Let's take a couple of minutes
to dive deep into the brainstem.
The brainstem is
composed of 3 sections:
the midbrain, the
pons, and the medulla.
Let's look at the major nervous structures
that exist in each of those 3 areas
and think about the
common strokes syndromes
that would present with
pathology in each of those areas.
We'll start with the midbrain.
The critical structures
that you should know
when considering a
stroke in the midbrain
are that this is home to cranial nerve
3, 4 and the vertical eyes center
as well as strength on one
side of the body or the other.
Here we can see cranial nerve
3 as it exits in the midbrain.
We see the nucleus of cranial
nerve 3 line just medially.
At the posterior aspect or the
dorsal aspect of that nucleus
is the nucleus of the Edinger-Westphal,
which controls the parasympathetic
fibers for cranial nerve 3.
And then importantly,
the cerebral peduncles
run on the ventral
aspect of the midbrain.
And these are the critical
structures to remember
when we're considering
a midbrain pathology.
Sometimes the medial lemniscus which
controls sensory information is important
and the spinothalamic track.
The spinothalamic tract
controls pain and temperature,
medial lemniscus is
vibration and proprioception.
And those can help us to further
localize a stroke in the midbrain.
So what types of stroke
syndromes do we see?
Well, we we need to remember
cranial nerve 3 lies medially,
the cerebral peduncles
and the anterior lateral
system lies laterally.
So there's 3 stroke syndromes
to consider in the midbrain.
The first is a medial
And this is a stroke that
affects those perforators,
those pontine or midbrain perforators
right off the basilar artery.
Medial strokes will affect cranial
nerve 3 and the cerebral peduncles.
Patients who will be weak
on one side of the body
and on the opposite side, the side of the
lesion will see a cranial nerve 3 palsy.
The second presentation is that
of a lateral midbrain stroke.
There we often don't see
cranial nerve 3 palsies
but we do see problems with the anterior
lateral system and the medial lemniscus
in addition to varying
degrees of weakness,
involvement of the cerebral
peduncles, the anterior lateral system
and the medial lemniscus.
So we see hemisensory loss,
motor weakness and we
can see loss of both,
vibration and proprioception fibers.
If the entire side, if one entire
side of the midbrain is involved,
we see cross findings.
On the side of the lesion,
the eye is down and out,
there's a cranial nerve 3 palsy
and that secondary to unopposed
action of the 4th and 6th nerves
when cranial nerve
3 isn't working.
Cranial nerve 3 also
controls the parasympathetics
and so that affected eye will
be dilated and unresponsive.
That's a 3rd nerve palsy.
On the opposite side
of the 3rd nerve palsy,
the patient will have paralysis
of the face, arm and leg
as a result of dysfunction of the
corticobulbar and corticospinal fibers
that descend in
the crus cerebri.
This is a critical stroke
syndrome to be able to recognize,
it's a midbrain stroke syndrome.
Let's go one section down
to the level of the pons.
What things live in the pons
that we need to be worried about
for stroke patients that
may have a pontine stroke?
Well, the pons is home to cranial nerves
5, 6, 7 and 8 as you can see here.
It is the horizontal
that's where the PPRF or the pontine
paramedian reticular formation lives
and controls horizontal gaze.
we also see the corticospinal tract
running in the ventral aspect
of the pons which is critical,
medial aspect strokes can
cause weakness in this area,
the medial lemniscus runs
just dorsally to that
and we can see those are the
critical structures to evaluate
a pontine stroke.
So what are the major stroke syndromes
we should recognize in the pons?
first is the medial syndrome.
Medial syndromes where the stroke
involves the pontine perforators
will affect the
corticospinal tract primarily
and result in contralateral
weakness or hemiparesis.
Laterally we can see involvement
of the 5th cranial nerve
in contrast to the midbrain where
cranial nerve 3 exits medially.
Cranial nerve 5 exits
laterally as you see here,
so we can see varying degrees
of weakness and sensory loss
in addition to sensory loss
on one side of the face
in the V1,
2 and likely 3 distribution.
In addition, there's one important
structure that lives in the pons
that can present with a
unique stroke syndrome.
And that stroke's affecting the
medial longitudinal fasciculus.
As you recall, the MLF connects the
6th nerve to the opposite 3rd nerve.
It allows our eyes to move
together when we look laterally.
Strokes affecting or
any pathology affecting
the medial longitudinal
will cause the eye not to look
in impaired adduction of the eye.
So when the patient
tries to gaze right,
a problem with the MLF will result in
inability of the left eye to look right.
