Persistent Sciatic Artery Aneurysm Presenting with Limb-Threatening Ischemia: A Case Report and Review

Abstract

Persistent sciatic artery (PSA) is a rare congenital vascular anomaly that occurs when the sciatic artery fails to regress during fetal development. This failure to regress is often associated with superficial femoral artery (SFA) hypoplasia and the PSA then becomes the dominant arterial inflow to the lower limb. PSA is prone to several complications due to its anatomical course that exposes it to repeated trauma, with the most common complication being aneurysm formation. Here we describe the case of a 64-year-old female patient who presented with acute right lower limb ischemia due to embolization from a partially thrombosed PSA aneurysm.

VASCULAR DISEASE MANAGEMENT 2010;7(3):E82–E85

Key words: aneurysm ligation, lower-limb ischemia, superficial femoral artery hypoplasia, vascular anomaly

Introduction

The sciatic artery is a continuation of the internal iliac artery and in early embryological development it serves as the principal blood supply to the developing lower limb. As development progresses the femoral arterial system becomes the major arterial inflow to the lower limb and the sciatic artery atrophies. Persistence of the sciatic artery (PSA) was first described by Green in the Lancet in 1832,¹ and the first account of a PSA aneurysm rupturing and resulting in death was by Fagge in 1864.² PSA is extremely rare and has a reported incidence of just 0.05% by angiographic studies.³ A recent review by Van Hoft et al⁴ found there were 122 published cases of PSA from 1964 through 2007. We found another 12 cases reported in the literature since 2007 for a total of 136 cases published since 1964. Ikezawa et al⁵ found in their review of the literature that PSA had no gender predilection, a mean age of presentation of 54 years, and it occurred bilaterally 22% of the time. PSA is prone to atherosclerotic changes and is associated with aneurysmal change in 46% of all cases.⁴ The most frequent symptoms associated with a PSA aneurysm are a painful pulsatile buttock mass, sciatic neuropathy caused by sciatic nerve compression and lower limb ischemia caused by thrombosis or distal embolization. Here we describe a case of PSA aneurysm presenting with lower limb ischemia treated surgically with aneurysm ligation and femoral-popliteal bypass.

Case Report

A 64-year-old African-American female presented to the emergency department with severe right leg pain that had started 3 months prior and had been progressively worsening. The patient described the pain as starting in the right buttock and traveling down the back of the leg. Pertinent medical history included hypertension, obesity and Type II diabetes. Physical examination revealed normal femoral and popliteal pulses bilaterally, normal dorsalis pedis and posterior tibial pulses on the left and a cool right lower extremity with severely diminished dorsalis pedis and posterior tibial Doppler signals. In addition, the 1st and 5th digits appeared grossly necrotic, so the patient was admitted and sent to the angiography suite for an abdominal aortogram with distal runoff. The aortogram (Figure 1) was remarkable for a prominent right internal iliac artery with a fusiform aneurysmal dilatation approximately double the size of the more proximal artery. This large artery was determined to be a PSA due to its origin from the internal iliac, its lateral course along the sciatic notch, sluggish flow compared to a normal superficial femoral artery (SFA), and finally, for its torturous and dilated course through the lateral thigh with final runoff into the popliteal artery. The right illiofemoral arterial system appeared hypoplastic, and the right SFA tapered to an end high in the thigh with no connection to the popliteal artery (Figure 2). There was severe tibial disease with proximal occlusion of all three vessels without distal reconstitution (Figure 2). The above findings established the diagnosis of a “complete” type of PSA. The patient’s symptoms were thought to be due to expansion and embolism to the tibial vessels from the right sciatic artery aneurysm. Therefore, thrombectomy was first attempted in the tibial vessels, however, because of the chronicity of the thrombosis, it was unsuccessful. For similar reasons, we believed that thrombolysis would not have been effective; therefore, the patient was taken to the operating room for ligation of the PSA aneurysm and revascularization. The PSA was ligated at its junction with the above-knee popliteal artery using a medial popliteal approach. Femoral-popliteal bypass utilizing a 6 mm polytetraflouroethylene (PTFE) prosthesis was then performed to restore distal flow to the lower limb. The patient tolerated the procedure well, but her pulses remained barely detectable by Doppler in the dorsalis pedis and posterior tibial arteries postoperatively. Unfortunately, the patient later required a right below-knee amputation (BKA) due to the foot having been ischemic for so long prior to presentation. At follow-up 1 year later, the patient is ambulating well with a prosthesis and reported no complaints or symptoms of claudication. She will be followed up periodically with computed tomographic (CT) angiography and duplex ultrasound. If there is evidence of PSA aneurysm enlargement, or if the patient develops symptoms consistent with compression of the surrounding neurovascular structures, endovascular treatment via coil embolization/occlusion or surgical ligation of the aneurysm will be considered.

