330 Neuroanatomy: Draw It to Know It
Brainstem Arteries ( Advanced )
Here, we will draw the brainstem arterial supply. We will
begin with the four common brainstem arterial territo-
ries as originally defi ned in the 1960s by Gillian and
Lazorthes. First, draw one half of an axial composite of
the brainstem: a compression of all three brainstem
levels. Th en, designate the thin paramedian region as the
anteromedial group. Now, divide the remainder of the
brainstem from anterior to posterior into the anterolat-
eral, lateral, and posterior groups.
Next, we will make a table of the specifi c vessels that
supply the brainstem. Note that although our list will
not be exhaustive, it will cover the major arteries. First,
indicate that within the medulla, the anteromedial group
is supplied by the anterior spinal artery and direct verte-
bral artery branches; the anterolateral group is supplied
by the anterior spinal artery and the posterior inferior
cerebellar arteries; the lateral group is supplied by the
posterior inferior cerebellar arteries; and the posterior
group is supplied by the posterior inferior cerebellar and
posterior spinal arteries. Now, encircle the key medullary
arterial vessels: the anterior spinal artery and the poste-
rior inferior cerebellar arteries. Next, note that the
common source for these arteries is the vertebral arteries.
As a clinical corollary, ischemia to the posterior inferior
cerebellar artery results in lateral medullary syndrome,
called Wallenberg’s syndrome.
Now, let’s label the pontine arteries; the fi rst three
groups are supplied by basilar branches that travel pro-
gressively farther distances to their targets. Indicate that
the anteromedial group is supplied by the pontine para-
median arteries; the anterolateral group is supplied by
the short pontine circumferential arteries; the lateral
group is supplied by the long pontine circumferential
arteries and the anterior inferior cerebellar arteries; and,
lastly, the posterior group is supplied by the superior cer-
ebellar arteries: note that the posterior group is found
only in the upper pons — it is not present in the mid- or
lower pons. Th us, most of the pontine arterial supply
comes in the form of circumferential arteries that origi-
nate from the basilar and either travel a short distance
(the pontine paramedian arteries), a mid-distance (the
short pontine circumferential arteries), or a long distance
(the long pontine circumferential arteries). Th e posterior
portion of the pons receives additional supply from
the anterior inferior cerebellar artery, inferiorly, and
the superior cerebellar artery, superiorly. Note that the
common source for these arteries is the basilar artery.
Basilar ischemia can produce pontine basis strokes,
which can cause locked-in syndrome.
Next, let’s label the midbrain arteries. Th e anterome-
dial group is supplied by basilar tip and proximal PCA
branches; indicate that from inferior to superior, these
branches are called the inferior and superior paramedian
mesencephalic arteries and the thalamoperforate arter-
ies. Th en, show that the anterolateral group is supplied
by PCA branches: the collicular and posteromedial
choroidal arteries. Next, indicate that the lateral and
posterior groups are also supplied by the collicular and
posteromedial choroidal arteries in concert with the
superior cerebellar arteries. Now, let’s encircle the key
arteries that supply the midbrain: the paramedian mes-
encephalic and thalamoperforating arteries and the col-
licular, posteromedial choroidal, and superior cerebellar
arteries. Note that the common source for these arteries
is the PCAs or distal basilar artery. When basilar clot
produces ischemia to the proximal PCAs, large midbrain
strokes can occur and produce a so-called “top of the
basilar” syndrome.^1 – 5