Bilateral persistent sciatic artery: a case report of a rare variant with clinical implications

Artéria ciática persistente bilateral: variante rara clinicamente significativa

Tiago André Moura Rodrigues¹, Madalena Ramalho¹, Tiago Ferreira², Augusto Ministro², João Leitão¹

¹Department of Radiology, Hospital de Santa Maria, Lisbon

²Department of Angiology and Vascular Surgery, Hospital de Santa Maria, Lisbon

ABSTRACT

Keywords: Persistent sciatic artery, anatomic variants, aneurysm, lower extremity, CT-Angiography

RESUMO

Embora rara, a persistência da artéria ciática é uma variante anatómica com significado clínico, uma vez que está frequen­temente associada a complicações como formação de aneurismas, trombose e isquemia distal. Apresentamos o caso de um doente com sinais de isquemia subaguda do membro inferior direito e uma massa pulsátil na vertente inferior da região glútea homolateral. A angiografia por tomografia computorizada demonstrou a existência de uma artéria ciática persistente bilateral, à direita complicada por aneurisma parcialmente trombosado e embolização distal para a artéria poplítea. O tratamento cirúrgico incluiu a realização de um bypass femoro-poplíteu, a laqueação da artéria poplítea acima da anastomose e a embolização da lesão aneurismática.

Palavras-chave: Artéria ciática persistente, variante anatómica, aneurisma, membro inferior, Angio-TC

INTRODUCTION

During early embryonic life, sciatic arteries are the major arterial structures providing blood to lower limb buds. Normally, they progressively regress and their function is completely replaced by femoral arteries at around the 3rd month of gestation(1). However, in an estimated 0,05% of population(2), the sciatic artery does not completely invo­lute, and therefore becomes persistent. The persistent sciatic artery can be complete or incomplete, unilateral or bilateral and co-exist with a fully or underdeveloped superficial femoral artery(3). Despite its rarity, identifica­tion of PSA has clinical importance, because it is frequently associated with complications such as aneurysmal lesions, thrombosis and variable degrees of distal ischaemia(4). Failure to identify a PSA can also lead to poor surgical plan­ning and management.

We present the case of a 76 year-old man with chronic right lower limb claudication, which had progressed to rest pain during the previous 2 weeks. No episode of trauma and no history of smoking, hypertension or diabetes were noted.

Physical examination was remarkable for a pulsatile mass at the right inferior gluteal region. The right extremity was cold, with slow capillary refill time. Both femoral and popli­teal pulses were palpable, but pedal and posterior tibial pulses were absent.

The left extremity showed signs of chronic vascular disea­se, but was asymptomatic.

CT angiography of the abdominal aorta and lower limbs revealed a bilateral persistent sciatic artery, with comple­te persistence on the right side and incomplete on the left. As opposed to PSAs, the superficial femoral artery was incomplete on the right side and complete on the left (Figure 1, 2 and 3). Furthermore, a 4.3-cm partially thrombosed saccular aneurysm was identified in the retroischiatic segment of the right PSA (Figure 4), and an occluded segment due to embolization was demonstrated in the infragenicu­lar popliteal artery (Figure 5). No pedal flow was seen and only a faint opacification of the distal segments of the peroneal artery was present.

DISCUSSION

We presented a rare case of bilateral and asymmetric PSA (complete on the right and incomplete on the left). Interestin­gly, femoral and PSA arteries development alternated in an inverse manner, as they establish dominant blood flow to the extremities. According to the classification of PSA by Pillet et al.(5), this would represent a type 2a persistence on the right and a type 3 persistence on the left. To our knowledge, this is the fifth case of combined-type PSA (complete on the right and incomplete on the left) published in literature(1).

Diagnosis of PSA and related complications is made on clinical grounds and imaging findings. We would like to point out that in our particular case, Cowie's sign (dimi­nished or absence of femoral pulse in combination with palpable popliteal pulse) was absent, since there was still an incompletely developed femoral artery on the right. Doppler ultrasound can provide valuable initial informa­tion about the extent and severity of peripheral vascular disease, although CT angiography is usually necessary to confirm the diagnosis of PSA, evaluate possible complica­tions and plan surgical approach.

Although not fully understood, some authors suggest that the high rate of aneurysm formation in PSA is due to its anatomic location, which favours overstretching during flexion of the hip joint and repeated trauma against the sacrospinal ligament, piriform muscle and hip(2,6).

There are different therapeutic options, but embolization of PSA aneurysm is often preferred over exclusion, since the latter is associated with sciatic nerve injuries. Another factor to take into consideration is the type of PSA present, because an additional bypass may be needed in the scenario of an incompletely developed femoral artery, as in our case.

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^*Autor para correspondência

Correio eletrónico: tiagomourarodrigues@gmail.com (T. Rodrigues).

Recebido a 2017-03-11;

Aceite a 25-10-2017;