Friday, October 26, 2012

Persistent Sciatic Artery

(Ref 1)
In the embryo, the sciatic artery forms as a branch of the umbilical artery and originally supplies the whole embryonic lower limb bud.

As the embryo develops, it regresses to the level of the popliteal artery...

... and then eventually involutes completely as the iliofemoral system replaces the sciatic artery system. The only portions that remain are segments of the popliteal and fibular arteries... as well as portions of the inferior and superior gluteal arteries.

Rarely (0.025 - 0.05%), the sciatic artery persists into adult life. There is variability in the degree of how much it persists -- anywhere from complete persistence from the internal iliac artery to the poplitieal, to partial persistence with connection from the internal iliac artery through multiple collaterals. Angiographically, it should be suspected when there is enlargement of the internal iliac artery relative to the external, and an abnormal common femoral artery. It is reported as bilateral 25% of the time.

 The peristent sciatic artery runs along with the sciatic nerve and passes into the thigh through the sciatic notch somewhat like the superior and inferior gluteal artery (see yesterday's post).

(ref 2)

The persistent sciatic artery is fragile and can be damaged by normal activities, such as sitting.  Repeated trauma leads to early atherosclerotic change and early aneurysm.  In fact aneurysm of the sciatic artery is reported in 15-40% of cases, there is a high rate of thromboembolism in the artery, and it can cause neurologic symptoms through compression of the sciatic nerve.

On palpation, these patient have the confusing finding of an absent femoral pulse, but an intact popliteal pulse ("Cowie's sign").

Fat sat T2 post contrast image shows a large aberrant vessel deep to the right gluteus maximus without a visible right femoral common femoral artery.  This patient had a persistent sciatic artery (note pulsation artifact)

A coronal image of the same patient as above, demonstrating a large aberrant right lower extremity artery, coursing deep to the gluteal musculature. Persistent sciatic artery.

Incidentally, the persistent sciatic artery was first noted in 1832 (Lancet, "On a New Variety of the Femoral Artery")

1. Wanga B, Liub Z, Shenb L. "Bilateral persistent sciatic arteries complicated with chronic lower limb ischemia" International Journal of Surgery Case Reports. Volume 2, Issue 8, 2011, Pages 309–312
2. Pershad A, Srivastava A, Dima C. "Pulseless Right Groin… Bounding Distal Pulses"  Journal of Invasive Cardiology. August 2011.
3. "Rutherford's Vascular Surgery"  Cronenwett and Johnston. 7th ed. 2010.
4. Bower EB, Smullens SN, Parke WW. Clinical aspects of persistent sciatic artery: Report of two cases and review of the literature. Surgery 81:588–595.