Discussion

In the developing embryo, the sciatic artery develops along with the limb bud as the axial artery. The sciatic artery is then normally superseded and annexed by the femoral artery as it extends off the internal iliac artery.⁶ Failure of this process in the first 3 months of embryonic life results in atresia of the SFA system and a PSA.⁷ There are two basic types of PSA according to its relationship with the femoral artery. In the “complete” type, the PSA continues into the popliteal artery and serves as the principle blood supply to the lower extremity. This type occurs in 63% of people and is most often associated with a hypoplastic SFA which ends at the adductor canal.⁵ In the “incomplete” type, the PSA is hypoplastic and the SFA remains, as in normal anatomy, as the principle supply to the lower extremity. Anatomically, the PSA is a continuation of the internal iliac artery. It takes the path of the inferior gluteal artery and courses through the greater sciatic foramen below the piriformis muscle to enter the thigh, where it may accompany the posterior cutaneous nerve or lie within or adjacent to the sheath of the sciatic nerve. Symptoms of sciatica that can confuse the diagnosis of PSA may arise here because these structures are subject to compression by the aneurysmal PSA.^5,8 The PSA then continues on the posterior aspect of the adductor magnus, inferior to the gluteus maximus, until it reaches the popliteal fossa where it is continuous with the popliteal artery. The most common site for aneurysmal dilatation is what was observed in our patient at the level of the greater trochanter, just under the gluteus maximus muscle. The exact causes of aneurysm formation are unclear, but may be due to the relatively exposed position of the artery in the buttock region, which lends itself to frequent trauma from external forces, somewhat similar to hypothenar hammer syndrome. Another interesting explanation for aneurysmal dilatation put forward in the literature is that of a congenitally hypoplastic vessel that possess less elastic elements than normal arteries, thereby predisposing it to aneurysm formation.⁶ Clinically diagnosing a PSA can be difficult due to its similarities to the presentation of sciatica, as was the case in our patient who complained of pain “running down the leg.”⁷ A pulsating buttock mass is pathognomic for PSA. Patients may present with thrombosis, arterial insufficiency secondary to distal embolization or unexplained sciatic pain as a result of compression of the sciatic nerve. PSA aneurysm also carries a risk of rupture, but only a few cases have been reported in the literature.^2,9 To make a definitive diagnosis, one can use CT angiography, magnetic resonance angiography (MRA) or contrast arteriography, which are useful for both identification and surgical planning. Bilateral imaging is also important, since 22% of PSAs occur bilaterally. The most significant problem with arteriography is that a large volume of contrast medium is required because the blood flow is extremely slow in the PSA. The PSA is usually ectatic, and therefore it is large, torturous and slow-flowing, which can result in poor visualization of runoff vessels. The goal of PSA aneurysm treatment is to eliminate a potential embolic source or rupture if an aneurysm has developed, adequate perfusion of the lower limb and relief of compressive symptoms. Treatment varies depending on whether the PSA is symptomatic or asymptomatic and whether it is a complete or incomplete type. Some of the major presenting symptoms that occur in 91% of symptomatic PSA patients are intermittent claudication, limb-threatening ischemia, a pulsating mass and neurological symptoms resembling sciatica.⁴ If there is no aneurysm or the aneurysm is asymptomatic, several cases have been reported of successful noninvasive management, i.e., following the patient clinically and performing frequent ultrasound imaging.^10,11 Symptomatic incomplete PSA aneurysm can be treated via exclusion of the aneurysm by embolization or ligation alone.¹² A complete PSA with an aneurysm, however, requires exclusion and simultaneous revascularization to avoid lower-limb ischemia. Outcomes in the literature are generally favorable with surgical management, with only 8% of reported cases reviewed requiring amputations.⁴ Since our patient had a symptomatic PSA aneurysm, our approach consisted of obliteration of the aneurysm by distal ligation of the PSA in conjunction with a femoro-popliteal bypass. Options for revascularization included graft interposition, iliac-PSA bypass and femoro-popliteal bypass. We believe that the femoro-popliteal bypass is the preferred method because it is free from risk of graft compression and alleviates any future complications associated with the segments. The use of stent grafts for repair of PSA aneurysms have been reported and offer the advantage of a single endovascular intervention, but the anatomic location and their propensity for compression and trauma may put these grafts at high risk for fracture, migration or occlusion.^13,14 We met the goals of treatment, but a BKA was still necessary because the amount of ischemic damage that had occurred before presentation was irreversible. However, by performing a femoro-popliteal bypass, we were able to limit the level of amputation to below the knee.

Conclusion

PSA is a rare, congenital vascular anomaly that may not be immediately recognized by the vascular specialist. A high index of suspicion is needed due to the high risk of aneurysmal dilatation with subsequent thrombosis and distal embolization that can result in limb-threatening ischemia. Surgical intervention remains the mainstay of treatment for a complete PSA aneurysm due to anatomic location and the need for revascularization after aneurysm ligation.

References

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12. Ooka T, Murakami T, Makino Y. Coil embolization of symptomatic persistent sciatic artery aneurysm: A case report. Ann Vasc Surg 2009;23:411:e1–e4.

13. Fearing NM, Ammar AD, Hutchinson SA, Lucas ED. Endovascular stent graft repair of a persistent sciatic artery aneurysm. Ann Vasc Surg 2005;19:1–4.

14. Gabelmann A, Kramer SC, Wisianowski C, et al. Endovascular interventions on persistent sciatic arteries. J Endovasc Ther 2001;8:622–628.

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From West Boca Vascular Surgery, Boca Raton, Florida, *Union Memorial Hospital, Baltimore, Maryland, and Saba University School of Medicine, Saba, Netherlands-Antilles.

The authors report no conflicts of interest regarding the content herein.

Address for correspondence: Mojtaba Gashti, MD, Union Memorial Hospital, 3333 N. Calvert St., Suite LL08, Baltimore, MD 21218. E-mail: smgashti@hotmail.com