The lenticulostriate branches
are small diameter penetrating arteries that arise directly from the
MCA stem and supply most of the internal capsule and basal ganglia.
Blockage of a branch that supplies the internal capsule may produce
a tiny infarct (or lacune) in the posterior limb of the internal capsule
where the corticobulbar and corticospinal tracts run on their way
from the motor cortex to the brainstem and spinal cord. Corticobulbar
fibers are believed to lie in the most anterior in the posterior limb,
followed in turn by corticospinal fibers for arm and then the leg.
Depending which lenticulostriate branch is occluded, a lacunar
infarct might affect only part of these fibers, producing contralateral
paralysis of just the lower face and arm, or perhaps just of the arm
and leg.
In this patient, a tiny
lacunar stroke produced major deficits because of its location. In
other cases, small lacunar strokes produce no abnormalities detectable
on neurologic exam. The old real estate broker's adage about 'location,
location, location' is particularly applicable in this situation.
Spontaneous unwanted, involuntary movements (so-called extrapyramidal
motor syndromes) following an ischemic stroke are rare, but when
they occur they may be the consequence of occluding lenticulostriate
vessels that normally supply the basal ganglia.
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