Acute limb ischemia caused by a thrombosed persistent sciatic artery aneurysm: a case report

¹Department of Cardio-Vascular and Thoracic Surgery, Mont-Godinne University Hospital, Yvoir, Belgium, ²Vascular and Endovascular Surgery Department, Valenciennes General Hospital, Valenciennes, France

^&Corresponding author
Simon Landsweerdt, Department of Cardio-Vascular and Thoracic Surgery, Mont-Godinne University Hospital, Yvoir, Belgium

Introduction    

Persistent sciatic artery (PSA) is a rare anatomical anomaly resulting from the inability of the sciatic artery to regress during embryological development. The sciatic artery serves as the primary source of blood supply to the lower limb in early development, but regresses as the femoral artery takes over this function [1]. However, in cases of PSA, the sciatic artery remains the dominant blood vessel supplying the lower limb, resulting in the hypoplasia of the femoral artery. The presence of a PSA significantly increases the risk of aneurysmal development and thromboembolic events, which can lead to lower limb ischemia [1]. We report the case of an 83-year-old woman who presented a lower left limb acute ischemia caused by a thrombosed PSA aneurysm (PSAA).

Patient and observation     

Patient information: the patient is an 83-year-old woman admitted with a clinical history of acute and severe pain in the left lower limb for 8 hours, followed by pallor, coldness, and hypoesthesia in the left forefoot. She had a surgical history of total thyroidectomy and interannexial hysterectomy. She is also being treated for mammary adenocarcinoma, intraductal papillary mucinous neoplasms (IPMNs), arterial hypertension, and dysthyroidism.

Clinical findings: clinically, all vital signs remained stable. The popliteal, pedal, and posterior tibial pulses were abolished with motor and sensitive deficits in the left forefoot. There were no clinical signs of ischemia in the contralateral lower limb.

Timeline of current episode: the patient did not experience any instances of pain, pallor, or hypoesthesia in the left lower limb, nor any vascular problems, prior to the day of admission.

Diagnostic assessment: initial blood tests showed a small inflammatory syndrome, but the CPK level remained normal (leukocytes: 12.92 x10⁹/l; CRP: 28mg/l; CPK: 94UI/l). CT-scan revealed a type 2a left persistent sciatic artery (Figure 1), with a 61mm diameter aneurysm located in the gluteal region. Thrombosis was extended from the PSA to the below-the-knee popliteal artery (P3 segment), with embolism in the anterior tibial artery (ATA), posterior tibial artery (PTA), and the fibular artery (FA) (Figure 2 and Figure 3).

Diagnosis: thrombosis of the PSAA with extension into the below-the-knee popliteal artery, resulting in acute ischemia of the left lower limb.

Therapeutic interventions: an immediate surgical procedure was performed with a prosthetical femoro-popliteal bypass using a non-armed Dacron graft. The proximal anastomosis was performed on the common femoral artery, and the distal one on the below-the-knee popliteal artery (P3 segment) using an ortho-anatomical tunneling. This procedure was complemented by thrombectomy of the distal popliteal artery, ATA, and tibioperoneal trunk using the Fogarty technique. A ligature of the proximal popliteal artery was also performed during the surgery. To conclude the procedure, a plain angiography was performed to confirm bypass patency and a sufficient outflow in the PTA. Secondary to a vasospasm, a reduced flow was found in the ATA and the FA, without any residual thrombus (Figure 4). The surgery was performed with intravenous administration of heparin (bolus of 50IU/kg) and antibiotic prophylaxis with cefazolin (bolus of 2g intravenous).

Follow-up and outcome of interventions: early postoperative follow-up showed no significant complications. An arterial Doppler ultrasound was performed 3 days after surgery, confirming a good patency of the bypass and a good outflow within the infrapopliteal arteries. The patient was discharged after six days with antiplatelet therapy and curative dose of low molecular weight heparin (LMWH) injections. Nine weeks later, the bypass and all leg arteries remained patent according to the ultrasound doppler. The clinical examination showed no signs of lower limb ischemia with full recovery of sensory and motor deficit. The patient still described some residual pain in the surgical wound but did not describe any walking pain. Due to oncological history, it was decided to maintain the LMWH injections for another six months.

Patient perspective: the patient expressed optimism about achieving full recovery and emphasized her desire to maintain the same quality of life she had prior to admission.

Informed consent: the patient provided written consent for the publication of her clinical details and history.

Discussion     

Persistent sciatic artery (PSA) is a rare vascular anomaly occurring in 0.03-0.06% of the population [1]. This anatomical variation was first described by Green in 1832 and referred to as “a new variety of femoral artery” [2]. Persistent sciatic artery is an extension of the internal iliac artery, which becomes the main blood supply to the lower limb, depending on its type (Figure 1) [3]. The first report of aneurysmal degeneration of the PSA was made by Fagg in 1864. Persistent sciatic artery is unilateral in 70% of cases. Aneurysms are present in 48% of cases, while occlusion of an artery distal to the PSA occurs in 6% [1]. Originally, PSA was classified into five types [3]; however, a simpler and more physiologically relevant classification was later proposed. This system divides PSA into two categories: complete (63-79%), where the PSA remains continuous and serves as the main lower limb artery, and incomplete, where the PSA is hypoplastic with an interruption along its course [4]. During the early embryologic development, the embryonic blood flow to the legs is provided by the sciatic artery originating from the umbilical artery. Normally, as the external iliac artery forms during the third month of embryological development, the sciatic artery regresses and becomes a part of the inferior gluteal artery. In some cases, the sciatic artery fails to regress, resulting in a PSA [5]. The main age of diagnosis is 57 years old, with a slightly higher incidence in women (56% females, 44% males) [1]. Persistent sciatic artery is often symptomatic, with up to 58% of patients experiencing various symptoms such as intermittent claudication, ischemia, or pulsating mass when an aneurysm is associated. Neurological symptoms, such as sciatic nerve compression by an aneurysm, are rare [6]. Due to its unique anatomy, PSA is exposed to significant mechanical stresses induced by flexion/extension from the hips, which favor arteriosclerosis and aneurysmal formation [7].

