Persistent sciatic artery (PSA), first reported in 1832 by Green [1], is a rare vascular anomaly characterized by the persistence of the sciatic artery, which typically regresses during embryonic development. In normal development, the axial artery is the primary source of blood supply to the lower limb in early embryonic stages. As development progresses, the femoral artery forms and gradually takes over as the main blood supply. In contrast, the middle segment of the axial artery regresses, leaving behind a short remnant known as the sciatic artery. PSA occurs when the axial artery fails to regress and instead persists as a significant source of blood flow to the lower extremity. This rare vascular anomaly has an estimated incidence of 0.03%-0.06% [2,3].

Some cases of chronic limb-threatening ischemia have been reported in relation to atherosclerotic stenosis, thromboembolism, and aneurysmal lesions in the context of PSA [2,3]. However, insufficient clinical experience may prevent therapeutic intervention and lead to delayed diagnosis. Consequently, we believe that clinicians should be alerted to hinder the progression of chronic limb-threatening ischemia and amputation by reflecting upon this case study.

Non-invasive, non-interventional single case report studies do not require Ethics Committee approval. In lieu of a formal ethics committee, the principles of the Helsinki Declaration were followed. The authors obtained the written publication consent of the patient for the case details and images.

A 79-year-old woman presented with a progressively worsening cold sensation and numbness in her right foot. The patient’s medical history included hypertension, aortic valve insufficiency, congestive heart failure, and a history of smoking. Her previous attending physician had prescribed amlodipine and candesartan. Electrocardiogram revealed normal sinus rhythm, and there was no history of paroxysmal atrial fibrillation. Although the patient’s right ankle-brachial index (ABI) was 1.20, her toe-brachial index (TBI) was unmeasurable. Contrast-enhanced computed tomography angiography (CTA) demonstrated heavy calcification, stenosis, and partial thrombosis of a right PSA extending from the level of the greater sciatic foramen to the greater trochanter. Imaging revealed that the popliteal artery originated from the PSA; further, the superficial femoral artery was hypoplastic and had no continuity with the popliteal artery (Fig. 1A). Endovascular therapy (EVT) with stenting was thought to be avoided due to lesion compression in the sitting position. The patient refused any invasive procedures, and the attending cardiologist did not strongly recommend direct intervention. Instead, symptoms were managed with oral medications, consisting of statin, warfarin and limaprost alfadex. The patient’s prothrombin time-international normalized ratio (PT-INR) was closely monitored and maintained within the target range of 2.0-2.5. An attending cardiologist provided follow-up care for the next four months before referring her back to her previous clinic. During this period, her PT-INR remained well controlled.

Figure 1. (A) Preoperative enhanced computed tomography showed the right persistent sciatic artery (PSA) joined with the popliteal artery (PA). The superficial femoral artery (SFA) was hypoplastic and discontinued to the PA. The arrowheads demonstrate heavy calcification and stenosis of the PSA. The PSA was partially thrombosed without aneurysmal lesion, and the diameters of the right common femoral artery and the distal PSA were 8.2 mm and 7.8 mm, respectively. (B) Postoperative enhanced computed tomography. Femoro-popliteal (FP) bypass grafting is patent. PSA was ligated at the distal anastomosis site.

