels.
Multiple atherosclerotic lesions (Answer D) are the most common cause of acute limb ischemia in adults older than 50 years. Although this patient has a history of dyslipidemia and stable angina, indicating possible peripheral arterial disease, the findings of imaging studies suggest PSA aneurysm as the most likely cause of the patient's symptoms.
History of femoral fracture (Answer E) with a contemporary vessel injury could have caused a pseudoaneurysm of the common femoral artery. However, the CTA findings demonstrating hypoplastic femoral vessels and a persistent sciatic artery exclude the diagnosis of a traumatic pseudoaneurysm.
Educational Objective
Persistent sciatic artery is a congenital vascular anomaly that occurs during the third trimester of gestation. The absence of proximal femoral pulses with palpable distal pulses (Cowie sign), is pathognomonic of the disease. PSA is commonly complicated by aneurysm formation and in most of these cases it constitutes the main arterial supply of the lower limb (i.e. complete type). Moreover, PSA aneurysm has been associated with a higher risk of intramural thrombus formation and eventually with a higher risk for distal embolization and limb loss. Thus, PSA aneurysms should be treated when they are diagnosed.1-3
References
- Ahn S, Min S-K, Min S-I, et al. Treatment strategy for persistent sciatic artery and novel classification reflecting anatomic status. Eur J Vasc Endovasc Surg 2016;52:360-69.
- Shaffer W, Maher M, Maristany M, Ustunsoz B, Spieler B. Persistent sciatic artery: a favorable anatomic variant in a setting of trauma. Ochsner J 2017;17:189-94.
- Ahmad W, Majd P, Luebke T, Gawenda M, Brunkwall JS. Clinical outcome after surgical and endovascular treatment of symptomatic persistent sciatic artery with review of the literature and reporting of three cases. Vascular 2016;24:469-80.
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