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Emergency Radiology

E2326. Persistent Sciatic Artery: A Favorable Anatomic Variant in a Setting of Trauma

Wallace E1,  Shaffer W2,  Spieler B1,  Ustunsoz B.1 1. Louisiana State University Health Sciences Center,, New Orleans, LA; 2. Access Radiology, Slidell, LA

Address correspondence to E. Wallace (eric.wallacejr@gmail.com)

Background Information: Persistent sciatic artery (PSA) is a rare congenital anomaly of the blood circulation in the lower limb due to the persistence of an artery that normally regresses within the first 3 months of embryonic development. Its incidence is estimated to be 0.025–0.04%, with 50% of known cases being the right side, 20% left side, and less than 30% bilateral. Most are asymptomatic in their youth and present between the ages of 40–50 years old. Recently, at our institution, a 19-year-old man presented to the emergency department after sustaining a gunshot wound to the left medial midthigh. Physical examination and imaging revealed a bullet in the left midthigh at the expected location of the left femoral artery (FA). Additionally, dilated bilateral internal iliac arteries and patent bilateral persistent sciatic arteries that coursed adjacent to the sciatic nerve and formed the dominant circulation of both lower extremities were noted. By lacking an FA due to PSA, this patient avoided serious vascular injury and possible death from exsanguinations if the bullet would have injured the FA in the medial thigh.

Educational Goals/Teaching Points: Radiologists should be aware of anatomic and developmental variants, particularly if the imaging findings and clinical picture are discordant. PSA is a rare congenital anomaly and is often asymptomatic. CT angiography (CTA) or MR angiography (MRA) are the most comprehensive modalities for evaluation as digital subtraction angiography (DSA) may lead to false-positive results.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques: PSA can be diagnosed with Doppler ultrasound, CTA, or MRA. DSA can also be used for PSA diagnosis and planning of its surgical repair. Characteristic PSA findings on DSA include enlargement of the internal iliac artery or a hypoplastic femoral artery. Popliteal and tibial vessels are often difficult to visualize on conventional angiography due to slow flow in the dilated PSA. This may lead to false impression of arterial occlusion. Lower limb ischemia secondary to PSA may also be misdiagnosed as an FA occlusion if the catheter tip is placed directly into the external iliac artery or FA. Such placement would reveal a tapered FA. Tapering effect of hypoplastic vessels may have the appearance of occlusion. Identification of the PSA as the major inflow vessel is critical to avoid an inappropriate bypass of a hypoplastic FA that appears occluded on angiography due to its underdevelopment. Several authors recommend CTA due to the aforementioned shortcomings of angiography. CTA is a more comprehensive study that detects the relationship of the artery to the bony and muscular structures, sciatic nerve, presence or absence of a sciatic vein, FAs, and collaterals. CTA also provides information on the presence and size of an aneurysm, degree on intramural thrombosis, and PSA occlusion. MRA provides similar information. Characteristic findings on CTA are visualization of smooth tapering of the FA and the distal stump of a PSA, or an occluded vascular structure that had previously followed the sciatic nerve, both of which help to make the diagnosis of a total PSA occlusion.

Conclusion: PSA is a rare congenital vascular anomaly. Due to the high incidence of associated abnormalities, PSA should be included in the differential diagnosis of lower limb ischemia or suspected aneurysm formation. PSA are of doubtful clinical significance when found incidentally at imaging; However, this variant anatomy can be of benefit in the setting of trauma, as in this case.