Or if the patient were
to look to their left,
a problem with the right MLF would cause
an inability of the right eye to look left.
That's called an INO or an
and it comes from a problem with
a medial longitudinal fasciculus
or lesion in this case
stroke in the pons.
And so when we think about pontine
strokes or large pontine strokes,
the two findings we want to think
about, the crossed findings
are on the side of the lesion,
we see ataxia of the limbs,
and gait abnormality as a result
of loss of cerebellar fibers
and the pontine nuclei and
that's on the side of the lesion.
Opposite the side of the lesion, we can
see paralysis of the face, arm and leg
as a result of impairment of the
corticobulbar and corticospinal tract.
And variable impairment
of touch proprioception
as a result of medial
That crossed finding is important
for localizing to a pontine stroke.
we get to the level of the medalla,
the lowest part of
the spinal cord.
This is home to cranial nerves
9, 10, 11 and 12.
There's no eye movement involvement
in the level of the medalla
except problems in the
medalla can cause nystagmus
as a result of descending
We can see prominent
vertigo and nausea
as a result of this vestibular
nuclei involvement in the medalla.
We see crossed face
body sensory loss,
and we can even see
hiccups and yawning
as a result of cranial nerve 10
and other autonomic cranial
nerve function in the medalla.
Here are the critical
the spinal tracts of cranial
nerve 10 and its nucleus.
The nucleus of cranial nerve
11 lies in the medalla.
The pyramids which carry the motor function
in the cortical spinal tract are here
and decussation here,
so we can start to see
crossed findings from
a motor standpoint.
The lateral corticospinal tract
is present in the medalla.
And we see the fasciculus
gracilis and cuneatus
which carry sensory nerve function,
the dorsal column function,
the vibration and proprioception in
the dorsal aspect of the medalla.
So when we think about the important
stroke syndromes in the medalla,
we can have high medullary strokes
in the cranial aspect of the medalla
and low medullary strokes in the
caudal aspect of the medalla.
In the upper part
of the medalla,
the corticospinal tract has not crossed
over in the pyramidal decussation.
So we see that sensory loss and
motor loss are on the same side,
and that's contralateral
to the lesion.
That's an important
We don't see corticobulbar
dysfunction, and so facial loss,
loss of motor function in the face
or sensory function in the face
are not present for
a medullary stroke.
In a lower medullary strokes,
after we've seen crossing
of the corticospinal fibers
at the pyramidal decussation,
we see that sensory loss occurs on
the opposite side as the motor loss.
we would expect the motor loss to be
on the side of the lesion and the sensory
loss to be opposite the side of the lesion.
In addition, we can see a varying
range of parasympathetic dysfunction
nausea, vomiting, hiccups,
and other parasympathetic
and sympathetic dysfunction
as a result of loss of cranial nerve
9, 10, 11 and 12 nuclear function.
And then lastly,
we can divide the brainstem into
the ventral portion of the brainstem
and the dorsal portion
of the brainstem.
The dorsal portion of the brainstem
is home to the cranial nerve nuclei,
that's where they live.
And so brainstem lesions can
present without motor weakness
and just cranial nerve
nuclear weakness or lesions
from problems affecting the
dorsal aspect of the brainstem.
Typically, these are the
deep perforating arteries
of the basilar
that are affected.
In the ventral aspect
of the brainstem,
that's home to the motor
tracks, the corticospinal tract,
the medial lemniscus tract.
So brainstem lesions involving
only the ventral tracts
can cause a pure
usually with equal face,
arm and leg if the pons is involved.
And there may be no other
signs, no cranial nerve signs
as a result of
absence of dysfunction
in the dorsal part
of the brainstem.
And so here's a table that's
an important reference
as you're considering some of
the major stroke syndromes,
their vascular territory,
and they're presenting signs or symptoms.
We see that left MCA strokes have
a characteristic presentation,
often with aphasia
and the other
findings you see here.
In contrast, right MCA
strokes don't involve aphasia,
but present with similar
hemiparesis and hemisensory loss
and neglect and other
right-sided brain symptoms.
Left PCA strokes frequently
present with occipital dysfunction
and visual impairment,
visual field defects.
Similar to right PCA strokes,
which present very similarly
with visual field defects.
Vertebral strokes have a
distribution that is deep
within the brainstem and
that medullary region.
And so we see the
dizziness, vertigo, nausea,
quadriparesis that are
present in medullary strokes.
There are number of penetrating artery
distribution strokes, the lacunar strokes,
ventral pons and thalamus.
And you can see here some of the
characteristic, signs and symptoms
for each of those