Neuroanatomy Draw It To Know It

328 Neuroanatomy: Draw It to Know It

Arterial Borderzones

Here, let’s use coronal slices through the cerebrum to
draw the arterial borderzones. Vascular insuffi ciency
within these arterial borders produces a clinically
important form of cerebral infarction, called borderzone
infarct. First, draw a coronal section through the cere-
brum and label the general superfi cial, leptomeningeal
arterial supply, and then label the deep, perforating arte-
rial supply. Th e anastomoses (ie, collateralizations) that
exist between the superfi cial, leptomeningeal arteries and
the deep, perforating arteries are limited to capillary con-
nections, which cannot sustain arterial perfusion in low-
blood-fl ow states. Indicate that infarcts that occur within
these borderzones are called “end-zone infarcts,” so
named because these arteries are essentially end arteries.
Now, draw another coronal section through the cere-
brum. Here, we will focus on the borderzones that exist
in between the superfi cial arterial territories. Indicate
that the ACA supplies the supero-medial hemisphere,
the PCA supplies the infero-medial hemisphere, and the
MCA supplies the lateral two thirds of the cerebral
hemisphere. Next, label the borderzones between these
arteries. Again, the anastomoses that exist within these
borderzones are insuffi cient to maintain cerebral perfu-
sion in low-blood-fl ow states, resulting in stroke; infarcts
to these borderzones are called “watershed infarcts.”

Now, let’s label the somatotopic cortical representa-

tion of the body, known as the homunculus. We do so in

order to understand the clinical eff ect of an important

type of watershed infarct — the MCA/ACA borderzone

infarct, which produces the “man in a barrel” syndrome.

Th e homunculus lies along the pre- and post-central g yri,

laterally, and the paracentral g yri, medially. First, show

that within the homunculus, the tongue lies inferiorly.

Th en, above it, show the face and then the hand above it.

Th e tongue, face, and hand take up a disproportionately

large area within the cortex relative to their actual size in

the body. Now, continue counterclockwise around the

convexity of the hemisphere, and include the arm and

hip. Th en, hanging over the medial face of the hemi-

sphere, draw the leg and foot. Note that the foot termi-

nates superior to the cingulate g yrus.

Th e somatotopic sensorimotor area that corresponds

to the borderzone between the MCAs and ACAs

encodes the proximal arms and legs. So when an ACA/

MCA borderzone infarct occurs, patients have weakness

of their proximal arms and legs with preservation of

hand and feet strength; they act like a “man in a barrel.”

To demonstrate this clinical eff ect for yourself, sit with

your arms at your side and wiggle your fi ngers and toes

but be unable to raise your arms or your legs.^1 , 2 , 4 – 8

FIGURE 19-5 Coronal section of arterial borderzones. 1, middle cerebral artery; 2, perforating arteries; 3, medullary arteries; 4, anterior cerebral
artery; 5, posterior cerebral artery. Used with permission from Bogousslavsky, J., and L. R. Caplan. Stroke Syndromes, 2nd ed. Cambridge and New York:
Cambridge University Press, 2001.