another questionable question?
#185 from 2004
"Which statement is true regarding the vascular supply to the spinal cord"
A. Paired anterior spinal arteries... (obviously false)
B. Posterior spinal artery is a single vessel... (obviously false)
C. The watershed region is supplied only via the radicular arteries.
D. The artery of Adamkiewicz provides circulation to the lumbosacral region.
Author's answer C -
and explanation: there is a watershed zone from T4-6 vulnerable to ischemia, the artery of Adamkiewicz enters between about T9 and T10.
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Hemisphere's counterpoint: The question asks the spinal cord supply, but the radicular arteries proper do not supply the spinal cord, they supply the spinal nerve roots and terminate before anastamosing with the spinal arteries. Source: Frank Netter see plate 157 and 158 and his commentary at the bottom of the pages. Only the segmental medullary arteries go on to anastomose with the anterior spinal artery and thereby supplying the spinal cord proper. Additionally, while Adamkiewicz can enter between T9-10, it can actually enter anywhere from T5-L5 (source: spine secrets) and according to Hollingshead textbook of anatomy most commonly enters at L1. It's blood supply does eventually anastamose with the anterior spinal artery and go on to supply the lumbosacral enlargement of the spinal cord.
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My Netter is from 1997. Both it and Slipman's Interventional Spine-2008- list distal proximal arteries supplying nerve roots turning into proximal radicular arteries feeding into ant & post spinal arteries. However I looked on Grant's Atlas 2009 via the web and it diagrams radicular arteries supplying the nerve roots which then turn into segmental medullary arteries which run along rootlets before anastomosing with ant & post spinal arteries: Backing up what you wrote.
I would think Grant's Atlas trumps Slipman's book. Perhaps the question was written a while back before there was consensus on what to call those arteries.