Management of the PSA depends on symptoms and complications. Asymptomatic patients without aneurysmal degeneration do not necessarily require surgery but require an annual clinical and imaging follow-up with Doppler ultra-sound. However, urgent repair is necessary for PSA with aneurysmal degeneration, sciatic nerve injury, or thromboembolic events leading to acute limb ischemia. Management of a persistent sciatic artery aneurysm (PSAA) involves both exclusion of the aneurysm and revascularization. Open surgery with femoro-popliteal bypass, using either a prosthetic or venous graft, is the preferred method of repair. Exclusion of the aneurysm typically include ligation of the proximal popliteal artery or intraoperative endovascular embolization of the PSAA [8]. Conservative approaches with bypass procedures using the PSA pathway have also been described, such as Common Femoral Artery (CFA)-PSA bypass or a PSA interposition graft placement after aneurysmectomy. The advantages of using PSA interposition graft are shorter bypass graft lengths and preservation of femoral vessels for later surgeries; however, we should underline the risk of potential damage to the sciatic nerve during exposure [6]. Given the PSA susceptibility to earlier atherosclerotic and recurrent aneurysm formation, femoropopliteal bypass remains the most common choice. Endovascular stent graft placement is a less invasive option with a lower risk of sciatic nerve damage and should be considered in high-risk patients. However, stent graft-related complications like endoleak, stent migration, and graft occlusion can occur. A hybrid approach may also be effective to treat PSAA, such as open thrombectomy of the PSA with stent graft insertion in the PSAA or bypass combined with ligation of the proximal popliteal artery and embolization of the PSAA [6]. There are no established guidelines for the management of PSA due to its low prevalence, especially in the case of asymptomatically PSAA with no size threshold for repair. Since PSA is an embryonic remnant of the iliac artery, it is suggested that repair may be considered at an aneurysmal size of 40mm, according to the The European Society for Vascular Surgery (ESVS) guidelines [9]. Further research and long-term follow-up remain necessary to develop more definitive guidelines.

In 2016, Ahn et al. introduced a new classification system for PSAs based on the Pillet-Gauffre classification while taking into account the degeneration of aneurysms [6]. They suggested that patients with class I and II PSAs without aneurysmal degeneration could be managed conservatively, while all class III and IV PSAs require bypass surgery and ligation of the proximal popliteal artery for aneurysm exclusion [10]. However, no evidence-based size threshold for the treatment of PSAA has been established.

Conclusion     

The absence of standardized treatment guidelines due to the rarity of PSA highlights the necessity for additional research and long-term follow-up studies. In this case, the successful management with a femoro-popliteal bypass and distal thrombectomy restored perfusion and led to a favorable recovery without major complications. Combining open and endovascular surgical techniques offers a flexible approach to managing PSAA, depending on individual patient factors and anatomical considerations. This case adds to the limited but expanding knowledge base on PSA, emphasizing the importance of tailored treatment strategies.

Competing interests     

The authors declare no competing interests.

Authors' contributions     

Patient management: Simon Landsweerdt. Data collection: Simon Landsweerdt. Manuscript drafting: Simon Landsweerdt and Simon Bertrand. Manuscript revision: Simon Landsweerdt, Simon Bertrand, Antoine Guéry, Erol Lerisson and Asmae Belhaj. All the authors have read and agreed to the final manuscript.

Figures     

Figure 1: classification of the persistent sciatic artery; type 1: a complete sciatic artery with a normal superficial femoral artery; type 2: a complete sciatic artery with an incomplete (a) or absent (b) superficial femoral artery; type 3 and 4: an incomplete sciatic artery, only the upper part (3) or the lower part (4), with a normal superficial femoral artery; type 5: a complete sciatic artery emerging from the median sacral artery (MSA) with an incomplete (a) or fully absent (b) superficial femoral artery; figure was created with BioRender.com

Figure 2: computed tomography angiogram of pelvis and left leg; (A) sagittal view showing the thrombosed PSA indicated by blue arrow; (B) sagittal view showing the aneurysm in the gluteal region indicated by white arrow; (C) coronal view showing the aneurysm and thrombosed PSA indicated by yellow arrow; (D) axial view showing the 61mm aneurysm; (E) axial view showing the left PSA running at the posterior face of the leg (black arrow) and the right superficial femoral artery (SFA) (green arrow)

Figure 3: reconstruction of a computed tomography angiogram of the abdomen and pelvis; preoperative reconstruction of a computed tomography angiogram (CTA) showing a left type 2a PSA; blue arrow is showing the hypoplasic superficial femoral artery (SFA); 2b white arrow the persistent sciatic artery; 2c red arrow the deep femoral artery

Figure 4: per operative arteriography of the left lower limb; arteriography realized at the final stage of the procedure, after the fogarty procedure; blue arrow is showing the patent graft bypass; white arrow the distal popliteal artery; red arrow the TP trunk; purple arrow the anterior tibial artery (ATA); black arrow the posterior tibial artery (PTA); yellow arrow the fibular artery (FA)

References