Persistent sciatic artery presenting as an acutely ischemic limb.

Persistent sciatic artery (PSA) is an extremely rare vascular phenomenon, with a prevalence of 0.025% to 0.04% in the general population. We present the case of a 72-year-old man with a thrombus-containing PSA aneurysm that caused embolic acute limb ischemia. We also discussed the PSA classification systems, common presentations, rarity of the pathology, and high rates of severe complications.

Persistent sciatic artery (PSA) was first described by Green et al in a postmortem case in 1832 and angiographically by Cowie et al in 1960. PSA is an extremely rare vascular phenomenon, with a prevalence of 0.025% to 0.04% in the general population and <200 cases reported worldwide, with ≤25% having bilateral presentations.

PSA has an embryologic origin. In the first 6 weeks of embryogenesis, the lower limb buds are primarily supplied by the sciatic artery (SA), which runs with the sciatic nerve as it exits the pelvis. By week 8, the SA drastically changes—the proximal SA forms the superior and inferior gluteal arteries, the middle regresses, and the distal SA forms the peroneal and popliteal arteries. By week 12, the primary arterial supply to the leg is via the iliofemoral artery and superficial femoral artery (SFA). When the SA sometimes fails to regress, it can become the predominant arterial supply in the form of a PSA. As the PSA exits the pelvis through the greater sciatic foramen, it has a tendency to become compressed, resulting in post-stenotic dilation and aneurysmal degeneration, which was first described by Fagge.

Case report

The patient provided written informed consent for the report of his case details and imaging studies. A 72-year-old man had presented to an outside emergency department with a 3-day history of sudden-onset dull right leg and calf pain at rest that had worsened in the 6 hours before presentation. The patient was otherwise asymptomatic and denied chest pain, palpitations, dyspnea, leg trauma, and recent air travel. He had hypertension and dyslipidemia, was a nonsmoker, and denied a family history of aneurysmal or connective tissue disease. The vital signs, electrocardiographic, and biochemical values were within the normal range.

Examination revealed a cold right leg below the knee with markedly reduced sensation and motor function. The right foot appeared mottled, with a prolonged capillary refill time compared with the left. The femoral and popliteal pulses were palpable bilaterally. No pulses were palpable in the right foot. However, normal palpable pulses were present in the left. The handheld vascular Doppler examination detected a weak monophasic dorsalis pedis signal in the right foot with absent posterior tibial and peroneal artery signals. Triphasic signals were detected in the left foot vessels. Rutherford class IIb acute limb ischemia was diagnosed, heparin was administered, and urgent computed tomography angiography was performed. The angiogram demonstrated a thrombus-containing PSA aneurysm in the right buttock with embolization of a clot into the proximal right anterior tibial and tibioperoneal trunk (Fig 1). The PSA measured 11 mm distally to the end of the aneurysm compared with 9 mm for the contralateral SFA. Given its posterior location deep in the thigh, it was not considered useful as the origin of a conduit. Distal reconstitution of the anterior tibial artery (ATA) and posterior tibial artery was present at the level of the mid-right tibial–fibular region. Congenital hypoplasia of the right common femoral artery (CFA; 8.5 mm vs 1.25 mm on left) and superficial femoral artery was noted. No abnormalities were present on the left (Fig 2).

Fig 1

A, Computed tomography angiogram showing a right persistent sciatic artery (PSA) exiting the pelvis posteriorly. B, Aneurysmal dilation of the right PSA immediately after exiting the pelvis with a large thrombus burden. C, Right PSA at the level of the mid-femur with an atretic native superficial femoral artery anterior in the Hunter canal. D, Thrombus-filling defect in the right leg at the level of takeoff of the anterior tibial artery and tibioperoneal trunk.

Fig 2

Three-dimensional reconstruction from computed tomography angiogram showing a right persistent sciatic artery (PSA; red arrow) with a diminutive right superficial femoral artery (SFA; white arrow).

The patient underwent emergency right CFA to tibioperoneal trunk bypass with an in situ great saphenous vein (with the popliteal artery and tibioperoneal trunk opened to facilitate embolectomy), ligation of the infrageniculate popliteal artery, Fogarty embolectomy of the popliteal artery, three tibial vessels, and four-compartment fasciotomy. The tibioperoneal trunk was chosen as the distal target, because clot was present in both the proximal ATA and the tibioperoneal trunk. Thus, the popliteal artery was opened across the origin of the ATA onto the tibioperoneal trunk to facilitate the embolectomy, forming the area for the distal anastomosis. On postoperative day (POD) 2, the fasciotomy site was closed at the bedside. On POD 3, via the left CFA, two 14-mm × 8-mm Amplatzer plugs (Abbott, Chicago, Ill) were deployed to seal the PSA aneurysm at the level of the lesser trochanter distally and internal pudendal artery origin proximally. Completion angiography showed sluggish flow through the embolized segment of the PSA aneurysm (Fig 3). Vascular duplex ultrasonography performed on POD 5 demonstrated a patent bypass with excellent tibial waveforms and a normal ankle brachial index. On POD 7, the patient was ambulatory and was discharged home with instructions to take aspirin without anticoagulation therapy.