Over the following 16 months, the patient experienced a gradual worsening of the cold sensation in her right foot, despite no remarkable changes in ABI. However, a month later, she experienced a sudden onset of severe right foot pain, and was admitted to the cardiology ward of our hospital. The PT-INR was 1.98, the right ABI had decreased to 0.91, and the TBI remained unmeasurable. An initial diagnostic catheter angiography revealed 90% calcified stenosis in the partially thrombosed PSA, as well as thrombotic occlusion of both the anterior and posterior tibial arteries (Fig. 2). The right peroneal artery was patent. The patient initially refused invasive therapy for several days; however, the cardiologists eventually persuaded her to undergo direct intervention. A secondary angiography was performed after ten days of drip infusion therapy with alprostadil, continuous heparinization, and oral sarpogrelate hydrochloride. The anterior tibial artery was found to be recanalized with 90% distal stenosis (Fig. 3). An ad hoc EVT for the lower leg was performed using plain old balloon angioplasty, which reduced the stenosis of the anterior tibial artery from 90% to less than 25%. However, EVT for the posterior tibial artery was unsuccessful. The pain and cold sensation were temporally ameliorated, but still persisted. Ultimately, the patient was referred to our department for surgery. Upon referral, her right foot pallor had already deteriorated. Preoperative CTA findings confirmed a partially thrombosed calcified PSA without aneurysmal lesions. The diameters of the right common femoral artery and the distal PSA were 8.2 mm and 7.8 mm, respectively (Fig. 1A). On day 5 of the EVT, a right femoro-popliteal (FP) artery bypass was performed using an 8-mm diameter expanded polytetrafluoroethylene graft. Additionally, ligation of the PSA proximal to the distal anastomosis was performed to increase inflow volume and avoid distal embolism (Fig. 1B). Postoperative Doppler ultrasound revealed audible signals in both the posterior tibial artery and dorsalis pedis artery. Skin perfusion pressure test values in the right calcaneal and ankle joint regions were 59 and 63 mmHg, respectively. However, despite these findings, foot necrosis continued to progress (Fig. 4). Additionally, during the postoperative course, the patient developed congestive heart failure due to aortic valve regurgitation, requiring dobutamine for five days. Noninvasive bilevel positive airway pressure therapy was introduced for respiratory support. A postoperative echocardiogram revealed a reduced left ventricular ejection fraction of 49% with severe aortic valve insufficiency and right coronary cusp prolapse. However, intracardiac thrombus was not detected. Furthermore, the patient was undernourished, and her serum albumin level dropped to 2.2 g/dL. On the 38th postoperative day, a below-knee amputation was eventually performed (Fig. 4D).

Figure 2. Primary catheter angiography. (A) Right persistent sciatic artery (PSA) stenosis with heavy calcification and partial thrombus from the greater sciatic foramen level to the greater trochanter (arrowhead). (B) Occluded right anterior and posterior tibial arteries with thrombus. DFA, deep femoral artery; SFA, superficial femoral artery.

Figure 3. Secondary catheter angiography. The right anterior tibial artery was recanalized with 90% distal stenosis (arrowheads). The right posterior tibial artery was occluded (arrows). Endovascular therapy for the posterior tibial artery was unsuccessful because the guidewire did not cross the lesion.

Figure 4. Postoperative progression of right foot necrosis on the (A) 14th postoperative day, (B) 21st postoperative day, and (C) 35th postoperative day. On the 38th postoperative day, a below-knee amputation was eventually performed (D).

PSA is a very rare vascular anomaly of the lower extremity. The most widely used classification system was first described by Pillet et al. [4] and then modified by Gauffre et al. [5] based on anatomical features, such as lower limb continuity of PSA and femoral artery. However, an unclassified type has been previously reported [6]. Therefore, Ahn et al. [7] proposed a new simple classification system along with treatment options based on anatomic features and the presence of aneurysm (Table 1, 2). The present case is classified as Type 2a in the Pillet-Gauffre Classification and Class III on the Ahn-Min Classification. According to this classification, the proposed treatment strategy is “bypass and ligation of PSA.” In this study, we followed the recommended treatment approach for the patient.

Table 1 . Ahn-Min Classification compared with classical Pillet-Gauffre Classification.

Class		SFA	PSA	Aneurysm	Pillet-Gauffre Classification
ScPc	Class I	Complete	Complete	−	Type 1, 5a
	Class Ia			+
ScPi	Class II	Complete	Incomplete	−	Type 3, 4
	Class IIa			+
SiPc	Class III	Incomplete	Complete	−	Type 2a, 2b, 5b
	Class IIIa			+
SiPi	Class IV	Incomplete	Incomplete	−	None
	Class IVa			+

SFA, superficial femoral artery; PSA, persistent sciatic artery; ScPc, complete SFA and complete PSA; ScPi, complete SFA and incomplete PSA; SiPc, incomplete SFA and complete PSA; SiPi, incomplete SFA and incomplete PSA..