Fig 3

Postoperative angiogram showing a catheter in the right common iliac artery, with opacification of the persistent sciatic artery (PSA) with an aneurysm at the level of the femoral neck (Left). Two Amplatzer occlusion devices (Abbott) were deployed to isolate the aneurysm and prevent further risk of growth, rupture, and distal embolization (Right). Postoperative surgical groin staples can be seen.

Discussion

PSAs are rare vascular anomalies first anatomically classified by Pillet et al into four types in 1980. Gauffre et al modified the classification system reported by Pillet et al, by adding a fifth type (Fig 4). Type 1 includes patients with a complete PSA and a normally developed SFA. Type 2a includes patients with complete PSA and an incompletely developed SFA that does not reach the popliteal artery. Type 2b patients have a complete PSA and absent SFA. Both types 3 and 4 have normally developed SFAs with incompletely developed PSAs proximally and distally, respectively. Type 5 is similar to type 1, with the major difference being that the PSA originates from the median sacral artery, with either a fully (type 5a) or partially (type 5b) developed SFA (Table). Our patient had had type 2a using the Pillet-Gauffre classification, because the SFA ended in the above-the-knee area without direct communication with the popliteal artery.

Fig 4

Classification system of Gauffre et al for persistent sciatic arteries (PSA; gray). Red indicates superficial femoral artery (SFA).

Table

Comparison of Ahn-Min and Pillet-Gauffre classifications of PSAsa

Ahn-Min classification	PSA anatomy	SFA anatomy	Aneurysm	Pillet-Gauffre classification
				Types I and Va
Class I	Complete	Complete	Absent
Class Ia	Complete	Complete	Present
				Types III and IV
Class II	Incomplete	Complete	Absent
Class IIa	Incomplete	Complete	Present
				Types IIa, IIb, Vb
Class III	Complete	Incomplete	Absent
Class IIIa	Complete	Incomplete	Present
				None
Class IV	Incomplete	Incomplete	Absent
Class IVa	Incomplete	Incomplete	Present

PSA, Persistent sciatic artery; SFA, superficial femoral artery.

Classifications based on SFA anatomy and the presence or absence of aneurysmal degeneration.

A systematic review by Ahn et al of 147 studies with 171 patients with PSAs found that women (n = 103; 60.6%) were more likely to present with PSAs than were men (n = 67; 39.4%). Aneurysmal degeneration of the PSA was noted in 50.7% of the patients, with no difference in laterality at presentation (55 [32.2%] were right sided, 61 [35.6%] were left sided, and 55 [32.2%] were bilateral). The most common presentations were asymptomatic (n = 63; 29.6%), buttock mass and pain (n = 45; 21.1%), intermittent claudication (n = 41; 19.3%), acute limb ischemia (n = 16; 17.8%), and critical limb ischemia (n = 16; 7.5%). Using the Pillet-Gauffre classification, 17 (8.2%) were type 1, 155 (74.9%) were type 2a, 9 (4.3%) were type 2b, 13 (6.3%) were type 3, and 13 (6.3%) were not classified. Most patients (n = 74; 39%) had undergone open surgical repair, followed by observation (n = 68; 35.8%), endovascular repair (n = 31; 16.3%), and a hybrid approach (n = 17; 8.9%).

The presence of Cowie's sign is pathognomonic for the PSA diagnosis and described as an absence of a femoral pulse but strong distal pulses in the ipsilateral knee and feet. However, our patient had a negative Cowie's sign.

Ahn et al proposed a novel classification system for PSAs in 2016. They added the presence or absence of aneurysmal degeneration to the previously established Pillet-Gauffre classification system. Class I of their classification system includes Pillet-Gauffre type I and type Va, class II includes types III and IV, class III includes types IIa, IIb, and Vb, with class IV a new category not covered by the Pillet-Gauffre system. No evidence-based size cutoff for the treatment of PSA aneurysms has been established. The system proposed by Ahn et al aims to ease decision-making for vascular surgeons by suggesting that patients with class I and II PSAs without aneurysmal degeneration can be treated conservatively but that all class III and IV PSAs require surgical ligation of the proximal popliteal artery with bypass to exclude the aneurysm.

Conclusion

We present a rare case of a patient with a thrombus-containing PSA aneurysm presenting as an acutely ischemic limb secondary to embolization from the aneurysm that was successfully treated with bypass, proximal popliteal artery ligation, and embolectomy.