Adapted from the article of Ahn et al. (Eur J Vasc Endovasc Surg 2016;52:360-369) [7]..

Table 2 . Proposed treatment strategies based on the Ahn-Min Classification.

Class	First recommendation	Others
I	OMT	None
Ia	Embolization	Resection after embolization
II	OMT	None
IIa	Embolization	Resection after embolization
III	Bypass+ligation of proximal popliteal artery above the distal anastomosis	None
IIIa	Bypass+ligation of proximal popliteal artery above the distal anastomosis+embolization	Covered stent
		Interposition graft
		Bypass+An resection
IV	Bypass	OMT
IVa	Bypass+embolization	None

OMT, optimal medical treatment; An, aneurysm..

Adapted from the article of Ahn et al. (Eur J Vasc Endovasc Surg 2016;52:360-369) [7]..

It has been reported that 31%-63% of PSA cases were associated with limb ischemia, and 25% presented with chronic limb-threatening ischemia [7]. Despite surgical treatment, amputation rates due to thromboembolic complications range from 8%-10% [3,7]. Belmir et al. [8] reported an amputation rate as high as 25%. Some reports of recurrent occlusion or ischemia even after endovascular treatment or bypass surgery have been published [9,10]. However, these reported cases involved patients with a typical history of ischemic symptoms, such as intermittent claudication, severe limb pain, and pallor. In addition, the patients in these case reports presented with occlusion of PSA or bypass graft. In contrast, our patient had atypical chronic ischemic symptoms of the lower extremity confined to the foot before the surgical procedures, and the PSA was patent on examination. Nonetheless, appropriate surgical revascularization or other direct therapeutic intervention at an early stage of the disease could have prevented limb amputation in this case. The unsuccessful EVT for the right posterior tibial artery, along with the lack of distal recanalization, including the plantar arteries, suggest that recanalization of the anterior tibial artery alone may not have been sufficient to salvage the limb. Also, the multiple distal embolization from partial thrombus in the PSA likely contributed to the progressive and irreversible events of foot ischemia. In this case, performing EVT targeting the stenotic site of PSA was considered challenging. Therefore, we performed a staged FP bypass and PSA ligation after EVT of the lower extremity. However, in retrospect, performing the surgery immediately after the initial event or concurrently with EVT might have been more beneficial. Furthermore, the patient’s congestive heart failure-associated low output syndrome and hypoalbuminemia-induced plasma volume reduction may have adversely affected the peripheral ischemia even after bypass surgery. Yun et al. [11] reported two cases where bypass surgery was not required despite distal embolization. In those cases, distal circulation was preserved via the collaterals from the deep and superficial femoral arteries, and there was no risk of recurrent distal embolization. However, our patient lacked effective collaterals, making direct revascularization essential. The discrepancy between the ABI and TBI values may have initially misled the attending physicians. However, medial arterial calcification appears to be the explanation for this discrepancy. In heavy atherosclerotic cases, calcium deposits in the muscular middle layer of the arteries, increase the stiffness of the arterial wall, which results in pseudonormalization of the ABI value [12].

In conclusion, the limited clinical experience with PSA, owing to its rarity, may hinder timely therapeutic intervention. Therefore, early therapeutic intervention following onset of the first ischemic symptom is likely to yield greater benefits than conservative treatment. Moreover, patients should be offered appropriate treatment based on the prognosis of PSA.

None.

The authors have nothing to disclose.

Concept and design: KK. Analysis and interpretation: KK. Data collection: KK, TF. Writing the article: KK. Critical revision of the article: all authors. Final approval of the article: all authors. Statistical analysis: None. Obtained funding: none. Overall responsibility: KK.